Possibly a Blower In Reverse?
Hello John, Don's scenario is possible as it could have had the larger Atomic 4 aboard at one time. Do you know the history of your boat? Because of the diesels' (assuming you have one aboard now?) need for lots of air, its possible a previous owner installed one and lead the air into the engine compartment in some fashion. Look for an entry hole for a bilge blower air hose. I have done this on my OD25 as I have sealed the majority of my engine box and soundproofed the interior of the box. I wired a blower in reverse to pull outside air into the engine box to supply the diesel with air. I left some space around the transmission as it exits the box as an air exit point. Kinda like supercharging your diesel....vroom...vroom.Don