This boat can, crossing a river (9)
I believe the answer is:
catamaran
'this boat' is the definition.
(catamaran is a kind of sailing vessel)
'can crossing a river' is the wordplay.
'crossing' is an insertion indicator.
'river' becomes 'tamar' (I've seen this before).
'a'+'tamar'='atamar'
'can' enclosing 'atamar' is 'CATAMARAN'.
(Other definitions for catamaran that I've seen before include "Twin- hulled vessel" , "One vessel" , "Sailing vessel" , "Twin-hulled craft" , "Vessel with twin hulls" .)