A piece of fishing tackle on the sea (6)
I believe the answer is:
afloat
'on the sea' is the definition.
(I've seen this in another clue)
'a piece of fishing tackle' is the wordplay.
'piece of' says to take the initial letters.
'tackle' becomes 'loat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The initial letter of 'fishing' is 'f'.
'a'+'f'+'loat'='AFLOAT'
Can you help me to learn more?
(Other definitions for afloat that I've seen before include "At sea, on the water" , "On the surface" , "Still solvent" , "Aboard ship" , "Out of debt; at sea" .)