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Valiente 10-06-2007 02:47 PM

Water tank replacement options
 
I have two roughly 100 gallon freshwater tanks suspended beneath my side decks on either side of the engine compartment. They are supported on struts to the framing below (it's a steel boat) and there is about two feet of "curved space" below each oblong tank. They are about 18" W x 48" L x 22" H.

The tanks are SS and to judge by the noises they make flexing when full in a seaway, they are unbaffled.

I wish to make new tanks that are fitted to the curve of the hull down low. The boat is currently a tad tender (although I am very much lightly loaded at the moment), and I feel that putting the tanks down low will lower the CG, lower the "slosh" factor, will permit "from above" hose barbs and inspection ports and will free up considerable space above the tanks for large, light things that can stand the warmth from the engine, which will still be a good three feet away on either side. It would also allow a more sensible water fill and manifold set-up and would vent UP instead of the current down into the keel bilge.

My questions are these:

Would it be best to stick with two large SS tanks as is the case now?

Would a set of four or more be better for ballast, "slosh" and cross-containmination issues?

Is there a case for "bladders" of the Plastimo type? If so, how is remaining capacity gauged on such a tank?

Am I missing any obvious tank building materials suitable for a steel boat? What are the best ways to secure tanks firmly and yet isolate them from hard points and corrosion issues? (Once they go in, they aren't going to move unless its' absolutely necessary).

Thanks. I want to do the right thing here.

dohenyboy 10-06-2007 02:57 PM

Avoid bladders -- they break, leak eventually and don't use all the available space
Plastic tanks will never corrode

billangiep 10-06-2007 10:21 PM

Val..I'm also working on my fresh water system..leaning more toward the plastic type....here's a couple sources.
http://www.tank-depot.com/browse.aspx?id=8

http://www.ronco-plastics.net/

Sailormann 10-07-2007 03:15 AM

Plastic - or if you're feeling rich - Monel. Plastic will absorb a bit of taste but it dissipates quickly. Monel lasts pretty well forever. Stainless will eventually corrode. Bladders are standard equipment on MacGregors.

sailingdog 10-07-2007 03:18 PM

Rigid plastic tanks are probably the best way to go. I would recommend four tanks, since it would provide better protection against contamination, and allow you spread the load out more for ballast purposes.

Another option is to have fiberglass tanks made. They can be made custom to fit your boat, and may be a better choice in terms of strength, weight and longevity.

USCGRET1990 10-07-2007 03:28 PM

Quote:

Originally Posted by sailingdog (Post 203364)

Another option is to have fiberglass tanks made. They can be made custom to fit your boat, and may be a better choice in terms of strength, weight and longevity.

I agree with this as well...in that it is a design issue, you might want to bounce it off these folks, as some of them are builder/designers and quite knowledgeable:

http://www.boatdesign.net/forums/sea...archid=1086045

Rockter 10-07-2007 03:31 PM

I would avoid bladders unless you really must. I found it difficult to keep the water fresh.

Valiente 10-08-2007 12:32 AM

Thanks for all the suggestions, people: bladders were suggested to me by a boat repair guy, and they were but a passing fancy.

Plastic tanks of the HDPE variety might be nice and I concur that four 50 gallon tanks make considerably more sense. There's no reason I can't have inspection ports and the stand-offs, bracing and strapping are simpler with a smaller tank as long as I eliminate any chance of chafing or friction.

I would do a fibreglass keel tank, but these are not keel tanks, but "either side of the engine bay" tanks.

I'll throw out another question: What do people think of the new(ish) snap-together plumbing fittings for marine use, given the low pressures involved and the tendency of hoses to discolour and get grotty?

Here's an example of what I mean: it strikes me that from deck fill to tap, the less metal I have the better, which is the opposite of how I feel about through-hulls and fuel manifolds.

http://www.globalspec.com/FeaturedPr...Valves/46269/0

US27inKS 10-08-2007 12:54 AM

I've used some of those plastic fittings. Make sure your lines are cut square, and push the lines all the way into the fitting. Otherwise they are fabulous. You can assemble the plumbing on your boat in minutes. There is actually a marine plumbing supplier offering these, but I can't remember who. Stick with the Watts brand. Better to pay the HD price than the WM price.

sailingdog 10-08-2007 01:25 PM

I'd second what US27inKS said. :) HD is much less expensive.


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