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From the Editorjune_1_001

I’m pleased to announce that the dates for the third Trawler and Motor Vessel Technical Training Workshop have been established, the event will take place on October 3-4, in Deltaville, Virginia.  You can learn more by visiting www.stevedmarineconsulting.com/trawler-workshops .  Please also view our flyer.

I’m also pleased to share with readers a special discount available only to SDMC Ezine readers, from Top Shelf Marine.  I’ve known and worked with the folks at Top Shelf for years, they are a class act and offer innovative and useful products.  You can learn more about the offer by scrolling down.  Regarding this offer, readers will no doubt be asking themselves, ‘What’s in it for Steve?’ The answer is, satisfied readers, and nothing more. I receive no commissions or compensation from any manufacturer, of any product offered or mentioned in the Marine Systems Excellence Ezine. If the day comes where I do, rest assured, I’ll make it amply clear to my readers.

This February two mariners were plucked from their 43-foot Australia-bound sailing vessel 150 nm off the coast of New England, in the midst of a blizzard.  That sentence alone is rife with red flags, ’43-foot sailing vessel’, ‘New England’, ‘blizzard’ and ‘January’ simply aren’t words that should be used together by any prudent mariner, unless in the course of an educational, i.e. ‘Don’t try this at home’, analysis.  The crew of two (if ever there was a society full of seemingly natural born sailors, Aussies are it, making this even more inexplicable) purchased the boat on eBay for $10,000.  “We’ve never done anything like this. Dad’s not even a sailor, but he’s a quick study,” commented Jason McGlashan in an interview with the Newport [Rhode Island] Daily News. ‘Nuff said.  A Coast Guard helicopter navigated through low visibility and near-hurricane force winds to affect the rescue, conditions at the time were 25-foot seas and 60 mph winds.  Kudos to the brave air crew who completed this mission.

NWS Ocean Prediction Center

Among other features, the compact barometric pressure gradients, and ample wind feathers on this sea surface weather map, centered over New England during the ill-fated voyage, should strike fear into the heart of any prudent mariner

I wish I could say that these folks are the exception.  Sadly, however, they are not.  Each winter, and during often clearly predicted equinoctial gales, mariners who exercise very poor judgment are snatched from vessels (nearly all of which are conspicuously floating on their lines) along the US East Coast. Last January a catamaran was abandoned in much the same manner, off North Carolina, it was a new boat (on a veritable shake down) with a professional skipper.   Lucky for these folks, the region has what is likely the most complete rescue safety net in the world, which includes Coast Guard, Navy and Air National Guard assets among others.  The rescue personnel, many of whom I’ve spoken with during annual Naval Academy Safety at Sea symposiums, love what they do and never ridicule those they rescue.  That’s a credit to their professionalism, however, they are being placed in harm’s way for little or no good reason, and there has been loss of life among these dedicated pros while performing these rescue feats.  And then there’s the issue of the cost to the taxpayer, helicopters are extremely expensive to operate.

I have a theory as to why the incidence of such rescues seems to have increased.  Prior to GPS seafarers who didn’t know how to navigate celestially remained close to shore.  This was a training ground of sorts.  These folks gained experience, and if they opted to go off shore, they invested the time and effort to learn how to use a sextant and sight reduction tables.  For better or worse, this is no longer the case, anyone who can push a button can venture off shore.  To be clear, I’m not faulting those who don’t know how to use a sextant, clearly it’s a dying art (I haven’t taken my sextant out of its box, other than to occasionally gaze at it lovingly), GPS is a wonderful thing and has probably saved countless lives and prevented innumerable accidents.  Still, I believe there is a connection between its proliferation and those being rescued.


Before setting off on any voyage, know the limitations of your vessel and her crew, and make sound decisions regarding the season and weather

The other half of this electronic equation is the proliferation of EPIRBS.  Again, it’s an invaluable tool I heartily embrace, one that has saved many lives.  Now, however, seasick, cold, scared crews can press the ‘come get me’ button and a few hours later they are being hoisted to a warm cabin and hot coffee.  It’s very tempting no doubt if you’ve gotten yourself into a jam by setting out to sea in mid-winter with an untried vessel.

For those genuinely in peril through no fault of their own, of course none of this applies.  However, if these unnecessary incidences continue to occur it’s possible we will see government legislation requiring cruisers to have rescue insurance, something responsible mariners surely don’t want to be forced into.  Lastly, good mariners heed weather readily available forecasts; no responsible mariner would consider a voyage in a small vessel, from New England in January even if a gale and blizzard wasn’t in the forecast.  Look for an upcoming in-depth analysis of this event by Marine Systems Excellence contributor, author and circumnavigator Ralph Naranjo.

This month’s Ezine continues on last month’s theme of propellers, covering the ins and outs of propeller removal.  I hope you find it both useful and interesting.


SDMC Special Offer


The SDMC Marine Systems Excellence E-zine readers are being offered a special 15% discount on their Top Shelf Marine Products purchase.  Please visit www.topshelfmarine.com and upon checkout, enter the promo code SDMC (case sensitive) to receive your discount.

DB on shaft large

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Propeller Installation

Steve D’Antonio

Copyright SDMC, Inc. 2015


The lapping process involves rotating the propeller clockwise and counter-clockwise several times on the shaft, then checking the condition of the machinist’s dye to determine the level of interface between the two.

A few years ago I delivered a seminar in which I discussed the procedure for propeller installation.  The number of steps involved in executing this process came as a surprise to many of the attendees.  In my experience, in roughly three out of four propeller installations the necessary steps are not followed.  During the years that I worked as a marine mechanic and then boat yard manager I established a protocol that I believe leads to secure, reliable propeller installation.  While you may not undertake this work yourself, you certainly can insist and ensure that others follow these important steps.


Inspect shaft tapers for any signs of corrosion, pitting, scoring or any irregularity.  Pitting, shown here, would require repair or replacement of the shaft.

Inspect both the prop shaft taper and the propeller bore, the cone shaped hole in the center, for dents, scoring, corrosion or defects of any kind.  It’s important that these surfaces be clean and free of any irregularities.  Be sure to inspect the keyways (the rectangular troughs) on both the shaft and prop as well, along with the key for similar issues.


Keys should fit snugly into keyways, not too loose and not too tight.  If the key is too loose, the propeller can move independently of the shaft, which in turn will lead to keyway damage.


Keyways should be clean and free of debris or scale, to ensure the key fits properly, and avoids binding of the propeller during installation.  

The key should fit into the propeller and shaft keyways with only slight effort, if it’s too loose it will rock, allowing the propeller to move independently of the shaft.  If it’s too tight, the propeller might bind while being installed, which will lead to a balance and vibration problem.


Lapping compound, shown here having been applied to a shaft taper, has the consistency of we sand.  It removes material from the prop bore, allowing a custom fit between bore and shat taper.

The first time a propeller is mated up with a shaft, whether both or either are new, they should be lapped to ensure a proper fit.  Lapping is essentially custom fitting a prop to a shaft using an abrasive compound that’s designed for installation of intake and exhaust valves in engine cylinder heads.  The process involves applying machinists dye or, “Prussian blue”, to the shaft taper, over which the lapping compound is applied; the latter has the consistency of wet sand.  The propeller is then placed onto the shaft taper and rotated by hand 180° in either direction a dozen times or so.  Doing so grinds away some of the material in the prop bore, establishing a custom fit.  The prop is then removed and the lapping compound washed off.  The dye that remains tells the installer if he or she has completed the lapping process, roughly 85-90% of the shaft taper should be dye-free or exposing the silver shaft material beneath.  If this level of fit has not been achieved, then the process must be repeated until the 85-90% engagement is achieved.



Machinists dye, typically blue or purple, acts as an indicator, determining where the shaft and prop are making contact.  The goal is to achieve at 90% contact, which means 90% 0f the dye is removed after successful lapping.

Once the lapping is complete all of the lapping compound should be thoroughly washed from the taper and propeller bore (it’s water soluble).  The propeller should then be placed onto the shaft as far as it will go, without the key installed.  Using a sharp awl, scribe a line in the shaft at the point where the forward section of the propeller hub ends.  Remove the prop, install the key and then apply a light coating of liquid lubricant such as CRC 6-56 or WD 40 to the shaft taper and key.  Only a few drops of lubricant are required, don’t overdo it, the purpose for the lube is only reduce the likelihood of binding as the propeller is installed over the shaft, not to aid in propeller removal in the future.

The beauty of the tapered engagement, like the one that’s used for propeller and shaft installations, is that it is designed to ensure both components remain firmly attached to each other, some would say seized or stuck.  Little thought should be given to future separation when a propeller is installed; when the correct tools are used, as detailed in last month’s column, it rarely presents a problem.  However, problems nearly always arise when an installer, often with good intentions, makes an attempt to ease or aid removal at some point later in the vessel’s life.  These well-meaning but ill-fated attempts often involve the use of grease or anti-seize compound applied to the shaft taper during propeller installation.  When incompressible, viscous materials of this sort are placed at the interface between otherwise tight-fitting taper and bore, a hydrolock can result, which prevents full engagement of the propeller and the shaft.  Utilizing this approach will almost certainly lead to movement between the propeller and shaft once they’ve entered service.  This in turn often leads to damaged propeller bores and shaft tapers, sheared keys or loose and in some cases lost propellers.  Make no mistake about it; using anything on a shaft taper other than a very light coating of liquid lubricant is simply a recipe for failure, and a violation of most propeller manufacturer installation recommendations.



A smooth jaw wrench, shown here, is designed for turning hex nuts, while pipe wrenches rely on sharp, hardened teeth, which are designed to turn pipes by cutting into them.  Pipe wrenches should never be used on hex nuts, doing so invariably leads to damage.

The next step calls for the final installation of the propeller onto the propeller shaft.  Push the propeller into place and then install the large, full height nut using a smooth jawed, hex wrench.  Do not use a pipe wrench, pipe wrenches are deigned to grip round surfaces, like pipes, buy cutting into them with hardened, serrated teeth, the last thing you want to use on a hex nut.


Sidebar: If the nuts are stainless steel, the potential for galling exists.  Galling occurs between highly loaded threads,often when they are the same material and especially where stainless steel is concerned.  When fasteners are tightened heat is generated and micro-welding occurs, transferring material from one thread to the other, damaging both in the process.  It can be prevented with light lubrication, by applying a light coating of lubricant, again 6-56 or WD40, to the threads.  For the most part bronze nuts are self-lubricating, and thus immune to this phenomenon; they are, therefore, preferred over stainless steel.


Bronze propeller nuts are self-lubricating and as such less prone to thread galling.  The nuts shown here are installed in the correct order, half height nut first, then full height nut.


Stainless steel nuts are susceptible to galling, a phenomenon wherein the threads overheat and metal is moved from one thread to the other, when installed on a stainless steel alloy propeller shaft.  This can be avoided by lightly lubricating the threads.

The prop can be held in place by wedging a sturdy block of wood between a propeller blade and the vessel’s hull.  While this method sounds crude, it’s well accepted and prescribed by industry experts and propeller manufacturers.  Once the large nut is tightened inspect the forward end of the propeller hub to ensure it has reached or overtaken the line scribed in the shaft earlier.  If it has, then you can rest assured that the key and taper are not causing any binding.  Now, remove the large nut and install the smaller, half height nut, tighten it and then reinstall and tighten the large nut.  While this may appear counterintuitive, half height nuts, sometimes known as jam nuts, are often installed last, ABYC, the Society of Automotive Engineers, the USCG and others call for this “small nut first” approach.  Here’s why, when the first nut is installed and tightened, it carries the entire load.  When the second nut is installed, much of the load is transferred to it and logic dictates that the nut with the most threads should carry the bulk of the load.  Installing the large nut first initially draws the shaft fully onto the taper using the maximum number of threads.  Finally, install a stainless steel, not brass, cotter pin that is large enough to fill the entire hole in the shaft’s end protrusion.  Following these propeller installation guidelines will ensure that the prop stays put until there’s a good reason to have it removed.

For more commentary and specifications regarding propeller nut installations, please open this PDF, Prop Nuts.


For more information on the services provided by Steve D’Antonio Marine Consulting, Inc. please e mail Steve at info@stevedmarineconsulting.com or call 804-776-0981


Steve D’Antonio

Copyright 2015 SDMC, Inc.


From the Editorjune_1_001

When you last heard from me I was still in China.  I’m preparing this month’s feature column while returning from the Miami International Boat Show.  A week prior to this show I completed a month-long travel odyssey, which began inVirginia and took me to New Zealand, Australia, China and Turkey.  When I returned to the Richmond, Virginia airport, 30 days after leaving, I “crossed my outbound track” as sailors say, completing a circumnavigation by air.  Turkey was an eye-opening experience, I found the people warm and inviting, the food and especially the bread particularly tasty after a week in China, and the historical landscape, as well as the geography, stunning.  Turkey boasts over 10,000 registered sites of antiquity; the Roman ruins rival those in Italy.  While there I visited several boat building shops, and undertook sea trials on an unusually calm Mediterranean Sea.  In the coming weeks Katie will post photos from all of these locations to the gallery section of the SDMC website.

Depending on your point of view, boat shows are either a much anticipated event or a necessary evil (undeniably the former for me, I love each and every one I attend).  On the day before the show began I shared an elevator with a marine industry professional from a well-known, large firm.  We exchanged a few boat show pleasantries after which he said, “I hate rich people”.   I’ve encountered this attitude on too many occasions.  Before he made this fateful statement I recognized the ‘industry thousand yard stare’, one that cries out, ‘In spite of the fact that I spend all day on boats in idyllic locations I still  hate my job”, and the show hadn’t even started.  That encounter reminded me of another I had while on a pre-purchase inspection sea trial a couple of years ago.  The professional captain, hired by the broker, to pilot the boat for this purpose, handed me his business card with a smirk, under his name it said, “It’s not my fault you bought a boat”.  I handed it back to him and said “I won’t need this, and the boat business doesn’t need people like you”.  Folks like these are also fond of using the worn out tag lines, ‘The happiest days of a boat owner’s life are…’, ‘A boat is a hole in the water into which…’ and ‘Boat stands for break out another…’.  Because I detest them so much, and because I have no wish to perpetuate them, I’ve intentionally left these axioms incomplete.  When I hear my professional peers use these phrases, I take them to task, pointing out that if their boat owner customers laugh at them it’s only because they are being polite.  As a boat owner, when you encounter this unprofessional attitude, I encourage you to make it clear, sometimes that can be accomplished with nothing more than silence, it’s unappreciated.  If you are a professional, I appeal to you to assist me in eradicating this mindset, if for no other reason than it’s bad for (your) business.

The show itself was busy, with a variety of new and interesting products, some of which I recently wrote about on the SDMC Facebook page.  These include Fleming’s new 58 model (hull #4 was on display, I took hull #3 from the UK to Germany last May and subsequently wrote a review of the vessel, which will be printed in PassageMaker, my final submission to this publication, next month).  Burr Yacht Sales’, the Fleming East Coast dealer, display was a hive of activity, the boat has garnered strong interest, and with good reason.  I also spoke with Jeff Druek, proprietor of Outer Reef Yachts.  Jeff shared with me photos of Outer Reef’s first, soon to be completed, all vinyl ester resin infused fast cruiser, the Trident series, which is being built in 55, 65, 75 and 98 models.  Their first T-550 will be launched at the Cannes boat show this September.  They will also premier in the US at the fall 2015 Fort Lauderdale Boat Show. These are being built at Outer Reef’s yard in Croatia.

There was no shortage of hybrid vessels and systems at the show, and on that subject, as many readers know, I’m a skeptic of these systems.  In brief, they are extremely complex, and most manufacturers are only able to offer limited dealer support.  The 600 pound gorilla in the room is, of course, a minuscule, if any, enhancement in efficiency.  When I debated this editorially with my colleague Nigel Calder last year, he admitted that for trawlers (his testing has been on his own sailing vessel) the added “gain” is realized in enhanced support for house loads via a much larger battery bank.  That logic was lost on me then and remains so now, as we already have proven large battery banks and high output charging systems, which don’t impinge, for the most part on the reliability of the apex system, propulsion.  When I bring this up with hybrid propulsion  manufacturers, as I did during the Miami show, they point to small gains under very narrow operating circumstances.  Even then, the gains are in the low single digit percentage points, to which I can’t help think, ‘is it worth it?’  When I brought up the issue of support with a sincere and knowledgeable hybrid manufacturer, one who espoused the virtue of his redundant Airbus-inspired system, he responded by saying most troubleshooting, and even some repairs could occur via the internet.  Let that sink in for a moment, via the internet…using a Wi-Fi, cellular or satellite modem.

When boat owners ask me how they should prepare for extended or offshore passages, aboard vessels that use already complex yet conventional propulsion and other systems, I advise them to become as knowledgeable and self-sufficient about their vessel and its gear as possible, and assume they will have no outside assistance.  Now add to that equation an esoteric, aviation-like in its complexity, hybrid propulsion system and you can understand my reluctance to embrace this technology.  I believe it’s no coincidence well-respected production builders of blue water capable vessels, Fleming, Grand Banks, Kadey Krogen, Marlow, Nordhavn, Outer Reef and others have continued to avoid hybrid propulsion, in spite of the fact that many buyers would purchase them if offered.  Does this mean there’s no place for marine hybrid propulsion systems?  No, there are applications where it can be made to work, while offering enhanced efficiency.  However, for the time being, I don’t believe these include offshore passage making vessels.  For hybrid propulsion, and for that matter all marine systems and manufacturers, I advise both boat owners and industry professionals to ask sometimes difficult questions regarding support, warranty coverage and of course efficiency vs. cost/complexity before considering this path.

This month’s Marine Systems Excellence column delves into the subject of propeller removal.  I hope you find it both interesting and useful.


Proper Propeller Removal

Don’t Let this Happen to You

A number of years ago, as I was strolling through a boat yard, my idea of sightseeing when I travel, I came across a mechanic who was in the process of removing a propeller.  He was using a technique which, even writing about it well over a decade later, makes me cringe.  He’d removed the propeller’s nuts and in their place had installed what was later aptly referred to as a “bang nut”, an over-sized, closed end brass nut.  The bang nut was screwed onto the shaft; however, it was stopped short of making contact with the propeller hub.  Once the nut was installed, it was hammered on using a substantial maul.

As each blow connected with the bang nut, the shock wave was transmitted up the propeller shaft, through the coupling, into the transmission’s bearings and gears, on to the engine block, where it was ultimately absorbed by the flexible motor mounts.  After a score of mighty swings the mechanic was visibly fatigued and perspiring heavily, yet the propeller remained fast with the shaft.  With each swing the propeller reverberated with an ear-splitting twang.  After a brief rest he resumed and the propeller ultimately yielded, sliding aft into the nut with a subdued clunk.


This strut bears mute testimony from abuse by blunt force.  A hammer was likely used to strike the forward end of the propeller hub, landing glancing blows on the strut in the process.

The physics of this approach are straightforward enough, with each blow, the shaft, transmission and engine were driven forward a fraction of an inch.  The mass of the propeller encouraged it to be left behind in that forward advance, eventually forcing it to separate from the shaft taper.  The technique worked, but at what price?  It’s likely that removing a propeller using blunt force of this or any kind, including striking the forward end of the propeller hub directly, driving the propeller aft, damages or shortens the life of transmission components, gears, bearings etc.  Pound for pound, transmissions are among the most costly pieces of gear aboard your boat, and repairing or replacing them is always a pricey and unpleasant experience.  In short, this technique and others like it should never be employed for propeller removal.

It’s Tempting But…

Some have proffered that the way to make it easier to separate a prop from its shaft is to take removal into account during assembly.  Toward that end, using anti-seize, grease or another release agent on the shaft taper is often advocated.  Make no mistake about it; under no circumstances, once again, should this practice be used.  Virtually every propeller manufacturer’s installation guidelines make it clear that props should be installed “dry”.  The one exception to this rule is an extremely thin application of lightweight machine oil, onto the shaft taper, is acceptable in that it will help prevent binding.


This propeller was installed with grease, remnants of which can be seen at the propeller to shaft interface.  The propeller was ruined in short order because it shifted on the taper each time the transmission was engaged.  Grease is viscous and incompressible, traits which virtually ensure that the propeller will fail to fully engage the shaft.

The primary goal is to make certain a propeller, once installed, stays put.  Using anything (grease and other viscous materials are incompressible, making a hydrolock scenario very likely) between a propeller’s bore and the shaft taper only increases the likelihood of movement between the two, which in turn can lead to sheared keys or worse, a lost propeller.  If removal is challenging, that’s a good sign, machine tapers like those used on shafts are truly amazing in their ability to reliably unify disparate parts, a desirable trait where propellers are concerned (I’ll cover propeller installation next month).

Removal Options

As desirable as it is to ensure a solid fit between a propeller and shaft, there will come a time when the two must be separated.  Fortunately, there are a variety of means of easily doing this, without damaging the propeller, shaft or transmission.


Hydraulic propeller removal tools are versatile and will work with most propellers.  They are, however, costly.

For boat yards, the Cadillac of propeller removal tools relies on the power of hydraulics.  Combination tool kits are available to remove propellers, shaft couplings and strut-mounted cutless bearings.  These tools enable yards to quickly and easily disassemble these components using a hand operated hydraulic pump, which actuates a ram, which in turn applies thousands of pounds of continuous rather than shock force to an assembly.  If you are in need of propeller service or shaft coupling removal, it’s well worth finding a yard that relies on a tool of this sort.


The “Dura-Mate” hydraulic prop puller kit manufactured by Durant Machine Company of Mystic, Connecticut.  This tool can also be used to remove propeller shaft couplings and shaft bearings. 

It’s worth repeating, under no circumstances should it ever be necessary to use shock force to disassemble any of the aforementioned components, propellers, couplings and cutless bearings.  As you might imagine, the convenience of this tool comes at a price.  A combination hydraulic prop, coupling, and cutless bearing removal tool costs several thousand dollars, and it’s large and heavy, in most cases it’s housed in a rolling dolly that’s about the size of a baby carriage.

Alternatively, mechanical, scissors-like prop removal tools are also available.  These are comparatively compact and lightweight, and much less expensive.  While useful, these tools do have limitations.  Primarily, they are incapable of imparting as much force a hydraulic tool, and they must be able to “reach” between two adjacent propeller blades, a requirement that may not be possible with some four and most five blade propellers.


A scissors style propeller removal tool.  These work for smaller, and three blade props.  Four blade props often don’t offer enough clearance between blades.

Yet another option relies on a custom made yet exceedingly simple pulling mandrel.  This arrangement consists of three high strength threaded rods and a plate that uses the propeller shaft end as its fulcrum.  The rods are screwed into matching threaded holes that have been bored and tapped in the aft end of the propeller hub.  Some propellers come from their manufacturer with these holes (If you are ordering a new prop or new boat, request them); some include just two holes which I would argue is inadequate for this process, some have no holes.  In any event, the holes can be easily added by most propeller shops; however, this cannot be done while the propeller is installed on the shaft.


In order to use some propeller pullers, the propeller’s hub must be drilled and tapped, with two and sometimes three holes.  To keep them free of debris, these holes should be filled with stainless steel or plastic Allen head screws.

With careful measurement and a simple drawing, most machine shops could make a custom tool for you at relatively low cost (I would argue that these should be provided as an option or standard by every boat builder, for their propeller arrangement).  The plate need not be made from exotic alloys, ordinary mild steel is more than adequate provided it’s painted and lightly oiled.  The threaded rods should be high strength; they can be easily purchased off the shelf.


The PropSmith is a compact, low impact means of effectively removing as well as installing (no other puller can make that claim) propellers, it is virtually fool-proof.  No inboard vessel should be without one.


The PropSmith, when stored in its plastic box, takes up roughly the same area as two hardback books.

The final approach, and one I favor, relies on a method that bears some resemblance to the pulling mandrel, however, it uses a purpose made tool known as a PropSmith.   The PropSmith also requires a trio of threaded holes in the prop’s hub, however, its fulcrum plate engages the shaft’s threads, holding it rock steady and making it especially useful for in water use by a diver.  Because of this threaded shaft engagement, an added benefit of the PropSmith is its ability to aid in installation of a propeller, pushing it firmly onto the taper.


A custom-made screw type puller.  These are simple and relatively easy to make, most machine shops could fabricate one for a few hundred dollars from readily available materials.

It’s not unreasonable to suggest that every vessel carry its own means of propeller removal, even if you never intend to undertake this task yourself.  Why is this necessary?  If you find yourself in a boat yard for planned or unexpected propeller work, and you see a mechanic making his or her way toward your boat carrying a large hammer and a bang nut, you can intercede with your own tool; you know it will work well, it will work quickly and you can be confident that it won’t cause any damage in the process.

Text and photos by Steve D’Antonio

Copyright © 2016

From the Mastheadmasthead

I want to hear your thoughts…
Customer care, it’s a subject about which every boat owner is concerned, and about which many are deeply frustrated.  As a student of customer service I pay attention to the details, I have been accused of obsessing over them, when it goes right, and when it doesn’t.  I keep a “customer care file”, which is filled with examples of both, I added to it just this afternoon after having lunch at a local cafe with clients (the service was excellent), sadly though too many stories are the those with unhappy endings.
I spent the better part of my career as a service provider, managing boat yards, endeavoring to provide the very highest quality customer care, and learning a great deal about what works, and what doesn’t.  Since then, I’ve spent the last nine years as a consultant and advocate for boat owners and buyers, helping make certain these folks are treated properly by the marine industry, boat builders, brokers, boat yards, and marine equipment manufacturers.

As an experienced troubleshooter, I’m a firm believer in finding the source of the problem and correcting it, rather than reacting to the symptom.  Customer care is no different, and as such, when given the opportunity I leap at the chance to write, or lecture on this subject at the source, for my marine industry colleagues.   I’ll do just this when I deliver a lecture at the annual International Boat Builders’ Exhibition (IBEX), held in Tampa Florida in October.  The title of the presentation is “Customer Care – Building Relationships”.  I want to make sure I share with attendees the very latest from the front lines.  Toward that end I’m asking Marine Systems Excellence readers to share with me your thoughts and experiences on customer care, what is important to you, what frustrates you most, and most important of all, what makes you want to return, what builds loyalty?   Send your thoughts to asksteve@stevedmarineconsulting.com

I’ll share a selection of these responses, leaving out all names, in an upcoming column.  If you don’t want your comments shared, even anonymously, please indicate this with your note.

Thank you.

Photo Essay: Expansion Tank Corrosion


Not to be confused with a recovery tank or bottle, the expansion tank on closed cooling system engines is part of the pressurized cooling circuit; it’s typically where the pressure cap is located.

In applications where a coolant recovery bottle is not use, an air space must remain within the expansion tank.  As the engine warms up, the coolant expands, filling this void, and when it cools off after being shut down the coolant contracts, at which point air from the engine room is drawn into this area through a check valve in the pressure cap.  When the coolant level is checked in an engine set up in this manner, when cold, the coolant cannot be filled to the level of the pressure cap neck.   If it is, when the engine warms up, coolant will overflow via the cap’s pressure relief mechanism, leaking out beneath the engine.  While undesirable, this is normal.  Thereafter, when the engine is cool, an air gap will remain in the expansion tank.

Coolant contains corrosion inhibitors, which prevent the formation of rust and corrosion; however, they are only effective if the metals they are protecting are submerged.  When exposed the protection is forfeited, and in this environment, corrosion is sure to ensue.  Fortunately, the bulk of the cooling system’s passages, especially those within cast iron blocks, exhaust manifolds and cylinder heads are, or should be, submerged in coolant at all times. However, an expansion tank that is not equipped with a coolant recovery bottle exposes its upper regions, the expansion zone, every time the engine cools off, after shut down, which can lead to corrosion, particularly in the case of cast iron expansion tanks, like the one shown here.

This scenario is yet another reason to equip closed cooling systems with a coolant recovery bottle, and the appropriate pressure cap for that application.  When so equipped, the expansion tank remains filled with coolant, and air-free, regardless of whether or not the engine is running or stationary, hot or cold.

Ask Steve


[For inverters] Since the negative 12V cable is going to the negative bus bar, and the chassis ground needs to go to the negative bus bar, why can’t you jump from the chassis ground to the negative 12 terminal?   I have a Magnum 2812 inverter/charger, and when I posed this question to their technical support person (since mine has the smaller green wire), he really didn’t have an answer for me or could tell me why the larger cable is recommended in marine applications but not necessarily for non-marine applications.

