DIY Diesel Tank Planning Advice

[zstine]

I have read some threads regarding DIY tanks and I just want to run my plan by the community to see if I missed something important...
I'm doing it custom because it is pyramid shaped with the top cut off and no off shelf fits well. Buying custom is cost prohibitive as I have many materials on-hand. The tank will hold about 20gal. I plan to use 11/32 exterior class rtd sheathing for my core. Stitch and glue assembly with epoxy fillets followed by 3 layers of 10oz. epoxy/glass tape on all seems, then 3 layers of 10oz epoxy/glass over both inside and outside of the ply. I plan to put GPO3 FRP piece in place of the wood core where the fittings go. This tank will be used to gravity feed my main tank, in lieu of running it as a second tank. Because it is a gravity drain feed, I want to put the fuel fitting near the bottom of the tank. A no-no for gas, but is this allowable per ABYC for Diesel? I plan to paint the outside of the tank for cosmetic reasons, but will leave the epoxy/glass uncoated on the interior as I have previously had interior coatings fail in tanks causing blockages. Any problem leaving the inside raw epoxy/glass layup? my largest panel is about 12" x 32" and will have a baffle mid span. Is 11/32" ply core, with 3 layers of 10oz epoxy/glass sufficient for strength and sealing out the Diesel for this size span? Any added comments welcome.
thanks
zach

[Lepke]

I suppose you read this: WEST SYSTEM | Modifying and Customizing Boats - Wood/epoxy composite tank guidelines

Many years ago when there were many wood fishing vessels, I made a bunch of plywood/epoxy tanks for water, fuel and even a couple for gas. The insides were well cured before using, but not coated with other products.
For laws check with the USCG regs. My boat has a 200 gallon day tank with a bottom supply going to my racors, and has been inspected by US and Canadian CG for passenger service, but it may be a grandfathered issue.
I would use 1/2" ply as a minimum. I don't like gravity feed tanks, because people forget, misjudge how much room is in the main tank and then there is an overflow. One option is vent the main tank to the upper tank and that tank's vent is the working vent. A bottom supply will be a weak point for leaks and needs to be an excellent job. The USCG is great to work with, understanding, but a person making several fuel spills can get a breathtaking fine.
If you ever plan to sell the boat, I'd get an opinion from a surveyor.

[TeddyDiver]

Originally Posted by zstine

Any problem leaving the inside raw epoxy/glass layup? my largest panel is about 12" x 32" and will have a baffle mid span. Is 11/32" ply core, with 3 layers of 10oz epoxy/glass sufficient for strength and sealing out the Diesel for this size span? Any added comments welcome.
thanks
zach

A couple of strokes of epoxy on top of the layup inside the tank

[zstine]

thanks for the link Lepke. Yes, I've read that before and it talks to a wood construction just sealed with 20mil of epoxy barrier coat. I was going to do 3 layers of epoxy/glass and would have 45mil, though I may go a bit thicker and/or go with the 1/2" ply for structural concerns.

yup Teddydiver, a neat coat of epoxy to make it smooth is a definite.

I've been shopping for the fuel sending unit, filler neck, and other fittings and found some stupid expensive prices... like $75 just for a filler neck fitting!? Who has these parts for reasonable prices?

[Squanderbucks]

I see no reason to use the wood/glass construction you mentioned for such a small tank. Complicates the process and makes the tank heavier, and less easily repaired/modified in the future if needed. I you feel you must make it out of wood do so then finish the inside smooth and coat with wax or polyvinyl alcohol and put all 6 six of your layers inside. When cured peel off the wood and throw it away.
Alternatively, get a piece of foam that is dissolved by acetone and shape it to the size you want and cover it with all of your fiberglass then drill your hole for pickup and pour in the acetone and the dissolve out the foam. This tank would be totally seamless. 20 gallons probably doesn't need a baffle.

If you really want to have a sawed out form to go by - get a sheet of fiberglass panel at Home Depot the kind that is used for pre-finished bath walls. It is textured on one side and smooth on the other. Use it as a mold as first described or use it the way you described with wood. You could put all your layers on the inside except for the top. No need to paint as it comes white already.
Whatever method you use I suggest using colorant in your last layers of resin to avoid paint. Painting the tank with regular paint just makes it harder to do future repairs or additions.

[pdenton]

If you check it out polyvinyl ester is more chemical resistant than epoxy to petroleum products. Also there are widely different blends of polyester and many of epoxy. Some are very bad and can cause engine damage. Speak to an expert. Find out about "blush".
pdenton

[GILow]

Originally Posted by Squanderbucks

If you really want to have a sawed out form to go by - get a sheet of fiberglass panel at Home Depot the kind that is used for pre-finished bath walls. It is textured on one side and smooth on the other. Use it as a mold as first described or use it the way you described with wood. You could put all your layers on the inside except for the top. No need to paint as it comes white already....

Sounds like a good technique. I should give it a try.

