Don't know what kind of boat you have, but you might try a search..... This question has been asked before.......
I have a 19' window boat, and I've tried open propane heaters, and now I use a Coleman ProCat. It's not as dangerous, and works great on cold days. It works less well on cold and rainy days. I also have a small 12v clip-on fan for the windshield. My