Evaluation and Prediction of the Rudder Torque Performance of a Ship in Turning Maneuver

Abstract

In order to rotate a rudder smoothly, the maximum rudder torque during a navigation is important for the capacity of a steering gear. However, compared to a lot of studies on rudder normal force, there has been still a few studies and open data on rudder torque. A rudder is commonly positioned behind a hull and exposed in the complex flow where the wake flow shed from the hull is accelerated by the propeller. Moreover, in maneuvering, an oblique flow comes into the rudder position. Therefore, it is difficult to understand the characteristic of rudder torque, and more investigation is required.

In this study, free-running model tests with a 1/61.2 bulk carrier model installing a mariner-type rudder were conducted. They were carried out under full and ballast load conditions, and the rudder torque performance in turning maneuver was investigated. Captive model tests were also conducted with a variety of propeller loads and the influence of the propeller load on the rudder torque was studied. CFD analysis was used then to visualize the pressure field on the rudder surface, and explain the mechanism of the influence. Eventually, a simple polynomial equation related to a propeller load was presented to estimate an average application point of rudder normal force. Incorporating this equation to a standard maneuvering mathematical model (MMG model), we could roughly simulate the rudder torque measured in turning maneuvers.