Hard getting on part of ship (4)
I believe the answer is:
hold
'part of ship' is the definition.
('hold' is part of 'ship')
'hard getting on' is the wordplay.
'hard' becomes 'h'.
'getting on' becomes 'old' ('getting on a bit' means 'old').
'h'+'old'='HOLD'
(Other definitions for hold that I've seen before include "Contain" , "Have or possess" , "Clasp" , "Ship's storage area" , "Retain" .)