watercraft vs vessel

watercraft and vessel both are nouns.

Word	Noun	Adjective	Verb	Adverb
watercraft	Yes	No	No	No
vessel	Yes	No	No	No

As nouns, watercraft and vessel are synonyms defined as:

watercraft (noun)	vessel (noun)
a craft designed for water transportation	a craft designed for water transportation
skill in the management of boats	an object used as a container (especially for liquids)
	a tube in which a body fluid circulates