As sent when there's a bit of a hole in a ship? (3)
I believe the answer is:
sos
'as sent when there's a bit' is the definition.
I can't judge whether this definition defines the answer.
'hole in a ship?' is the wordplay.
'hole' becomes 'O' (O looks like a hole).
'in' is an insertion indicator.
'a ship?' becomes 'SS' (prefix in ship names eg SS Great Britain).
'o' inserted within 'ss' is 'SOS'.
'of a' acts as a link.
Can you help me to learn more?
(Other definitions for sos that I've seen before include "Mayday call" , "Appeal for help" , "Help initially, Mr Morse" , "urgent appeal" , "Distress call" .)