Patrol boat (6)
I believe the answer is:
cutter
'patrol boat' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cutter that I've seen before include "Slicing tool of fast sailing ship" , "Sailing vessel" , "Ship's boat" , "Slicer, chopper, carver" , "Small sailing ship or a knife" .)