The Design of a Propeller for a U.S. Coast Guard Icebreaker Tugboat

The design process for an icebreaker tugboat propeller is presented and considerations involving cavitation, vibratory forces and propeller installation and removal are discussed. The design point for the propeller is maximum thrust at 5 knots full power ahead with pitch selected to give bollard operation at 245 rpm. Good astern thrust at bollard was desired and 75 percent of ahead bollard thrust was provided as a minimum. Preliminary design using series data predicted a propeller with a blade area ratio of 0.70 and a pitch ratio of 0.73 would give the highest astern performance at 85 percent of ahead bollard thrust and still fall within the design point restrictions. Intermediate design involved lifting line calculations at the free route condition with a maximum predicted speed of 14.86 knots at full power.