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Raw Water Plumbing Etiquette

I looked at the plumbing arrangement, scratched my head and marveled at how it had managed to survive for this long. A ball valve was attached to a through-hull fitting, each with different, and therefore incompatible, threads, to which a pipe nipple and plastic strainer were attached. I was certain it wouldn’t withstand an application of 500 lb. for 30 seconds—the long-established ABYC guideline detailing recommendations for seacock installations. On the contrary, I suspected it might fail if I simply leaned against it.


Where this and many other raw water plumbing installations fail is in their robustness. While ABYC guidelines regarding seacock installations are amply clear—the aforementioned 500-lb. rule I have discussed in previous articles and columns—they are mute on the subject of raw water plumbing beyond the seacock and inside the vessel. I believe this is a liability in that a failure of any of these components could flood or sink a vessel just as handily as a failed seacock. The saving grace being, presumably, that in the event of such a failure the seacock could be closed, provided the vessel is occupied and provided the seacock is not submerged by the time the leak is discovered.

In June 2011, a Nordhavn 75 Expedition Yachtfisher sank at its slip in San Jose del Cabo, Mexico. The culprit was the failure of an after-market installation of a device known as a tuna tube, which is used to keep live bait. The plumbing for this component utilizes 2-inch inside diameter raw water plumbing, connected to a seacock, which was open. The failed component utilized a PVC pipe fitting that was secured in place with a nut similar to those seen on domestic sink drains. Predictably, much discussion circulated around internet forums regarding the failure, watertight bulkheads, bilge pumps, and high water alarms. Interestingly, few of these discussions centered on the real cause of the sinking—the plumbing.


While there were, in my opinion, virtually no new lessons to be learned from this unfortunate event, there are lessons worth reiterating. Foremost is the need to ensure that all raw water plumbing installations are rugged, durable, and robust. This includes any component that, if it should fail, will allow water to flood or be pumped into the vessel—engines, generators, washdown, watermakers, and air conditioning systems, among others. In the latter two cases, a failure of plumbing on the outlet or pressurized side of the pump, even if above the vessel’s resting waterline, can lead to rapid and catastrophic flooding because rather than simply flooding, the water is being pumped into he vessel. Many vessels are left unattended with air conditioning systems operating, making them ripe for a failure of this sort.

I’m often surprised by the lack of robustness when inspecting installations for these systems. The primary failings are excessive leverage, and poor support, imparted by long, rigid fittings that often rely on gossamer plumbing components and materials. The combination is a veritable recipe for failure.

While its use is often fiercely defended by its devotees, with rare exceptions, PVC plumbing has no place in raw water installations. It is used within, or as an integral part of equipment, by some chilled water air conditioning and watermaker manufacturers. In those cases, if a failure occurs in theircomponent, you or your insurer may have some legal recourse, which is still a less than an appealing prospect. I have seen, on many occasions, PVC components used by installers of this and other equipment, to facilitate the various plumbing requirements in the field, as it were. In this case, should a PVC plumbing failure occur, it’s difficult to see how they would not bear some responsibility for damages.

In my experience, PVC is frequently used out of convenience, rather than being the most suitable material for the application. A wide variety of shapes and sizes are readily available from any hardware or home improvement store. Many point to its enviable and seemingly indestructible record ashore. However, while it works well in domestic applications, a shipboard environment, with extremes of temperature, g-force, foot and gear traffic patterns and vibration, is significantly more stressful. I have encountered multiple PVC failures, more than enough to convince me that the material is ill-suited for raw water applications.

Alternatives include bronze alloys such as ASTM B62, sometimes referred to as 85-5-5-5, because it consists of 85 percent copper and 5 percent each of lead, silicon, and zinc. Although available in only a limited range of options, fiberglass is an excellent alternative for conveyance of raw water, as are plastics specifically designed by their manufacturers for marine, raw water applications. These include Forespar’s proprietary reinforced Marelon as well as Marine East’s line of raw water plumbing fittings, among others. Regardless of which material is used, it must be well supported, and other than a pipe to hose adapter, nothing should be plumbed directly and rigidly to a seacock—hose should always separate seacocks from other components and fittings.


Hose used for raw water applications must be equally as durable, and without exception, it should be specifically designed and rated by its manufacturer for the application. Most clear, flexible PVC hose lack a marine raw water rating. The primary weakness in most clear, PVC hose is its susceptibility to chafe, especially when it is warm, crushing, and kinking.

Ideally, hose used for raw water applications should be clearly embossed or printed with the manufacturer’s name and model, and ideally, its intended use. Marine raw water and wet exhaust hose (it’s typically black) that carries a SAE J2006R rating is ideally suited for this application. It’s rugged, durable, and crush resistant, as is opaque PVC sanitation hose (it’s usually white). These hoses are also more expensive and more difficult to route than lighter weight clear PVC hose.

For suction applications, particularly engine and generator intakes, the wire-reinforced J2006R variety should be used. When in doubt, contact the manufacturer or distributor of the hose and ask, “Is this hose rated for marine, seawater use, and is it warranted against failure in such applications?”

While there are no specific ABYC guidelines for raw water plumbing within the vessel, my personal regulation goes something like this, ‘If it’s too weak, too fragile, or too flimsy to stand on, then it’s not robust enough.’ Essentially, every raw water plumbing component, hose, pipe, strainer, valve, or manifold should be strong enough to stand on, and of course all seacocks should be able to withstand the aforementioned 500-lb., 30-second torture test. If any of your raw water components fail to meet these guidelines, then they need to be re-engineered or replaced with ones that do.