Unnecessary sewing implement on ship (8)
I believe the answer is:
needless
'unnecessary' is the definition.
(similar in meaning)
'sewing implement on ship' is the wordplay.
'sewing implement' becomes 'needle' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'ship' becomes 'ss'.
'needle'+'ss'='NEEDLESS'
(Other definitions for needless that I've seen before include "luxury" , "Without reason" , "Uncalled-for" , "Unnecessary, avoidable" , "Otiose" .)