Forthcoming time on board yacht at sea (6)
I believe the answer is:
chatty
'forthcoming' is the definition.
(thesaurus)
'time on board yacht at sea' is the wordplay.
'time' becomes 't' (abbreviation).
'on board' means one lot of letters goes inside another (inserted letters are taken on board).
'at sea' indicates an anagram.
'yacht' is an anagram of 'chaty'.
't' going into 'chaty' is 'CHATTY'.
(Other definitions for chatty that I've seen before include "Fond of talking" , "given to blethering" , "Talkative or garrulous" , "Communicative" , "Given to amiable talk" .)