Sailor that's dead smooth (5)
I believe the answer is:
drake
'sailor' is the definition.
(explorer Sir Francis Drake)
'dead smooth' is the wordplay.
'dead' becomes 'd' (abbreviation in government records).
'smooth' becomes 'rake' (raking is a kind of smoothing).
'd'+'rake'='DRAKE'
'that's' acts as a link.
(Other definitions for drake that I've seen before include "Elizabethan circumnavigator" , "Seaman" , "flyer" , "Captain of the Golden Hind, d. 1596" , "Hoe user" .)