Ship sealer (3)
I believe the answer is:
tar
'ship sealer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tar that I've seen before include "Road-dressing for a sailor?" , "Road surfacing or old sailor" , "Tobacco residue; sailor" , "Cigarette residue - old word for sailor" , "Sticky black stuff" .)