Crossword Genius

Flier going round old vessel (4)

Ross

I believe the answer is:

boat

I'm a little stuck... Click here to teach me more about this clue!

'vessel' is the definition.
(I know that vessel can be written as boat)

'flier going round old' is the wordplay.
I cannot quite see how this works, but
'round' could be 'o' (round can mean a round object) and 'o' is found within the answer.
The remaining letters 'bat' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for boat that I've seen before include "See 18" , "Vehicle for travelling over water" , "Water craft" , "See 12 Down" , "Vessel for travelling on water" .)

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