Yacht is at sea in old Black Sea region (7)
I believe the answer is:
scythia
'old black sea region' is the definition.
(I've seen this before)
'yacht is at sea' is the wordplay.
'at sea' indicates an anagram.
'yacht'+'is'='yachtis'
'yachtis' anagrammed gives 'SCYTHIA'.
'in' is the link.
(Other definitions for scythia that I've seen before include "Ancient region of SE Europe and Asia" , "old Black Sea region" .)