Boat and raft don't have legal definitions, they're vessels.
Vessel, as used in reference to shipping, includes ships of all kinds, steamboats, steamships, barges, canal boats and every structure adapted to navigation from place to place for the transportation of persons or property. An employee of a maritime vessel may be able to see compensation for injuries under general maritime law, the Jones Act, or seek workers' compensation under the Longshore and Harbor Workers' Compensation Act (LHWCA) or the applicable state's workers' compensation laws.
The following is an example of a Federal Statute defining the term Vessel:
According to 18 USCS § 2311 [Title 18. Crimes and Criminal Procedure; Part i. Crimes; Chapter 113. Stolen Property] Vessel means “any watercraft or other contrivance used or designed for transportation or navigation on, under, or immediately above, water.”
You should print this out and shove it in your friends face.