Jim Wolfe


This is an excellent question and one that isn’t asked often enough.  I’m a little disappointed the Magnum employee couldn’t answer it, however, in all fairness, it’s not their mandate, it’s ABYC’s.

Think of it this way, and to use an analogy, in household wiring, for a receptacle for instance, there are three wires, the black hot (similar to DC’s positive), the white neutral (the “negative”), and the green safety ground.  You could jump the safety ground connection to the neutral and effectively achieve the same end, the neutral is ultimately grounded (called a bootleg ground), however, doing so is prohibited.  The notion is, the safety or chassis ground is so important, it has to be its own, dedicated, normally mon-current carrying wire, whose only job is to carry fault current and then only long enough to trip a circuit breaker or blow a fuse.  And, of course that wire needs to be large enough to carry the maximum possible fault current, that which could be supplied by the DC positive.

I hope that explanation helps clarify the reasons why this is required.



I recently purchased a “vintage” 1973 Tartan 41 with a bare aluminum spar.  The mast and hardware are substantial and appear to be in great shape except for the many streaks and bare spots cause by the halyards chafing against the aluminum over the years…. not a pretty sight but only cosmetic.  I was thinking of painting the spar until I read your article in Cruising World “Bare is Better” (the article was referred by Rick at Jamestown Distributors) and have decided to hold off on the painting project.

What would you recommend as an alternative to painting as a way to spruce up the old aluminum spar and reduce the streaking and bare spots to provide a more unified appearance, as well as a way to help protect the sails from additional gray spots caused by contact with the aluminum mast?

Any suggestions are greatly appreciated and I look forward to your newsletter.

Best regards,

Tom Regan


It’s a truism, paint and aluminum, for the most part, make for a less than permanent bond.  It’s important to remember, however, while the bond is tenuous, there are a variety of ways to improve its durability and longevity.  If cosmetics are important, then paint for a spar may be an acceptable choice.  However, it’s anything but necessary from a corrosion perspective, it may even hasten corrosion should water make its way between paint and the spar’s surface, and it’s far more maintenance intensive.  You can read a more detailed article on the subject on my website at https://stevedmarineconsulting.com/paint-and-aluminum-how-to-ensure-a-good-mix-2/

Most modern unpainted spars are anodized.  Unfortunately, that’s not a practical alternative after the spar has been manufactured.

As another alternative, you might simply choose to polish the spars surface.  Doing so would give it an appearance not unlike a modern, unpainted commercial aircraft (or many fighters and bombers built during WWII, in the later stages of the war, when painted and camouflage were no longer deemed necessary), many of which are completely or partially unpainted (saving in build and maintenance costs, as well as improving fuel economy as unpainted aircraft weigh less).  A high polish will slow down the oxidation process, and it will reduce aluminum “shedding” to sails and lines.

Yet another alternative would be for a uniform mat finish.  This would look a little bit like the nose of the Spirit of St. Louis, Charles Lindbergh’s aircraft, although that finish had a uniform swirl pattern.  While slightly less corrosion resistant, the dull finish will be easier to maintain and “touch up”.



Is there a particular battery tester you recommend?

Ann Evans


I’ve been testing batteries for my entire 28-year career, and during that time I’ve developed, not surprisingly, some strong opinions.

I’ve followed the thread on the Nordhavn Owners’ Group forum and have not weighed in, primarily because I’m not a true believer in conductance type testing for large, deep cycle batteries.  Conductance, sometimes called digital, testers were designed to test automotive and truck starting batteries.  The primary manufacturer, Midtronics, own website says, “Automotive OEM dealers and service organizations around the world choose the Midtronics PBT-200 professional battery tester for its proven conductance technology and test algorithms.”  The key word is ‘automotive’.   The primary market for these tools was, and remains, auto and light truck dealerships and auto parts stores.

I was an early adopter of the technology, when I ran a boat yard I invested in two units, first and second generation models.  The results they provided for deep cycle batteries were all too often peculiar at best and suspicious at worst, condemning batteries that worked well, and passing batteries I knew to be defective.  The results they provided for starting batteries were more consistent.  Therefore, for anything other than start batteries, my preferred tool has been a carbon pile tester.  This essentially applies a ‘real-world’ load to a battery using a large resistor.  Two gauges clearly show the voltage and current the battery is carrying, and the operator measures the time they carry it (typically 15 seconds).  In short, carbon pile test results don’t lie, the battery either has the actual amps or it doesn’t.   There is a price to be paid for this accuracy, however, carbon pile testing can be hard on batteries, especially older or borderline batteries.  If the batteries are flooded, and the electrolyte is low (batteries with low electrolyte should never be load tested, or used for that matter) the heavy load can induce a spark, which can ignite hydrogen gas within the battery case, which in turn can cause an explosion.  This can’t happen with AGM and gel batteries.

Having said all this, there’s still hope for conductance testers.  The challenge is, the manufacturers of these products have had to come up with algorithms that work for a variety of battery sizes, brands and internal design (flooded, gel and AGM); that’s no easy feat.  Over the years the manufacturers of these tools have learned and refined the algorithms, which means false results are far less common.  Midtronics now offers a tester, the EXP-1000 HD,battery tester specifically designed for heavy duty, deep cycle and large battery bank applications.  While still not as reliable as the carbon pile tester, it is now reliable enough to use in applications like yours, and it’s smaller and safer.  However, don’t be lulled into a false sense of security, while conductance testers are safer, it would be very difficult for them to induce an explosion, you still must use caution when working around batteries.  Remove all metal jewelry, including rings, and wear eye protection, an inadvertent short can send a blob of molten metal sailing through the air.



I have been in the marine world my entire career starting in commercial fisheries and crew boats in the Louisiana oilfield and have always used an ant-seize compound when installing anything on a rotating shaft. That’s just the way it was. The goal was to make the boat propeller easy to remove from the shaft whenever necessary including by a SCUBA Diver. I realize there are now more environmentally friendly compounds but the goal remains the same, make it easy to remove the prop when needed.

Recently I helped a new boat owner launch his boat and the props were installed incorrectly, port was on starboard and vice versa. We had to pull the boat to remove the props. The props sit on a tapered shaft with a key way with 2 nuts and a cotter pin to secure the prop on the shaft to prevent slippage.

Since the boat had only been it the water less than 5 minutes there was no marine growth to blame for the props being stuck on the shaft. A prop puller was required with a little extra ump on the puller bolts. I asked the guy why they did not use never seize and he answered, “We never do.” When I followed up with why not, no one seems to have an answer. So Steve, what IS the answer? And while we are on this subject, which nut goes on first, the half nut or the whole nut?

Captain Chris Caldwell


This is a great question, and one many professionals ask.  Propellers do get stuck on shaft tapers, and that’s precisely the goal.  Putting aside the fact that the props were reversed, a neophyte error to be sure, and one I hope a professional yard didn’t make, the fact that the props were “stuck” on the shaft after just five minutes in the water is a good sign, it means they were installed properly, and the yard worker’s answer regarding the prohibition against anti-seize was one I would have been relieved to hear.

Given the choice, a propeller that comes loose from a shaft when it’s not supposed to is far worse than a propeller that’s stubbornly stuck when it comes time for removal.  In fact, if it’s not stuck at the time of removal, something is wrong.  The tapered shaft and bore for propellers and shafts, as well as for all machinery applications, is used to ensure no movement occurs between the two components once they are fully engaged.  While the inclination to ease disassembly is understandable, it flies in the face of the very goal of the taper, a semi-permanent connection between two components that are under considerable load.  Automotive differential flanges often use the same approach.

Assembling these components using grease or anti-seize can have two possible deleterious effects.  First, a lubricant can allow the prop and shaft to move independently of each other.  After all, that’s what lubricants do, they reduce friction and promote movement.  Clearly, in the case of props and shafts that’s undesirable.  Second, a viscous and incompressible material like grease or anti-seize can create a hydro-lock scenario, preventing a propeller from fully engaging the shaft taper.  In either case, the prop and shaft will ultimately move independent of each other every time the engine is shifted into and out of gear.  Once the prop begins to move in this manner, it will gall the shaft key as well as its own keyway.  Eventually the key may sheer, allowing the propeller shaft to spin freely within the propeller bore, inducing a permanent neutral scenario.  I’ve encountered greased shaft tapers on relatively new boats, the grease having been installed by the boat builder for the very purpose you noted, to ease disassembly, which resulted in wallowed out prop and shaft keyways, the former irreparably.

Prop shaft tapers should be lightly oiled, to prevent binding when the propeller is pushed onto the taper, no other lubricant should be used.  The prop should be pushed fully onto the taper without the key installed first, the shaft should then be scribed at the forward end of the taper.  Remove the prop, install the key (again lightly oiled), and then the prop.  Using the full height nut tighten it using a smooth jaw wrench (never a pipe wrench), drawing the prop onto the shaft taper.  The prop should go up to or past the scribe line, ensuring the key is not creating a bind.  Then remove the large nut, install the half-height nut, tighten it, then install the full height nut, and tighten it.  The reason for the nut order is as follows, the second nut, when tightened, will unload the first nut, transferring the majority of the load in the process.  Thus, it’s desirable to have that load carried by the nut that has more threads.  Also, the half-height nut is better able to conform to the face of the prop hub than the full height nut, ensuring better engagement.  The ‘half height nut first’ arrangement is specified by a variety of government, manufacturing and standards setting bodies, including ABYC, SAE, USCG, most propeller manufacturers and the US Navy.  If the prop nuts are brass (manganese bronze actually, which is a form of brass), then their threads require no lubricant.  If, however, the nuts are stainless steel, and the shaft is as well, there is a risk of galling, and as such the threads should be lightly oiled or, better still, coated with low tension thread locker such as blue LocTite 242, which will act as a thread lubricant until it sets.

Text and photos © 2019 Steve D’Antonio Marine Consulting, Inc.

Photo Essay: Manual Tiller Steering

Steering, along with propulsion and watertight integrity, is one of your vessel’s core systems, one that must be kept operational at all costs.  Without these capabilities you are either adrift or sinking.

Steering systems on most small vessels fall into one of two categories, cable over sheave or hydraulic.  While both can be made exceptionally reliable if properly designed, installed and maintained, failures do occur.  Vessel operators should be prepared for such failures, for cable systems a spare cable/chain assembly, or at least the ability to temporarily repair a cable section using bulldog clamps, is a must.  Where hydraulic systems are concerned it gets a bit more complex; spare hydraulic fluid is a must, while replacement hose sections and field-installed hydraulic hose ends, these are also comparatively inexpensive and easy to install, also make very good sense.

In the event a failure occurs, one that cannot be repaired at sea, a fall back option should be available; typically, this takes the form of a manual tiller.  Most are designed to engage the rudder stock using a socket arrangement.  For hydraulic systems a relief valve must also be installed, without it, it may be impossible to move a rudder without disconnecting the hydraulic ram, a task that could be time consuming and may leave the rudder with no stops and no damping effect.  If installation of the manual tiller requires the removal of a deck access plate, make certain that the key required to do so is readily accessible.

In the image shown here, taken aboard a vessel I inspected, the manual tiller does not fully engage the rudder stock.  It’s unlikely this tiller would work for very long.

If your vessel is equipped with a manual tiller, it should be tested, you should be able to have it operational in no less than three minutes; imagine you’ve lost steering while you are entering a narrow inlet, canal or cut, with wave action and wind.  Time yourself, how quickly can you unship the tiller, remove the deck plate, engage the rudder stock and open the relief valve?

A comment on Series and Parallel; What does it mean?

I use a mnemonic to remember the difference between parallel and serial connections. Years ago I used to shop at a grocery store called Pac-n-Sav. So I remember that, and I remember that Parallel Adds Current –n- Serial Adds Voltage. Easy!

Donald Million

Ask Steve


I have a Cal 24 sailboat with only one battery that I use a trickle charger from a battery charger. I haven’t sailed it in several years, and then really only during the day, so the battery by now is dead.

However, I’m thinking of a bigger project.

Some background:

Let’s say I have a water wheel, and a permanent magnet generator (PMG) similar to an altered alternator which produces voltage from the water wheel.

This PMG based on wiring the rectifiers can deliver either 24 or 48 volts. The maximum RPM I’m guessing is 1200 rpm’s delivering about 2000 watts.

Let’s say I have four (4) 12 volt 100 amp hour batteries. I could wire these four batteries in several different configurations, e.g., parallel, series, and parallel series depending on what I need to achieve for output energy needs.

If I wire them all in parallel, I could have 12 volts with 400 AH

If I wire them all in series, I could have 48 volts with 100 AH

If I wire them in parallel-series I believe I could have 48 volts 400 AH

I believe you mentioned in your article that batteries like to be charged at a particular rate to achieve the longest life of a battery. I don’t know how to determine what the optimal rate is, but here is my question…..

Based on the three different wiring battery bank configurations above, does wiring batteries in the various configurations change the optimal charging of the batteries to maximize life expectancy, or does charging a bank of batteries regardless of how many batteries are wired and in which configuration they are wired not have anything to do with charging the bank, as charging a battery bank is determined by only the optimal charging rate of one single battery within the bank?

In other words, is charging a battery bank driven more by the optimal or desired charging rate based on one single battery within the bank, or based on how the bank is wired in total.

I’m guessing that whatever the answer is to my above question will ultimately determine how to adjust the PMG, power sources, etc., to ensure it produces the desired charging rate to achieve maximum life for all batteries.

Thank you,



In broad terms, battery banks are wired for the voltage required by the vessel, typically 12 or 24 volts, and then charged at that voltage.  The required charge profile is established by the battery manufacturer, however, it’s relatively standardized for flooded batteries, with some variations for specific brands of SVRLA (Gel and AGM) batteries.  You should always consult the battery manufacturer’s charging requirements, and then ensure your charge source, alternator, shore charger, solar panel, water generator etc., is delivering that profile using a dedicated regulator.

Battery charge profiles are typically measured in volts, while charge acceptance rates are measured in amps.  A battery’s capacity is measured in Amp-hours, which is simply amps delivered over time.

