I just bought at 1998 Smokercraft Fazer. The seller said it was a 17 foot, so I'm thinking it's a 178. The boat has no motor. I looked at a couple for sale. One had a 115 hp and the other had a 120 hp motor. I'm going to be using the boat on the river and in the bay. Should I stick with at 115 or 120, or can I go smaller?