Full Scale lcebreaking Stresses on Propellers of the Polar Star

Abstract

The POLAR Class icebreakers were the first large high powered icebreakers to use controllable pitch (GP) propellers. During their first three years of operation, significant structural problems were encountered with the internal mechanisms of the propellers. The initial failures were due largely to lack of understanding the loads imposed on the propeller by ice. The Coast Guard decided to have the internal components of the propellers redesigned and rebuilt with the maximum strength that could be fit inside the same hub. At the same time the David W. Taylor Naval Ship R&D Center (DTNSRDC) instrumented the links and propeller blades to make stress measurements while actually breaking ice. This paper briefly discusses the structural failures, the failure analysis, the design changes, full scale trial instrumentation, stress measurements, and computerized analysis of stresses along with fatigue life estimates. The loads are not high enough to cause yielding of any of the structural components of the redesigned propeller, but are high enough to cause some fatigue damage. A computer program was written to analyze the stress data; the results are being used for predicting fatigue life, and for obtaining a statistical representation of the loads applied.