Snorkeller generally starts to go off course (7)
I believe the answer is:
diverge
'snorkeller' is the definition.
I can't tell whether this defines the answer.
'generally starts to go off course' is the wordplay.
'starts' says to take the initial letters.
'to' means one lot of letters go next to another (I've seen this in other clues).
'go off' becomes 'diver' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'course' becomes 'e'.
The initial letter of 'generally' is 'g'.
'g' put after 'diver' is 'diverg'.
'diverg'+'e'='DIVERGE'
Can you help me to learn more?
(Other definitions for diverge that I've seen before include "Turn apart" , "separate" , "conflict" , "Turn aside" , "Go different ways" .)