Mike - " I don't yet know how much smoke will make it up from the underwater exhaust into the well."
Very neat about the dory.
About an engine in a confined area, when doing dynometer engines tests in a well ventilated engine room we inadvertently discovered that opening or closing the door could have a huge affect on the brake horsepower and the temperature of the engine for the test. We ended up taking out a whole wall for ventilation purposes and made ambient temperature, pressure and humidity corrections too.
Double any ventilation openings for an engine space, and then double them again. All an engine is is a pump and any unnecessary restrictions just hurts performance, a lot.
Talador