 The hydrodynamic couplings that allow over 100% slipping between input and output shafts were used in difficult ice conditions to increase propeller torque and protect the main engines from large torque variations resulting from propeller blades hitting the ice.The fully locking mechanical clutches were used to improve fuel efficiency when the ship is operating in open water or light ice conditions.Because the power output per shaft of the SA-15 class freighters was at that time one of the highest among icebreaking ships, second only to the "Arktika" class nuclear icebreakers, the propeller of the ship was of extremely robust design.