Massachusetts rules, FYI
source: http://www.state.ma.us/dfwele/dle/dlefaqs.htm#RequireAm I required to register my boat? State law requires the registration of any boat that is powered by a motor and operated on public waterways in Massachusetts. Registration is required even if the motor is not the primary means of propulsion for that boat. Some examples of boats that require registration include fishing boats with motors, recreational motorboats, canoes or sailboats that use motors, and personal watercraft such as Jet Skis or wet bikes. Boats exempt from registration requirements include those that do not use motors, boats used exclusively on private lakes smaller than 10 acres, and documented vessels (large boats that are issued a marine document and registration through the U.S. Coast Guard). Vessels used solely by a city, county, state, or federal agency will be issued a certificate of registration and number at no charge.