Solutions for cavitation in marine propellers

With the introduction of the marine propeller back in the early 19th century, cavitation during operation has always been a limiting factor on efficiency of ships. Cavitation in marine propellers develops when the propeller operates at a high speed. To combat cavitation, ships have to operate at a lower speed than maximum that their engines could produce, increasing operating costs and lowering efficiency. Ever since the introduction of the propeller, solutions for cavitation had developed and tested.

As the name suggests, this systems uses a set of nozzles to help reduce and prevent the likelihood of cavitation in propellers. This system was developed by Samsung Shipping which is based in South Korea. In order to reduce the possibility of cavitation happening in marine propellers, a set of nozzles are placed on the hull of the ship directly in front of the propeller. These nozzles spray out compressed air over the propeller that creates “a macro bubble”. This bubble completely encompasses the propeller that is in operation. With the differing characteristics of the seawater outside of the bubble and the air inside, a zone develops that has the ability to reduce the “resonance frequency”. Due to this reduction, cavitation is less likely to occur during operation of a marine propeller.

To determine how effective this nozzle system could be, multiple tests were carried out with the nozzles and without them. In these tests, it was discovered that the resonance frequencies and the likelihood of cavitation could be reduced by up to 75%. Those who conducted these tests also tried two different arrangements of the nozzles to find out which one was more effective. The first arrangement used only one nozzle, which though it used considerably less power than the other option, it was not nearly as successful. The multi-nozzle system, on the other hand, gave much better results but required more power to operate.

While this nozzle system has major drawbacks particularly in its power requirements, the possibility of cavitation in the operation of marine propellers is reduced considerably. Thus, to some ship owners and operators, the cost of installing these nozzles and operating them is outweighed by the benefits of increased efficiency in their propellers.

The Air-Filled Rubber Membrane, so it’s called, uses the same principles as the Nozzle System to reduce cavitation in marine propellers. Since the Nozzle System requires a large source of energy to operate, the creators sought to create a system that has the same results but is cheaper to operate. This membrane builds on the lessons learned in designing the Nozzle System and uses a pocket of air to prevent cavitation but does not require nozzles or compressors. While at the same time as limiting the cost of operation, this membrane provides just as much protection against cavitation as the nozzles do.

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Wikipedia