vessel vs watercraft

vessel and watercraft both are nouns.

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

As nouns, vessel and watercraft are synonyms defined as:

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