July 13, 2011 - During the engine install I had put 5 gallons of diesel into each tank and immediately pumped it out to get rid of any desidual gasoline in the tanks.  During that operation I discovered that the port tank had a leak at its forward end.  However, the starboard tank seemed fine.  So I put five gallons of diesel in the tank for the engine test run.  Last week I decided to fill the starboard diesel tank the rest of the way.  So I bought 10 gallonns of diesel (two five gallon cans) at the local lobster wharf and poured five gallons into the tank, giving me about 9 gallons in the tank.  When I did that I immediately smelled diesel.  Lifting the floorboards in the cockpit showed that the leak was at the aft end of the tank.  The fuel tanks in the boat are two 45 gallon aluminum tanks that were installed during the 1995 refit.  The tanks are cylindrical, but taper from 14" diamter at the forward end to 10" diameter at the aft end.  They are 84" long.  They were custom made to fit the hull and were mounted with their aft ends higher than the forward ends.  Anyway, I was really disappointed to find that BOTH tanks were leaking.

I saw two possible fixes to the leaking fuel tanks.  One fix was to remove the tanks, clean them out and have the leaks welded up.  A chat with a local welder suggested that repairing the tanks would cost $300+ for each tank.  For some reason he was reluctant to weld a fuel thank that hadn't been VERY thoroughly cleaned.  Consequently, no matter how clean I got the tanks he would clean them again to his satisfaction before welding them.  The second option was to replace the aluminum tanks with new tanks.  If I used plastic tanks (i.e., Moeller below deck tanks), the cost wouldn't be all that high.  After some thought I decided to replace the aluminum tanks with new Moeller plastic tanks.

I decided to start with the starboard tank.  The first step was to open up the cockpit sole above the tank.  The sole is made from tongue and groove vertical grain douglas fir.  So I started removing bungs and lifting planks out.  After I had enough planks out to create a large enough opening to lift the tank out, I removed the fuel gauge sender and used that opening to pump as much fuel as possible out of the tank.    I got all but about 1/16" of fuel out of the tank.  Next I shored up the cockpit sole along the edges of the opening and then cut the deck beams out in the opening.  After that I removed the bracing that held the tank in place and lifted the tank out.

The picture above shows the hole in the cockpit sole where the tank was.  The following three pictures show the tank and the leaks I found.

Starboard aluminum fuel tank with F150 for scale.  Note tha taper in the cylindrical tank.

I found that the tank actually had holes at both ends where the tank had been touching the frames.  The forward hole was blocked with a precipitate and wasn't actually leaking, but it was only a matter of time.  I think that the leaks were caused by a reaction between the red lead paint on the frames and the aluminum tank.  Everywhere else that the tank touched the structure of the boat, the installers had put thin rubber sheeting between the tank and the boat.  I have no idea whay they didn't do the same where the tank touched the frames at the forward and aft ends.

These tanks are repairable if they can be adequately cleaned out, but I have decided to abandon them.  After a lot of measuring, I decided to go with a Moeller 20 gallon plastic tank as the replacement for the 45 gallon aluminum tank.  I also decided not to puit the new tank under the cockpit sole.  Instead, I mounted it at the outside edge of the cockpit on the sole, but inside some cabinet work.  The picture below shows the new tank in place with the partially repaired cockpit sole.  I am going to make a lift out hatch to fill the forward opening to allow access to the area under the sole for storage.

It doesn't show well, but the tank base has a 4" high plywood box around it except where it butts up against the framing for the side panels of the cockpit.

I still have one more tie-down strap to attach on the new tank, but can't do that until after I bung all the screw holes in the new planking because two holes are partly under the piece of wood the hold down will be attached to.  I should have the lift out panel finished tomorrow.  Once that panel is built, I will bung the screw holes, varnish the new wood and then put the cabinet panels that cover the tank back.

This new tank is 25 gallons smaller than the old tank.  However, given that I expect a fuel consumption of about 1/2 gallon per hour at cruising speed, the 20 gallon tank will give me about 36-37 hours of run time on a tank fill, for about a 250 nautical mile range on a tank of fuel.  In addition, I will be able to determine exactly how much fuel I have left in the tank at anytime simply by opening a cabinet door.  When I fill the tank the first time, I will do it in 5 gallon increments and will mark the tank after adding each increment.  I will then put a calibrated strip on the tank marked at one gallon increments.  In addition, because the tank is smaller, the fuel will be fresher than it would be in a larger tank.

At present I don't intend to replace the port tank this year.  It will be a spring project for next year.

The total cost for this repair came out to just under $400 including repairing the cockpit sole.

July 15, 2011 - Since my last update I have lift out panel to finiah the repair of the cabin sole.  The picture below shows the panel in place.  It is made from T&G douglas fir like the rest of the sole.  There is trim around the panel made from ipe.

At the bottom left of the picture above you can see a cup of bungs for the screw holes.  After I took this picture, I spent 45 minutes on my knees glueing the 101 bungs into the screw holes.  Tomorrow I will trim the bungs and put the first coat of varnish on the new sole.  Actually, I plan to varnish the entire starboard side of the cockpit sole.  Before I do the varnishing, I will put the final tie-down strap on the tank and connect the fuel gauge wiring.  This reapir took some time because I made sure to line the new planking up with the old.  You can also see the stainless steel lifting ring in the lift out panel.