Slim American operated boat (8)
I believe the answer is:
trimaran
'boat' is the definition.
(trimaran is a kind of sailing vessel)
'slim american operated' is the wordplay.
'slim' becomes 'trim' (both can mean skinny or slight).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'operated' becomes 'ran' ('run' can be a synonym of 'operate').
'trim'+'a'+'ran'='TRIMARAN'
(Other definitions for trimaran that I've seen before include "Sailing boat with three hulls" , "Sailing vessel" , "Three-hulled yacht" , "Ocean vessel with three hulls side by side" , "type of boat" .)