Can come up in long boat (7)
I believe the answer is:
pinnace
'boat' is the definition.
(historical type of small boat)
'can come up in long' is the wordplay.
'come up' is a reversal indicator.
'in' is an insertion indicator.
'long' becomes 'pine' (to pine for someone is to long for them).
'can' reversed gives 'nac'.
'nac' put within 'pine' is 'PINNACE'.
(Other definitions for pinnace that I've seen before include "Small boat" , "Ship's boat - nice nap (anag)" , "Vessel" , "tender" .)