ice breaker

Boat that opens up a navigable passage through ice.

rear propeller

Screw driven by a powerful engine to propel the ice breaker.

stem propeller

Screw that pulls up water from under the ice sheet to weaken its support thus making it easier to break and move.

stem

Reinforced part of the boat’s prow that crushes the ice with its weight and then pushes it aside to open a channel.