Fat wobbly behind (3)
I believe the answer is:
aft
'behind' is the definition.
(aft means towards or at the end of a ship)
'fat wobbly' is the wordplay.
'wobbly' indicates anagramming the letters.
'fat' is an anagram of 'AFT'.
(Other definitions for aft that I've seen before include "Towards the back on board" , "Towards rear (of ship)" , "Towards the rear at sea" , "behind boat" , "At the back of a ship" .)