Transport by road to drop a large ship's frame in port (4)
I believe the answer is:
hull
'port' is the definition.
(I know that Hull is a port)
'transport by road to drop a large' is the wordplay.
'transport by road' becomes 'haul' (as in haulage of goods).
'to drop' indicates named letters should be taken away.
'large' becomes 'L' (eg in clothes sizes).
'haul' with 'a' taken away is 'hul'.
'hul'+'l'='HULL'
'ship's frame in' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
(Other definitions for hull that I've seen before include "Frame of a ship" , "Body of a ship - port" , "Shell; a port" , "Shell of boat" , "North-eastern port" .)