Cathy capsizes the sailing boat (5)
I believe the answer is:
yacht
'the sailing boat' is the definition.
(I've seen this before)
'cathy capsizes' is the wordplay.
'capsizes' indicates an anagram (I've seen 'capsizing' mean this).
'cathy' is an anagram of 'YACHT'.
(Other definitions for yacht that I've seen before include "Pleasure-boat" , "Small pleasure boat" , "Light sailing-vessel for sport" , "Sailboat" , "Cathy (anag.)" .)