Text and photos by Steve D’Antonio
Copyright © 2017
Photo Essay: Raw Water Plumbing
It’s a subject I’ve covered on countless occasions, and in spite of that editorial frequency, it’s one I believe can’t be revisited too often. The stakes are high indeed; a failed otherwise simple and inexpensive hose, clamp or pipe fitting can mean flooding, tens of thousands of dollars’ worth of damage, the loss of a vessel and even loss of life. Yet, in the inspections and consultations I carry out I see far too little attention paid to these critical components.
Let me begin by clarifying the definition of ‘raw water plumbing’. This essentially encompasses any pipe, hose, valve or similar fitting that conveys seawater or the water upon which the vessel floats. Where this plumbing is concerned there are, unfortunately, few hard and fast rules. American Boat and Yacht Council guidelines specify what’s needed for seacock installations, among other things they must be able to withstand 500 lbs of static force for 30 seconds, applied to their most inboard end, without failure. On other raw water plumbing ABYC is for the most part silent. My own criteria for such plumbing, while perhaps unscientific, is straightforward enough, if you can’t stand on it it’s probably not robust enough.
The plumbing scenario shown here, one that supplies seawater for a water maker, is the proverbial accident waiting to happen. Not only is it severely stressed, the hose itself, clear wire reinforced PVC, is unsuitable for raw water applications. It simply lacks the necessary robustness and abrasion resistance required for raw water hose use. Located several feet below the waterline aboard a 70+ foot vessel, a failure would lead to rapid flooding. Hose used for most raw water applications should carry an SAE J2006 rating, and at the very least it should be rated specifically for raw water use, wherein a failure would result in raw water flooding.
Thank you again for your great content on your website – you are a must-read at our small boat building operation.
In your article “The Engine Room’s Unsung Hero; Motor Mounts”, Jan 24, 2017 you say; “Rotating the adjustment nut on the mount stud (these threads should be lightly oiled to prevent galling, however, anti-seize compound should never be used…)”.
What is wrong about using anti-seize compound, and in general, where should anti-seize compound be used?
Particularly because of their cyclical loading, applying anti-seize compound to motor mount adjustment stud threads virtually guarantees they will become loose (I found this out the hard way years ago when repowering a yacht club launch that, as you can imagine, shifted from forward to reverse all day long, I had applied anti-seize to the stud threads and no matter what I did thereafter, no matter how much I tightened them, they insisted on loosening; I finally used brake cleaner and removed all the anti-seize, after which the nuts stayed put). Once a mount loosens, the alignment must be re-checked, making this a time consuming process. Torqueing then properly and then coating with a corrosion inhibitor is, therefore, my preferred approach. A thread locking compound can also be used for added security
Similarly, and while not uncommon, anti-seize compound should also never be used on propeller shaft hubs, or propeller bores (or nuts). Doing so prevents the propeller from engaging the hub and getting stuck there, which is essentially the goal of a tapered interface.
Where to use anti-seize…? That is a very good question. For stationary and non-cyclically loaded threaded components that are prone to corrosion, or seizure, or galvanically incompatible parts, stainless fasteners and aluminum for instance, anti-seize may be appropriate, but so are other approaches. In many cases, anything that excludes moisture from the thread, such as polyurethane sealant, is often all that’s needed. Truth be told, while I have several tubs of anti-seize in my shop, copper, nickel and aluminum based, I rarely use them these days. It’s also worth noting, any time a threaded fastener is lubricated, with oil, grease, anti-seize or thread locking compound, the torque value changes, it goes down (most torque charts provide dry as well as lubricated torque values). Therefore, many “wet” threads are, I believe, inherently under-torqued.
I just read with interest your article on Potable Water Systems.
I have one question.
Why should a filter be after the pump? I read no explanation on that point or maybe I missed it.
We filter the water from the dock to the SS on board water tanks. I’m hoping and will check that the plastic tube from the tank to a filter to the pump is rated for potable water use, then it travels to the house and hot water tank, to the house thru copper.
It would seem to me that a filter in line would be either a pull to or a push from the pump and I can’t think what difference it would make.
I can rearrange my tubing to accomplish either, I’d just like to understand why?
Thanks again, as always, for your information and the way you provide it to your fans.
Regarding filtration before or after the pump, this is a good question, and one that should have received more clarification in the article, many pump manufacturers specifically call for the installation of a strainer before the pump, essentially a screen to prevent large debris from jamming the pump, and the finer sediment filter after the pump. The reason for the post pump filtration is to reduce the likelihood of cavitation.
If the flow of water into the pump is impeded, even slightly, the pump impeller will cavitate, making for irregular water flow. However, pumps are less sensitive to back pressure, and are capable of pushing water though filters that are heavy with sediment, with little problem.
I recently experienced a clogged fuel line upstream of the dual Racor 500MA’s. The boat, a 46’ mono- hull powered by a 75 HP Yanmar, had just crossed a lumpy Gulf Stream after a 1200 mile delivery from the Caribbean. The engine began to lose power until it wouldn’t turn more than 1000 rpm. After changing out the filters without an improvement we spliced the genset fuel line over to the Yanmar and that set us going well again.
The next morning we found a clump of black fiber stuck in the ninety degree fitting connecting the primary fuel line to the dual Racor manifold. Problem solved.
Now I’m looking to install a crude (50 micron?) filter near the fuel tanks to prevent this from recurring but I can’t find a suitable unit. Racors roughest element is 30 micron. Any suggestions?
While the problem you describe is rare, I have encountered it on at least one occasion, with the clog occurring in a similar location, at the selector valve for a tandem Racor assembly. The offending material in my case was fibers left behind after a tank cleaning; those carrying out the cleaning used synthetic oil absorbent pads, which they wiped over the inside of the tank. These left behind filaments which accumulated in, and clogged the filter valve. It can be both disconcerting and dangerous. Installing a coarse strainer may help, however, it would have to be checked and cleaned as often as the primary and secondary fuel filters, and a clog could still occur in the plumbing as it did in your case. It should be installed between the tank and the primary filter, a valve should already be present at the tank, in the supply line, enabling the fuel supply to be isolated when checking the strainer. The strainer should comply with ABYC H-33 standards, which primarily means it is designed for fuel use (and metallic), and capable of withstanding exposure to flame, without leaking fuel, for a minimum of 2.5 minutes.
You might find such a strainer by searching McMaster Carr Supply, using the words “standard strainers”
I love your column.
I am looking for a little pump that will suck up that last quart of annoying water in my bilge, especially in a little aft compartment which seems to be lower in the water than the main bilge pump can access.
For bilge “drying” you have two options. One, use a remote, displacement, self-priming pump. This sort of pump is mounted well above any water, with a hose that leads down into the lowest part of the bilge. A strainer or “foot valve” is installed on the end of the hose to catch debris and to direct the suction as low as possible, enabling more water to be removed.
The second option is to use one of the new low profile submersible pumps. These are centrifugal, rather than displacement, and thus are not self-priming, however, that’s doesn’t matter because their pick up vents are so low they can suck up water much like a self-priming pump. Whale Pumps makes a nice version called the SuperSub.
The remote mount, self-priming pump can probably be coaxed to get more water out of a bilge, especially if there’s a small well, so if that’s your goal I’d go that route (this pump will need an inline strainer). If ‘most but not all’ meets your needs, then go with a low profile, centrifugal submersible model, they are more reliable and less prone to clogging.