fishing boat vs fishing vessel

fishing boat and fishing vessel both are nouns.

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

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

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

Other synonyms of fishing boat include fishing smack.

fishing boat (noun)	fishing vessel (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