Vesijetit

Vesijetit is the Finnish term for water jet propulsion systems used to generate thrust for boats by accelerating water through a nozzle. They are employed on a range of vessels from small recreational boats to larger high-speed craft, offering certain handling and performance advantages in shallow or congested waters.

The operating principle involves drawing water into an intake, accelerating it with an impeller driven by the engine, and expelling it through a nozzle. Thrust is produced by the change in momentum of the water. Steering is achieved by deflecting the jet with a movable nozzle or steering vane, and some designs provide reversing capability through a deflector or bucket. The system eliminates external propellers, reducing the risk of injury and damage in shallow water or in areas with debris.

Two main families of vesijetit are commonly used: open waterjets and pump-jet systems. Open waterjets rely on a direct impeller and nozzle configuration, while pump-jets enclose the impeller in a duct with stator vanes, improving efficiency and cavitation resistance on certain vessel sizes. Key components include the water intake, impeller drive train, diffuser or volute, nozzle for thrust direction, and steering and reversing devices.

Applications span patrol boats, rescue vessels, fast ferries, racing craft, and pleasure boats, especially where shallow drafts or tight maneuverability are valued. Advantages include high maneuverability, shallow-water operation, and the absence of exposed propellers. Limitations can include reduced efficiency at some speeds, intake vulnerability to debris, and higher maintenance costs compared to conventional shaft propulsion. Vesijetit have become common where quick response and precise handling are prioritized.