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A pump-jet or more commonly a water jet is a marine system that creates a jet of water for propulsion. The mechanical arrangement may be a ducted propeller with nozzle, or a centrifugal pump and nozzle. The first functioning pump-jet engine was created by New Zealand inventor, Sir William Hamilton in 1954.

Contents 1 Advantages 2 Disadvantages 3 Sources 4 See also

[edit] Advantages

Pump jets have some advantages over bare propellers for certain applications, usually related to requirements for high-speed or shallow-draft operations. These include:

• Increasing the speed before the onset of cavitation, due to the raised internal dynamic pressure
• High power density (with respect to volume) of both the propulsor and the prime mover (since a smaller, higher-speed unit can be used)
• Protection of the rotating element and making operation safer around swimmers and aquatic life
• Improved shallow-water operations, since only the inlet needs to be submerged
• Increased maneuverability, by adding a steerable nozzle to create vectored thrust
• Noise reduction resulting in a low sonar signature; this particular system has little in common with other pump-jet propulsors and is also known as "shrouded propeller configuration"^[1]; applications:
  • submarines, for example the Royal Navy Trafalgar-class and Astute-class, the US Navy Seawolf-class, the French Navy Triomphant class, and the Russian Navy Borei class.
  • torpedoes, such as the Spearfish and Mk 48 weapons.

[edit] Disadvantages

• Can be less efficient than a propeller at low speed
• More expensive
• Higher weight in boat due to entrained water
• Will not perform well if boat is heavier than the jet is sized for
• Can become clogged with debris e.g. seaweed^[2]

[edit] Sources

1. ^ FAS Military Analysis Network: MK-48 Torpedo
2. ^ http://www.grc.nasa.gov/WWW/K-12/airplane/aturbf.html

[edit] See also

• Propulsor
• Personal water craft
• Jet ski
• Jetboat
• Wetbike
• Kitchen rudder
• Water rocket