While there are some advantages to connecting batteries in series rather than parallel, to avoid voltage imbalances, it would be impractical to do so simply for charging purposes.  Set the bank up for the voltage you need, sounds like 12 volts in this case, and thus paralleled 12 volt batteries, and then use and charge it in that configuration.



We are working on a new 38’ build and want to use PEX tubing for potable water delivery and for deck wash raw water lines. Though the tubing will run below decks, we have a concern about ultraviolet light exposure to the PEX since light may at times enter areas with the tubing through hatches, etc. I have been told that there is a significant risk of PEX failure if exposed to UV. If this is the case, is there a recommended protection system (e.g. painting the tubing)?

Tony Dean


Most modern, medium to large production boats utilize PEX for potable water as well as heating and some chiller air-conditioning systems, and have for a number of years.  I have yet to encounter many PEX failures, and as far as I’m aware none as a result of UV exposure.

Having said that, if exposed to sunlight PEX can degrade and fail, and this is true of most non-UV stabilized plastics. The exposure leads to embrittlement and eventually rupture.

In a document form Zurn, a large supplier of PEX plumbing, the issue is summed up as follows…

“Zurn PEX UV Resistance Like most plastic materials, PEX is subject to UV deterioration and must not be exposed to sunlight, either direct or indirect. Outside storage is not recommended, but if necessary, the tubing must be covered with a material that will protect it from UV light. Failure to do so will void the warranty. However, in the circumstance that a project is delayed, Zurn PEX tubing has UV stabilizers that are designed to protect the tube for up to 6 months. In this circumstance, protective measures should still be taken to limit UV exposure.”

For applications where PEX is exposed to sunlight for an extended period, on deck or in a cockpit for instance, it must be shielded or sleeved.


Hello Steve: 

I am in my 2nd year of owning a 1985 Oceania 35 Taiwanese trawler (3rd owner).  The boat is in Lake Ontario but has travelled to Florida twice over the years by previous owners. My question is, even though the boat is bonded, there is no anode on the stern of the hull.  There are two anodes on the two drive shafts and two on the rudders and that’s it.

I’m thinking of tracing all the green wires this spring to see where they end up.  I do know they attach onto the diesels, but there are no anodes in the engines either.  What to do? The previous owner kept a good log book, but no mention of issues.

Thanks for your help.

Barrie Marfleet



It’s never a bad idea to trace, and inspect the wiring in a bonding system, especially aboard an older boat.  Be sure to look closely at each one of the connections for corrosion and tension, all should be clean and tight.  My protocol is to remove each one, make sure the ring terminal is in good condition, clean it and the attachment surface with a ScotchBrite pad, apply conductive paste such as T&B Kopr-Shield, make the connection, and then spray with a corrosion inhibitor such as CRC Heavy Duty Corrosion Inhibitor.  You can check the integrity of the bonding system, using a multi-meter, while the vessel is hauled out.  The maximum resistance between any anode, and any protected metal should not exceed one ohm.

As far as attaching anodes to the bonding system, it’s essential if you want cathodic protection.  I can’t explain why the builder wouldn’t do this unless they expected the rudder anodes (assuming the rudders are bonded as they should be) to act in this role.

Ideally, anodes should be included in the bonding system, these are typically installed on the transom.  You can read more about bonding systems here https://stevedmarineconsulting.com/bonding-systems-and-corrosion-prevention/.



Our 1979 Watkins 36 ac has an integral diesel tank in our keel.

We are doing an electrical conversion to the boat.

The only way to remove the tank would be to cut the keel off and rebuild it.

Any thoughts as to how to clean the tank for a shower sump?  Or fill it with… something? (Foam…?)

As a professional that sells my time and knowledge I hate asking this but I just cannot find any info on this topic.


Steve Thorburn


Cutting the keel off to access the tank is definitely out, just in case there was any doubt regarding that option.

You don’t mention the tank material, however, if it’s metallic, steel or aluminum, then using it as a shower sump is ill advised, as corrosion will undoubtedly become an issue.  You could, however, install a dedicated non-metallic shower sump into the remnants of this tank, once you’ve removed the top.

In a case like this, the most effective means of dealing with a diesel tank involves cleaning it using a hot water pressure washer.  The interior of the vessel should be masked/curtained off and negative pressure applied to this area during the cleaning process, to prevent diesel fumes or splatter from entering the cabin.  If the tank is metallic, it should be emptied, and then gas-freed using compressed air, pumped into it for a minimum of 24 hours, to remove diesel fumes, after which cutting can begin.  Solids should then be scraped from the tank bottom.  Hot water pressure washers will emulsify and remove diesel residue; as the tank is being washed the waste water should be pumped out of the tank into a barrel.  After being allowed to separate, the fuel/oil residue can be removed from the surface of the water and properly disposed of.

If the tank is steel the interior should then prepared for paint and coated with a two-part epoxy suitable for metal priming.  Doing so will prevent it from rusting and eliminate any residual diesel odors.  Coating the inside of a diesel tank, and ensuring adhesion, would be problematic only of the tank were to be placed back into service for fuel use.  In this scenario, some paint adhesion failure, the result of traces of diesel left behind, would not be an issue.

Text and photos © 2019 Steve D’Antonio Marine Consulting, Inc.

From the Masthead

I turned the key and absolutely nothing happened, no dash lights, not even a click from under the hood.  My wife’s new car, a 2018 GMC Terrain diesel’s battery was stone-cold dead.  The culprit…the back hatch was impeded from closing fully thanks to cargo that had come adrift, which left the dome light on as well as some portion of the dash lights and computer.  Because we are in the midst of a move all of my shop tools, including my AGM-based start pack (which I’ve previously written about here) and heavy-duty battery charger/booster, and 16-foot long 4/0 (I made these myself) jumper cables, are in a different location than the Terrain.  It was a scenario I’ve rarely experienced, all of my key tools were elsewhere; I’ve rarely felt so powerless.

As I stood in the garage contemplating my plight, briefly considering using my AAA membership, for the first time ever, and how ignominious that would be, I gazed around the mostly barren space for inspiration.  My eyes came to rest on a black Pelican style-case, about the size of a small Igloo cooler, a KBi MiniHD ultracapacitor start pack; could this be my salvation?

Kold Ban International or KBi, Inc. has been making aids to engine starting for over three decades, including a cold weather diesel ether injection system, and more recently capacitor-based booster systems.  I first encountered them back in the early 2000’s when they sent me a sample of their ultracapacitor “battery” for evaluation.  It was intriguing, made in Russia it was able to easily start a 6-cylinder diesel engine multiple times with no difficulty, and yet unlike a lead acid battery it contained no electrolyte, would last for tens of thousands of cycles, recharged in seconds, and weighed a fraction of a traditional battery’s heft.  The only problem was its price, it was too expensive.   Fast-forward to 2019, KBI is now making their own supercapacitor-based starting systems using domestically-made capacitors (which enables far more competitive pricing), offering a permanently installed unit, the KSM, and a portable start pack, called the KrankingKART Mini HD, both of which I’ve tested extensively, however, not under anything other than simulated no-start conditions, not until the above-described dead battery scenario.

Two of the attributes of the ultracapacitor-based MiniHD and KSM is their ability to be recharged very quickly, typically in under one minute, and the time they will hold this charge without requiring a re-charge, advertised as several months.  The MiniHD sitting in my garage had been untouched since I completed my testing of it in late 2017, it was then moved to an unheated offsite storage unit, then recently to my temporary residence; it hadn’t received a charge in nearly 18-months.  I picked it up, dusted it off, pressed the volt meter test button and was initially relived to see that it illuminated.  That elation was, however, quickly followed by disappointment, it read just 12.2 volts, otherwise dead for an ordinary lead acid battery.  Yet another attribute of ultracapacitors, and unlike a traditional battery, is their ability to provide sufficient starting current even when their voltage is low; but would it work now? I opened the hood and hooked up the heavy-duty solid copper alligator clips to the vehicle’s dead battery and pressed the MiniHD’s relay button, which brought its ultracapacitors online, and then crossed my fingers and turned the ignition key.  The Terrain’s diesel engine roared to life; and the MiniHD recharged to 13.8 volts in less than a minute, leaving it ready for the next jump start.

Through my testing I knew what the KSM and MiniHD ultracapacitor start devices were capable of, however, this was a test I had not contemplated, allowing your last ditch emergency back up start device to lay dormant for a year and a half, and then call on it to start an engine whose battery isn’t weak but totally dead, something it’s not designed to do.  Try that with a conventional AGM-based start pack and you’ll almost certainly be disappointed.  In short, I was already a believer in the KBI technology; this event, however, has only served to reinforce that opinion.

For more information on KBi ultracapacitor start devices visit KSM and MiniHD.

This month’s Marine Systems Excellence eMagazine feature covers the subject of series vs. parallel electrical connections.  I hope you find it both interesting and useful.

Series and Parallel; What does it mean?

Building larger battery banks often involves a combination of series and parallel connections.

While I was the manager of a boat yard, and after contending with numerous job applicants who claimed to know a great deal more than they actually could demonstrate, I devised a prospective marine mechanic’s and electrician’s screening exam.  It consisted of fifty multiple choice questions evenly segregated into mechanical and electrical categories; if a candidate came along and claimed to ‘know it all’, and then some, the exam quickly separated those who could from those who could not.  The exam also included a practical, in the form of a box full of twenty-five numbered parts and tools that had to be matched up with their respective identifications, which were provided on a printed ledger; all one had to do was match the number to the described part or tool.  If you were genuinely knowledgeable and experienced, and you could differentiate a gram scale indicator from a glow plug, you would do well and would likely be hired.

I didn’t consider the exam to be overly difficult; when testing the content on my most skilled employees, those who I knew had what I (and author Tom Wolff) referred to as “the right stuff”, they obtained perfect or near-perfect scores.  However, it was rigorous and many found it challenging indeed, a fact that was demonstrated every so often by the behavior of some exam-takers.  On a few occasions I would check in on the candidate to see how he or she was doing only to find the chair empty, the exam partially completed; they were never seen or heard from again.  Others asked if they could take it home.

Invariably, the electrical questions that ensnared even many seasoned professionals involved the subject of series and parallel connections.  While the concept in and of itself is anything but complex, many folks, even professionals, have a hard time fully grasping just what it means and how it relates to real-world marine electrical systems and, as importantly, troubleshooting, installation instructions and digital multimeter use.

Series, Parallel and Battery Banks

Perhaps the most common example, and just as commonly a frequent source of misunderstanding, involves batteries.  Battery banks are often made up of individual batteries connected in parallel to provide increased amp-hour or reserve capacity as well as increased cranking amperage.  In short, no pun intended, the definition of parallel electrical connections means like terminals are connected, positive to positive and negative to negative.

For instance, a single 12 volt battery of the 8D group size will typically provide about 250 amp-hours of reserve capacity and 1300 cold cranking amps or CCA.  If two of these batteries are connected in parallel, the figures essentially double with the notable exception of the voltage (demonstrating the electrical ‘no free lunch’ rule), the amp-hours go to 500 and the CCA capacity (this is a measure of the number of amps a battery provides for 30 seconds at 0°F, not to be confused with marine cranking amps or MCA, which is measured at 32°F) reaches an impressive 2,600 amps.  Adding more batteries to this equation has the same effect; voltage remains the same, while amp-hours and cold cranking amps are added.

Paralleling batteries, connecting like terminals, positive to positive and negative to negative, yields higher reserve or amp-hour capacity, as well as cranking amps, while maintaining the same voltage as each individual battery.

What if, however, the vessel’s electrical system is 24 volts, a scenario that requires a different battery arrangement to achieve that voltage?  That changes the equation while continuing to observe the no free lunch rule, albeit in an inverse manner.  Two 8D batteries connected in series will yield 24 volts; however the amp-hours and CCA will remain the same, 250 and 1300 respectively.  Series connections are made by connecting unlike terminals of different batteries, positive to negative.  While that may seem counter-intuitive, connecting positive and negative, it is completely natural to do so for disparate batteries, it’s the same process used to create 12 volts within a single battery, by connecting the positive and negative terminals of multiple individual cells within a single battery.  These connections are usually, but not always, hidden under the battery’s case.

Batteries Other Than the 12-Volt Variety

Using the same series logic, 6-volt batteries can be connected in series to make twelve or 24 volts, with the same caveats, voltage is added while amp-hours and CCA remain constant based on each individual battery’s capacity.  Connecting batteries in series has several advantages, chief among these being they resist charging and voltage imbalances that are common in large battery banks that consist of batteries connected in parallel.  Very large battery banks may be made up of 2-volt batteries, twelve for a 24 volt system.  Each of these may be rated at as much as 1200 amp-hours.  Here’s your test, if you create such a bank, for 24 volt applications, using these 2-volt batteries, what will the overall amp hour capacity of that bank be?  While you are thinking about that consider this,  WWII diesel-electric “Fleet Class” submarines used two volt cells, 250 of them, (in two banks of 125 each), connected in series, providing 250 volts DC and 4000 amperes of current, which was used to operate electric propulsion motors and house loads while submerged.  These batteries were behemoths; each was eighteen inches square and four and a half feet tall.  The answer to the above question…1200 amp hours; remember, when connecting batteries in series voltage is added while amp-hours remain constant.

Large 24-volt battery banks are often created using an amalgamation of both series and parallel connections.  Four 6-volt batteries may be connected in series to create 24-volts, essentially one 24-volt bank, groups of which are then connected in parallel to increase amp-hour capacity.

Measuring Voltage and Amperage

A thorough understanding of series and parallel is also required when working with measurement tools such as digital multimeters or DMMs.  Voltage measurements are made in parallel, which means that after setting your DMM to volts DC (or AC if you are measuring shore power, generator or inverter voltage), the test leads are paralleled with whatever is being measured, the red test lead is placed on the positive battery terminal or source and the black test lead is placed on the negative terminal or source.  Ampere measurements, on the other hand are made in series.  For example, if you wanted to determine how many amps a light fixture used, you would separate the positive (or negative, it doesn’t matter) lead from the power source, a switch perhaps and, after setting the DMM to AMPS DC, insert the meter’s leads into the circuit, the red test lead on the power supply side of the circuit, the switch terminal, and the black test lead to the wire leading to the light, thereby completing the circuit.  The DMM becomes part of the circuit, the lamp lights and the meter reads the current flow, to a point.

