Fuel tank

[Squanderbucks]

I would not use the wood epoxy or wood fiberglass sandwich construction except in areas where you know that the tank will not be exposed to getting wet from time to time. That is if spaced up off the bottom above where water can accumulate. Wood when cycles from wet to dry expands and contracts and the epoxy or fiberglass cracks leading to leaks which are difficult to repair as the fuel saturated wood is then difficult to bond to.
Easiest is to purchase a moulded plastic tank. For wierd or custom shapes consider one out of fiberglass for diesel.
Build your mold out of plywood, MDF or most anything you like to work with and then you get exactly what you want. Be sure to build in filler, vent. return, and gauge fittings as well as anchor points and cleanout port, etc.
I replaced the two OEM 100 gallon steel tanks on SquanderBucks 30 years ago with fiberglass ones and they have served ever since. Fiberglass does not sweat nearly like metal does either. Also, saved well over 100 pounds of dead weight.

[Milfordadkins]

I had tossed around the idea of wood molds, i have two rolls of 22oz woven roving that would be ideal for custom tankage lol. Plus i enjoy the idea of having extra fuel, cause you never know.

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[Squanderbucks]

Excellent. Coat interior of the mold (I like smooth prefinished Masonite for my molds) with Polyvinyl alcohol (PVA) as a mold release. Small molds can just be taped together with aluminum A/C ducting tape else reinforce forners and put together with 1X2 lumber and drywall screws. Use clay pressed into the corner seams of the tank to round out the corners. Mold in a 1 inch flat lip around the top (use 1X2 again around top of mold) to bed the separately molded top onto. Best to have a layer of something between layers of woven roven. Example Wet out mold, one layer of cloth, one layer roven, one layer mat, one layer of roven. Possibly, if you run out of what roven you have get additional material - maybe Bi-axial to finish out one more layer on the inside. Good wet coating of resin on the inside so it is nice and smooth so it doesn't give crud a gripping surface.
Since yours is to be a long will need a couple of baffles in it to reduce fore/aft sloshing. Maybe 2 clean-out ports due to the baffles.

[zeehag]

i will be having custom made intrinsic over keel fg tankage built in my formosa-th eold gone now tank was there--the folks before po placed a crappy plastic pick up truck undersized tank which is pure fail..converting my 2 water tanks to fuel, and adding another tank for water and ultimately a watermaker. but the fuel tanks will be intrinsic and fg. those places where the former tank was located is unsuitable for stowage of anything, as water enters and flows there.
fg is only substance acceptable in my bilges, or any other wet bilges for tankage at this time. the 40 yr old stainless water tanks are still good, except for the welds.

as for construction and shape--cardboard--the heavy stuff, is excellent for fg. it was used by boat builder i knew--hank mc kune--in repairing, and has as much strength as does wood with fewer issues. i learned a lot from that old coot. incredibly interesting. hand laid all his boats, never used chopper nor other compromise solutions exceopt cardboard in repairs--is strong as anything else once epoxied and enclosed with glass.

[Milfordadkins]

Won't run out. 2 full rolls. 80yrds x 36in wide. Will be couple weeks before i start on tank or tanks haven't decided on 1 or two tanks yet.

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[CorJH]

Since yours is to be a long will need a couple of baffles in it to reduce fore/aft sloshing

Sloshing is indeed an issue too!

[Rhapsody-NS27]

that's a lot of fiberglass.

A fuel tank down in the bilge area needs to be protected. My boat was designed/built to have its fuel tank in the keel/bilge, below the engine. It was held in with 2-part expanding foam and thickened resin on the edges to cap it off. The resin part cracked, water got down into the foam and water sat there against the aluminum tank. I removed it all when I found out there was a leak and found two holes and a LOT of low spots only paper thin.

Other owners have replaced their tanks for the same reason and many have coated their replacement tanks with fiberglass before placing it back down into the keel. Some have sealed the empty space in more glass to seal it off and others have left air space between the tank and hull so water wouldn't stay trapped.

One person, replaced their tank with a fiberglass tank using boards he made himself out of epoxy for the baffle/front/tops and since 2005, he's had no issues with it. His fuel capacity went from 25 gal to 39 gal from using the space that was taken up from foam. I decided to build mine from fiberglass as well and still in the middle of the project. Not easy work and if it's all successful, my boat will have a tank that will last a long time.

I had also thought of 2 tanks at one point, but decided one large tank will be a good way to go. Instead of Epoxy, I decided to go with vinylester. Smelly stuff, but read it's good for this purpose. It's been a learning experience throughout. For a few flat pieces, I used a mirror sprayed down with PVA, laid down a layer and wet it out one at a time to start with, then built up additional layers once it was in place.

Best of luck to you, how ever you end up doing it.

[Milfordadkins]

Sounds like i am going with fiberglass, gonna put it in keel area

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