Least expensive loan for a
boat and only way for a longer term in NZ is to borrow against the equity of your house, then apply that
money to your
boat. Buy the boat outright and pay off the loan on your house instead.
If no house, you’ll be likely looking at a 2nd or 3rd tier lender and your interest rate will be relatively high - at least double the home loan rate). In NZ max term for a
marine loan is 5 years. AUS is a much larger market so take a look there.
However, which country do you live in and where will you keep your boat? You won’t get a loan on a boat in a different country.