Generally at sea (2,3,4)
I believe the answer is:
in the main
This clue is a double definition.
'generally' is the first definition.
(I've seen this before)
'at sea' is the second definition.
('the main' is an old name for the sea)
(Other definitions for in the main that I've seen before include "Swimming" , "All things considered" , "Generally - at sea?" , "mostly" , "Where schools are found" .)