Got on vessel in eastern sea (8)
I believe the answer is:
embarked
'got on' is the definition.
(embarking is a kind of getting on)
'vessel in eastern sea' is the wordplay.
'vessel' becomes 'bark' (bark is a kind of vessel**).
'in' means one lot of letters goes inside another.
'eastern' becomes 'e'.
'sea' becomes 'med' (abbreviation of Mediterranean).
'e'+'med'='emed'
'bark' put into 'emed' is 'EMBARKED'.
(Other definitions for embarked that I've seen before include "Set out on a voyage" , "Went on board ship or plane" , "Began (on project)" , "Having set sail" , "Got on" .)