Persuade helmsman to skirt area (4)
I believe the answer is:
coax
'persuade' is the definition.
(to coax someone is to persuade them)
'helmsman to skirt area' is the wordplay.
'helmsman' becomes 'cox' (coxswain on a boat).
'to skirt' indicates putting letters inside (skirt can mean to go around).
'area' becomes 'a' (maths abbreviation).
'cox' going around 'a' is 'COAX'.
(Other definitions for coax that I've seen before include "Persuade; type of cable" , "sort of cable" , "Gently persuade" , "Attempt to manipulate" , "lead not to get wires crossed?" .)