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Old 22-09-2012, 09:25   #1
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Fiberglass Diesel Fuel Tank

I'm in the process of refitting my sailboat for offshore and I'm planning on replacing my corroded black steel 62-gallon diesel fuel tank with a fiberglass one.
Does anyone have any experience on designing and installing a fiberglass tank? It will be non-integral, baffled, etc. but I don't know about whether it can be made from sheet fiberglass. I've read Nigel Calder's words on tank construction and the Feb. 2011 Practical Sailor had a great article by Ken Hankinson on fiberglass tank construction. Any other tips from anyone?
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Old 22-09-2012, 09:47   #2
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Re: Fiberglass Diesel Fuel Tank

I have built many and am in your area. For non-integral you can build in a product like Coosa board and then glass heavily inside and out, but it makes for a pretty heavy tank. Integral is lighter and often easier. It can be done lighter with fiberglass flat stock, but it's very difficult because stock that is thin enough and thus light enough is too flexible. By the time you make it thick enough to be stiff it's heavier than Coosa. I often coat the interior of the tank with 2000e, 5-6 coats. It can be a difficult job. For non integral I build the tank without a lid, glass in all the baffles, coat the interior except for the top 4" or so, then bond on the lid and do all it's tapes through the inspection port and finish the 2000. Works great, never had one come back.
Of course you can also mold a non-integral tank to get a part that is both more than strong enough and fairly light, but that becomes more of a process and can constrict tank size and shape as the mold has to built with a positive release, unless you want to split mold, which is madness for a tank.
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Old 22-09-2012, 10:15   #3
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Re: Fiberglass Diesel Fuel Tank

Hi. Good to hear from you. You sound very experienced on making fiberglass tanks. We're currently in Port Townsend, but it would be wonderful to have a conversation with you. For background, the existing steel tank is 24" wide, 30" long, 24" high forward, and 16" high aft. The tank has been removed from the boat. Scheduling is an issue as the tank has to go in before the engine is installed.
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Old 22-09-2012, 10:22   #4
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Re: Fiberglass Diesel Fuel Tank

Annie, this is just an idea, but you might want to determine if your original tank actually needs replacing? Steel that is rusting looks like hell, but may not be very serious, or may only be serious in a small area which can be repaired easily. If the tank can be removed without having to be cut up, then take it to a good welding shop to see if it is repairable. It might only need a few spots on the bottom of it replaced. If it is repairable, then have them put some nice size accsess holes in the top so that you can sand blast the inside when you blast the outside to prepare for a modern coating system. The accsess holes will be good for later tank cleaning. This may sound like a lot of work, but I think you will find that it will be less work and money than building a glass tank and you wont have to change your tank mounting or plumbing. With all that being said, there is nothing wrong with a well built fiberglass tank, but I would lean towards checking on the price of a good repair before starting on building new.. The tank has to be pulled anyway so a trip to a welding shop for an estimate wont be much trouble.____Just my 2 cents worth._____Grant.
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Old 22-09-2012, 10:39   #5
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Re: Fiberglass Diesel Fuel Tank

Grant, that's not a bad idea. The mild steel tank is 26 years old but it holds diesel and there are no holes that I can see. Lots of rust, though, and at least one area where it looks like a repair was made. I shudder to think of putting it back in the boat. It was a real beast to remove in one piece. We would want to install inspection ports, an additional pickup line, and beef up the mounting for offshore. And I would have to convince my husband. Doesn't hurt to get it checked out. I like ideas like yours that come from this forum.
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Old 22-09-2012, 12:05   #6
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Re: Fiberglass Diesel Fuel Tank

Annie-
You will find it cheaper to construct a new tank out of steel - not to mention quicker -simple job with the old tank out of the boat to be used as a pattern - a good epoxy coating will take care of the rust problem for years as long as you keep it dry. 26 yrs isnt an old tank - it probably only needs to be sandblasted & re-coated (if youre lucky) crummy job for sure but it sounds like youre 1/2 way there. A good fab shop should be able to build you a new tank in 2-3 days + 1-2 days for painting & coating. The cost of the material is minimal compared to FG. You are in the best place around for this kind of a job although somewhat high priced.
Good luck!
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Old 22-09-2012, 12:13   #7
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Re: Fiberglass Diesel Fuel Tank

As someone who builds glass tanks, I'm with the other guys. If it doesn't leak you may want to just blast and coat it. For a tank that small glass doesn't really make sense unless you are doing it yourself and your skills lie in that direction. For much larger tanks which can be very difficult to remove and replace it can be a real money saver, but in this case I don't think it's the economical way to go.
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Old 22-09-2012, 12:26   #8
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Re: Fiberglass Diesel Fuel Tank

Go to the West System site and they have directions on building FG tanks. They don't really recommend it but they want it done right if you do it.

