Ship's outside northern port (4)
I believe the answer is:
hull
This could be a double definition.
'ship's' is the first definition.
(thesaurus)
'outside northern port' is the second definition.
'hull' can be an answer for 'port' (I've seen this before). I'm not certain of the 'outside northern' bit.
Can you help me to learn more?
(Other definitions for hull that I've seen before include "Body of a ship - port" , "Conscious" , "Ship's bottom" , "Framework of ship" , "Main body of ship" .)