Powered Boat

where can i find a 3 inch solar powered boat fan?

If you mean vent fan, you can find it here:
http://ecatalog.westmarine.com/full.asp?page=0545&LinkBackProdId=149254
In the West Marine Catalog. I’m sure you can buy it at other marine stores as well.
I installed one on a previous boat. It markedly cut down on [...]