Fuel fill flange leaking water on to top of fuel tank

[Cigatoo]

Speaking of fuel tanks.
A common problem is the fuel fill flange leaking rain water onto the tops of the tanks causing rust and rot. On the Grand Banks the fuel fills are in a 3-inch hole through the teak deck and underlying fiberglass. Sealing between the flange and teak deck is difficult. Also, like it or not, water finds its way between the teak deck and underlying fiberglass. Inevitably it drips on to the top of the tank.

I read the following fix years ago on the Grand Banks forum.

Remove the fuel fill port. Getting to the hose clamps is difficult but doable. Mine were accessible from behind a plywood panel under the settee. Loosen the clamps. Unscrew the three screws and pry up the filler flange from the deck.

Once the fuel fill flange is removed cover the remaining fuel filler hose so you don’t drop stuff in the tank. I stuffed paper towel into the hose and then covered the opening with tin foil.

You will need a 3 inch and also a 4 and ½ inch hole saw on the hole saw arbor together. (pictured)

Using the 3-inch hole saw (as a centering guide) drill a 4 and ½-inch hole in the teak decking down to the fiberglass. Then remove the teak deck cut outs and discard. Clean up

Use the same 3 inch and 4-inch hole saw combination to make wooden donuts. I used a piece of 3/8 inch mahogany that I had laying around and made a couple of donuts. (pictured)

Clean the deck hole with acetone, sand everything to give it some tooth, vacuum, and clean with acetone again.

Mix up some epoxy and coat everything in and around the hole with un thickened epoxy

Thicken the epoxy and epoxy the donuts into the hole being sure to coat everything well with epoxy.

I used two 3/8-inch-thick donuts. This left them a little proud of the deck. Once everything was cured, I used a belt sander to level everything off with the deck.
I now have a nice flat round wooden flange to re bed the fuel filler flange to.

 

[ABfish]

Genius. I've never seen the double hole saw trick, but I'm filing that away for future use.

 

[cks]

Brilliant!!!
Simply Brilliant!

 

[Bmarler]

I made an arbor for my hole saw that puts the inner saw in upside down. Doesn’t work for making the doughnuts, but very handy for going up a size or two.
I wish I could say it was my idea, but I stole it from somewhere, I just don’t remember where.

 

[Comodave]

I would leave the donut proud of the deck so that water will run around the fitting and may not leak down and onto the fuel tank.

 

[TJM]

Comodave is correct, water WILL find a way to flow into holes. Proud deck fittings, if done right save years of aggravation later in life.

 

[Pete Meisinger]

You occasionally see fill spouts up two or three inches above the deck. Good idea, but a real tripping hazard.

pete

 

[Comodave]

I would have them proud about 1/2”. That way rain water will flow around the filler and not over it.

 

[Cigatoo]

I understand the rain water leaking in from the top of the teak decking. However I will bet you lunch that there is not a 30 year old GB (or other boat with teak decks for that matter) that doesn’t have water finding its way between the teak deck and the underlying fiberglass. The leaks could originate forward of the fills and then work its way aft and leak into the fuel fill holes from between the two surfaces. In fact my guess is that this is more prevalent then water that originates from rain on the teak deck at the fuel fill.

 

[Comodave]

Agree, but why not take every reasonable step to eliminate leakage? It is an easy thing to do when repairing the deck around the filler.

 

[Jerbro]

On changing the fuel filter setup to a duplex Racor on our ST35 we found 20 litres of water in the fuel tank (that’s 2 large buckets worth)… I thought it may have been leaking through the fuel filler, but that was sound… the only explanation we could find was a previous owner filling it with water by accident (the water filler is hidden at the rear of the boat, but the fuel filler is next to the waste pump out)… Beneteau provided some schematics when we investigated this, including the fuel tank set up as we were also considering a fuel polisher install… diagrams attached just in case they are of help to the community here…