Tragic story indeed.

guessing here,,, if the nozzle shutoff kept activating isn't that an indication of a clogged vent for the tank? If the vent was clogged it would possibly vent into the bilge. The gasket they mentioned might have been on some sort of access cover of the fuel tank. If it was bad it would vent into the bilge because of a clogged vent. Running the blower with the bilge full of fumes would take quite a while to clear. With that big of an explosion there must have been quite a bit of fumes in the bilge.

But then,,, I don't even know if there was a vent to clog on the gasoline powered vessel.

I'm surprised he didn't open the boards and sniff as mentioned above. That's kind of a no brainer with a gasoline engine.