Vehicles
Jet skis and waterjets
No propeller underneath: an impeller in a tube shoots a jet out of the back.
- Impeller diameter
- about 140–160 mm
- Impeller speed
- about 7,000–8,000 RPM
- Top speed
- up to around 100 km/h
- Type
- mixed-flow or axial
Numbers are rounded, typical values — real machines vary.
How it moves
Water is sucked in through a grille under the hull, sped up by an or impeller inside a tube, and shot out of a steerable nozzle at the back.
Throwing water backward pushes the craft forward — the same idea as a , but with the rotor hidden inside the hull. That is a .
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Why not a propeller?
No blades sticking out means it can run in very shallow water and is much safer for swimmers. Steering comes from turning the jet nozzle, not a rudder.
Large waterjets also push fast ferries and some navy ships.
Physics you already know
The job is lots of flow at modest head — the zone of high , where axial and mixed-flow impellers win.