Repairing an integral fiberglass water tank

[welshwind]

I now know why Beneteau's are referred to as BendyToys . After beating into 6-8 foot waves with short intervals (don't you love Great Lakes sailing), I discovered that my forward water tank (an integral tank under the v-berth) has somehow been breached. I put water in and it reasonably quickly finds its way to the bilge .

Anyone have any experience in doing a repair such as this. I've got great access to the top of the tank, so I'm thinking these would be the steps:
1) Cut a reasonably small access hole in the top of the tank.
2) Use either a mirror with a flashlight or use my video camera to look inside the tank and try to figure out where and how bad the breach is
3) Expand the access hole in the appropriate direction
4) Use epoxy or fiberglass to do the repair (Anyone have a preference? Plus's or minus's of either approach)
5) Cover the access hole with an Bomar Access Hatch. I've seen them come a large as 10x27, so I'm hoping I won't need an access hole larger than that.

Anyone have a better idea? Any and all comments are welcomed (boy, did I just open myself up for it!)

[sailingdog]

It might be easier for you to figure out where the leak is by shining strong lights around the outside of the tank, and looking for the light inside the tank, rather than using a flashlight inside the tank.

I would use an epoxy filler, like MarineTex to fill the crack. But I would highly recommend coating the repaired area with something like CeramKote 54, which is an epoxy coating designed for use in potable water tanks.

[danjarch]

If the tank is sealed, close off the vent, then stick a hose in the fill tube and stuff it till you can get it to build up pressure. This should force water out fast enough to find the leak. Once you find the leak, fix it from the out side.

[danjarch]

On second thought. Disconnect the fill hose. Make a hose that can connect to an air compressor. This way if you spring any other leaks, it won't flood the cabin. This is how you test tanks and plumbing professionaly. Then fix from the out side.

[welshwind]

Thanks for the responses so far ... a bit more information about what I am up against...

Beneteaus use a hull/liner production method. Thus, as best I can tell, this integral tank is between two cross beams of the liner in the forward v-berth. I holds about 110 gallons of water. The aft part of the tank is covered by finished plywood which is screwed into the top of the tank using a cleat method (a good thing) but fastened to the liner at the bottom via slots and adhesive. I'd like NOT to disturb this if I can help it (though that might not be an option). The filler hose, vent and the output all come off the top of the tank. If the breach is at the bottom (and since the water appears to be exiting the tank in such a way that it is getting between the liner and the hull as it makes its way to the bilge and NOT on the topside of the liner where I could see it flow), I'm thinking the breach is actually in some portion of the liner. Thus, getting access to the outside to either shine bright lights or to fix it is not possible (unfortunately).

Again, thanks for the thoughts. If this additional information inspires other thoughts, please share. The choice of expoxy and coating was very helpful.

[sailingdog]

How much does the tank drain when you fill it?? If it drains almost completely, the you know the leak has to be located on the bottom or near the bottom edge of one of the sides. Knowing how much of the tank drains out will give you an idea of how high up on the tank the leak is located, and reduce the amount of time and areas you have to spend looking at.

[welshwind]

SD - Your point is well-taken. I believe that it is basically completely draining. I can't say for sure as I did turn on all the faucets when I realized that my just-filled tank was emptying into the bilge. Nonetheless, the water continued to flow for a long time and my faucets started to sputter within a few minutes afterwards. That, coupled with the fact the water is running under the liner instead of over the liner (where I would see it), will make me first look at the bottom seams and along the bottom edges.

[camaraderie]

Can you see where the tank outlet hose connects? May just be a simple failure there if the water is draining quickly.

[welshwind]

It appears that, unlike my starboard tank, the outlet for the integral tank is actually on the top of the tank. The filler hose, vent, and another hose are all connected to fittings on the top of the tank. The 'other' hose I mentioned is the same type and has the same markings as the hoses that interconnect the pump with the faucets and the hot water tank. Therefore, I'm assuming it is the outlet. I will most certainly trace the hose from the water pump back to the tank to make sure that is the case. It would be nice to simply find out the hose fell off. A lot less work.

[RichH]

Cut a large access hole in the top of the tank.
Structurally repair the breach (this time use large radiused fillets on all the 'corners' with WEST or equivalent over structural cloth tape reinforcement of ALL the seams/corners.
COVER all internal repairs and any other exposed 'fiberglass' with FDA/NSF approved lining-epoxy "rated for potable water service". Just roll-on TWO or THREE thick coats. do websearch for "NSP-120" + 'epoxyproducts' ... or go to the INTERLUX COMMERCIAL Division website.

Glass-in the cutout that you made in the top - using potable water grade lining epoxy as the 'resin' .... structurally 'overlay' the joints with WEST, FG cloth etc. .... or add a 'flange' to the cut out and tank and bolt/stud-together using rubber gasketing (silicone preferred) --- a gasket supply house will easily cut one for you from stock or buy the sheet and carefully cut the gasket yourself.