At sea, generally (2,3,4)
I believe the answer is:
in the main
I believe this is a double definition.
'at sea' is the first definition.
('the main' is an old name for the sea)
'generally' is the second definition.
(I've seen this before)
(Other definitions for in the main that I've seen before include "Where schools are found" , "For the large part" , "On the whole" , "Where ships are" , "All things considered" .)