How do I replace my fuel tank?

Here’s a question I’d like to pose to the group. My plan to launch early this season were dashed when I opened the boat up for the first time in about a month to a reeking odor of diesel fuel. Turns out my 125 gal fuel tank has finally given up the ghost after 29 years and has been leaking into the bilge all winter. All I could find to identify the leak was an area of the tank along the rear bottom seam that seemed to be weeping fuel. My tank sits directly under the cockpit behind the companionway bulkhead. There’s no way short of tearing the entire aft section of the interior apart and cutting the tank up into smaller pieces that I’m going to get this tank out. Even if I can accomplish the removal, what kind of tank am I going to be able to replace it with? Any hard tank of any suitable size will not be able to be installed without majorsurgery both to the interior and the exterior. After a lot of thought, I’ve come upon a much more radical but probably easier solution. What I’m proposing is to open the hull underneath the tank and drop the tank out in one piece. I could then either repair the tank (not likely) or use it as the female “mold” for an all fiberglass tank; i.e. encase the tank in fiberglass, then remove it, leaving the FRP shell as the new tank – lighter, stronger and corrosion proof. The hull cut-out would be re-used to fill the hole in the hull and the new glassed area should be as strong or stronger than the original. After all, if I were to hole the hull on a reef, I’d do much the same as a repair. I’d like to know the following:

1) Please verify that the hull below the waterline is solid fiberglass
2) I’ve heard of ethanol damaging FRP tanks. Does marine diesel contain ethanol?
3) Has anyone built an FRP tank? Do I need to use anything special to create the new tank; ie is West System Epoxy sufficient or is there something else?
4) Does anyone see any problems with this plan that I’ve probably overlooked?

All comments will be very much appreciated. Best Regards, Vince Salese #005, Witch of the Wave, Hull #5

a. Your solution seems radical, indeed! Won’t you have to tear out the interior in order to fiberglass the hull section back in? Sounds to me like you want to put a removable floor into the cockpit and go in that way. Maybe, you should contact Collin Harty http://buildinggalene.com/, still lists an 80 gal aluminum tank for ‘Tag Sale’. I have a similar tank, I think. It fits in neatly through my companionway and down below the removeable pilothouse floor boards (soles), just aft of the galley bulkhead.. My floor timbers were spaced for it. Mine is v-shaped, sloping down foreward and up sideways to fit the centerline of the hull bottom. But, I don’t have any propellor shaft; I have a saildrive with the engine under the aft cockpit. Lots of luck with your problem. Lester Helmus (#010, Insouciance)

b. Tell you what I did when our steel tank gave up the ghost a year ago (luckily I was on board on the hard and could organize a drum). Same problem as you: tank too large for the opening. Took an angle grinder to the thing and got it out in 3 pieces. Designed and ordered two new polyethelene (??, black, weldable plastic in any case) tanks from a Turkish supplier, dropped number one, and shoved it to the stern, dropped number two and hooked it up to number one. Case closed. Only problem: the design was not executed faithfully and we now have tanks with about 2/3 the previous capacity. Hope this helps. Gerry and Brigitte Stuurop (#087, Octopus I).

c. If your tank is structurally sound, and it sounds as if it is with only weeping or a pin hole, and if you can access it by installing a new access through the cockpit sole and a port(s) into the tank top; I would check out a product called “RED -KOTE”. It was developed in Australia to repair tanks in place. Go to Damon Industries, Alliance, OH, www.DamonQ.com regards, Ray Sullivan (#068, not yet identified)

d. Thanks for the comments and believe me I will take every suggestion, criticism, encouragement etc before I take a saws-all to my hull. Coincidently, after posting my question last night, I found this website that explains exactly what I was intending to do http://marlowmarine.com/fuel_tankreplacement.htm First a couple of things. #005, Witch of the Wave is a rear cockpit not a center cockpit – just a clarification. Luckily I don’t have a finished interior in the aft section behind the companion way bulkhead. It’s nothing but painted plywood used for storage. We call it the garage. Yes I could cut and remove all that to access the tank, but I still couldn’t get the tank out in one piece unless I also remove the cockpit floor. Reglassing and refinishing the cockpit sole and reinstalling the interior is as daunting a prospect as cutting the hull so long as, and here’s the key, the section I cut is solid fiberglass – I just don’t want to deal with the Airex core for some reason. Cutting the tank certainly is easier but, as Gerry implies, I’d have to compromise on the replacement tanks. Removing the tank intact means I have a plug mold for a new fiberglass tank. Is it your opinion(s) that I’d be compromising the hull’s strength? I’d grind down the seam/cut area before cutting so as to leave room to lay-up as much as 3/8″ of new matting before fairing the whole area. When I reinstall the cut-out section I’d epoxy “glue” the seam and lay-up matting both inside and out side. I would think that this section would actually now be stronger than the surrounding area. My biggest challenge is to reinstall the cut-out in exactly the same position to maintain my shaft alignment because, of course, the shaft strut sits smack dab under the tank. Keep the comments coming. I’m not going to cut anything inside or out until this is well thought out and planned and any and all alternatives are exhausted. Whatever I do, I am going to document it fully so others can learn from my experience good or bad. Best Regards, Vince Salese.

e. Hello Mr Vince Salese, I think the solution of cutting the hull would be the right thing to do. I suggest you:

1st Check to see if you have two tanks or only one big tank,
2nd Cut a hole in your floor to get access to your tank,
3rd Take your tank out through the hole and cut it up so that you can get rid of it by way of your companionway,
4th Install a new tank in place with “Vinylester Resin”. If you need, I could send you the number etc.

This method is the only way that you will avoid having a bigger problem then what you have now. Best, Gaëtan Duchesne.

f. My previous boat, a Fisher 37, had a similar problem. The fix was to have a custom fuel bladder made that was installed through a hole cut in the top of the old tank. The repair was done by a company in Seattle WA but I do not have any contact information. I would hesitate to cut a hole through the hull unless it was a last resort. David Williams (#154, Sunshine).

g. I’m in the process of replacing my fuel tanks. The tanks are located under the pilot house deck, aft of the navigator’s seat and just forward of the aft bulkhead. The pilot house deck is divided in half for excess to the transmission/ prop shaft thru a hinged lid and aft of that is the deck over the 2 fuel tanks. I’ve got the deck above the tanks removed and just today removed the tanks themselves, what a job. I’m looking for someone to build the tanks locally. If anyone is interested I’ll take pictures and send them to you. John and Anita Baumgartner (#116, Bright Eyes).