West marine sell a FAN for boats. and I can Testafy its awesome. 50 bucks.. but WELL worth it. link at bottom.

these things put out GOOD air, suction to the cabin hatches to pull in cold air.. and have 2 speeds, softer blades if you put your face into drunk at night going to piss, and draw LIKE NO CURRENT. can run it for EVER and not drain a battery.

http://www.westmarine.com/webapp/wcs..._511&langId=-1