Re: Sea Chest
Must be an epidemic of manifold rebuilds! We are in the process of redoing ours. While I LOVE the idea of a seachest, the original Amel implementation on our Super Maramu (#160) always bothered me a bit since there were no valves other than the main seacock. The ability to isolate the individual circuits either in an emergency or for routine maintenance while in the water always seemed an oversight.
A crusty old sailor who has surely forgotten more about boats than I'll ever know had a strong opinion about raw water systems. You should be able to hit it with a 5 pound sledge, or stand on it with your full weight, or hit it with a torch, and not worry about it ever breaking or leaking. Feeling that was a pretty good approach, I have always looked askance on any raw water system made of PVC parts which tend to be brittle and fragile to external impact. Marelon is strong and resilient. PVC--not so much. Also, PVC is very susceptible to the heat of even a small fire. Even if the fire gets extinguished, you could lose your boat from flooding due to melted plastic plumbing.
We installed a system made of solid bronze pipe fittings. Certainly more expensive than plastic, but much, much stronger. You get what you pay for.
The engine is fed directly with a connection directly off the strainer, and a tee with a reenforced 1 1/4" hose carries water over to the "pump pad".
If you are changing your manifold, whatever material your chose, be sure that the piping runs DOWNHILL continuously to any centrifugal pump. ANY place that air can get trapped will result in difficulty of the pumps priming. I have always used check valves on the discharge of each AC pump since these centrifugal pumps offer no resistance to back flow and would allow air to be pulled back into the system. The engine, generator, and RO system are all positive displacement pumps (more or less!) that offer significant resistance to reverse flow and do not need separate check valves.
In most cases, I have found that 35mm and 1.25 inch hose and hose fittings are pretty much interchangeable.
Bill Kinney (and Karen Smith)
Annapolis, MD, USA