Perhaps your dilemma is far worse than you suspect. If you have a leak into
a foamed area and that foam is not closed cell, you have foam that will be
waterlogged. If also in that same cavity you have end grain glass exposed,
you will also suffer osmosis. I am afraid you have a winter project redoing
the entire area. The cost of NOT doing that will be far worse.
Steve

"Cornelis Koger" wrote in message
...
My Draco 2500 twincab has been repowered with VW td engines and tunnel
drives of my own design, for which I have added a 1 ft long box to the
stern. In fact it is an extension of the hull that supports the 2 tunnels,
rudders etc.
Although I've spent many hours on my back under the hull laminating and
painting, now that the boat is back in the water, a steady trickle of
water is entering the bilge through one of the holes where the stern tube
is bolted to the stern. The bolts are not visible outside, they are in a
grp walled cavity filled with polyurethane foam.
I would have bet anything that the construction is watertight, but I'm
glad I didn't.

My plan is to locate the hole by pressing a sponge soaked in dye against
the suspected area, with a helper inside who looks for a color change of
the incoming water.

Is anyone familiar with a product or procedure that can successfully seal
a small hole in a submerged object?