ok- I have this 21' stripped down islander. It is super light and I currently have a 1993 evinrude 150 on the back of it. I only use a qtr throttle when we are out and about on the river and in the bay. I dont need to go 50 mph everywhere I go, we do alot of shallow water fishing and mostly cruise to and fro. I am wondering how small of a motor could I get away with on my boat?? Any ideas? I am hoping someone might have some experience in this area. A local shop told me that I could go as small as a 75 hp but a 90-115 hp would be ideal in the event I wanted to pull a tube or something.