[zstine]

Originally Posted by pdenton

If you check it out polyvinyl ester is more chemical resistant than epoxy to petroleum products. Also there are widely different blends of polyester and many of epoxy. Some are very bad and can cause engine damage. Speak to an expert. Find out about "blush".
pdenton

Thanks, pdenton. I didn't know epoxy could be an issue chemically. I have over a half gallon of epoxy from US Composites on hand that I plan to use. So, I will call them to ensure no issue.

[zstine]

Is there any restrictions on how close a shore power connection is to a diesel fill deck fitting?

[Rhapsody-NS27]

I'm in the middle of a fuel tank project with fiberglass... but not using epoxy, using vinylester for the reason pdenton mentioned. I did a lot of research for about a year before I even bought materials and everything I saw said vinylester was more chemical resistant. I have a small piece of cut fiberglass from flat stock I made sitting in a cup of diesel and there has been no change in the glass or resin. Acetone does dissolve the cured resin a bit and good for cleaning tools, but when I looked it up, vinylester isn't resistant to acetone anyway, but diesel is just fine.


While you could possibly leave the inside bare, it was advised to me to include a painted interior (Interlux 2000E barrier coat) and a fuel tank liner. While I haven't reached that point in my project, just wanted to pass on what was suggested to me.


Good luck.


Pictures:
layup for flat pieces
initial layup for inside tank (in the keel)
flat panel cut to shape for forward part of the tank
forward piece in place
shaping baffle
top pieces mostly cut to shape.

and that's where I'm at so far. Just need to fine tune a few things and wait for it to warm up again, but the top will soon be able to be set in place, where I can then continue the layups to strengthen the top. I'm using 18oz woven roving w/ 1.5oz chopped mat.

[zstine]

Originally Posted by pdenton

If you check it out polyvinyl ester is more chemical resistant than epoxy to petroleum products. Also there are widely different blends of polyester and many of epoxy. Some are very bad and can cause engine damage. Speak to an expert. Find out about "blush".
pdenton

Originally Posted by Rhapsody-NS27

I'm in the middle of a fuel tank project with fiberglass... but not using epoxy, using vinylester for the reason pdenton mentioned. I did a lot of research for about a year before I even bought materials and everything I saw said vinylester was more chemical resistant.

Thanks you guys! I just got off the phone with US composites and they said the 635 epoxy I have is not impervious to Diesel. They said you can build with it, but recommended coating the inside with "steelflex". Coatings worry me because if they fail it will plug up the fuel lines, kill the engine (in a tight channel with many rocks for sure) and be a headache to fix.. I'm looking into buying Vinylester and going un-coated. Any recommended sources for Vinylester at a decent price?

[Rhapsody-NS27]

Originally Posted by zstine

Thanks you guys! I just got off the phone with US composites and they said the 635 epoxy I have is not impervious to Diesel. They said you can build with it, but recommended coating the inside with "steelflex". Coatings worry me because if they fail it will plug up the fuel lines, kill the engine (in a tight channel with many rocks for sure) and be a headache to fix.. I'm looking into buying Vinylester and going un-coated. Any recommended sources for Vinylester at a decent price?

As I researched, I made estimates on supplies and ended up going with Fiberglass Supply (Surfboards, Windsurfers, Kayaks, Canoes, Boats , Autos and more) for the Vinylester (look under Polyester Resins for it). I ended up getting two 5 gal buckets and on the second one now. Then, you'll see that the type they have is Hydrex 100. There's datasheets out there you could look up.


It's a lot different working with vinylester than epoxy. It smells SO much worse (get a face mask and organic vapor filters) and requires 1.25% ratio of catalyst. I have a digital scale and in grams, comes out to 80:1 (resin:MEKP)

[zstine]

I'm about to buy Vinylester resin, first time use of this compound... I've used PVA to aid surface cure before with polyester, but the supplier's web page says to use styrene wax. Can you use PVA with Vinylester just like you can with polyester resin? I have some PVA on hand....

[Rhapsody-NS27]

Originally Posted by zstine

I'm about to buy Vinylester resin, first time use of this compound... I've used PVA to aid surface cure before with polyester, but the supplier's web page says to use styrene wax. Can you use PVA with Vinylester just like you can with polyester resin? I have some PVA on hand....

I made my own flat pieces for bulkheads. I used a mirror, sprayed several (thin) coats of PVA, waited until it dried, then laid glass/resin. I used 3 layers of 18oz woven roving with 2 layers of 1.5oz chopped mat in between. PVA wasn't needed on the surface. Once it cured, I used something wedge shaped under a side/corner to lift it up, then just peeled/washed the PVA off. Once cut to shape and in place (I was/am making mine in place in the keel), I then added additional layers to give it more strength... I think I put as much as 11 total layers alternating between woven and mat.

Hope this helps.

[tkeithlu]

The gravity feed is OK by ABYC for diesel. We actually use two agricultural 300 gallon gravity feed tanks filled with "Baffle Balls," which prevent surge, as our main tanks, and two reserve military 200 gallon tanks that have baffling. They gravity feed transfer pumps to shift the reserve to the main tanks when they get low. We did once end up bailing out about 60 gallons that got loose in the engine room because I forgot to open the return line from the engine. We ran it through a filter, into the tank, and proceeded. Gotta love diesel and hate gasoline.