I object when old craft's brought back (3)
I believe the answer is:
but
'i object' is the definition.
(used to introduce an objection)
'old craft's brought back' is the wordplay.
'old craft' becomes 'tub' (old-fashioned term for a boat).
'brought back' shows that the letters should be reversed in order.
'tub' written backwards gives 'BUT'.
'when' is the link.
(Other definitions for but that I've seen before include "Only; apart from" , "Conjunction meaningn on the other hand" , "Nevertheless, on the other hand" , "SECOND PART OF 10" , "Except; nevertheless" .)