EROCAV - Erosion of Ship Propellers and Rudders - the influence of Cavitation on Material Damages
Overview
Background & policy context:
The shipping market shows a strong industrial need for merchant ships with very high efficiency combined with low levels of propeller induced noise and vibrations. The maximum power for single screw ships - which are dominating in the merchant fleet - has grown from 30 to more than 60 MW over the last two decades. In parallel the speed of the ships and therefore the loading on the propeller increased. The interaction of the propeller and the hull is a challenging problem mainly due to the inhomogeneous inflow to the propeller. Cavitation has a severe influence on noise and vibrations, as well as on the propeller performance. Cavitation in fluid flow can additionally cause erosion resulting in severe material damage with a number of negative consequences like damage to propellers (propulsors) which may end even in a total loss of propeller blades, excessive vibrations and loss of efficiency which will increase the impact of emissions on atmospheric pollution.
Objectives:
The main aim of the work is to develop a practical tool to assess the risk of erosion on ship propellers in an early design stage. New and improved methods to predict the occurrence of erosion on ship propellers need to be developed. This will lead to improved testing equipment and to new or improved methods for the design of ship propellers and rudders. Improved propeller designs from the erosion point of view will reduce the cost for repair and will lengthen the lifetime of the product propeller. This means that in various cases observations of erosive cavitation have to be made both at model and full scale in order to determine the criteria for erosiveness of cavitation. Prediction methods in model tests need to be defined as well as calculation methods for the assessing of the possibility of cavitation induced erosion.
Methodology:
The aims have been reached by extensive full scale and model investigations. Propellers and ships with rudders with severe damages were included in the test cases. Additionally theoretical methods to predict erosion were developed. The main tasks of the research were to:
- Develop the knowledge about the mechanism of cavitation induced erosion;
- Extend the existing method to predict erosion in full scale by modeling the involved mechanism;
- Develop improved experimental test procedures for the reliable prediction of cavitation induced erosion;
- Reproduce in model scale the eroded zones on the propeller blades and rudders observed in full scale;
- Develop a practical estimation procedure based on main propeller parameters; and
- Improve the design procedures for rudders and propellers.
Share this page