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Old 12-24-2016, 03:42 PM
jdory jdory is offline
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Join Date: Aug 2015
Rep: 10 Posts: 59
Location: Nome, Alaska
catamarn: how to plumb water tank in each hull

I'm fixing up a 30' catamaran and adding plumbing now. I'm thinking I will put a water tank about mid-hull low down on each side. Port side is galley, other side is head/vanity. Easiest way to plumb the two tanks would probably be separately, but I can see being annoyed when one tank empties before the other. The tanks may be in the 18 gallon size each - that is biggest I can fit in there unless I build in the whole area. I guess that is an option - have all the water on one side - it might total around 50 gallons doing that. Not sure about all that weight just one side though. (Unfortunately I didn't plan well enough on the build part of the project to get tanks where they would be easier with gravity feed and centrally located. Probably require too much surgery now.)

Don't really want to pressurize the tanks since they would have to be depressurized to fill or collect rain water into, and having to add more valves and potentially more leaks that way.

Thought I could probably run a water line from each into the aft box beam and hook a pump somewhere in the middle. That would mean the pump would need a suction head or lift capability of around 5' from bottom of tank to pump, with a length of pipe around 12' or so. One question about that is would a pump like maybe a Shurflow AquaKing do that? I think so but would need to buy a pump to test to make sure. Need one anyway, perhaps.

If the pump is in that rear box beam then I would probably need to insulate it against overnight freezes (I'm in Alaska)..

One option is use manual pumps at sinks as well. But no electric pump would mean the tanks would remain separate.

As I type this, I flashed on another possibility. In the attached image I had planned on building the tanks in the bench areas marked "Seat". The other possibility might be doing some surgery and putting them in the area marked "Stowage" behind the mast in the center. I wouldn't have to fill those spaces - maybe a 20 gallon tank or so each side, still leaving a bit of stowage. I had planned to put batteries on one side there, but maybe they could go under the bench seat, or elsewhere. Thinking lithium for those so they will be a bit smaller than the other types, perhaps. I'm going to do some cockpit surgery anyway so it will open up those stowage areas temporarily. The tanks would be permanent afterward.

So sorry for the mental ramblings here.. but looking to see if I'm missing something obvious.
(BTW, the areas up front of the mast marked "Stow" have stringers running athwartship so hatches there will be quite small - no way to get a tank in.)

thanks, Jim

ps: the gif credit to Kurt Hughes
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Last edited by jdory : 12-24-2016 at 03:45 PM. Reason: mis spell
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