Check on board earlier sailing vessel (8)
I believe the answer is:
schooner
'sailing vessel' is the definition.
(schooner is a kind of sailing vessel)
'check on board earlier' is the wordplay.
'check' becomes 'ch' (I've seen this in other clues).
'on board' means one lot of letters goes inside another.
'earlier' becomes 'sooner' ('sooner' can be a synonym of 'earlier').
'ch' inserted within 'sooner' is 'SCHOONER'.
(Other definitions for schooner that I've seen before include "that carries sherry" , "A measure or glass for sherry" , "9 [CONTAINER" , "wooden vessel" , "Old sailing ship and tall sherry glass" .)