The cooler temperatures that I've experienced in northern Florida and Southern Georgia since I moved aboard in December seems to have given way to more regular warmer temperatures. Day time temperatures are now regularly in the 80's and some 90's F. And since boat hulls are not terribly well insulated (that 1/8 inch of fiberglass core just doesn't seem to help much), a closed up boat can get pretty warm.
Opening hatches can provide a breeze through the boat if the breeze is coming from the front of the boat, but when you are in a marina this doesn't tend to be the case very often. And to make things worse, big neighbor boats can block much of the breeze you could get if it were blowing from either side of the boat. So, when you are at a marina and plugged into shore power, air conditioning tends to be the go-to solution for cooling down a boat. Of course, this tends to be expensive if the marina meters and charges for electrical use.
Of course, as the heat arrived the air conditioner in one of my neighbor's boats went out. Being a monohull, all the opening hatches on his boat point upward and he was having a hard time getting airflow into the boat. I found all of this out when he was trying to rig up a small nylon scoop (it looked like a very small spinnaker) to try and catch the breeze. The scoop he had is designed to rig on a halyard and pretty much only directs air in that is coming from the front of the boat.
When I purchased my boat, it came with two Breeze Boosters for the hatches that I had yet to try. These devices stand up on their own so they can be turned into the breeze. I let my neighbor borrow one, and after a quick Google search, we figured out how to set them up. He was able to turn it into the breeze that was blowing across the beam of the boat (from side to side) and get air flowing into the boat. He said it made quite a difference and he is now thinking of getting some for himself.
A couple days after getting his AC fixed, it was a sunny day with a decent breeze blowing across the beam of the boat and the interior temperature on my boat was in the mid 80'sF and rising, so I decided to deploy the boosters myself. Placing one on each of the forward berth hatches and opening the salon door into the cockpit gave a nice breeze through the boat. It dropped the temperature in the boat down around or just below 80F and with air moving it felt much more comfortable.
So far, I have to say I'm impressed with these things. Since they don't need support at the top, they seem to work well for catamarans as well as monohulls and even powerboats. I even managed to get them working around the "safety bars" that surround my hatches...although it does somewhat limit the rotation options. The day I used them the temps were in the upper 80's outside, and my air conditioner stayed off all day. I consider that a win. I'm glad I have them.