Female eagle looking down on ship in port (9)
I believe the answer is:
sheerness
'port' is the definition.
(port on the Isle of Sheppey)
'female eagle looking down on ship' is the wordplay.
'female' becomes 'she' (I've seen this before).
'eagle' becomes 'erne' (erne is a kind of eagle).
'looking down on' is a charade indicator (letters next to each other) (in a down clue, some letters go above others).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'she'+'erne'+'ss'='SHEERNESS'
'in' acts as a link.
(Other definitions for sheerness that I've seen before include "Kentish Town" , "port" , "Perpendicularity; Isle of Sheppey town" , "Verticality; N. Kent town" , "Verticality (of, eg, a cliff); town on Isle of Sheppey" .)