Through-hulls

[Zanshin]

I am thinking of putting a desalinator on board a boat and think that if I add yet another dedicated through-hull the fiberlass hull will begin to resemble a swiss cheese and I'll have more bronze than glass below the waterline!

How important is it to have dedicated through-hulls for every system on board? Couldn't I combine this additional water intake with one of sufficient diameter? Is this a big "no-no"?

[Rockter]

You could have the intake come off (say) the engine side of the coolant filter for the engine, and you could readily tap into a sink outlet for the saline exhaust. That would save two through-hulls. You would not have to lift it out of the water, either.

When the engine was running, the intake would be at a lower pressure due to the coolant lift pump but it should still work. Make sure that the intake is looped below the water line, or it might not work with engine off.

I share your opinion about avoiding through-hulls.

[sailingdog]

You might want to setup a seawater manifold box instead of making another hole in the hull. I would use one through hull for the engine intake, which should be separate, and then one for the other raw water needs and the manifold box: sinks, washdown pumps, RO watermaker, etc...

This would allow you to eliminate all but two seawater intakes, but requires a bit more internal plumbing. I agree with putting the brine exhaust into one of the sink drains...it isn't any worse than the greywater coming from a sink.

[Zanshin]

I like the idea. I think I'll have to see if the diameter of the current through-hull is sufficiently large to accomodate the maximum flow, but if so then I can go about doing internal plumbing for the watermaker. Thanks.

[sailingdog]

Any questions on the manifold setup, let me know via PM.

[Zanshin]

I shall certainly do that. Right now I'm trying to figure out a system to move water around the 3 tanks - one of them will be for watermaker use only (so a back flush with chlorinated water won't ruin the filter) but then I'd like to pump that to either of the other 2 tanks. Do you have any recommendations for that system?

[sailingdog]

Sure, you could set up lines to the other two tanks from the RO water thank with check valves, to prevent water from flowing back into the RO water tank. Or you could use a vented loop to prevent water from flowing back into the RO tank. The check valve takes up less room though.

Probably the best setup would be a single line out from the RO water tank with a check valve, to a pump, that goes to a three-way diverter valve. That way you can go to either tank from the RO water tank, but the water won't go from either secondary tank to the RO water tank.

The diverter valve would have position one be RO->Tank1, position two be RO->Tank2, and position three be Tank1<->Tank2. That way no water can get back even if the check valve fails.

Hope that helps.

[Zanshin]

Thanks, that layout makes sense. What I was more worried about than the actual tubing was getting the water from the "clean" (or unchlorinated) watermaker tank to the 2 others - is a valve and the pressure from the watermaker itself sufficient to move the water or do I need to install a small pump? All the tanks are at approximately the same depth. I suppose a lot depends upon the watermaker and what the manufacturer states that the outlet back pressure can be.

[sailingdog]

I'd install a separate pump. That way you don't have to have the watermaker running when you're transferring water from the RO output tank to the storage tanks.

Check valves and vented loops both increase the back pressure on a line, so it makes sense to put in a separate pump.