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New Epoxy Fuel Tank

We replaced the fuel tank in Eva with an epoxy tank built into the hull, and in the process increased our fuel capacity by one half. See Pictures of the project.

It seems like darn near everyone has replaced the fuel tanks on their cruising boat.  Tanks are usually located low down in the bilge to keep the considerable weight of the fuel as low as possible. But what else is down in the lowest part of the boat? Sea water of course, and whether fuel tanks are made out of aluminum or steel they are going to corrode when sitting in sea water. Norseas have about the least accessible fuel tank imaginable, it is a tall skinny 30 gallon aluminum tank located directly under the engine. Plenty of fuel tanks in older Norseas have sprung leaks, and required replacing. Our beautiful Eva was no exception. We knew she needed a new tank when we bought her in 2005.  Actually the old tank had already been removed before we purchased the boat, but the project was stalled because of difficulty getting a new tank fabricated.

Material Choices
Norsea Solutions
The Ultimate Solution
Tank Fabrication

Material Choices - Initially we were inclined to have a new tank fabricated out of stainless steel so that we would not have the same corrosion problem. The two water tanks in Norseas are stainless, and they never give trouble, so why not make the fuel tank out of stainless as well? There are however some problems with this idea. First off, fuel tanks are rarely made out of stainless because the USCG does not approve stainless steel tanks for commercial vessels. Apparently stainless is not reliable as a fuel tank, well it appears that aluminum is not very reliable either.  But even if one wanted to fabricate a tank out of stainless, as some boat owners do have done, it is much more difficult to cut and bend the stainless sheet.  Then there was also the possibility of an integral fiberglass tank.  Initially I was skeptical of this idea, there must have been a reason that it was not done this way from the factory.

Norsea Solutions - By far the simplest solution to the leaking Norsea fuel tank was the brain child of the builder of our Norsea, Dean Wixom.  When Dean discovered that the fuel tank in his own Norsea was kaput he elected to simply encapsulate it in position.  He laid fiberglass over the front and top of the old tank, overlapping onto the hull.  Essentially he laid up a new fiberglass tank around the now defunct original tank.  The advantage of this was that he did not have to remove his old fuel tank.  The disadvantage of this was that diesel fuel would be in contact with the inside of the hull.  Dean's argument was that since the hulls were laid up with isophthalic as opposed to orthophthalic polyester resin, and therefor would be impervious to diesel fuel, there could be no problem.  A lot of Norsea owners were skeptical of the solution, and most have opted to pull out the old aluminum tank and put a new one in.  Everyone we know of who has done this reports that it was a whopper of a project.

The Ultimate Solution - The solution I came up with was inspired by Dean Wixom's unique solution, and factory integral tanks.  Looking at the bilge area and the old tank we realized that there was quite a bit more room around the old tank that was not utilized.  The original tank was supposed to be 30 gallons, but this volume varied from boat to boat, and usually ended up being more like 25 gallons.  The extra space was filled in with two part polyurethane pour foam.  After removing all this foam from the bilge I estimated the space to have an actual volume of at least 35 gallons.  I got to dreaming of using more of this space for fuel storage.  The logical solution was a fiberglass tank built into the hull.  Integral tanks of this type have been used on a number of production boats with isophthalic hulls, so why not.

Hull Prep - We first completely cleaned the inside of the bilge, removing all the old foam, washed out the oily diesel residue with hot soapy water, sanded the inside of the hull, and then washed the area down with solvent.  The hot soapy water scrubbing was done very thoroughly, so that the solvent wipe down could be a quick process.  I used a high quality organic vapor respirator and forced ventilation for the solvent wash, as using solvents in confined spaces can be hazardous.  When thoroughly de-greased, I painted the bilge with two coats of epoxy resin.  To be absolutely sure that the hull would not suffer from exposure to diesel oil I also laid light fiberglass cloth on the inside of the hull through the entire bilge area.

Tank Fabrication - I cut cardboard mock ups of the top and front panels of the tank as well as for a transverse baffle in the middle of the tank.  When these mock ups fit acceptably I traced their outline onto pieces of 1oz fiberglass mat, and cut the shapes out of the mat.  I set the mat pasterns onto wax paper and saturated them with epoxy resin.  When the resin had cured I had a set of custom fabricated fiberglass panels which would be the basis of the new fuel tank.  I first glassed the baffle and front of the tank into the bilge on both sides.  When the front and baffle were well glassed in place I set the two panels that make up the top in place.  The shape of the tank was now complete.  I glassed the panels in with layer after layer of 6oz cloth, overlapping up onto the original hull about 3 inches.  I continued to lay pieces of cloth over the top and front of the tank until I had built the thickness up to at least a quarter inch.  With this thickness of glass the new tank was rigid enough to support the weight of the engine during installation.

Plumbing - In the front area of the top of the tank where the plumbing fittings would be installed I added extra thickness to the lamination schedule.  For the fuel fill I cut a 1 1/4" hole in the top of the tank, and then glassed a piece of fiberglass tube on top of it.  The tube itself I manufactured by rolling up a piece of fiberglass mat, and holding it with a rubber band.  I made this tube about 1 1/4" in outside diameter, then saturated it with epoxy. When it had cured I trimmed the ends with a pair of sheet metal sheers. I glued the tube in place in the hole in the tank with thickened epoxy.  When the glue had cured I laid strips of fiberglass cloth, which I saturated in epoxy, on the top of the tank and up the sides of the tube. Finally I warped a piece of cloth around the tube, to hold the strips in place and make a uniform round finished product. This final wrap was held in place with a rubber band while the epoxy cured. The finished product was just the right diameter to slip a piece of 1 1/2" I.D. fuel fill hose over. A 1 1/2" hose bib could also have been used for the fuel fill, I was however not sure if the 3/8" thick tank top would have provided enough material to thread such a fitting into securely. I built the fill into the top of the tank to be assured that there would never be any leaks. For pickups I used 3/8 inch galvanized brake line soldered into 1/4" NPT to 5/16" barb brass hose bibs. I installed two pickups, one which goes all the way to the bottom of the tank, and another which is about 1" off the bottom of the tank. The motor is normally run on the lower of the two pickups, but in the event that the bottom of the tank becomes contaminated, the fuel lines can be switched so that the fuel is pumped from a higher level. The fitting that is not currently being used as a pickup serves as the return. These fittings, along with a hose bib for the vent, were installed into holes drilled and tapped in the top of the tank. A sending unit for a fuel gauge was also fitted. The finished product is a success. We were pleased to see that the tank actually took 39.5 gallons the first time we filled it up. In the past 5 years of cruising we have rarely needed to use more than half of our nearly 40 gallon capacity, but it is always really nice to know that it is there.


Copywrite 2010 by Michael Traum