From the Polar Star's website:
POLAR STAR's three shafts are turned by either a diesel-electric or gas turbine power plant. Each shaft is connected to a 16-foot(4.9-meter) diameter, four-bladed, controllable-pitch propeller. The diesel-electric plant can produce 18,000 shaft horsepower(13,425 kilowatts) and the gas turbine plant a total of 75,000shaft horsepower (55,925 kilowatts). Along with POLAR STAR's sister ship POLAR SEA, she is one of the largest ships in the US Coast Guard and the world's most powerful non-nuclear ships.
POLAR STAR has other unique engineering features designed to aid in icebreaking. An installed heeling system can rock the ship to prevent getting stuck in the ice. The system consists of three pairs of connected tanks on opposite sides of the ship.
Pumps transfer a tank's contents (35,000 gallons, 133 kiloliters) to an opposing tank in 50 seconds and generate 24,000 foot-tons (64,800 kilowatt-seconds) of torque on the ship. That goes a long way in rocking POLAR STAR loose from any tight spots.
http://www.uscg.mil/pacarea/cgcpolarstar/history.asp