Check on board earlier vessel (8)
I believe the answer is:
schooner
'vessel' is the definition.
(schooner is a kind of 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' placed inside 'sooner' is 'SCHOONER'.
(Other definitions for schooner that I've seen before include "that carries sherry" , "Two-masted sailing ship" , "Large beer or sherry glass" , "A measure or glass for sherry" , "Swift sailing vessel - sherry glass" .)