fishing vessel vs fishing boat

fishing vessel and fishing boat both are nouns.

Word	Noun	Adjective	Verb	Adverb
fishing vessel	Yes	No	No	No
fishing boat	Yes	No	No	No

As nouns, fishing vessel and fishing boat are synonyms defined as:

fishing vessel and fishing boat: a vessel for fishing; often has a well to keep the catch alive

Other synonyms of fishing vessel include fishing smack.

fishing vessel (noun)	fishing boat (noun)
a vessel for fishing; often has a well to keep the catch alive	a vessel for fishing; often has a well to keep the catch alive