Type of vessel (6)
I believe the answer is:
whaler
'type of vessel' is the definition.
(I know that whaler is a type of ship)
This is the entire clue.
(Other definitions for whaler that I've seen before include "Captain Ahab, e.g." , "Ship armed with harpoons" , "Mammal-hunting boat" , "Aussie tramp?" , "Seaman like Ahab" .)