The writer on ship in a port (7)
I believe the answer is:
messina
'port' is the definition.
(I know that Messina is a port)
'the writer on ship in a' is the wordplay.
'the writer' becomes 'me' (the person who wrote the clues).
'on' is a charade indicator (letters next to each other).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'me'+'ss'+'in'+'a'='MESSINA'
(Other definitions for messina that I've seen before include "City in Sicily" , "Sicilian port" .)