Building a custom tank stitch & glue--step by step

[James McMullen]

Before I go any further at all, I should mention that just like the Gougeon Brothers, I am in no way all at endorsing that anyone ever should build their own gasoline tanks, ever! The risk of making a mistake is dire indeed, and what's more, the new alcohol additives in gas these days will actively degrade and weaken many resins, including epoxies and non-specialized polyesters. DON'T TRY TO MAKE YOUR OWN GASOLINE TANKS! EXPLOSIONS ARE BAD!

But what I needed for Phoebe was a small, 4 gallon diesel fuel tank to fit in an abovedecks cockpit locker, and after reading and researching the issue, I decided that a stitch and glue ply/epoxy composite tank had many virtues and not too many downsides for my particular application. The Brothers Gougeon are a bit cagey on the issue of building fuel tanks. It's clear they are being very careful to limit their liability. They offer instructions that start like, "we don't necessarily recommend this, but if you were to do do this, you should do it like this." I agree with them. I'm not recommending or endorsing that anyone else be so foolish as to build their own diesel fuel tank, but I guess it might be interesting for you all to see what this fool did.

These are some of the considerations I took into account before starting out:
*I could relatively easily make a complicated shape to maximise my utilization of the space
*the epoxy/ply walls of the tank are pretty well insulated which reduces condensation problems
*it's a simple matter to make very smooth, well radiused inside corners and joints to eliminate crevices and sludge pockets
*aluminum and steel both have their various issues with corrosion and electrolysis
*I can't weld sheet metal worth a damn, but I have built a bazillion S&G structures

This technique should work just great for anyone wanting to build a fitted water tank, holding tank, buoyancy chamber or whatnot too.

To make a pattern for this three-dimensional shape, I started with a cardboard box and stuck little strips of cheap doorskin plywood to it with hot-melt glue to define the edges and boundaries of the cockpit locker. It doesn't have to be pretty, but you should pick up all of the limiting dimensions with your strips.



I then cut out plywood panels to match the facets of the shape and started tacking them together. For this project I used some scraps of a multi-laminate aircraft birch plywood, which as it is somewhat less rot-resistant is something I wouldn't generally use in boat construction, but for this project which is utterly and thoroughly encapsulated with epoxy and fiberglass inside and out it can't possibly matter. What does matter is no voids! Don't use CDX or any other crappy plywood.



The panels here are tacked together with little stainless brads, but it doesn't really matter all that much what you use. It could be wire stitches or zip-ties or duct-tape as long as you can hold the shape together sturdy enough until the epoxy fillets can cure. The routed slot is for a visual sight gauge of the fuel level--I stuck a little piece of clear lexan in it before glassing over it inside and out. I used quite a few layers of cloth both inside and out and then rolled on coat after coat of resin on the inside as per the Gougeon's not-instructions instructions. I took pains to get the inside pretty smooth.

[James McMullen]

And here's the tank all glassed up and assembled, with a skim of fairing putty on top ready for some finishing and sanding.



And here we are after the first coat of primer. I hadn't quite figured out where the fuel return fitting should be located yet:




The shape of the tank includes a sloping, angled bottom so as to provide a sump for gunk and water to settle below the fuel pick-up tube. The pick-up and return fittings are standard brass pipe fittings, installed by drilling an oversize hole, filling with epoxy putty to seal the edges and then tapping for the pipe-fittings. Caution: only some types of pipe-dope are diesel fuel rated!



Since it doesn't really matter what color a tank inside a locker is, I decided to test out some paint colors for the finish paint to see them better than you can on a paint chip. This here is the Petit Easypoxy Jade Green, which I just might use for a bootstripe or something. The 4" screw-in port is aluminum and has a fuel-rated neoprene o-ring. I decided to make the fuel-fill port double as an inspection/cleanout port on this little tank. Seemed silly to have more than one port for such a little guy. I still need one more small pipe fitting for a tank vent, though, which I haven't quite decided where to run yet.

It fits quite nicely. I'll use some strips of solid neoprene to pad out the contact points it sits on.

[Robert Meyer]

Just never fill it with gasoline. Ethanol will render the epoxy into jelly.

[James McMullen]

My diesel engine would hate it too.

[Gerarddm]

I know the motorcycle guys have a couple of vendors who sell special coatings for the insides of custom fiberglass gas tanks.

Tidy work, James, nice.

[Robert Meyer]

Food for thought on using ethanol gas with fiberglass lined tanks

http://egyptian.net/~raymacke/Cbnskif36.htm

[Yeadon]

Brother McMullen is prodigious.

Two questions: how will you fasten that tank inside that area? A strap?

