Engine Room Ventilation

Without mechanical ventilation the engine room averages about 30°F hotter than ambient. To help reduce the temperature John Niccolls, Knock Off #66, copying an idea he saw aboard Tosh Chontosh's Petit Wazu #20, built an engine room blower.  He used a 4" West Marine axial-flow fan and some dryer hose. The fan is mounted high in the engine room, where the hottest air is, and sucks air out via the engine room vent's water catchment box.  The fan is turned on and off with the same pilothouse breaker that controls the bilge blower.  Axial-flow fans move a lot of air but the downside is they're noisy.

Knock Off's Engine Room Blower