It's grim, getting set about by sailors! (5)
I believe the answer is:
stern
'it's grim' is the definition.
(synonyms)
'set about by sailors' is the wordplay.
'about' is an anagram indicator.
'by' says to put letters next to each other.
'sailors' becomes 'RN' (Royal Navy).
'set' is an anagram of 'ste'.
'ste'+'rn'='STERN'
'getting' is the link.
(Other definitions for stern that I've seen before include "Demanding < back" , "Severe, demanding" , "Severe; grimly serious" , "Grim, strict" , "Grim; severe" .)