Trailing edge adjustment for heavy running propellers

A propeller is engineered to last throughout the lifetime of a vessel. During its operation factors, such as biological growth on the hull and a change in operating conditions, can result in the relationship between the propeller and the engine being disturbed.

When the effect becomes too serious, engine overload is inevitable. In most cases, this is noticeable by black smoke emerging from the exhaust pipes. This results in higher fuel consumption and increased wear to the pistons, liners and valves, and with that higher maintenance costs. It is estimated that 20% of the world’s fleet suffers from heavy running propellers, whilst the solution by means of modification is within reach and has proven to be very effective.

The propeller is designed with a certain sea margin and/or light running margin to ensure efficient performance, even when the vessel is experiencing increased resistance like heavy weather conditions. When the propeller is heavy running, the rotation rate at service speed is reduced significantly. This means that full power absorption during conditions where there is increased resistance, or even during trials, cannot be realized normally. This could even affect the vessel’s speed during service conditions.

Causes:

  • Ageing of the engine (e.g. reduced performance due to wear of pistons and liners)
  • Increased hull resistance (e.g. mechanical deformation due to water impact or biological growth)Modification of the vessel (e.g. lengthening)
  • Incorrect design of the propeller (e.g. design based on incorrect data)
  • Change in normal operating conditions (e.g. change of route and weather conditions)

    Technical info
    The modification that Wärtsilä recommends is the trailing edge adjustment. It is a tailor made solution, meaning that detailed engineering is performed based on the propeller and vessel particulars given. Depending on the modification request, or the current geometry and installed power, cavitation, pressure pulse, and strength calculations are performed for both the original and modified propeller to ensure safe operation. The intention with trailing edge cutting is to increase the rotation rate of the shaft by decreasing the mean pitch. This is realized by lifting the trailing edge after a section from the trailing edge is removed.
    Benefits
    A trailing edge cutting will prevent overloading of the engine by adapting the mean hydrodynamic pitch. In addition to improved engine performance, other advantages to repairing a heavy running propeller include reduced fuel consumption and reduced wearing of the engine parts. In some severe cases, the vessel’s operating schedule is affected, and the modification will resolve this situation.  
    Application
    Fixed Pitch Propellers of any propeller brand

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