Fans
I learned about 12 volt fans years ago when we used to do a lot of racing. The sewer guy would be sweating bullets repacking the chute down in the cabin, and fans helped alot.I use two fans in the main cabin, one in the head, and another in each cabin. They don't draw that much current and really help. I also keep a large box fan (110volt) and use it at the dock constantly during summer. Of course, any time there is wind, or we are at anchor, we also use the windsock.I have all fans hooked to the lighting circuit breakers. While sailing during hot weather, I keep the main cabin fans on and control them with the breaker. Anyone going down below can flip one breaker and both fans are on. When going back topside, they are flipped off.For the main cabin, I use inexpensive oscillating fans. However, they are a little noisy to use in the berth areas. There, I use the more expensive Hella Turbo fans, which are much more quiet.Hope this helps.