Fiberglass covered steel fuel tanks

Aboard our 36' TT the diesel fuel tanks are steel but would appear to be covered with a layer of fiberglass. I have never seen this before on any trawler so I assume it's not common or original. Could this have been an add-on that would help the tanks last longer?

I have heard of it but not seen it. What I have read is coverings of this nature are not a good idea. The reason is that eventually the fiberglass loses it hold on the metal leaving a gap and moisture WILL then find its way between. The rust will be accelerated because it will not dry out. Of course a lot depends on preparation and the resin.
Epoxy resin is better since, with proper preparation, its hold on metal is far greater than polyester resin.

Keep the tanks dry. Any leaks at the deck fills, or elsewhere, allowing water to get on the tank may eventually lead to a problem should the sheath be breached in any way.

Just what I've read so take it for what you feel it is worth.

Hope you enjoy the boat. They are nice boats. We knew a couple or couples who had them over the years.

Interesting, never really thought about it that way, but until it develops a gap I guess they will be fine. I will have to look at them better next time I'm down at the boat. So far no deck leaks I have found yet.

Condensation may be an issue more so direct water contact. being two totally dissimilar materials, I would be more interested to see how it all holds up from a flexibility point of view.

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I have seen it on a number of far eastern trawler types. They were built that way. I assume it was done to keep water off the outside of the tanks since corrosion from deck leaks seems to be the most common problem with them.

Victoriana said:

Aboard our 36' TT the diesel fuel tanks are steel but would appear to be covered with a layer of fiberglass. I have never seen this before on any trawler so I assume it's not common or original. Could this have been an add-on that would help the tanks last longer?

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Is it really fiberglass with imbedded glass fibers or do you mean epoxy resin? I can see how it might well be a good idea to use epoxy to coat the tank to protect against external rust. Applied in this way, I would expect it to be a thin coat, not a half inch thick coating of fiberglass.

Chrisjs said:

Is it really fiberglass with imbedded glass fibers or do you mean epoxy resin? I can see how it might well be a good idea to use epoxy to coat the tank to protect against external rust. Applied in this way, I would expect it to be a thin coat, not a half inch thick coating of fiberglass.

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I believe ours are coated with an epoxy resin. The only fiber glass is where they are tabbed to the hull and or bulkheads. I can see the top of the tanks and they are also coated. I looks like it was brushed or rolled on. On our last boat we had the tanks replaced the manufacturer rolled on epoxy prior to the installation.

Mine has the fiberglass covered tanks, all six fuel and one waste. Personally I think it is a good idea. On mine there is both mat and resin quite thick. The weakness I see with this is that they did not glass tightly around the fittings thereby making it possible for moisture to get in between the glass and metal. One advantage I suppose is that it prevents flooding the bilge with diesel in the event of internal rusting or seam failure. In about 20 years I'll be able to report back on how much it contributed to the longevity of the tanks.

Steel fuel tanks layer of resin

Victoriana said:

Aboard our 36' TT the diesel fuel tanks are steel but would appear to be covered with a layer of fiberglass. I have never seen this before on any trawler so I assume it's not common or original. Could this have been an add-on that would help the tanks last longer?

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Hi I have 1986 Perfomance Trawler 38' with 2 150 gallon diesel fuel tanks ..very dry all around ,,but wondering how well these tanks will hold up..So far very pleased with the idea of coating with resin or fiberglass..They have made it for 30 years.I have had boat for 7 months.Tom.T

Capt Kangeroo said:

Mine has the fiberglass covered tanks, all six fuel and one waste. Personally I think it is a good idea. On mine there is both mat and resin quite thick. The weakness I see with this is that they did not glass tightly around the fittings thereby making it possible for moisture to get in between the glass and metal. One advantage I suppose is that it prevents flooding the bilge with diesel in the event of internal rusting or seam failure. In about 20 years I'll be able to report back on how much it contributed to the longevity of the tanks.

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I agree with Capt Kangaroo. I would be inclined to use polyester and mat because it shrinks as it cures, hopefully filling any voids around fittings.
I accompanied a fiberglass expert in the early 90's to go to a shipyard and estimate a bid on fiberglassing the propeller shafts on a US Navy ship.
I had never heard of it and I can't remember the reasoning behind it. Polyester and matt were used and they never had adhesion problems with fg to metal. The shrinking as it cures insured a tight bond.