Only part of the ship is in port! (4)

I believe the answer is:

hull

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'port' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for hull that I've seen before include "Shell; a port" , "Port ship's body - remove strawberry tops" , "North-eastern port" , "Main body of vessel" , "Shell of boat" .)

I've seen this clue in the Evening Standard.

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