Almost inert aboard pleasure craft (7)
I believe the answer is:
joinery
'craft' is the definition.
(joinery is a kind of craft)
'almost inert aboard pleasure' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'aboard' indicates putting letters inside.
'pleasure' becomes 'joy' (synonyms).
'inert' with its final letter taken off is 'iner'.
'iner' put into 'joy' is 'JOINERY'.
(Other definitions for joinery that I've seen before include "craft" , "Art of a worker in wood" , "chippy's trade?" , "Woodwork" .)