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Old 20-09-2016, 10:30   #16
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

I have no problem with home built fiberglass tanks for diesel because that is what I did for Squander Bucks back in 1990 and they have been going strong ever since. Each hold 100 gallons. They were not made from pre-fab panels but from a self built mold out of masonite. The "tub" was molded in one piece and the top separately - then joined. The only thing that I would have done differently today is to keep the baffles a little further from the top to allow easier air flow when filling. Elsewise they have been excellent.
My only observation about your construction method was the radius treatment on the interior. Polyester resin when unfilled or lightly filled with no fibers is very weak and very prone to cracking with age and especially if twisted or flexed. probably little flexing in this instance though - but sloshing? Unfilled resin continues to shrink for a long period of time and you may find pieces chipped off in the tank. Just pour a mixing bucket with 6 ounces of polyester and let it cure undisturbed. You will sometimes see it crack before your eyes. come back in a few days and most often it is unless it was cured very slowly. But even then it is not very strong. Adding a filler greatly reduces this tendency.
I have built a lot of boat parts (and entire flybridge ) out of pre-made fiberglass panels bonded partially over plywood and they have held up well.
Another way for molding in the radius when using pre-made panels is to tape the panels together in a box shape with the concave interior of wood home ceiling molding along all the edges and do the fiberglass tape application on the inside. Then peel off the wood and tape.
Be sure to mold in ports for fill, fuel return, vent, and fuel gauge. Never hurts to put in an extra one for possible future use. Mine have two separate fuel senders in each.
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Old 20-09-2016, 15:11   #17
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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Originally Posted by Squanderbucks View Post
I have no problem with home built fiberglass tanks for diesel because that is what I did for Squander Bucks back in 1990 and they have been going strong ever since. Each hold 100 gallons.....

Ouch. I can see where the boat got its name. :^). I won't ask how long 200 gallons lasts, we get through 20 gallons in a year.

Thanks for the tip on unreinforced resin. Did not know about that trap. Hopefully the fillets will prove to be small enough to hold up ok, but a few bits of resin floating around the tank would not be a total disaster. Ironically I put the fillets in because I felt the tank would "slap" without them. Now maybe the tank slapping will break them out.

At least they are not integral to the strength or integrity of the tank.


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Old 20-09-2016, 15:16   #18
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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Originally Posted by sailcrazy View Post
We recently had a new fuel tank made for our Taswell 43. It was made out of 10mm wall close-link polycarbonate, and has worked well for the last 4+years. But we do have one issue.....the tank has poly fittings installed for the refill inlet and vent, tank sender, fuel supply, and return line. Metal fittings were screwed in....but they all leak (just a little wetness around each opening). Anyone have any idea on a good product to use on the threads to seal them tight?

I am currently looking for a thread discussing this very issue. I think, from memory, the trick was to make the holes, fill them with epoxy, cut a thread into the epoxy (all this is probably done on your tank already) and then use something like 5200 when installing the threaded fittings. Of course the critical bit is "something like 5200", I need to find out if it was 5200 or something else. I will post back here when I find out, because I do need to find out.


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Old 20-09-2016, 16:16   #19
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

Good to see that polyester is expected to withstand diesel. Are there production vessels that use polyester tanks or tanks that share hull or bulkheads?
When I built my own vessel (late 70's) I was very short on $'s, so I purchased pre folded mild steel (one eighth of an inch thick). I welded up the metal and pressure tested the tanks using the local pressurised water supply. I did not realise just how dangerous this was but the two 350 Litre tanks survived although somewhat distorted. The testing did reveal a few leaks in my amateurish welding which were repaired. After more testing, I painted the outside with the usual zinc based primers, then installed the tanks. They are still there and I inspect their outsides regularly. They are still in perfect condition.
I run a large Racor filter system and cycle the fuel every six months or so. The tank breathers are very high above the tanks in an attempt to reduce the ingress of moist air.
As for stainless tanks, we should remember that stainless steel (of any alloy) cannot be sold as "rustless steel" because quite simply, it isn't. Stress problems, microscopic holes etc. Cost.
As for fittings I recall an event where a (on a friends yacht) the fuel return line (from the injectors) entered the main tank top via a 90 degree fitting. The fitting (probably worth about 3 $) cracked and when under sail and fuel weeped out. The owner and his wife could not stay inside due to the fuel smell.The "repairs" involved removal of half the galley carpentry.
There is some lesson here, but exactly what?
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Old 20-09-2016, 17:13   #20
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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Originally Posted by sailcrazy View Post
We recently had a new fuel tank made for our Taswell 43. It was made out of 10mm wall close-link polycarbonate, and has worked well for the last 4+years. But we do have one issue.....the tank has poly fittings installed for the refill inlet and vent, tank sender, fuel supply, and return line. Metal fittings were screwed in....but they all leak (just a little wetness around each opening). Anyone have any idea on a good product to use on the threads to seal them tight?
Hi a quick google came up with a zillion choices but this seems like it would do the trick
Permatex® Thread Sealant with PTFE - Permatex
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Old 20-09-2016, 17:22   #21
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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Hi a quick google came up with a zillion choices but this seems like it would do the trick
Permatex® Thread Sealant with PTFE - Permatex
That does look promising.
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Old 20-09-2016, 18:17   #22
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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Originally Posted by sailcrazy View Post
We recently had a new fuel tank made for our Taswell 43. It was made out of 10mm wall close-link polycarbonate, and has worked well for the last 4+years. But we do have one issue.....the tank has poly fittings installed for the refill inlet and vent, tank sender, fuel supply, and return line. Metal fittings were screwed in....but they all leak (just a little wetness around each opening). Anyone have any idea on a good product to use on the threads to seal them tight?
You need flange seals with poly tanks or welded fittings.

