Pump-jet
A pump-jet or water jet is a marine system that creates a jet of water for propulsion. The mechanical arrangement may be a propeller with nozzle, or a centrifugal pump and nozzle.
Pump jets have some advantages over bare propellers for certain applications, usually related to requirements for high-speed.
Other websites
Personal Watercraft Industry Association
American Watercraft Association
U.S. Coast Guard Boating Safety
Engineering