Marine vessel has the meaning given in 1 U.S.C. 3, except that it does not include amphibious vehicles. The definition in 1 U.S.C. 3 very broadly includes every craft capable of being used as a means of transportation on water.
40 CFR § 94.2
The definitions of this section apply to this subpart. They also apply to all subparts of this part, except where noted otherwise.