46 CFR §90.10-23

This term means any vessel indicated in column 5 of table 2.01-7(a) in § 2.01-7(a) of this chapter 65 feet in length or less which is propelled by machinery (including steam). The length shall be measured from end to end over the deck excluding sheer. This term includes a boat temporarily or permanently equipped with a detachable motor. For the purpose of this subchapter, motorboats are included under the term “vessel” unless specifically noted otherwise. The various classes of motorboats are as follows: