Water System Design Musings

[Benz]

I wash them out with a tiny bit of bleach in lots of water, then let them dry before re-filling. This has only needed to happen two or three times, or I should say, we've done it because it was convenient to do so, not because of some pressing need. All my bottles have stood up to three years of chafe and abuse--tossing into the dinghy to fill, etc--but we stow them so they don't knock around. There is no need for an airtight seal: not any plumbed water tank is airtight, either. We have used this, incidentally, offshore, inshore, catching rain, with questionable Central American muni water supplies: almost any imaginable water supply scenario that cruisers deal with. It's simple. It's cheap. It works.

[micah719]

Some great info coming in, thanks for the contributions! The integral tanks have one advantage over the bottles....built in flotation chambers. No reason not to have an abundance of portable containers, though.

[Benz]

If the tanks are full, they'll make poor flotation chambers. If not full, and flotation is needed (presumably because the ship is sinking, I'm guessing), won't seawater insinuate itself through the vent?
Water bottles also float when empty and tightly capped.

[micah719]

Even a full tank functions as a double bottom, and stiffens the whole structure. The throughhulls are cut to a minimum: just one intake for the seachest, and the outlet is above the waterline because the greywater only gets dumped when it needs to, in a place where nobody will whine. Composting head, so I can forego the pleasure of playing with a macerator and a sewage tank and all the whatnot. Very hard to make this boat leak, from above or below. Still, if it does, it will have to be something catastrophic to worry me, on account of the excess pump capacity and multiple watertight compartments; engine space, hold, two cabins fore & aft, saloon/galley, nav/seaberth section, and the head, not counting a multitude of lockers and the tanks.

What I had in mind with the easily disconnected Euro hi-flow compressed air fittings was to have the ability to completely isolate tanks at will, and that includes totally sealing them so nothing gets in or out no matter what somersaults the boat is doing. Having a large supply of water also means less reliance on whatever the source is, be it watermaker, rain, dew harvest, piped or bottled aboard. Tanks and bottles. Not keen on plastic though, with what I hear of BPA and such nasties coming out of it....

[Benz]

Forgive my ignorance of such things, but wouldn't even a tank with the fanciest euro-compressed air thingummy need a vent in order to get water in and out of it? To completely isolate the tank it seems to my untrained mind that you would need some sort of valve to seal off the vent, or vents, one for each tank. To do that when you thought you might be in danger of taking on water might take valuable time away from avoiding the danger of taking on water.
In my limited experience I have found that getting underway is such a hassle, with sailcovers, and stowage and anchors, and shutting the gate in the lifelines (seriously), stowing the dingy, etc, etc. that having any extra step to take such as isolating tanks and sealing vents before putting to sea would make the pre-sail checklist incredibly complicated. Half my checklist is usually deferred until we're underway, and often that deferment is regretted as I try to get the lifelines closed up while tacking out of a busy harbor (I'm not making this up).
I don't say your system isn't well thought out, or won't possibly work: I simply urge you, based on my cruising experience, to simplify.
Finally, as I think about compressed air fittings, aren't the apertures rather small for getting water through? How long will a tank transfer take with miniscule tubing? And will they hold up to perpetual wetness? And will spare hose be available in the proper sizes in other countries? I'd better stop. All the finest luck to you.

[micah719]

Perhaps I should build a mockup and post photos....