Discovered sailors' dining areas aboard very large ship (6)
I believe the answer is:
vessel
'ship' is the definition.
(I've seen this before)
'discovered sailors' dining areas aboard very large' is the wordplay.
'discovered' indicates the central letters.
'sailors' dining areas' becomes 'messes' (mess is a dining area on a ship).
'aboard' means one lot of letters goes inside another.
'very' becomes 'v' (abbreviation).
'large' becomes 'l'.
The central letters of 'messes' are 'esse'.
'v'+'l'='vl'
'esse' put inside 'vl' is 'VESSEL'.
(Other definitions for vessel that I've seen before include "Ship, or receptacle for liquid" , "Container - ship" , "Craft for water transportation" , "Large boat; container" , "Blood-carrying tube or a ship" .)