Effects of Cavitation on Rudder Forces

Rudder surfaces can experience severe cavitation at high speeds or in hard turns resulting in excessive noise, vibration and erosion. Methods to improve surface ship rudder performance are being investigated at David Taylor Model Basin. As part of this project, effects of cavitation on rudder forces were experimentally studied. These rudder cavitation tests were conducted in the Navy's Large Cavitation Channel (LCC) with the rudder model installed on a fully wetted ship hull. Rudder forces, surface pressure distributions and velocity distributions in the propeller slip stream were all measured. The existence of large flow angles at the rudder's leading edge makes the cavitation inception and cavitation patterns markedly different between the two sides of the rudder. Significant effects of cavitation on rudder forces were measured and are presented in two examples. If rudder cavitation occurs at full scale, estimates of the rudder drag and power consumption based on towing tank tests can be grossly in error.