foundering vs sinking

foundering and sinking both are nouns.

Word	Noun	Adjective	Verb	Adverb
foundering	Yes	No	No	No
sinking	Yes	No	No	No

As nouns, sinking is a hypernym of foundering; that is, sinking is a word with a broader meaning than foundering:

foundering (noun)	sinking (noun)
(of a ship) sinking	a descent as through liquid (especially through water)
	a slow fall or decline (as for lack of strength)
	a feeling caused by uneasiness or apprehension