You are missing the point, your batteries should not be getting too hot. If you can hold your finger on them for more than 30 seconds without it burning your finger then it should be fine. Any hotter than that and you have a set-up problem that needs to be addressed. Some people do use air scoops to help cool the air on the inside of the boat to help cool the motor, but if your batteries are overheating then that is another story.