A boat loan is a financial transaction in which one party (the lender) agrees to give another party (the borrower) a certain amount of money with the expectation of total repayment. The specific terms of a boat loan are often spelled out in the form of a promissory note or other contract. The lender can ask for interest payments in addition to the original amount of the boat loan (principal). The borrower must agree to the repayment terms, including the amount owed, interest rate and due dates. Some lenders can also assign financial penalties for missed or late payments.

Because a boat loan can contain many hidden costs such as interest payments and finance charges, many people tend to avoid applying for one until it becomes absolutely necessary. Purchasing a new boat almost always necessitates some form of financial loan, whether it be a marine mortgage or a boat loan. Interest rates on these types of large loans can be fixed at the time of the application or may vary according to the federal prime interest rate.