Determination of Propeller-Ice Milling Loads

In designing ice transiting ships, a major concern is the design of the propeller to provide adequate strength to resist ice loads due to propeller ice milling while still providing good propeller efficiency for open water observations as well as high icebreaking thrust at slow advance speeds. As a result, propeller design is a compromise between strength and efficiency. This is especially true for ice transiting ships that must transit long distances on ice-free routes and then perform difficult ice-breaking operations. The geometric properties of a propeller blade that provide good strength are blade width and thickness. Unfortunately, increasing these properties does not provide the best efficiency. Propeller design for ice transiting ships in general has tended to favor strength and reliability over efficiency in design compromises. The purpose of this paper is to outline a methodology for determining propeller ice milling loads as a function of propeller characteristics, propeller speed, ship speed, ice conditions and depth of ice milling to help in the propeller design process.