I don't think that coating an older tank is the way to go. It is just going to rust more and you will eventually going to get a lot of crap in your fuel.

Having another black iron tank made is not such a bad idea. After all the one you have has lasted a long time.
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Old 24-09-2012, 08:11   #9
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Re: Fiberglass Diesel Fuel Tank

So we're in that phase of a project when you learn that things are more complicated than you thought. Where to get tank fittings and inspection ports, what kind to get, etc. Based in good part on the responses to my post, we're going to talk to a fabricator here about a replacement steel tank. But one vacillates... at least at this point I'm doing parallel planning for fiberglass. (BTW, Minaret, I sent a PM reply to you on fittings).

The decision-making process is also challenging. My husband and I are refitting the boat together, as equals. This means that sometimes one day one of us is sure about a decision and the other is having second thoughts. This is a great forum! Your opinions are invaluable and I thank you for them. I hope that I can contribute more in the future.
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Old 24-09-2012, 08:25   #10
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Re: Fiberglass Diesel Fuel Tank

Why nor aluminum or plastic? Seems like less hassle to buy a tank that is professsionally manufactured that already meets CFR and ABYC standards for fuel tanks on boats.
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Old 24-09-2012, 09:35   #11
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Re: Fiberglass Diesel Fuel Tank

As background, we are preparing for going offshore in our 34' sailboat next summer and we are not intending to return to the PNW.

Plastic: I looked into plastic first. While our tank is small by many standards (62 gallons), a respected marine surveyor that I spoke to said the tank was too big not to have a baffle and baffles are difficult to fasten for plastic. We thought about two smaller tanks connected up but don't like all the fittings/hoses that would entail.

Aluminum: The corrosive properties of aluminum tanks discourage me, especially with the copper bonding in our boat. We have heard horror stories about quick deterioration when aluminum tanks and dissimilar metals accidentally came in contact. Also, to properly bed an aluminum tank we would have to considerably rework our bedding system (not sure that's the right term). I don't think the weight savings is significant for our tank and the cost of aluminum tanks is higher than steel.
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Old 24-09-2012, 10:01   #12
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Re: Fiberglass Diesel Fuel Tank

I get all my plumbing fittings here-


Plumbing | Fisheries Supply


If you go with a glass tank, I prefer to build my own inspection ports out of G-10 plate coated or occasionally for a smaller tank Starboard. Just install all hardware on the lid before installing it, makes it easy to glass in nuts for the port. I like to use high quality nylon plumbing fittings for a tank with no metal in it anywhere. It does help you sleep well at night...
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Old 24-09-2012, 10:30   #13
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Re: Fiberglass Diesel Fuel Tank

After all the work of getting it out while it's possible...... replace it one way or another! Is it in the bilge or aft behind the engine? or...? If it's in a dry location, then there are lots of options for a tank that small and easy shaped... you could even go with two tanks of plastic, thus eliminating the baffle issue.
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Old 24-09-2012, 17:44   #14
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Re: Fiberglass Diesel Fuel Tank

Build it out of plywood, include baffles, access plates, etc, then coat with West System epoxy. Quick, strong, cheap, and very custom. I've had mine about thirty-some years, and when I removed it a couple years back to install a fuel gauge, the plug came out smelling like the original plywood. I've built several this way. For insurance companies, you tell them it's a cellulose core composite fiberglass epoxy tank. Works every time.
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Old 26-09-2012, 16:38   #15
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Re: Fiberglass Diesel Fuel Tank

Seems to me a 62gall tank is awfull heavy for a 34 ft boat. My 38ft has a 50 gall tank and I am replacing it this winter,the new tank will be smaller. It would take me a long time to use 50gal, I would rather carry the extra in a couple of jerry jugs which may be required in far away places.
Just a thought, Bruce.
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