Barrels of rock taken off vessel, leading to questions (5)
I believe the answer is:
casks
'barrels of rock' is the definition.
'casks' can be an answer for 'barrels' ('cask' can be a synonym of 'barrel'). I'm unsure of the 'of rock' bit.
'taken off vessel leading to questions' is the wordplay.
'taken off vessel leading' becomes 'c' (I can't justify this - if you can you should believe this answer much more).
'to questions' becomes 'asks' (as in asking a question).
'c'+'asks'='CASKS'
(Other definitions for casks that I've seen before include "vessels" , "lots of beer" , "Large barrels" , "Barrel-shaped containers for liquids" .)