Depends on the age of the boat and size of the loan.

For a $21,000 boat loan at 7.5% you would have payments of $507/mo for 4 years. Some banks will let your spread that out a bit more to 7 years, which would make your payments $325/mo at 7.75%. Finally, taking it out to 10 years, the payment would be $257/mo at 8.25%. Rate usually goes up as term lengthens.

The rates I quoted are from my bank. CU's or community banks are a good bet on more reasoble terms.