[Bill Huson]

Ah - ethanol. Stock outboard race gas is not allowed to contain ethanol or many other additives. Yep, getting tough to buy "legal" gas. 20 years back I built numerous wood tanks with WEST resin. They worked great! Weirdness from the fuel testing device - fuel left an aluminum tank, or a polyprop tank for a spell, would go from legal read to DISQUALIFIED! But one could leave fuel in a WEST resin coated wood tank for a freaking week and it would still pass. I like wood fuel tanks! I HATE ethanol in gasoline. I love METHANOL in race engines! Ethanol should be left in liquor . . .

[AnalogKid]

I've just about finished restoring the diesel fuel tank of my Land Rover, just got to paint the top side one the bottom is dry. I used a product from POR15 called US Standard Tank Sealer. It creates a plastic coating inside the tank that is impervious to pretty much any solvent. It might be worth a try contacting the guys behind the product to see if it can be applied over a wood/epoxy structure.

[paladin]

Oh....I had a quart of some stuff we used for exotic fuels on liquid propelled rockets. Hard as diamond, difficult to scratch and gasoline or diesel didn't touch it. I gave one quart away to someone and should have another quart or two in the cabinet, somewhere....gotta look for it I guess.

[wizbang 13]

I'm on my 27th year of a 40 gal ply/diesel tank in Woodwind. The "no condensation " part, along with soundproofing, functions as advertised.
I did not fair the outside of mine though, James!!

[jerry bark]

OK, I gotta ask about the slot in the tank side, which appears to still be there when the tank is installed. won't it let the fuel out? what gives?

cheers
jerry

[Gerarddm]

It's a fuel level sighting port with clear insert.

[Todd D]

That doesn't look like fuel rated hose on the return. You need to use A1 rated hose for everything except the vent which should be A2 hose.

[Breakaway]

I think the Type A hoses are required for gas, not diesel.


Kevin

[James McMullen]

Gerard and Kevin answered for me, both correct.

[jerry bark]

It's a fuel level sighting port with clear insert.

Why did I not think of that???

cheers
jerry

[Yeadon]

This will be a biodiesel tank. Correct?

[James McMullen]

I have been told that biodiesel is not recommended for diesels that get infrequent light duty because of the increased risk of organic sludge and oleophilic bacteria growing in the fuel system. Since this is mostly a get-in-and-out-of-the-marina engine, I don't think I'm going to risk it for this little guy. I don't really intend to be a power-boater, I just want a very reliable and maintenance-minimal auxilliary for when I gotta use it. That's why I sprung the dough for this particular brand-new engine instead of re-building the old BMW or Volvo diesels I already had lying around.

[skaraborgcraft]

James, what engine did you buy for your hard earned dosh?

[James McMullen]

A Beta 10. Cute lil' thang, ain't she?

[Todd D]

The code of federal regulations may not require rated fuel hose for diesel systsms, but the ABYC (American Boat and Yacht Council) standards and NFPA (National Fire Protection Association) standards do. While ABYC and NFPA standards are not binding on anyone, my experience is that insurance companies take them as the gospel. The use of non-rated hose in a diesel fuel system would certainly cause your boat to fail an insurance survey and/or provide grounds for an insurance company to deny coverage.

Plus it is just common sense to use the best possible materials when building a new fuel system. Why cheap out to save $10 here.

[James McMullen]

That's USCG and ABYC certified Trident Marine Type B1 fuel hose on the abovedecks section of the return fuel line hose, fully according to spec for abovedecks applications of this purpose, Todd. The belowdecks and suction side of the system are all Type A-1, but I ran short for that last section and substituted stock on hand for that one foot piece there. But yes, it is very important that anyone who chooses to do fuel system engineering on their own knows exactly what they are getting into. If in doubt, don't do it!

[Todd D]

My comment was based on the appearance of the hose. In the pic it looks a lot like the reinforced clear plastic hose used for water systems. I agree B1-15 is fine in that application.

[pipefitter]

Nice job on the tank. With considering your time and materials, the loose confidence displayed by the product vendors, You could have gotten that tank built by a good aluminum fab guy such as myself, with inner baffles and pressure tested and warranted for about the same money when it is all said and done. You blow boat guys are so frugal.

[James McMullen]

Oh, you might be right, Pipefitter, but a big part of the enjoyment I get from my hobby is from being utterly self-reliant and figuring out how to do it all by myself. I never hire nobody else for nothin!. . .unless I just don't wanna do it. Plus, I did build it entirely from scraps and leftovers from paid-off projects except for the port and the fittings so all I'm really out for is my time. . .and I usually charge myself a fair and reasonable rate for recreation. And I could have done it out of aluminum if I had wanted to by just borrowing Mike's MIG welder, but I really do think the anti-condensation and absence of corrosion issues that Wizbang refers to were compelling for this tiny, hopefully very infrequently filled tank. Plus, I'm not a very smooth welder--I don't practice enough to ever get better than adequate. I just don't love it like I enjoy woodworking.