Cavitation

Bernoulli’s law indicates that the higher the velocities of water particles, the lower the pressure in that same water. In case this pressure drops below the vapour pressure, the water will vaporize on a local scale. This phenomenon is called cavitation and has a close resemblance with the phenomenon of boiling; however cavitation occurs at low pressure rather than at high temperature. Cavitation could occur on any location with high water velocities, for example on parts of propellers, rudders, shaft brackets, sonar somes, hydrofoils, etc.

Cavitation can be classified by;

- location: tip cavitation, root cavitation, leading edge or trailing edge cavition, suction side cavitation, face cavitation, etc.,

- form: sheet cavitation, cloud cavitation, bubble cavitation, vortex cavitation,

- dynamic properties: stationary, instationary or migrating cavitation.

Cavitation manifests itself by noise, vibration, thrust reduction and material erosion of the propeller blades, struts and rudders. The danger of cavitation on either propeller or appendages increases for higher ship speeds and higher propeller loadings.

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