Walk wearily when the sea trip is rough (7)
I believe the answer is:
traipse
'walk wearily' is the definition.
(I've seen this before)
'the sea trip is rough' is the wordplay.
'is rough' is an anagram indicator (a rough or broken ordering of the letters).
'sea'+'trip'='seatrip'
'seatrip' anagrammed gives 'TRAIPSE'.
'when' is the link.
(Other definitions for traipse that I've seen before include "Trudge around" , "Parties (anag.)" , "make slow progress" , "Tedious walk" , "long tiring walk" .)