Tactless, to admiral at sea (9)
I believe the answer is:
maladroit
'tactless' is the definition.
(thesaurus)
'to admiral at sea' is the wordplay.
'at sea' is an anagram indicator.
'to'+'admiral'='toadmiral'
'toadmiral' anagrammed gives 'MALADROIT'.
(Other definitions for maladroit that I've seen before include "Inept, clumsy" , "Inefficient, clumsy" , "Clumsy or bungling, ham-fisted" , "Awkward - unskilful" .)