 Multimeter voltage measurements are always made in parallel, with the red and black leads connected to positive and negative terminals respectively. 

Most DMMs will measure current in this manner up to about 10 amps, after which an internal fuse will blow, hopefully, before its circuits are damaged.  If you wish to measure larger amperages, you’ll have to use an inductive amp clamp, a feature found on many DMMs today, which senses amperage via an electromagnetic field, without ever making contact with the wire through which the current is passing.  It’s well worth the added expense to select a DMM that includes an inductive amp clamp, just make sure it measures AC as well as DC.

Current or ampere measurements are made in series, with the multimeter becoming part of the circuit.  For current measurements above about 10 amps an inductive amp clamp, like the one shown here, is often used.

If you can come to grips with the parallel and series concepts, many other electrical scenarios will begin to make more sense.  Take the time to learn these precepts, as well as learning how to use your DMM, you won’t regret it.

Text and photos © 2019 Steve D’Antonio Marine Consulting, Inc.

Photo Essay: Field-Made Bus Bars

Bus bars (it’s not spelled ‘buss’, the likely confusion arises from the fuse manufacturer, “Bussmann”) play a critical role in marine electrical systems, particularly those that are called on to convey high current.  Cases of heat generation, caused by high resistance connections that are loose, undersized or corroded, are not uncommon.

High quality bus bars are made from solid, oxygen-free (removing oxygen improves conductivity), copper with a minimum purity of 99%, and of course the cross section, the equivalent of wire gauge, of the bus bar must be capable of safely conveying the expected current.

An added bonus would include tin-coating, which would reduce the likelihood of oxidation or corrosion, although fully assembled bus bars can be sprayed with a clear coat to achieve a similar effect.  Where high current is concerned it’s best to use copper rather than brass.  By comparison of conductivity, silver is most conductive, with copper a close second, while brass is a distant 7th and bronze 8th.   Other than for low current applications, it’s best to use pure copper.

In the example shown in the accompanying image, three sheets of copper flat stock have been “laminated” together, to achieve the requisite ampacity or current-carrying ability.  This is a very poor approach indeed, the copper is heavily oxidized, making it likely that the resistance (along with gaps) between each layer is increased. Additionally, if one or two of the sheets were to lose continuity, if they cracked for instance, then the current would have to pass through the remaining sheets, possibly overloading them.  Using two small wires, rather than one large wire, to complete a circuit is a good analogy, it’s an acceptable practice only if one of the wires can safely carry the full load.

This laminated bus bar should be replaced with one made from solid copper.

Ask Steve

Hi Steve,

I found your site and after looking at your example inspection reports, I really admire your attention to details and understanding of ABYC (and common sense) guidelines.  I have a 2006 340 SunDancer and I have a couple of electrical connector questions.

I am relocating the AC circulation pump so that it is not mounted to the side of the main stringers where the bilge will collect water first.  I had a main bilge pump fail and it swamped the air-cooled AC pump so I am going to a March liquid cooled pump and moving it up while remaining well below the water line.  My question to you is how I should make the connection between the stranded wires from  the pump and the 120v circuit on the boat.  It’s my understanding that wire nuts are not acceptable for any connections as per ABYC so I’m wondering what I should use in the J-Box that is mounted on the transom?  They had but spliced and electrical taped the connections if I remember correctly.

Second question is about the bilge pumps themselves and how to best deal with the connections to the pumps.  I know the connections should be completely water tight and as high above the pump location as practical.  Do you recommend some sort of J-box that is waterproof and then use a terminal block for the pump and switch conductors?  I can’t find a single good example of how this should be done “right” online.

Thanks for your help in advance.

Ty Burger


You are wise to be cautious where shore power is concerned, as it presents a very real risk of both electrocution and fire.   The ABYC standards regarding alternating current, i.e. shore/genset/inverter power, connections are very clear, they must be housed within an enclosure.  Relevant entries from section E-11 include the following (I’ve added the highlight)… Junction boxes, cabinets, and other enclosures in which electrical connections are made shall be weatherproof, or installed in a protected location, to minimize the entrance or accumulation of moisture or water within the boxes, cabinets, or enclosures. In wet locations, metallic boxes, cabinets, or enclosures shall be mounted to minimize the entrapment of moisture between the box, cabinet, or enclosure, and the adjacent structure. If air spacing is used to accomplish this, the minimum shall be 1/4 inch (7 mm). Unused openings in boxes, cabinets, and weatherproof enclosures shall be closed. All conductors shall be supported and/or clamped to relieve strain on connections. All connections normally carrying current shall be made in enclosures to protect against shock hazards. Nonmetallic outlet boxes, flush device boxes and covers shall meet the requirements of UL 514C, Nonmetallic Outlet Boxes, Flush Device Boxes and Covers. Current-carrying conductors shall be routed as high as practicable above the bilge water level and other areas where water may accumulate. If conductors must be routed in the bilge or other areas where water may accumulate, the connections shall be watertight.

You are correct, use of wire nuts is prohibited.  Instead, I would recommend you use a terminal strip within the junction box, to which the wires can be attached using high quality, double crimp, nylon-insulated ring terminals, for more on those see this article.  Wires should enter the box from the bottom to prevent them acting as a water path or leader into the box, and make certain they are strain relieved so that when pulled on, they do not transmit tension to the connections.  If the area is damp, as it likely is, use a conductant pasted at the interface between the ring terminals and terminal strip (be careful not to create a conductant paste bridge between terminals).  The completed terminal strip should be coated with corrosion inhibitor.

As far as DC-powered bilge pumps are concerned, I wrote a detailed article on the subject a couple of years ago.  An excerpt follows.

A tinned-copper terminal strip with an insulating cover installed 4′ to 5′ (1.2m to 1.5m) above the bilge and then coated with corrosion inhibitor makes low-resistance connections secure yet accessible for inspection and testing. If this arrangement isn’t feasible, connections must be made as watertight as possible. Regardless of location, conductors should be coated with a conductive paste such as Thomas & Betts Kopr-Shield prior to installing crimp connectors. Connections should be made with high-quality heat-shrink tubing. When applying heat, be certain the resin completely encapsulates the wiring as it exits the tubing ends, and use caution when crimping such terminals, as overly aggressive dies can pierce heat-shrink insulation. Inspect the insulation carefully after heating, looking for areas that have been pierced. Secure all connections as far above bilge water as possible.

You can read the article in its entirety here


Hi Steve,

I found myself reading your piece about engine compartment fire extinguishers.  A few years ago, I put in a fire port in the engine bulkhead and got one of the expensive, liquid type engine room extinguishers. So I’m up to date on that item.

From reading your piece, I realize I have some more work to do.

Question 1:

I have a fan/blower which takes in air from the lazzaret and blows it onto the alternator to keep it cool.   I now realize it would be good to add a temperature switch (maybe from Klixon) that will cut off electricity to that blower if there is a fire in the engine compartment.  What would be a sensible temperature to have the blower switched off?  Maybe something like 180 degrees F?   Another temp switch can turn on a fire alarm.

Question 2:

Is it desirable to have an automatic shut down for the engine?  My boat was recently re-powered with a Yanmar 4JH5E.  The normal engine turnoff button is under a cockpit seat, in a space that is somewhat connected to the engine compartment.

In theory, it should be possible to have a temp switch turn off the engine, if someone can figure out the Yanmar wiring system so that the stop solenoid or fuel pump can be turned off.

Many thanks,

Ben Stavis


You’ve posed some good questions.  I’m afraid the temperature switch controlling the blower would not be the most sensible approach, as there’s no guarantee that the heat of the fire would trigger it at the right time.  Incidentally, most automatic fixed fire extinguishers are set to discharge at 175° F.  That’s not to say you couldn’t install such a system, I just wouldn’t place absolute faith in it to turn off the ventilation system in the event of a fire, or before discharging a fire extinguisher.

By the same token, relying on a temperature switch to turn off the engine would be very risky for two reasons.  One, and once again, you couldn’t be completely certain the switch would turn off the engine after a fire started, and equally as important, if the switch malfunctioned it could turn off your engine at an inopportune moment, when you were docking or passing in front of another vessel.  It is for this reason that high coolant temperature and low oil pressure alarms do not automatically shut down propulsion engines.

In order to be ABYC compliant, diesel-powered vessels equipped with fixed fire extinguishing systems (with a few exceptions, some of which include the use of fire ports, diesel and gas inboard vessels are required, for ABYC compliance, to have automatic fixed fire extinguishing systems) must also be equipped with automatic engine and ventilation shut down systems.  In your case, because you are relying on a manually discharged (I presume gaseous) fire extinguisher, used with a fire port, it is assumed you would serve as the engine and ventilation shut down ‘system’.  Therefore, it is imperative, in the event of a fire, that you shut down the engine and ventilation system before discharging the fire extinguisher.


Hi Steve,

I seem to have the odd boat question for which I can’t find answers in the usual places so I go to Steve D’Antonio.

My Gozzard 44 has a Westerbeke 82 with a coolant expansion tank which is kept 1/2 full. Recently, upon checking the level it was full to the brim. Drained it, then a few days later found it again full to the top.

I suspected the heat exchanger had a leak so did a coolant pressure test but it proved negative. Since the engine had 1500 hrs on it I replaced the HE believing the leak may occur only at temperature. But the expansion tank kept filling to the brim!

The only other place domestic water and coolant water comes in close contact is the water heater – in this case an 11 gallon Force 10 heater. Mechanics told me it was not possible for hot water to leak into the coolant in the heater.

Again, since the boat is 14 years old I decided to replace the heater with an identical Kuuma.  That seems to have solved the problem, the expansion tank has remained 1/2 full for months.

Since the pressure differential is 5 psi for the coolant versus 35 psi for the water system (when hooked up to shore water pressure could be 100 psi, although there is an inline pressure regulator). In theory it’s a possibility.

I imagine a little antifreeze mixed in your hot water shower wouldn’t be noticed but long term not very healthy. I emailed Kuuma with my story but surprisingly haven’t not heard back.




In short, the mechanic is mistaken, water heater heat exchangers can and do leak water into the cooling system.  Coolant is poisonous in strong enough concentrations, making this a very real concern.

The heat exchanger in the water heater can easily be pressure tested to confirm this is, or was, the source. If the old one is still around I’d do this if for no other reason than to satisfy my curiosity.  Some heat exchangers can be replaced, saving the hassle of replacing the entire water heater, and it can be inspected and tested for leaks.

As an aside, I’m no fan of aluminum water heaters, of which the Force 10 and Kuuma are two, they are more prone to corrosion-induced failures, including leaking heat exchangers.


Dear Steve,

The small fitting on my dripless shaft seals looks like it is plastic.

When I move the hose attached, it actually wobbles slightly. This does not seem right and looks like a potential leak if it were to break off or pop out. Do I need to pull the boat out of the water to replace this?

Jim Norton


You don’t mention the brand of seal, however, at least one seal manufacturer I know of, at one time, used a nylon pipe to hose adapter.  They have since switched to metallic in order to meet inspected vessel fire resistance requirements.   If it’s this one, then yes, I agree, it’s flexible and can appear flimsy.  However, I’ve never seen one fail.  My recommendation would be to contact the seal manufacturer to confirm it is original equipment, and to determine if they believe it should be replaced or updated.

Text and photos © 2019 Steve D’Antonio Marine Consulting, Inc.

From the Masthead

For those who don’t know it, Taiwan is a mecca for boat building and manufacturing of all sorts, everything from coffee pots and cookware to lathes and CNC routers are made here.  As I drive and ride through the country I marvel; it seems to be one giant workshop.  Yacht building is clustered around Kaohsiung, where you’ll find yards building Fleming, Outer Reef, Kadey Krogen and Horizon to name a few, as well as Tainan, where several Nordhavn models are built by the Ta Shing yard.

I’m sitting on a train (I love trains) traveling between Kaohsiung and Tainan as I write this month’s column.  I’ve been to Taiwan scores of times and consider every trip both an adventure and learning experience.  Although generalizations can be dangerous, I’ve visited and worked here often enough to safely draw some conclusions.  The Taiwanese people possess a variety of attributes, they are industrious, honest, and helpful to a fault, especially to foreigners; while crowded, their society is among the safest and most harmonious I’ve ever visited, I’m fairly certain in ten years of visits I’ve never heard a voice raised in anger.

A wooden cell phone charging box located in a regional Taiwanese train station.  There’s a sign above it, in English and Chinese, that lets passengers know that loaner cell phone chargers are available upon request.

Taiwan’s mass transit system is a marvel of efficiency and engineering.  Trains are fast, modern, clean, affordable and easy to navigate.  The high-speed train travels from Taipei in the north to Kaohsiung in the south, in about two and a half hours.   All three airports I’ve used, Taoyuan, and Songshan, located in the northern capital  of Taipei, and Kaohsiung located further south on the island, are modern, clean and efficient.  Taxis are inexpensive, and clean and their drivers are scrupulously honest, you can hold out your hand with coins and they’ll take the proper fare; they expect no tips and they make it their mission to get you to your destination as fast has humanly possible.  While few speak English, most have translation apps on their phones, making communication relatively easy, but I’ve learned it helps if you have your destination written in Chinese.

Most Taiwanese train stations have a safety officer, he or she will politely remind you to step back if you get too close the platform edge.

While hiking in a national park a few days ago I got caught in a downpour.  A Taiwanese family (three generations, that’s common) was walking alongside me, they quickly donned rain gear and brought out umbrellas.  I had a raincoat and rain pants, as well as a wide brimmed water proof hat, but no umbrella.  A young girl with the family warned me to put my cameras away quickly lest they get wet, she then inquired if I had an umbrella.  When I said I didn’t, she spoke to her mother in Chinese, then said to me, “My mother said you must take one of our umbrellas”.  I refused of course, but she and her mother were insistent; I eventually saw this fight would be futile, they weren’t going to stand for me getting rained on. At the end of the walk the deluge turned to a drizzle, I tried to return the umbrella to them but they refused, saying, “You keep, they are very cheap in Taiwan”.

The famous narrow-gauge Alishan Forest Railway.

Finally, if you like Chinese food, Taiwan’s variety is nearly endless, on every trip I encounter something new, like the century eggs I came across a few days ago at a market in Fenqihu.  Raw eggs are prepared by coating them in a mixture of clay, wood ash, calcium, rice husks and salt, and then aged for several months.  The taste is…unique.

