Diesel Leak Found, thoughts on proper install

[bilgeboy]

Some of you may be interested in this type of thing.

I started repairing a soft section of the bulkhead between the engine room and stateroom on the 32 a couple of months ago, and found it was saturated with diesel. This became real problematic, and fast. There were no leaking fuel lines, and no visible source of fuel. The bulkhead came out completely, as well as the stateroom floor. I also found the stringer under the starboard fuel tank to be saturated with diesel. It would leak very slowly through the stringer and put a sheen on the hull. I would clean the floor one day, come back and find the sheen returned.

I decided the tank must be leaking through the bottom, flowing into the dead space beneath the tank, into the stringer where I could not see, and then out the end of the stringer into the bulkhead. When I emptied the tank, the sheen stopped.

I pulled the engine and tank, learned alot, found the leak.



This is a great example of crevice corrosion on an aluminum tank.

I am not bashing Bayliner's installation of this tank. Its 20 years old, and thats pretty good. But it could have been done better.

The tank sits off the bottom of the "shelf" suspended by two strips of rubber or rubber-like material about an inch wide that run lengthwise under the tank, and these turn upwards at the ends of the tank and are sandwiched between blocking about 2" square. The blocking holds the tank in position. The picture above is where the rubber makes the vertical run between the tank and the blocking. It is the perfect place for moisture to sit, and this leads to crevice corrosion.

I read David Pascoe's web info on crevice corrosion and proper tank installation. Some folks here don't like him, but as far as I am concerned, he is right on the money.

Apparently anywhere moisture can hide against the aluminum, and exclude oxygen, will prevent the aluminum oxide formation that protects aluminum in the marine environment. Notice in the pic how the aluminum around this spot is in pretty good shape, but here it is pitted right through the wall.

The bottom of the tank was in pretty good shape, but I agree with Pascoe that the mounts to lift the tank off the shelf should be in the short direction, allowing the tank to breath more easily (any water that gets in can get out more easily).

There are also two short pieces of blocking at the back of the tank where the wood is right up against the tank wall. These are to prevent lateral motion, and you can see a similar effect here.



I am following Pascoe's advice on proper tank installation. I am using 1/4" starboard strips glued to the bottom of the tank with 5200, making sure the 5200 oozes out all edges of the strips to completely exclude moisture. I will not put blocking against the wall of the tank.



Here's a link to his article, well worth the read.

http://www.yachtsurvey.com/fueltank.htm

Enjoy,

Mike