An ace out at sea? (8)
I believe the answer is:
oceanaut
'an ace out at sea?' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'an ace out at sea?' is the wordplay.
'at sea?' indicates anagramming the letters (I've seen 'at sea' mean this).
'an'+'ace'+'out'='anaceout'
'anaceout' with letters rearranged gives 'OCEANAUT'.
Can you help me to learn more?
(Another definition for oceanaut that I've seen is " Skilled underwater worker or scientist - an ace out (anag)".)