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Cavitation of Ship Propellers

Cavitation in simple terms means pits or dents occurring on the surface of the propeller which in general do have diameter smaller than 1mm. These cavities are also called pitting.

In much broader terms, if I may express; the rotation of the propeller creates vacuum. This vacuum starts the evaporation of sea water as the pressure fell below to that of the sea-water pressure. Consequently, this phenomena leads to the formation of bubbles inside of which is full of water vapor. These resulting bubbles collide the surface of the propeller and hence they all burst damaging the propeller material. Because this phenomenon occurs on the surface of the propellers, is called cavitation.

Cavitation Surface

Cavitation Surface

Cavitation Surface

If we consider that the ship navigates in ton right (forward) direction, cavitation occurs on the ship’s front / head surface of the propeller. This part of the propeller’s surface is then named  Suction Side. Cavitation by itself is a matter of Fluid Mechanics and needs to be considered a specific issue of  liquids.

What are the causes that enhance cavitation?

The main cause increasing the cavitation is the insufficient quality of material used to produce the propeller. As the propeller revolution rate increases then cavitation rate consequently increases.

Cavitation on Propeller

An Instance for Cavitation on a Three Blades Propeller

What are the damages caused by cavitation on the surface of the propeller?

The variable pressure acting on the surface of the outer part of the ship hull below the water causes vibration of the vessel and thus results in decreased efficiency of ship’s navigation. The most important reason for this resulting variable propeller pressure is the formentioned cavitation occurring on the surface of propeller(s).

The resulting vibration when the ship is specially unloaded can be much more perceived and affects the comfort of life of seafarers in a negative way. It can also causes malfunctions of the electronic devices. Another negative impact of propeller cavitation is the result of having irregular force on the propeller shaft. Hence this can lead to hairline – cracks on the shaft and can also create very difficult problems in the repair process of the shaft in future. Cavitation is also one the most important factors that affects the life of the propeller. As the cavitation progressed the abnormal sounds can also be heard at the stern of the ship.

How can the propellers suffered by cavitation be repaired ?

Surface subjected to cavitation can be corrected by filling with welding rods that are made of the same propeller material .

Translation By: Huseyin Sahin

  • Mark Bell

    Dec 16 2012 tarihinde 15:25'de yazıldı.


    Good photograph.

  • r s bhatia

    Dec 16 2012 tarihinde 17:08'de yazıldı.


    Dear Sir,
    well explained in simple words but welding of blades need more details as full information may not be available from makers of propeller.

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