For initial registration of a boat trailer in Massachusetts, you'll also need proof of ownership. If you bought the trailer new from a dealer, the dealer will provide you with the Manufacturer's Certificate of Origin. This document establishes proof of ownership for boat trailer registration. If you purchased a used trailer, bring in the title of the previous owner with that person's signature transferring it to you. If the transfer was made by a bill of sale, bring the original of that document. [links]