Vessel, one empty — small boat (5)
I believe the answer is:
canoe
'small boat' is the definition.
(type of boat)
'vessel one empty' is the wordplay.
'vessel' becomes 'can' (type of container).
'empty' suggests removing the centre.
'one' with its centre taken out is 'oe'.
'can'+'oe'='CANOE'
(Other definitions for canoe that I've seen before include "Hunting vessel originating in Haiti" , "Light boat propelled by paddle(s)" , "Light, narrow open boat" , "A dugout" , "Light paddle-propelled boat" .)