PVC wins for me
I absolutely LOVE using CPVC for boat plumbing and if possible wouldn't use anything else. When designing a boat from the keel up, it is simple enough to lay out the plumbing runs so as to maximise the use of semi-rigid pipe. All plumbing runs should be clear and visually accessible anyway. The sanity of using forethought to lay them out logically will pay dividends in the future when you or someone else must trace them to repair the system or add a new component.I am currently replumbing my 1974 boat and designed and fabricated a two-tank manifold with a drain to the bilge and separate feeds to the galley and head sinks, all out of 1/2" CPVC. I think it took an hour or so to lay it out and about 15 minutes to put it together. The stuff is wonderful. You don't even have to cut the joints precisely, as you would have to with copper. Any sawn-off end, half-decently cut, with enough penetration into the fitting, will be fine. (I used a hacksaw to cut on a pencil line-- done.) It is strong enough for any onboard pressure-water system, will not corrode, weaken, or leak, transmits no ugly taste, and is chemically clean enough for potable water (most new houses are done with it). Worried about the glue, I asked the guy at the plumbing place about using it for even the gasoline fill. He said, the glue IS the pipe material; they are they same plastic and therefore share the same properties. When the glue sets up (in about 15 seconds!) the two parts and the glue are all fused together as one. It will not leak at the joint unless the fit was so bad there was no glue coverage somewhere. And CPVC is okay with gasoline-tank fills. I have not yet put the gasoline fill line together, but I am not worried about the fuel nozzle shoving the hose off and flooding the bilge with gasoline any more.The point about CPVC being inflexible is only partially true. I had to run a pipe up along the curve of the hull, from the bilge to underneath the bunktop, and was elated to find that it simply bent right up there. I glued an elbow on the end of it, slid it back into place, and let the elbow poke out the opening under the bunktop where I could reach it with another piece from under the galley. It was perfect. The stuff will make any reasonable bend along the sheer, against the hull, between two holes not perfectly in alignment, and so forth. It is flexible enough to withstand bending stresses and even vibration without cracking. I would, however, strongly recommend using a small section of hose between the pipe network and any fixed component such as a seacock or a toilet. This is good for 2 reasons:1. Too much vibration can always crack something, especially if ice or pressure can be involved. CPVC is not steel-- or hose.2. Maintenance is easier if you can detach the pipe network from components that could need service. A rule of thumb might be to provide a short length of hose between the network and anything that would ever have to be detached from it. Make sure the hose is long enough to bend out of the way to free up the component (maybe 4 - 6"?).To include hose, simply glue a threaded fitting on the end of the pipe, thread in a grey nylon hose barb, and then put in the hose. There are plenty of ways to adapt to odd sizes using adapters, either pipe-to-pipe or at the hose barb itself. (I even found a way to adapt to the Rule-only 1-1/8" bilge-pump size.)I used white nylon screw-down cable clamps to fasten the network and the tank manifold to the boat. Worked as though it'd been designed to.And you can always add to it. Just hack a section out with a hacksaw, manhandle the new section with a tee and slip-on couplings, and glue it back together.JC 2