Cabin Fans
We swear by the Endless Breeze fan: http://www.fantasticvent.com/products/endless_breeze/endless_breeze.html
It has 10 - 12" blades, and can move up to 900cfm. We use it all over the boat, but have a permanent mount in the aft cabin on the port side under the open port light. We run it at night and often turn it off as it gets too cool. At low speed, it only draws 1.2A. I did install a 12V outlet in the port side up high. An extension cord long enough to bring it back to us allows unplugging it. I thought about a switch in the extension, but it hasn't been a priority. You can buy this at WM or maybe an RV store. It's pricy as fans go, but is absolutely the best fan we've seen for sheer volume. We've had it for 4-5 yrs and never had a problem with it. Quality 12V appliances are expensive - relatively.
No question Hella makes a quality product as well. Like the Endless Breeze fan, the more efficient units are more costly to make. Here is one fan we considered for permanent mount in the aft cabin: http://www.svhotwire.com/port_fans.html
This two speed fan draws 0.5A and 0.25A on high and low respectively. It's 106cfm doesn't compare with the Fantistic Fan, but with about 200cf in the aft cabin it changes the air in 2-5 minutes. What attracted me to this fan that costs about the same as a Hella is that the Delux model comes with 3 mounting options. At the above link, you can see one option for mounting right in the open port.
Hope this helps
Warren & Pattie Updike
C320, #62, 1994, "Warr De
Mar" Frog Mortar Creek, Middle River