Yes, my boy, a nautical hero (5)
I believe the answer is:
jason
'hero' is the definition.
(I've seen this before)
'yes my boy a nautical' is the wordplay.
I cannot really understand how this works, but
'boy' could be 'son' (synonyms) and 'son' is present in the answer.
'a' is found in the answer.
A single letter 'j' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for jason that I've seen before include "Chief Argonaut" , "Greek hero who searched for the Golden Fleece" , "Greek hero, captain of the Argo" , "He sought the Golden Fleece" , "Greek hero, leader of the Argonauts" .)