While they aren’t really 100 years old, these Century Eggs do look like they’ve been around for a while.

If you have the opportunity to travel to Taiwan, for a boat building project or any other reason, I strongly recommend to take advantage of it, I have no doubt it will be a memorable experience.

This month’s eMagazine feature article covers the subject of auto-starting generators.  I hope you find it both interesting and useful.

Automatic Generator Starting

There should be a clear indication to those aboard as to when auto-start is enabled, this image represents a good example.

It’s a common challenge for live aboard cruisers who frequently anchor out rather than spend time dockside; how do you keep the batteries charged, reefers cold and other critical systems running if you are away from the boat for more than a few hours?  Until a few years ago there wasn’t an easy answer.  Lately, however, more and more boat builders and vessel owners are taking advantage of the same generator automatic start technology that’s been used in homes and businesses for years, with a few modifications, and some important caveats.

Home standby generators are triggered by a power outage.   When the power goes out, a relay starts the genset, allows it to warm up for a few minutes, and then actuates a motorized transfer switch, which does several things; It disconnects the house from the utility company supply so two power sources cannot be connected simultaneously (more on that below), a scenario that can lead to damaged equipment or a fire, and so the genset does not back feed the utility lines, potentially electrocuting an utility repair person, and it connects the genset’s output to the home’s circuit breaker panel (or some part of it, many systems are designed to operate critical, but not necessarily all, gear).

It’s worth reiterating, accidentally connecting the generator to a shore power/utility company source, thereby causing a “crash parallel” with the public utility, can have disastrous consequences. A breaker won’t react quickly enough to prevent mechanical and electrical damage to the engine. If the generator is running, it would not be unusual to break a connecting rod and eject it through the engine block and sometimes through a tank or hull.

All gensets should have local start and stop, however, those equipped with an auto-start system must also have a lock-out feature, that when actuated will prevent the genset from starting until actively reset or released.

Aboard a boat the scenario is similar, however, the trigger is typically house battery voltage rather than loss of shore power; if the vessel is at anchor it already has no shore power (although it can be set up to start if shore power is lost for vessels that are dockside and unattended).  At this stage it gets a little tricky, if all the owner wants to do is charge batteries, the triggering signal can be sent from an inverter/charger when it reaches a low voltage threshold.  With that signal the genset starts, and after a short delay the inverter/charger begins charging the batteries.  Once the charger switches to float mode, indicating the batteries are fully charged (and load therefore is very low), a stop signal is sent to the genset.  That approach is relatively straight forward, and importantly, with some exceptions (see below*) it requires no transfer switch.

*Depending on the size of the inverter bank and the idle or light load current, the AC load may be sufficient to cause a huge D.C. spike from the automatic voltage regulator  (AVR) to the exciter field, destroying the AVR and rotating rectifier diodes on the back of the main rotor. Starting or stopping a generator with an AC load connected is strongly discouraged by just about every manufacturer.

If, however, you wish to supply power from the genset directly, i.e. not via an inverter and batteries, to any other AC gear, such as reefers, or HVAC, the hardware must mimic the home design, using a transfer switch, one that does not connect loads to the genset until it has started, and disconnects loads before the genset shuts down.  It’s worth noting, an inverter/charger cannot invert and charge simultaneously, so if it is doing the charging, while that’s happening it’s not inverting, so AC loads will be left without power.  If you use a stand-alone charger in this role, instead of an inverter charger, most have no delay, so they begin applying a load to the genset before it has started.

Why the issue with loads being present at start up and shut down? Typically, when a genset is starting, or is in the process of shutting down, its voltage output is very low.  That low voltage can trigger very high current or amperage for inductive, or motor loads like refrigeration and air-conditioning compressors; high current and low voltage can cause damage to both genset and electric motors/compressors, and as such that scenario, a load being present at start up or shut down, must be avoided at all costs.

Dyna Gen’s TG410 and Northern Lights’ TSC generator controllers incorporate provisions for “warmup” and cool down that can send a battery voltage signal from the auxiliary connector to a relay controlling a load transfer contactor or switch. When properly configured, the signal is energized 120 seconds after the start command is received from either the external device or the Run button on the controller and de-energized when the Run command is turned off, but the generator’s engine is allowed to run an additional 120 seconds to cool down. This would be the minimum acceptable functionality of any control devices used in auto-start generators.

Newer smart genset controls often incorporate auto-start, as well as warm up and cool down timing features.

Beyond that, there are other issues to consider where auto-start is concerned.  The first involves the safety of those accessing the genset, whether vessel owner or service personnel.  Recently, while inspecting an auto-start equipped genset, it spontaneously started moments after I’d removed the enclosure cover.  It startled me to say the least.  Gensets equipped with auto-start must be equipped with conspicuous placards both on the enclosure and on the genset itself, and they must be equipped with a local lockout, i.e. a means of preventing it starting, which is located at the genset.  Additionally, auto-start gensets should be equipped with an audible and visual warning that is activated before starting; this can be wired to the glow plug circuit, thereby alerting those in the area that start up is about to occur.

Finally, if you opt for the auto-start route, and you intend to allow the genset to start while no one is aboard, you must be aware of the associated risks.  What happens if the engine or exhaust system overheats?  Ideally, most marine gensets will shut down automatically.  But what happens if that system malfunctions, and it doesn’t shut down?  That could be a catastrophic even if the vessel is occupied, however, there’s a chance that it would be noticed before a fire started.  Or, what happens of the vessel is hauled and the auto-start is not disabled, allowing the genset to start with no seawater for cooling?

Wet exhausts require a continuous flow of cooling water.  If it’s lost, even for a few seconds, the exhaust system hose, plastic and fiberglass components will quickly overheat; in a worst case scenario it could catch fire. 

In closing, when I shared a draft of this column with my colleague and friend Bob Senter of Northern Lights, he said the following, “Steve, what do you think of a recommendation to annually “prove” the functionality of safety shutdown switches used in auto-start equipped machines? A non-functional exhaust elbow temperature, or seawater flow, switch could create the conditions for an exhaust system fire or worse if seawater was lost for any reason. In my opinion, auto-start machines on recreational vessels without manned engine rooms present a plethora of hazards that haven’t been thoroughly explored and addressed.

When Boeing relied on one angle of attack sensor for the 737 MAX MCAS system (unless the buyer paid extra for programming the second sensor with a “disagree” light) it became a recipe for disaster. Perhaps TWO exhaust temperature switches might be a prudent minimum for recreational auto-start machines with seawater cooled exhaust systems.”

Most gensets incorporate automatic shutdown protection in the event of coolant and exhaust overheating, as well as low oil pressure.  If any of these fail to operate while the genset is running the results could be costly and dangerous, particularly in the case of a failed high wet exhaust temperature shut down switch. 

As usual, Bob makes some excellent points, ones well worth considering.  Genset auto-start is not a set and forget proposition, whether you are a boat owner or builder, you must be aware of, and willing to accept, the risks associated with internal combustion machinery that can start spontaneously and operate while unattended.


Text and photos © 2019 Steve D’Antonio Marine Consulting, Inc.

From the Masthead

The Value of Time

Not long ago, a client and I spoke about the work that was being carried out aboard a vessel he recently purchased.  He, his wife and their children plan to move aboard in the near future to begin their full-time cruising adventure.  For the moment, however, he’s still working and flying between his home and the boat every week or two to meet with mechanics, electricians, carpenters and other industry professionals, to review in-progress and upcoming tasks.  I’ve strongly encouraged him to take an active role in the refit, including onsite inspections and meetings, rather than attempting to manage these projects from afar; an approach that nearly always results in an unsatisfactory outcome.

After one such meeting, he lamented how one of the professionals with whom he met talked a great deal, although mostly about things other than the project he was working on for this client.  That caught my attention.  When I managed a boat yard my office had the proverbial revolving door, employees entered and left all day long looking for guidance, advice and assistance with various projects and challenges, it was frenetic to say the least.  Getting work completed in that environment could be challenging.  I adopted two techniques which were helpful, the first involved a mandate on my part, which went like this, “If you bring me a question, be prepared with your own answer”.  That approach ensured the person looking for help had given some thought to the problem, rather than simply coming to me for a quick fix.  The second included a time limitation, if someone stopped in and said, “I need help with this…” I’d respond by saying, “I can give you five minutes now, or we can schedule a longer meeting later today or tomorrow”.  Once the staff became accustomed to these guidelines, the number of visits, and their duration (and the time it took these folks away from their work), dropped noticeably.  One other factor played a role in the number of visits I received; the second floor office I used for a few years received fewer drop ins than the first floor office, I referred to the steps leading to it as, “The stairway of contemplation”, those who climbed them usually had a good reason for doing so.

In that role I learned a great deal about time management, while developing a keen sense of appreciation for those who valued my time, and their own.  Those who could share with me exactly what I needed to know, and little extra, received my appreciation and recognition.

Today, when I work with clients, I make an effort to respect the value of their time.  For my colleagues in the industry, keep in mind the value of your client’s time, share with them what they need to know quickly and professionally (give them what I call “the four”, what’s wrong, what will it take to fix it, how much will it cost and how long will it take, all in one shot), while keeping the small talk to a minimum, it will almost certainly be appreciated.

If you are a boat owner or buyer and you believe the value of your time is not being respected by those who you are paying for assistance, try using a variation of the “I have five minutes” tool.  For in-person or telephone conversations, preface the discussion by saying, “I realize you are busy and want to be respectful of your time, I just need 10 minutes to share with you this…”

This month’s eMagazine feature article covers the subject of damage control.  I hope you find it both interesting and useful.

The Ethos of Damage Control

Equal Measures Technique, Gear and State of Mind

Damage control events rarely occur in benign conditions; heavy weather is when gear, vessel and crew, are tested.

Every vessel operator, at one time or another, faces a damage control scenario, wherein a piece gear fails, sometimes benignly, sometimes catastrophically.  The “gear” could be anything from a failed raw water hose to a breached hull.  If it hasn’t happened to you, yet, you’ve been fortunate, however, the law of averages is against you, the more time you spend underway, the more likely this is to occur.

Excessively leveraged raw water plumbing components are a damage control scenario waiting to happen.

A well-maintained vessel is less likely to suffer avoidable failures that require damage control measures, or they may be less intensive.  However, regardless of a vessel’s operating condition, difficult to predict events, striking a submerged object or running aground, for instance can lead to flooding and the need to quickly and effectively deal with the results thereof.

By the same token, steering system failures and rig collapses all represent “opportunities” for a vessel’s crew to either rise to the occasion and stem the tide, figuratively as well as literally, or break out the EPIRB and abandon ship.  Naturally, the former is preferred wherever possible, keeping the vessel afloat, first and foremost, and then underway and self-sufficient, are priorities where damage control measures are concerned.

Hull damage like that shown here, suffered by this vessel while cruising to Bermuda, will test a crew’s damage control skills.


This is the most common type of onboard emergency that requires damage control measures, and it’s the one for which every vessel operator and crew should be prepared.

There are two primary types of flooding.  The first occurs as a result of a breach in the hull, from a collision with a submerged object or other vessel, grounding or a failed through hull fitting (this is the component that passes through the hull and interfaces with a seacock), or underwater hardware attachment point, such as a strut or shaft log.  It may also involve ‘down-flooding’, a phenomenon wherein water enters the vessel through an existing breach or opening rather than as a result of damage or a failed component; this could include a port, window or windshield, hatch or vent, even a shore power cable reel entry point.  This may also occur if the vessel heels or is awash as a result of heavy weather, or a grounding and “drying”, where the vessel heels over and is ultimately left high and dry as the tide falls, and then rises again. When this occurs, the vessel may heel enough to admit water from openings that are normally well above the waterline, with the most common being engine room vents, cockpit hatches and sail lockers.

Running gear components like struts, shaft logs and shafts are vulnerable to damage when running aground or striking submerged objects; which often leads to flooding.

In any of these cases water enters the vessel, often at a prodigious rate.  A one inch hole one foot below the waterline will admit 1,200 gallons per hour, while a two inch hole two feet below the waterline will admit over 6,000 gallons per hour.  If you’re thinking that a bilge pump can keep up with flood rates like these, particularly the two inch hole example, unless it’s of the ultra-high capacity “crash pump” variety (typically hydraulic, or small engine-powered), you can forget it, it’s simply not practical in most scenarios (for more on bilge pump system design and installation see pumps).

When flooding occurs, trash and building debris are invariably washed into bilges, and bilge pumps.  Keeping your bilges clean reduces the likelihood of clogged pump strainers.

The second type of flooding results from the failure of plumbing within the vessel, a parted raw water or stuffing box hose, or broken plumbing such as a sea strainer, air-conditioning, or wash-down pump or related components (more often than not these are the result of neglect).  The result is the same; however, water enters the hull envelope.  It’s worth noting, new vessels are not immune to these failures; builder errors in raw water plumbing component design, selection and assembly often result in leaks and occasionally flooding.

Nearly all flooding that is the result of failed below the waterline plumbing is preventable.  Inspect your raw water systems regularly.

According to BoatUS insurance claim statistics, fully 40% of all underway sinkings are the result of striking a submerged object, while 16% are the result of a broken propeller shaft or strut, and another 16% the result of damaged or deteriorated below the waterline plumbing.


The watch words where damage control is concerned are planning and preparation.  Priority must first be given to finding and stemming the source of the leak, then to dewatering the vessel.  If you can do both, that’s desirable, however, if you only have enough resources to attack one, it must be the water entry issue.  Successfully doing so means possessing a thorough understanding of your vessel and its various engineering spaces and bilges, this includes knowing the location of every seacock, and ensuring it’s readily accessible and functional, ideally these should be cycled no less than quarterly.  Toward this end, conspicuously post a chart identifying the location of every seacock (and fire extinguisher), and through hull fitting above and below the waterline, especially if you are cruising or racing with guests (in the latter case, post the chart in the head where those who are seated have no choice but to study it).

The responsible skipper should know where every through hull fitting and seacock is aboard his or her vessel.  A seacock “map” should be conspicuously posted aboard the vessel.


