Knowhow to start to fish in part of ship (4)
I believe the answer is:
keel
'part of ship' is the definition.
(I've seen this before)
'knowhow to start to fish' is the wordplay.
'to start to' indicates taking the first letters.
'fish' becomes 'eel' (eel is a kind of fish**).
The first letter of 'knowhow' is 'k'.
'k'+'eel'='KEEL'
'in' is the link.
(Other definitions for keel that I've seen before include "Beam on the hull of a vessel" , "Bottom of boat" , "Vessel stabiliser" , "Long timber" , "Coal-carrying vessel" .)