The failure mode for polyethylene is thermal but the low stiffness and low surface tension of fuels often leads to weeping.

Sealants will not work on polyethylene tanks.

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Old 20-09-2016, 18:17   #23
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

For sailcrazy, Rectorseal a pipe joint compound has solved a few diesel fuel leaks. worth a try. f
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Old 20-09-2016, 18:47   #24
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

Aircraft fuel tanks sometimes leek. There is a sealant for them. Don't know the cost but easyer than building new tanks ,does anyone know about it.?
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Old 20-09-2016, 19:26   #25
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

I had two 400 litre welded steel tanks epoxy paint on outside .They vented(when deck fills closed) thru a high up steel day tank. with a large condensation trap Tank was for oil stove and filled by return line from engine or pulse pump .Over flow was back to tank of choice. No rust or algae problems in 40 yrs. But the day tank trap worked overtime in this damp winter climate of BC.
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Old 20-09-2016, 19:30   #26
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

Yeah fuel doesn't go as far in a power boat for sure. As far as putting the fittings to a fiberglass tank here is what I did. In the areas that I wanted brass fittings for things like fuel pickup tubes, return lines, vents, etc. I built up the surface with additional layers of fiberglass (using prefinished smooth pieces would be perfect) to about 3/4 inch thick then drilled and tapped the holes with regular metal taps. The fittings were then screwed in normally with fuel resistant brown sealant such as Permatex Aviation. Larger holes such as filler pipe were made by glassing in 1-1/2 to 2-1/2" diameter fiberglass exhaust pipe that would fit your hose and deck fill.
A couple of nice things about fiberglass tanks are that they don't sweat, don't rot or rust and if the inside is smoothly coated a little resin rich in the last layers can be pretty smooth and not hold too much microbes and easily repairable. Easily cleanable if a port is engineered in at convenient spot. They should not be used for gasoline anymore now that alcohol is put in today's fuel because it eats up the resin and will ruin the engine parts. It might be ok if there was anyway to never put alcohol gas in the boat - but you never know what the next owner might do or if you might get caught in a place with no choice of alcohol free gas.
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Old 20-09-2016, 20:30   #27
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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Originally Posted by Defeverboat View Post
Aircraft fuel tanks sometimes leek. There is a sealant for them. Don't know the cost but easyer than building new tanks ,does anyone know about it.?
I priced a few of these. Honestly, it was cheaper to build a tank from scratch... possibly using precious metals.
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Old 20-09-2016, 20:45   #28
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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Originally Posted by Squanderbucks View Post
Yeah fuel doesn't go as far in a power boat for sure. As far as putting the fittings to a fiberglass tank here is what I did. In the areas that I wanted brass fittings for things like fuel pickup tubes, return lines, vents, etc. I built up the surface with additional layers of fiberglass (using prefinished smooth pieces would be perfect) to about 3/4 inch thick then drilled and tapped the holes with regular metal taps. The fittings were then screwed in normally with fuel resistant brown sealant such as Permatex Aviation.

This interests me. This is sort of what I expected to do but I thought epoxy would be needed for adequate strength. Are you saying you think polyester resin will be strong enough? (Provided, of course, there is adequate thickness.)



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Old 20-09-2016, 21:50   #29
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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As mentioned in article, and from personal training and experience as a Surveyor in the SAMS organization and ABYC certifications, in the USA, tanks need to have a label from the manufacturer stating compliance.



A home built tank would be a red flag! But to each his own, just wanted to put this out there to save someone a possible headache down the road.

Where is this label? We had our fuel tanks fabbed by American Tank (an amazingly reputable company that does tons of tanks) and there's no labels. The surveyor had no concerns for that matter.


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Old 21-09-2016, 08:18   #30
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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... but really the idea behind the panels was to provide just the framework for the tank itself. That way I was able to lay up a new tank inside the panels using CSM and poly resin. Easy.

Matt
Pardon my ignorance but couldn't you have used some thin marine ply, then glassed both sides? And wouldn't that have adhered better for a nice strong cored tank?
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