Parts always carried by a sea-going vessel (6)
I believe the answer is:
severs
'parts' is the definition.
(severing is a kind of parting)
'always carried by a sea-going vessel' is the wordplay.
'always' becomes 'ever' (synonyms).
'carried by' indicates putting letters inside.
'a sea-going vessel' becomes 'ss' (prefix in ship names eg SS Great Britain. I am not sure about the 'sea-going' bit.).
'ever' going within 'ss' is 'SEVERS'.
Can you help me to learn more?
(Other definitions for severs that I've seen before include "splits" , "Cuts or breaks off" , "Divides by cutting" , "Cuts or terminates" , "Cuts off or separates" .)