… boat's just capsized! (3)
I believe the answer is:
tub
'boat's' is the definition.
(tub could historically mean a small boat)
'just capsized' is the wordplay.
'just' becomes 'but' (but can mean 'just' or 'only').
'capsized' says the letters should be written backwards.
'but' reversed gives 'TUB'.
(Other definitions for tub that I've seen before include "Large plant pot" , "Container for yogurt, ice-cream" , "Carton" , "Low wide container" , "Small cask" .)