Several years ago, we posted a description of how we inspected and cleaned up the original Amel raw water manifold.
Last year, while we were doing a number of upgrades to Harmonie‘s engine room, we included the raw water manifold. We had a couple of problems with the original. Although we had not seen serious corrosion of this part, several other owners had them fail. Being a direct link to the ocean, this is not a good thing.
We also were uncomfortable with only having ONE valve to control all of the seawater users on the boat. An issue with any hose or connection, or any maintenance, anywhere, required shutting down everything, including the generator and main drive engine. We felt this was unacceptable. Out design brief required a valve to shut off each user.
Once we decided to upgrade the system design, we turned to the material to make the new system from. We felt there were three choices: Plastic, Stainless Steel, and Bronze.
We dismissed plastic as too fragile. Yes, we KNOW that Amel chose plastic for recent models of their boats, but my experience with plastic pipe fittings is not good. And it is even worse with plastic valves. (Note: There are a couple brands of “plastic” seacock on the market that are excellent, I am talking about standard domestic PVC plumbing valves here.)
I have had several plastic fittings fail under mechanical stress, especially the pipe to hose adapters. They are just not strong enough to deal with stresses and strains that might not be “normal” but certainly should be expected. Several times I have broken plastic fittings in the engine room when I accidentally leaned my weight against them while working on something else. In my opinion, the ONLY reason to use plastic is because it is cheaper. Fittings connected directly to the ocean are not places to save money.
I see no real technical reason to chose between stainless and bronze. Both are strong and essentially corrosion free in this application. We made our choice because when we started the project bronze was a bit cheaper, but that relationship changes frequently, driven mostly by the wholesale price of copper and chromium. If you use bronze, be 100% sure you are getting bronze, NOT brass. European and Chinese suppliers frequently sell brass into the marine market as suitable for salt water service. It is NOT.
Starting with the actual seachest, which we did not modify, the threads on the outlet are 1 1/2″ BSPP (British Standard Pipe, Parallel). These are compatible for low pressure work with NPS (National Pipe, Straight). Just do NOT use either British or National tapered pipe fittings here! The adapter nipple to go from straight pipe thread to tapered pipe thread was the most expensive fitting in the project.
In the following photo, the supply to the main drive engine goes out the bottom, and the hose off to the side carries water to the secondary manifold that supplies all the other uses. For those of you who might not be familiar with the weirdness that is pipe sizing, 1* pipe is about 1.25 inches inside diameter, and 3/4″ pipe is about 1″ inside diameter. Don’t ask why. It just is…
The secondary manifold was assembled and mounted as part of a major engine room refit when we installed our new generator.
This has changed just a bit the way we manage the boat. When we are sailing offshore, we now routinely shut the valves to the air conditioner cooling systems. We never use them while sailing, and in the very unlikely event of a hose or fitting failure we are not surprised with incoming water while away from help.
This system has been in place for two years, and there is nothing I would change about it.
Note that there might be a number of differences between the way Harmonie looks and the way your Super Maramu. Older SM had a separate water pump for each air conditioning unit, and out boat has two AC units. We have manual toilets, so no raw water feeds from the engine room to those, and the anchor wash down is fed from a through-hull in the bow.