Power line in front part of ship (4)
I believe the answer is:
prow
'front part of ship' is the definition.
(I've seen this before)
'power line' is the wordplay.
'power' becomes 'p'.
'line' becomes 'row' (row is a kind of line**).
'p'+'row'='PROW'
'in' is the link.
(Other definitions for prow that I've seen before include "Boat's bow" , "bows" , "Front of boat" , "Bow of a ship" , "Pointed front part of a ship" .)