In the case of a collision with a submerged object or a grounding, the most challenging aspect of carrying out your damage control plan often involves accessing the inside of the hull where the breach has occurred.  Cabinetry and other joiner-work often makes this very difficult, particularly if the vessel is equipped with a fiberglass liner.  You should, therefore, be prepared, to the extent it is possible, to cut, chop or smash joiner-work to get to the source of the leak.  This may involve the use of a hatchet (I prefer a kindling hatchet, these are blunter and heavier than conventional hatchets), and a maul.

High water alarms should be an essential part of every bilge pump system.  Here, a battery-powered, piercing annunciator (top) is impossible to ignore, however, the float switch (above) used to trigger it is too high, it should be located no more than two inches at most above the bilge pump’s own switch. 

The Damage Control or “DC” Kit

Once the breach has been accessed, break out your damage control kit, which should include, but by no means be limited to, the following.

  • Soft wood plugs (cedar is ideal, teak and other hard woods are undesirable), or one of the newer synthetic variety. I’m not an advocate of attaching a plug to every seacock; they get in the way and often deteriorate.
  • Two or three one-foot square 5/16-inch-thick sections of plywood, these are thin and flexible enough to conform to hull shape.
  • Wood or synthetic wedges to put pressure on patches, along with a few various lengths of 2”x2” “timbers” for shoring up a patch.
  • Square drive, stainless steel cutting point screws, often called PK (after the manufacturer, Parker-Kalon). These are designed to cut through sheet metal; however, they work very well on wood, fiberglass and aluminum.  With a cordless drill, and square driver bit, they can be used to secure patches in place.
  • Sealant, fast cure polyurethane is well suited to these repairs, it cures while wet.
  • Two part putty-like epoxy, it too cures underwater (Evercoat manufactures such a product).
  • Waterproof duct, “100 Mile an Hour” or “Rescue” tape, or your favorite equivalent, as well as a roll of self-amalgamating tape.
  • Stainless steel seizing wire.
  • Damage control putty.
  • A few patches (preferably slightly larger than your 1×1 foot plywood squares) of felt padding for filling voids. A light blanket also works well.
  • An exterior hull patch or collision mat.
  • Expanding foam in a spray can, it’s well suited to filling voids and placing pressure on patches. Available on line and form home improvement stores.

Of course, you can and should make use of other items that are already aboard your vessel, including cushions, pillows, mattresses, hatch covers etc.  An engine room hatch with insulation already attached can work very well as a pre-made form -fitting patch.  If you aren’t up to making your own, ready-made damage control kits are available off the shelf from Sea Kits.

Your damage control kit should include plugs that can be used to fill holes, this version is made from closed cell foam, it can be used to fill irregular-shaped gaps.

If the breach can’t be accessed from inside the vessel, you may have to resort to tried and true mariner’s trick of “fothering” a sail, or placing fabric patch on the outside of the hull.  This technique has been used many times over centuries of seafaring, notably by the crews of the Mayflower and Captain Cook’s HMS Endeavour.  If your vessel doesn’t have sails all is not lost, triangular hull patches or “collision mats” with lines affixed to each point are available.

Collision mats can prove useful in the event a damaged hull section cannot be accessed from the interior.

Give thought to your vessel’s design, what would happen if you ran aground on a falling tide and the vessel was left high and dry?   As mentioned previously, vessels equipped with vents in the hull could be susceptible to down flooding, and the same could be true of cockpit hatches.  Do you have a way to cover or secure these openings?  Suitably strong tape and heavy plastic may be all that’s needed.

Conventional Phillips head tapping screws, left, and cutting tip, square-drive screws, right, should be part of every damage control kit.  Both must be stainless steel to ensure they don’t rust while in storage. 

Internal Leaks

Internal leaks, those that come from failed hoses or plumbing, may be easier to deal with in that in many cases all that’s required to stop the ingress of water is closing a seacock.  That may be easier said than done, however.  If the leak is, by the time it’s noticed, under water, then finding it and determining if a seacock can stop it may be difficult.  If the source of flooding isn’t immediately clear, quickly closing all seacocks, other than those for the engine and generator, makes good sense.  Engine and genset plumbing should be inspected as soon as possible thereafter; however, disabling this gear by shutting seacocks can be a liability as it is a source of power for bilge pumps, and communications, as well as propelling the vessel to safety, rendezvous with assistance, a haul out, or even beaching if necessary.  While pumps will likely not be able to stay ahead of anything but a minor leak, they may buy precious minutes to find and fix it, so don’t discount their value entirely.

The consistency of peanut butter, proprietary damage control sealant can be forced into cracks and voids both inside and outside the vessel.

Failed hoses and pipes should be replaced if possible, and if not patched with tape, hose clamps and/or seizing wire.  The same is true for a stuffing box hose, a particularly debilitating failure in that replacement is impossible without hauling the vessel.  Stuffing box hoses should be inspected regularly for any signs of deterioration, cracking or leaks; at last one dripless stuffing box manufacturer stipulates a six year preemptive replacement interval, regardless of hose condition.  In the event of a failure, be prepared to wrap it with plastic, tape and splints if necessary.

Soft wood plugs, typically cedar, are old-school but useful, keep a supply aboard.


Many years ago, as a young member of the Naval Sea Cadet Corps, I had the opportunity to undergo damage control training aboard the USS Buttercup, at the naval base in Newport Rhode Island.  Buttercup was barge of sorts that floated, and sank at times albeit under controlled conditions, in an indoor pool whose cold, oily water lent an air of realism the exercise, its flooding and lurching machinations controlled by a salty Chief Petty Officer from a nearby control station.

Using patches, wedges, clamps, blankets and mattresses leaks were patched, and the vessel kept afloat using powerful venturi-type pumps.  This training drove home several points, chief among them are flooding can be extremely frightening, even when simulated, and you can never have enough DC gear or training in its use.

Soft foam rubber mat sections can be used to fill gaps and account for hull curvature when making patches.

More recently, two high-profile collisions between US warships, the USS McCain and the USS Fitzgerald, and merchant vessels, while controversial in and of themselves, reinforced the value of damage control, both vessels were saved as a result of their well-trained DC parties.  In light of that, it’s important to be prepared, make sure you have what’s needed in your DC locker, make sure you thoroughly understand how to use it quickly and effectively, and know where all of your through hull fittings and seacocks are located.

For more information on flooding and damage control, please read this article.  

Photo Essay: Hull to Deck Joint

Few boat building interfaces are as important as the one that occurs between the hull and deck.  The loads imparted to this joint are considerable, especially for vessels that encounter tumultuous conditions, including offshore power and sailing vessels, or those that work in heavy surf.  The “shoe box” arrangement like the one shown here can, provided it’s properly designed and built, be strong and resilient.  The intersecting surfaces should utilize an adhesive/sealant, and they must be free of gelcoat or paint (coatings can be pulled off the surfaces over which they are applied by aggressive adhesives).  Through bolting, as opposed to tapping screws, is a must where maximum strength is sought.

The bolt shown (the tapping screw is used to support the rub rail) in the accompanying image is stout, and there are many of them, and that’s good.  However, it relies on a large fender washer, which does not rest squarely on the inside surface of the hull; it is distorted as a result.  The fasteners adjacent to it have the same issue.  Over time these washers may shift, leading to loose nuts and a compromised structure.  Washers and backing plates must always be fully supported on a flat surface.  In this case, an oblong backing plate would have proved a better choice.

Ask Steve

Hi Steve,

Fuel guy pumped a mix of gas and diesel into large yacht.  What is the best repair?

Your help appreciated.

Andrew Bate


It’s difficult to provide a definitive answer not knowing the contamination rate, however, assuming the engines haven’t been run, the lowest risk approach in a case like this is to pump the fuel out of the tanks, which will almost certainly call for opening and accessing the tanks to ensure the fuel below the pick-up tube is removed.  Depending on the size of the tanks and how much gasoline was added, this may or may not be necessary, as the remaining tank “bottom” will be diluted with new diesel fuel (diesel and gasoline will mix readily).  Caution must be used in the clean out/pump out process as the added gasoline will lower the diesel fuel’s flash point, potentially making an otherwise safe fuel vaporize and become explosive at room temperature.

If the tanks aren’t opened to ensure complete removal, and diesel is added, a sample of fuel should be drawn from the tank after refilling and sent to a lab for testing, to determine gasoline content, before engines are run, and fuel should be circulated through fuel supply plumbing to ensure no high concentrations of gasoline exist.

Depending on the dilution rate, the fuel may have to be taken away as contaminated gasoline, which is hazardous waste.  After that has been carried out, the tanks should be filled with diesel, and if any fuel plumbing is connected to tank bottoms or is gravity fed, fuel should be circulated through these fuel lines, to ensure no vestiges of gasoline remain.


Dear Steve,

Do you recommend using PEX for water systems on boats? Is it code approved?

If not, what do you recommend, that is code-approved?


Bruce Colglazier Pappas


Polyethylene tubing or PEX is both desirable and commonly used for new vessel construction and refits.  It’s easy to install, durable and imparts no odor or taste to water, it’s suitable for both hot and cold water applications.  As far as being “code approved”, I can’t answer for all PEX plumbing, and not all PEX is approved for potable water applications.  However, PEX is commonly used in home construction, where such approvals are mandated.  Ultimately, the plumbing you select should carry an NSF 61 or “potable water” rating or approval.

You might find this article on the subject useful in the selection and installation process.  https://stevedmarineconsulting.com/potable-water-systems/



I have a 1996 48′ ocean super sport. My starboard fuel tank has a leak and will have to be replaced. Have you had any experience with cutting the side of the boat out to replace a fuel tank?  The tank is 270 gallons and that is the only way to replace it. I keep the boat on the Bohemia River on the upper Chesapeake Bay and am trying to find a yard that has experience with this. Any advice you could offer would be great.


Matthew Hicken


I’ve replaced scores of fuel tanks in all manner of power and sail vessel in my career.  In no case have I ever cut a hole in the hull of a fiberglass vessel to do so, and that’s no accident.  While that may have been easier in some cases, the risk it poses of compromising the integrity of the structure, through secondary bonds in a stressed structure that experiences slamming loads, is simply too great.  The alternative may require some ingenuity on the part of those undertaking the work.  I’ve removed engines, and cut existing tanks into pieces and replaced them with multiple tanks designed to fit through available access.  I’ve also cut small holes in cabin tops, through which crane cables were lowered, to lift engines out of the way, and then slide them out on temporary dollies, or poked the boom of a crane into the cabin to lift an engine in that fashion.

Finally, cutting a hole of this size in an FRP hull is not only ill-advised, it may affect your insurance coverage.  My strong recommendation would be to find a yard with the experience and expertise needed remove and replace the tanks without compromising the hull.


Hi Steve:

Many thanks for your informative columns in the many boating magazines I read. I have learned a huge amount.

Question:   When using caulking I understand it is advisable not to tighten the caulked fitting down all the way. This will squeeze out the caulking material. How much should the fitting being caulked be initially tightened and how long should I wait to do the final tightening? I read that 3M 5200 takes a week to cure. Do ship yards wait a week to launch boats using this material underwater?

I appreciate your help and information


Dave Stiller


The simple answer to your question is I don’t recommend waiting until sealant cures to tighten hardware.  That approach is, I believe, while often advocated within the marine community by do it yourselfers, flawed, for two reasons.  One, if the part is loaded, a cleat, windlass, winch, stanchion etc, then the cured sealant, which isn’t a gasket in the traditional sense, is likely to split when compressed, which then leads to loose fasteners and leaks.  Two, few yards are in a position to evaluate the cure time and return to re-torque fasteners at a later date, and thus the risk of improperly tightened fasteners is increases significantly.  Sealant is designed to fill voids, and that’s all it needs to do in hardware bedding applications.  This article explains the issue in greater detail https://stevedmarineconsulting.com/caulk-and-sealant-selection-and-use/

From the Masthead

Just as I began to write this column I received an email from a colleague, he manages the physical plant for a large medical complex.  Among other things we discussed our shared frustration at the lack of expertise and professionalism among many technicians.  He shared a story wherein a factory-trained generator technician spent hours (miss) diagnosing a failed genset battery charger, and then provided a repair quote for $3,400.00.  My colleague repaired the problem himself in about 20 minutes; it was literally a single burned connection.

I suggested that the current record low unemployment, as good as it is for the country, and job-seekers, is a silver cloud with a black lining.  As sources for qualified staff are depleted, employers are prone to accept less and less capable individuals, that in turn doesn’t bode well for boat owners and consumers (I don’t care for that word, when did we go from “citizens” to “consumers”?).  I’ve been guilty of it myself, so I can’t necessarily blame them, you tell yourself you can train them, mold them, and improve them.  Sometimes you can.

Beyond technical capacity, and an above average level of curiosity about how things work, and why they fail, those carrying out boat building and repair tasks must also possess solid personal traits, and good work habits.  I’ve always believed that if employees have this foundation, they could be trained to do most jobs.  Our conversation then turned to exactly what makes for a good employee, which reminded me of a cheat sheet I created for those coming to work at the boat yard I managed.

Every new employee was given a copy of the employee handbook, which was twenty five or thirty pages long.  After reading it he or she was asked to sign a document indicating they had read and understood it.  Of course no one can remember all the details in a document this long; I wanted to give new hires an indication of what was really important to me, along with the details that spelled the difference between failure and success, in a one page format. I sat at my desk pondering how I could give folks this head start when my eyes passed over a framed photo of my father, standing in front of the Taegu Army Post in Korea, in 1952.

With that inspiration, I created the following.

This business welcomes you as an employee if…

  1. You report to work on time and are ready to begin working at 7:30AM, and do not depart before 4:00PM without permission.
  2. You take your AM, PM, and lunch breaks at the appointed time and for the allotted time.
  3. Your appearance is neat and you are respectful to customers and your fellow employees, and you refrain from using foul language especially when customers are present (that could be any time).
  4. You report to work with the tools and gear (warm clothing, gloves, foul weather gear etc.) to do your job.
  5. You do not abuse the telephone or cell phone privileges.
  6. You take the necessary precautions to protect the boat you are working on while keeping it neat and orderly.
  7. You clean up after yourself in the shop, yard and skiff when finished with a project.
  8. You take care of shop tools and equipment, returning them to the proper storage location, clean and ready to be used by the next worker (blades/bits removed from reciprocating saws, sawzalls and drills). If you damage a tool, boat or piece of equipment, or if you discover that it does not work properly, report it immediately.
  9. You do not throw cigarette butts or trash on the yard.
  10. You fill out your time card completely, properly and at the end of each work day.

