Old ships say filling empty cabins (7)
I believe the answer is:
cutters
'old ships' is the definition.
(historical type of ship)
'say filling empty cabins' is the wordplay.
'say' becomes 'utter' (to utter something is to speak or say it).
'filling' means one lot of letters goes inside another.
'empty' suggests removing the centre.
'cabins' with its middle taken out is 'cs'.
'utter' going into 'cs' is 'CUTTERS'.
(Other definitions for cutters that I've seen before include "Boats; tailors" , "Sloops" , "Scissors, maybe, or fast sailing-ships" .)