Boozer on board tramp ship (7)
I believe the answer is:
pinnace
'ship' is the definition.
(type of ship)
'boozer on board tramp' is the wordplay.
'boozer' becomes 'inn'.
'on board' means one lot of letters goes inside another (inserted letters are taken on board).
'tramp' becomes 'pace' (both can mean to walk).
'inn' inserted within 'pace' is 'PINNACE'.
(Other definitions for pinnace that I've seen before include "Small boat" , "tender" , "Vessel" , "Ship's boat - nice nap (anag)" .)