At sea the rain warrants cover for head (7)
I believe the answer is:
hairnet
'cover for head' is the definition.
(I've seen this before)
'at sea the rain' is the wordplay.
'at sea' indicates anagramming the letters.
'the'+'rain'='therain'
'therain' is an anagram of 'HAIRNET'.
'warrants' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for hairnet that I've seen before include "Tonsorial restraint" , "It protects locks" , "In heart (anag)" , "Lock-keeper" , "A woman may wear this" .)