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A new calculation method for the steering forces of a pod propulsor is presented. This method is also applied to a hybrid propulsion where a shaft-line-driven main propeller is located straight in front of a contra-rotating propeller, powered by an electric pod.
In the calculations the pod unit is divided into four parts: a rotating propeller, a strut, a motor housing and a fin. The forces are calculated separately for each part. Interaction between these parts is estimated by using simplified methods. The required input data consists of the open water characteristics of both propellers and a simplified outline geometry of the pod unit. The method is developed to the first quadrant of the pod propeller and applies only to steering angles that are less than the stall angle of the pod unit. The calculation method has been validated by comparing its results with the results of an extensive model test program. Transverse and longitudinal forces are estimated rather accurately. The accuracy is significantly improved for a high loading of a propeller. The calculation method applies better to a separate tractor pod. However, the results are good also in the hybrid propulsion case. |
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