On Tue, 03 Apr 2018 12:59:38 +0100, Harry Bloomfield
wrote:

Chris Green expressed precisely :
The boat has a diesel engine (sitting immediately above the bilges)
which sucks air in from the outside and (presumably) blows it out of
the exhaust. The engine was running for several hours yesterday and
Saturday so that would, I guess, have cleared things a bit. So the
accumulation is probably only over the last 24 hours since yesterday.

If I were worried, I would be inclined to rig up a fan to blow air into
the lower reaches of the boat to forcefully stir it up and out. It
would be wrong to put the fan in the bilge, where it might ignite the
collected gas.

More effective, would be something like a vacuum cleaner hose, which
you could drop to the bottom and suck the gas out - except for the fact
that the gas would then pass through the vacs motor. LPG leaks in boats
are a deadly combination, due to it being heavier than air.

Surely not? Electrical equipment in the vicinity of a gas leak. Why
do you think mobile phones are banned at petrol pumps?