Bottom of ship’s bunk (5)
I believe the answer is:
bilge
This clue is a double definition.
'bottom of ship's' is the first definition.
(bilge is the lower part of a ship)
'bunk' is the second definition.
(thesaurus)
(Other definitions for bilge that I've seen before include "Lower part of hull; nonsense" , "Very long film, book etc" , "Rubbish - water in boat" , "Piffle - part of hull" , "Filthy water that collects in the bottom of a boat" .)