Just the same new vessel there at sea (12)
I believe the answer is:
nevertheless
'just the same' is the definition.
(thesaurus)
'new vessel there at sea' is the wordplay.
'new' becomes 'n'.
'at sea' indicates anagramming the letters.
'vessel'+'there'='vesselthere'
'vesselthere' anagrammed gives 'evertheless'.
'n'+'evertheless'='NEVERTHELESS'
(Other definitions for nevertheless that I've seen before include "In spite of everything" , "Still" , "at any rate" , "Notwithstanding" , "However" .)