In lifeboat, couple busy (2,4)
I believe the answer is:
at work
'busy' is the definition.
(I've seen this before)
'in lifeboat couple' is the wordplay.
'in' is an insertion indicator.
'lifeboat' becomes 'ark'.
'couple' becomes 'two' (I've seen this before).
'ark' going around 'two' is 'AT WORK'.
(Other definitions for at work that I've seen before include "Engaged in one's duties" , "Active" , "busy" .)