US Coast Guard Icebreaker Polar Star is refloated after overhaul on Mare Island. While not the USA's biggest icebreaker, it is the only one classified as heavy, which means it can break a path through six foot thick ice at a steady 3 knots. We have two larger icebreakers, but they are classified as medium as they can only continuously break ice four-and-a-half feet thick. They can all break thicker ice by backing and ramming, but that is much slower procedure.
The propellers on this ship are 16 feet in diameter and the pitch on all blades is adjustable, which means you can get more push at low speeds when you need it. AP Photo/U.S. Coast Guard.
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