Ventilation for boats with gasoline below decks has been a requirement for many decades. My guess is that your Cal
was intended to be used with the gasoline tank in the cockpit
, not down below, or otherwise there would have been a ventilation system in place from the builder
. A 3" diameter vent hose will be more than enough, and 3" bilge
fans are readily available. Generally the intake has a forward facing scoop and the exhaust faces back. Since you already have larger holes I think the best approach is to mount 3" scoops onto the 6" plates for the existing holes, and then you can cut out a second hole in one plate for the wire and hose. You must always run the bilge
fan for 5 minutes before starting the motor
. Or just use a tank in the cockpit and avoid the nuisance.
Normally the exhaust hose must draw from the lower third of the hull
. I'm not sure how that fits into your situation but you should consider meeting that standard.