Vision certainly is required in Boat Race crew (8)
I believe the answer is:
eyesight
'vision' is the definition.
(eyesight is a kind of vision)
'certainly is required in boat race crew' is the wordplay.
'certainly' becomes 'yes' (I've seen this before).
'is required in' indicates putting letters inside.
'boat race crew' becomes 'eight' (I've seen this before).
'yes' inserted inside 'eight' is 'EYESIGHT'.
(Other definitions for eyesight that I've seen before include "Ability to see" , "View" , "perception" , "Power of vision" , "Faculty of vision" .)