Black salt? (3)
I believe the answer is:
tar
I believe this clue is a double definition.
'black' is the first definition.
(I've seen this in other clues)
'salt?' is the second definition.
(both can informally mean a sailor)
(Other definitions for tar that I've seen before include "'Thick, dark, sticky liquid (3)'" , "Product of coal" , "used by those who pay to work on deck" , "Jack < to blacken" , "Dark viscous stuff" .)