Plywood Fuel Tanks

[fallguy]

Thanks @Rumars . Every conversation with you is educational.

he is great; an encyclopaedia of boat knowledge

Are you going to be subject to survey John? Private message me if u like.

So, in order to build a plywood tank; if you think you can get away with it, there is no way to seam the inside at the top without a hole in the tank that is then only tabbed on the outside. The only way I can imagine in my Covid fog to build a tank would be to glass over a bladder a solid glass tank. But this is infinitely more difficult than sending out for one.

I suppose, let's say you cut a 6" hole in a plywood top and that allows you access for inside tabbing. Then you could lay plastic in the bottom of the tank and then laminate a round piece of glass onto the cutout that was say 2" around and then pull the plastic and thixo bond the fiberglass to the tank top. But man, lotsa work. Then the fittings gotta be right, too.

I happen to have an aluminum belly tank here. How big is the hole midship dimensionally?

 

[DogCavalry]

The box in the middle is 46" by 42" by 13".

 

[DogCavalry]

The surveyor drops by all the time. Generally he really likes what he sees.

 

[DogCavalry]

My tank budget is us$15 a gallon/ US$4/liter. That would pay for some HDPE, a welder, and some practice.

 

[Rumars]

Sorry, I'm just a regular guy, plenty I don't know.

To increase the glueing area for a plywood tank top one laminates the fiberglass flange beforehand using a former (taped piece of ply), then sticks the lid on with thickened epoxy. There will be some squeezeout but that is unavoidable, because of the baffles one can not tape or clean the fillets unless there is a handhole in each compartment. There are other ways, like having an outward flange or a overlapping lid (like a shoe box).

One fast but heavy way to make a tank is to use G10 (or the fire resistant version FR4), according to the chemical resistance charts it is unaffected by ethanol and gasoline (check with your supplier). One could laminate thin G10 to ply to decrease the weight, and conventionally fiberglass the outside. Baffles can be HDPE pipes wedged in the box.

There are also dedicated tank sealers that also work with fiberglass, this way regular resins can be used, for example this one: Alcohol Resistant Gas Tank Sealer | Aircraft Spruce https://www.aircraftspruce.com/catalog/appages/gastanksealer.php

 

[DogCavalry]

This is exciting stuff... well to me. Maybe my standards are low. Anyway, there are a number of ways to build a good tank.

 

[gonzo]

Plastic tanks have to be labelled by the manufacturer to be compliant with EPA for evaporative regulations. That means a home made tank is not allowed. As far as gluing a lid, you would have to show that it complies. The testing and engineering alone will cost you more than a professionally built tank. Is there a reason you can't install a rotomolded tank?

 

[DogCavalry]

Rotomolded tanks are on back order, until forever apparently.

EPA regs for evaporators haven't come north yet, thank god.

 

[DogCavalry]

Proposed tank location. Alternate possible.

 

[fallguy]

I have a belly tank aluminum; good condition.

60" long 10" deep for 6" wide, 7" deep on the sides, needs about 3" for fill clearance,
23" wide

probably of no use to you, but went out n measured it

I get 52 gallons; probably awful light on amount needed...

 

[fallguy]

I feel like you need to be able to make a longer tank DC.

What would it take to reach under that bulkhead for space?

 

[DogCavalry]

The big bulkhead with the door? That's the primary structure. Can't cut it. Could put tanks inside, if outside under the sole can't work.

 

[ondarvr]

There has always been ethanol fuel resistant resin to make fuel tanks, it's just prior to E10 no one used them. Every manufacturer has a few in their lineup, getting them now may be a bit more difficult though.

 

[DogCavalry]

You can always try your hand at HDPE welding.

@Rumars , can you recommend a suitable rig for a job on this scale?

 

[DogCavalry]

I'll make plywood glass epoxy tanks, or weld up some HDPE tanks.