People in boats one rams at sea (7)
I believe the answer is:
oarsmen
'people in boats' is the definition.
(I've seen this before)
'one rams at sea' is the wordplay.
'at sea' is an anagram indicator.
'one'+'rams'='onerams'
'onerams' anagrammed gives 'OARSMEN'.
(Other definitions for oarsmen that I've seen before include "Male rowers" , "Crew - moaners (anag)" , "possibly eight in a row" , "A sermon about rowers" , "People in boats" .)