Sea salt eroded navigational aids (7)
I believe the answer is:
atlases
'navigational aids' is the definition.
'sea salt eroded' is the wordplay.
'eroded' indicates an anagram.
'sea'+'salt'='seasalt'
'seasalt' with letters rearranged gives 'ATLASES'.
(Other definitions for atlases that I've seen before include "Cartographical works" , "Collected charts" , "Sea-salt (anag)" , "navigation aids" , "Book of maps" .)