But I'm a diesel guy - never wanted a sailboat with a gasoline engine
Same here. All I have is a theoretical knowledge and what I'm questioning is, "Why do you need an inlet vent ?" The underside of the engine is in communication to the bilge area so isn't that the preferable source of air into the engine compartment ? There are an infinite number of ways for air to get into the engine compartment without a separate inlet hose.
I run my engine along with a cooling exhaust fan and nobody seems to be short of air :
And finally, given the internal friction of the inlet hose, I would have to doubt it contributes anything in the way of air flow into the engine compartment for removing gasoline vapours after refueling.
Anybody else have a small gasoline engine and does it have an air inlet to the engine compartment ?