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Adding an Access Hatch to the Fuel Tank

Summary
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The fuel tank under the port cockpit lazarette was in need of some cleaning and inspection (inside). I had suspected some intermittent fuel problems being due to the dreaded black slime.......

I had two choices - I could wrestle the tank out from under the cockpit (looked like about 1/2" clearance) and try to clean it as it was, or I could cut through the lazarette bottom and then into the tank.

I chose the latter since I may have needed to do it again at some point, or needed to get into the tank for other reasons.

I bought two circular deck hatches to use. One was the standard round plastic type that would sit in the bottom of the lazarette floor. The second, appropriately smaller in diameter (to fit through the first hatch) was stainless since it would be in contact with the diesel fuel. I couldn't find anything else suitable (aluminum, etc.), so I coughed up a LOT of money for the stainless one of the right diameter.

The tank is polyethelene and I had (have) concerns on two fronts; the first is whether or not any gasket material will make a good enough bond between it and the stainless hatch and the second was whether, without any internal backing ring, there would there be any warping or distortion of the plastic relative to the rigid metal hatch. I would just have to wait and see.

The first thing was to cut out the lazarette floor. I did this with the Rotozip being very careful to stay above the tank. As you can see, I selected the location right over where the fuel gauge sender is. My boat never had this sender connected to anything. The white polyethelene is translucent and you can see the fuel level just by looking at the side of the tank. I decided I would stick with this method.

Next, I test fit the stainless hatch on the top of the tank and inside the lazarette hatch.

Then I installed the inner (stainless) hatch. I used some HUGE fender washers to try my best to alleviate the concern of warping referenced above. The stainless flange had studs mounted into it that went through into the tank. I used a rubber gasket and some good 3M gasket compound to try to seal it to the tank plastic. I didn't think until just this point whether the winch handle would raise high enough to clear the lazarette floor and hatch and still be able to turn the stainless hatch top. Luckily it did. You can see some fiberglass strips I had to epoxy in in order to make the outer hatch flange seal to the ribbed bottom of the lazarette.

Lessons Learned

Sloppy doesn't pay.