Make saint transgress, coming about in boat (8)
I believe the answer is:
canonise
'make saint' is the definition.
(to canonise someone is to make them a saint)
'transgress coming about in boat' is the wordplay.
'transgress' becomes 'sin' (sinning is a kind of transgressing).
'coming about' is a reversal indicator (about can mean backwards or around).
'in' is an insertion indicator.
'boat' becomes 'canoe' (canoeing is a kind of boating).
'sin' back-to-front is 'nis'.
'nis' going within 'canoe' is 'CANONISE'.
(Other definitions for canonise that I've seen before include "Regard as a saint" , "Make a saint" , "Elevate to the sainthood" , "Declare officially to be a saint" , "Get into sacred writings" .)