Following these common sense rules will ensure you’re getting off on the right foot, and hopefully begin a long, enjoyable relationship with this business.

Later on I added, “10a: You don’t ask to borrow money, the company pick-up truck or tools, until after your first annual review.”

Unraveling the Corrosion Mystery

Galvanic corrosion occurs when dissimilar metals are connected and exposed to an electrolyte like seawater.  This strainer  installation is a textbook example of what not to do, bronze, mild steel and galvanized steel.  Not only are these metals incompatible, mild and galvanized steel should not be used for raw water applications.

Corrosion; it’s veritably inescapable and ever-present, yet it is among the most misunderstood of all onboard phenomenon.  Hardly a week goes by where I don’t receive a call or e mail regarding a seemingly vexing corrosion problem.  And no wonder; virtually every cruising, and small commercial and military, vessel is built using a wide range of metallic components, thereby susceptible to corrosion, from bronze seacocks and iron engine blocks, to stainless steel and aluminum deck hardware and copper wiring.  Add water to this mix, especially seawater, or electricity and the results can be heart achingly unpleasant and costly.  While a cloud of misconception so often unnecessarily shrouds the truth behind the cause and prevention, of corrosion, it’s not especially difficult for marine industry professionals, and boat owners alike, to gain a working knowledge of this seagoing malady.

Aluminum and copper alloys like bronze are among the least compatible metals.  Here a bronze raw water strainer is supported by an aluminum bracket.  Airborne moisture alone would be enough to cause a problem, albeit slowly, however, every time the strainer is serviced, the two metals get doused with seawater, accelerating the corrosion process.

Corrosion’s Yin and Yang

While there are many varieties, which are specific to different metals, from aluminum’s poultice corrosion to stainless steel’s crevice corrosion, there are two overarching mechanisms that affect most vessels.  These are galvanic or dissimilar metal, and stray current, corrosion.

Galvanic or Dissimilar Metal

Galvanic corrosion occurs when dissimilar metals are placed in contact with each other, or are otherwise electrically connected via a wire or other conductor, and exposed to an electrolyte, which in this case is simply fresh or seawater, or even high humidity, with seawater’s enhanced conductivity predictably accelerating the process.  Galvanic corrosion is electrical in nature, with the electricity being created by the dissimilar metals and electrolyte, much like a battery, albeit at a very low rate, typically measured in thousandths of a volt or millivolts.

While virtually any two metals will interact with each other in this scenario, those that are further apart on the galvanic series or scale will interact to a greater degree, or more aggressively.  Metals that are located at the most noble, and most corrosion resistant, end of the galvanic series include exotics such as graphite, gold and titanium, as well as 316 stainless steel, and nickel-chrome alloys used for propeller shafts, while those toward the least noble end of the series, magnesium, zinc, and aluminum alloys, are significantly less corrosion resistant.

In some cases galvanic corrosion can occur even if metals are not in direct contact with each other; here water dripping from a bronze pump has corroded its aluminum support structure.

Dissimilar metal combinations that are especially problematic include copper (and copper alloys such as bronze and brass) and aluminum, and to a lesser degree stainless steel and aluminum.  In fact, because of the nether region it inhabits on the galvanic scale, virtually any metal placed into contact with aluminum, and in the presence of moisture, will cause the latter to corrode.  In 1895, before this phenomenon was thoroughly understood from a boat building perspective, the Herreshoff –designed and built America’s Cup contender ‘Defender’, was assembled using a nickel-aluminum alloy hull above the waterline, and bronze plate below the waterline, over steel frames, with bronze rivets throughout, creating a battery-like galvanic mélange.  It wasn’t long before it had to be scrapped, the hull plating had pitted so heavily it was no longer seaworthy, (but not before she fulfilled her intended purpose; winning the Cup).

Aluminum fuel filter housings like the one shown here are often plumbed with galvanically incompatible brass pipe to hose adapters, primarily because the latter are readily available.  Mild steel plugs have also been used on this installation, they too are inappropriate, all should be stainless steel, and installed with a fuel resistant thread sealant.

Examples of galvanic corrosion that can be found aboard the average vessel include brass hydraulic steering cylinders or bronze seawater strainers supported by aluminum brackets, aluminum fuel filter mounts plumbed with brass fittings (often used on outboard applications, where they are very much exposed to the elements), and to a lesser degree aluminum deck and mast hardware installed using stainless steel fasteners.

While less of an issue than some other metal combinations, aluminum can suffer from galvanic corrosion when in contact with stainless steel and water.  Here, a recessed stainless steel screw traps water, setting up a galvanic cell; corrosion has already begin to set in on this new nearly boat.

However, the very best example of galvanic corrosion is one that’s intentional; sacrificial zinc anodes attached to underwater metals such as propeller shafts, through hull fittings, struts and rudders, and then to the vessel’s bonding system , as well as heat exchangers.  The ignoble zinc (zinc is one of three possible sacrificial metals that can be used for cathodic protection, the other two are aluminum and magnesium, zinc should only be used in seawater, and magnesium is suited only to fresh water; while aluminum can be used in fresh, brackish or sea water) corrodes, while protecting the metal to which it’s attached.  To learn more about anode selection, see this article.

The most effective means of preventing galvanic corrosion is to avoid using dissimilar metals in scenarios where they will come into contact with each other, or where they are otherwise electrically connected.  Where this is unavoidable, inserting between them an insulator, which can take the form of a non-conductive material, or in some cases another metal that is benign to both, is yet another form of galvanic corrosion prevention.  Non-conductive materials include pre-fabricated fiberglass or epoxy-based sheet (avoid using non-reinforced plastics such as Starboard in highly loaded structural applications), while stainless steel is often used as an insulator between aluminum and copper-based alloys, between aluminum fuel tanks and brass (a copper alloy) valves for instance.   While the two are technically still connected, the stainless steel bushing provides the necessary degree of isolation; however, this approach would not be acceptable for submerged or continuously wetted components, and under no circumstances should bras be used in raw or sea water applications, as it will suffer from yet another type of corrosion, dezincification.

This zinc-bearing brass stern tube is suffering from dezincification, evidenced by its pinkish hue, which is a form of galvanic corrosion.

While galvanic corrosion is typically a localized event, occurring aboard a given vessel from its own dissimilar metals, it can also occur between vessels.  This concept can be somewhat confusing and is understandably the source of a great deal of misinformation, including the “hot marina” myth.  Inter-vessel galvanic corrosion occurs when, for instance, two vessels, which are near each other both plug into shore power.   In doing so the green AC safety ground wiring for each vessel, which are common with bonded underwater metals such as seacocks, struts and shafts, become connected regardless of whether or not the shore power is energized.  To reiterate, the moment shore power is plugged in, AC safety grounds and bonding systems between vessels are interconnected.  When this occurs, intact sacrificial anodes, or less noble underwater metals such as aluminum stern drives, on one vessel may begin protecting underwater metals on another vessel(s), one whose anodes are depleted.  Except for the fact that the shore power cord must be connected, this phenomenon has little if anything to do with the marina, or shore power per se, can occur even if the power is off; it remains a galvanic phenomenon.

Hull-mounted anodes, these may be zinc, aluminum or magnesium, can be connected to the bonding system, and thereby provide protection for all connected underwater metals.

As insidious as this scenario is, it is easily thwarted using either a galvanic isolator, or an isolation transformer.   Galvanic isolators block, up to 1.4 volts (which is above the typical galvanic corrosion voltage threshold), of DC voltage on the AC shore power safety ground wire, while still allowing AC fault current to flow freely, which is critical from a safety perspective.  Because galvanic corrosion is DC in nature, the electrical interconnection of adjacent vessels is prevented by the galvanic isolator.  Isolation transformers take this a step further, by isolating all shore power connections, including the AC safety ground, between the vessel and the dock, thereby blocking any level of shore power cable-related inter vessel conductivity.  Every vessel equipped with a shore power system should utilize one of these devices to prevent shorepower safety ground-induced galvanic corrosion.  Galvanic isolators are relatively inexpensive, while transformers are more costly; the latter however, offer additional benefits in addition to absolute isolation.

Galvanic isolators are the first line of defense against galvanic corrosion that originates aboard nearby vessels.  They are comparatively  inexpensive, and easy to install, every vessel equipped with shore power should have one.  The one you select should meet ABYC Standard A-28.

While it is a potentially serious and costly phenomenon, galvanic corrosion occurs at a stately pace, typically over the course of weeks if not months and years.  With proper alloy selection, isolation and cathodic protection, it can be minimized if not eliminated.

Shore power transformers, when wired in isolation mode, provide an effective and all but impenetrable barrier to corrosion that originates on other vessels, or in places other than aboard the vessel on which they are installed.

Stray Current

This form of corrosion differs from galvanic corrosion in that it only occurs in the presence of an outside source of electricity; which is, with very rare exceptions, a vessel’s own DC electrical system, or battery or battery charger.  Shore power, i.e. AC voltage, does not, again with very rare exceptions, cause this type of corrosion.  If it did, the DC voltage blocking ability of a galvanic isolator would be ineffective.  Rare though it may be, when it does occur, AC-induced stray current corrosion is of greatest concern where aluminum-hulled vessels are concerned, as well as those equipped aluminum stern drives.

Stray current corrosion is extremely destructive and it occurs comparatively quickly, it qualifies as a corrosion emergency, as it’s capable of impacting a vessel’s watertight integrity in a matter of days if not hours.

The typical stray current corrosion scenario involves a faulty electrical connection that is located in, or close to, bilge water or one that makes contact with a submerged metal.  Contrary to popular belief, electricity does not seek ground; it seeks a return path to its source.  In the case of stray current corrosion that’s the vessel’s battery.  Current leaking into bilge water may travel to a through hull fitting, then into the water in which the vessel is floating, then on to the propeller and shaft, which are grounded to the DC negative system via the engine block, and thence back to the battery.  In this example, the propeller will almost certainly suffer from severe and rapid corrosion.   Unlike galvanic corrosion, which occurs comparatively slowly,  stray current corrosion moves with startling rapidity, potentially destroying a propeller, shaft, thruster, sail drive or stern drive in a matter of days.

Sacrificial anodes, galvanic isolators, and isolation transformers offer little if any protection against this electrical scourge (isolation transformers can be beneficial for preventing stray current corrosion that originates on other vessels).  The most effective means of preventing stray current corrosion is by observing sound, American Boat and Yacht Council (ABYC) -compliant wiring practices, particularly in and around bilge areas.  Bilge pump and float switch connections should be made no less than 18 inches above the base of the pump.  The primary reason for doing so is to improve reliability; however, this approach also reduces the likelihood of stray current corrosion.  If this is impractical, then connections should be made completely water-proof using heat shrink butt splices or stand-alone heat shrink tubing, and if necessary application of silicone sealant, and connections should never be allowed to lay in bilge water, regardless of water resistance.  A detail as seemingly innocuous as improperly crimping, and thereby piercing, a heat shrink butt splice can create a path through bilge water for stray current.  While this applies to all electrical junctions made in the vicinity of bilges, stray current corrosion can occur virtually anywhere aboard a vessel when a positive DC conductor makes contact, directly or indirectly, with a submerged metallic structure.

Bonding systems are an essential part of a fiberglass vessel’s ability to prevent or minimize corrosion.

Yet another means of preventing or diminishing the effects of stray current corrosion involves the use of a bonding system (where fiberglass vessels are concerned, bonding systems are strongly recommended; their installation guidelines are detailed in ABYC Standard E-2, “Cathodic Protection”).  Bonding systems are one segment of a vessel’s overall grounding system, which encompasses the DC negative, AC safety ground, and lightning ground systems, all of which are inter-connected.

Bonding system connections live a difficult life, they are often located in bilges and exposed to water and foot traffic.  Bonding connections should rely on machine screw connections, rather than on tapping screws or hose clamps.

In brief, a bonding system electrically interconnects underwater metals and many metallic machinery components, including through hull fittings and seacocks, rudder and propeller shafts, struts, and strainers.  There are two primary benefits to bonding; with the first being the mitigation of stray current corrosion.

Moving components, like the rudder post shown here, require some special techniques for making long-lasting bonding connections.

In the scenario described previously, wherein voltage is “leaking” into bilge water from a defective bilge pump connection, if the seacock through which the fault current flowed was bonded, all or most of the current would return to its source, the battery, rather than through the water in which the vessel floats, thereby eliminating or minimizing the damage to the propeller.

Using the “home run” system, where each bonded component is wired directly to a bonding bus, is an ideal approach that typically yields low resistance connections.

The second benefit to utilization of a bonding system relates back to galvanic corrosion and its prevention.  Bonded metals are nearly always dissimilar, silicon bronze seacocks, stainless steel alloy shafts, and manganese bronze propellers for instance, which violates the aforementioned guidelines on galvanic corrosion.  Bonding systems, however, are an exception to this rule with good reason; one additional component is included in this metal cocktail, a sacrificial hull-mounted zinc, aluminum or magnesium anode.  These are commonly installed on the transom of planing vessels, and on hull bottoms, sometimes recessed, on displacement vessels.  Connecting underwater metals to each other, and then to an anode follows the ‘bond and protect’ protocol, a proven approach that works provided a handful of guidelines are followed.  Chief among these is ensuring low resistance connections are made between bonded components and hull anodes, the standard for which, established by ABYC, is stringent indeed, a maximum of just one ohm.

Resistance between protected underwater metals and sacrificial anodes must be kept to a minimum, no more than one ohm (this one fails to meet that standard), in order for protection to be afforded.

Aboard the vast majority of vessels I inspect, bonding systems, and their connections specifically, are in abominable condition, they are green, crusty, loose or broken all together.  Like any other system aboard your vessel, the bonding system should be periodically inspected and maintained.  Corroded or otherwise poor connections should be cleaned or replaced.  If doubt exists about the integrity of the system, resistance between components should be checked, while the vessel is hauled out, using an ohm meter.

Corrosion, and its prevention, need not be mysterious, and while its analysis is often deemed a black art, it is in fact anything but; its causes have been studied and are very clearly understood.  While the above guidelines will help prevent the most commonly encountered corrosion mechanisms, if your corrosion problem defies explanation, only entrust its analysis to an ABYC certified corrosion specialist.