Three-hulled boat (8)
I believe the answer is:
trimaran
'three-hulled boat' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for trimaran that I've seen before include "Sailing boat with 3 hulls" , "Sailing boat with three hulls" , "Three-hulled yacht" , "Three-hulled vessel" , "type of boat" .)