Butterfly on empty tray that represents sailors (9)
I believe the answer is:
admiralty
'that represents sailors' is the definition.
'butterfly on empty tray' is the wordplay.
'butterfly' becomes 'admiral' (admiral is a kind of butterfly**).
'on' is a charade indicator (letters next to each other).
'empty' means to remove the middle letters.
'tray' with its middle removed is 'ty'.
'admiral'+'ty'='ADMIRALTY'
(Other definitions for admiralty that I've seen before include "Department of 1 across in charge of the Navy" , "UK state department in charge of the Royal Navy" , "HQ" , "Former Department in charge of the navy in Britain" .)