Building fiberglass fuel tank with limited materials

[pagu]

Hi all, I'm new to this forum and thanks very much to the conveners for this facility.

OK here's my question. It's pretty basic, but I'd appreciate any ideas on ways to achieve ? with very limited materials I have on hand.

I want to build fibreglass, removable fuel tanks, around 100 L volume for two 24' diesel inboard powered launches I have in the Solomon Islands. The boats are pretty run down, came out of a scrape heap and I've been fixing them up.
Rebirth of the M.V Pagu
You have to understand that compared with building in Australia (where I'm from) or most other places forum members will be reading this, what's available in way of materials in the Solomons is EXTRELELY LIMITED. I can buy polyester resin, mat and gelcoat but that's about it, so I need to work with the few materials that are available locally.

I was thinking about just making a simple rectangular female mould out of cardboard and duct tape. Brace it with timber. Line it with sheet plastic, spray that with silicon lubricant for the release agent then lay up.

That's the idea I have in mind and I don't see any reason why that wouldn't work? Doesn't matter if finish a bit rough, as long as finished job is strong and functional. I'm not bound by any rules and regulations regarding tank construction. The country is pretty regulation free. One of the many reasons I love the place!

It's a simple construction method achievable with the basic materials I can muster there and should suffice for me to build a strong rectangular shaped tank. I haven't put this to the test yet and wondering if anyone has any advice on other very simple techniques that might be better?

Thanks very much.

 

[73Chrysler105]

Re: Building fiberglass fuel tank with limited matrials

Re: Building fiberglass fuel tank with limited matrials

I don't believe Polyester Resin is Feel resistant and is definitely not waterproof it is water resistant just not proof. I wouldn't want anything that could leak water holding gas in my boat. You would have to coat the inside of the tank with something that was not gasoline permeable in order for this to work. I wish I could build my tank with my epoxy resin as it would be so much easier but i am not sure if even that is gas resistant enough.

 

[jigngrub]

Re: Building fiberglass fuel tank with limited matrials

Re: Building fiberglass fuel tank with limited matrials

I did a google search on it and it looks like you can:

polyester resin diesel fuel - Google Search

... but, I don't think I'd trust a home made fuel tank because I'm not a tank engineer/designer and I'm sure there's more to it than just slapping some fiberglass together... but it's your boat and you can do whatever you want to it.

 

[ondarvr]

Re: Building fiberglass fuel tank with limited matrials

Re: Building fiberglass fuel tank with limited matrials

Many types of polyester will work for diesel fuel tanks, but VE would be the way to go. You will most likely need to special order whatever resin you use because what they have locally may not do the job, sometimes it can also be difficult to find out much info on it. Go to one of the local suppliers, the company they buy from should be able to supply a suitable resin. I typically recomend fuel tanks be made out of something else though.

Nothing is actually waterproof, there is just varying degrees of water resistance, but for all practical purposes most polyesters would be considered waterproof, not fuel proof though.

 

[Woodonglass]

Re: Building fiberglass fuel tank with limited materials

This ^^^ is true. I'm always a bit confused where the misnomer that Poly is NOT water proof, comes from. GelCoat is a Polyester based product as well as the resin that 99.9 % of all MFG boats are made from. I have never seen one drop of water "OOZE" thru a Gelcoated Poly based laminated boat. People leave em in Floating Docks Year round for YEARS and they never let one drop of water thru the hull, unless there's damage. I'm amazed with statements saying the contrary. Chemical Resistance IS another matter all together.

In case you want to know...
Polyester Resin Chemical Resistance
Vinylester Resin Chemical Resistance

Almost all of the NEW underground Gasoline (Ethanol included), Federally Regulated storage tanks, are built from some formulation of Fiberglass resin and cloth.

 

[73Chrysler105]

Re: Building fiberglass fuel tank with limited matrials

Re: Building fiberglass fuel tank with limited matrials

Reading through some of those links Jig posted some worked some didn't one did a test and its not the gas or diesel that has a problem it's the ethanol that eats up the polyester and Epoxy bonds. So as long as you can only use Ethanol free gas or diesel you will be fine. Around here everything has Ethanol in it so I will have to stick with Aluminum.

Polyurethane tanks on the other hand have not had any issues besides getting hard when old and cracking.

 

[Ned L]

Re: Building fiberglass fuel tank with limited materials

Hello Pagu. Nice looking boat, a good find. Seems you were lucky with the engine, nice and clean looking. Being diesel I think you can do what you want to with the idea of a fiberglass tank. For another idea, can you build a plywood box for the tank and then fiberglass it very well inside and out? For either method you would need to make the tank as an open top box and then make a separate fiberglass panel that would be glued and fiberglassed on the top. a couple of things I would suggest 1) build in two or three "baffles" inside the tank. Baffles will help to make the tank much stronger, and stop the fuel from sloshing around when the boat rolls. The baffles need only the corners cut off a little bit to let the fuel move inside the tank.

2) I would make maybe a 6" - 10" round access hole in the top of the tank with a gasketed bolt on cover. This will let you work inside the tank as you glue the top on. (you will be able to fiberglass the top to the sided on the inside and outside.)

 

[Woodonglass]

Re: Building fiberglass fuel tank with limited materials

Great Advice there ^^^^

 

[Ned L]

Re: Building fiberglass fuel tank with limited materials

Thanks. ---- Being diesel (and his very limited resources) I think he does have options here. I would NEVER suggest this if his fuel were gasoline. (Back in the 1970's there was a boat building company called "Jersey" (they built fairly nice sport fishermen) that used fiberglass tanks for a couple of years. It wasn't long before people started having a really hard time getting insurance for them because the fuel tanks acutally started weeping the gasoline. If you rubbed your hand on the outside of the tank you could smell the gas. - Many owners ended up replacing the tanks.)

 

[Woodonglass]

Re: Building fiberglass fuel tank with limited materials

It all depends on the Resin being used. Different formulations yield different capabilities. Like I said before, Almost all the underground Gasoline Storage tanks are made from glass now. It's NOT the same resin and glass used in Boats...That's for Sure!!!!

 

[a1964rn]

Re: Building fiberglass fuel tank with limited materials

Here's a couple of links that may help:
Composite Fuel Tank Construction

http://www.practical-sailor.com/newspics/charts/8912byofiberglasstanks.pdf

There's more info out there, you just have to do some research.

 

[Teamster]

Re: Building fiberglass fuel tank with limited materials

I have nothing to add other than that is a cool old boat,.....

Looks like a great place to live,....