Fiberglass Fuel Tanks

[boatlover24]

Hello all. I'm designing some fiberglass fuel tanks for my boat. I've made the mold for it, but now can't decide exactly how to lay it up. Amazingly, I'm stuck on the first step. I'm not sure whether or not to use gel-coat as the surface layer (female mold). All the stuff I've been reading on the internet never mentions gel-coat, just resin. But a buddy of mine said that a boat manufacturer he knows layed it up like that, with the gelcoat face on the inside of the fuel tank to help insulate the glass. But it just seems to me that gel-coat could contaminate it or break down over time. Any thoughts would be greatly appreciated!

[Dutch Peter]

A gell-coat is just a thin layer of resin, applied in the mold and allowed to harden untill it feels sticky ("gell time" I believe). The function is to seal of the ends of the glass fibres, to prevent capillary action. It will not break down and not contaminate your fule as it is a resin.
Actually, I would advice you to use a gelcoat to prevent the capillary action of the fuel, as this is creeping much faster as water does.
Also, look in the forum archives, this subject has been posted before!

[Dutch Peter]

Some interesting info:

http://boatdesign.net/forums/showthread.php?t=278

[Buckle]

Without wanting to seem rude, you guys are totally missing the point. Gel coats have a number of functions, primaily to pretect the laminate and to give a cosmetic finish etc. They can also play an important role in reducing osmosis occurring.

However the most important factor to consider is to select a suitable resin system. Without this, your tanks will leak and breakdown. GRP tanks are big money in this industry and have a limited life depending upon the fuel inside. Therefore must be designed appropiately.

You cannot use standard, cheap and cheerful isothalic or orthalic polyester resins. You will need a resin system suitable of withstanding the harsh environment. A range of vinylester/DCPD resins exist these days. There must cheaper than epoxies. Consult ur local major resin supplier. They would also be able to give advice on suitable, recommended layups.

Changing your resin system is also only one part of the design process. You will need to use powder bound mats, not elmusion based mats. You will also need a very thick monolithic laminate. If you dont, you will be in trouble cos your tanks will start leaking. Also your tanks will need a full cure before use in operation.

Finally best of luck mate, you will need it. Hope you are good at laminating. Make sure you have zero voids to avoid osmosis etc. Consider infusing the tanks from the word go if you know how to minimise voids etc.

Buckle