Usually the way it works is the more you borrow the lower the rate. Here's an example....
http://www.suntrust.com/personal/Loans/Marine/rates.asp
some lenders require a certain length of loan, like the 10 year loan I was "forced" to get on an outboard, but there was no penalty to pay off early. You have to shop around and you can "play" the best rate you find against the dealers rate. Many times they will match it and save you the hassle. They don't like it when you leave to find financing because most likely you won't be back.