To some, the Coast Guard Cutter Polar Star, with 75,000 horsepower, more than 2-inch thick hull and 13,500 tons of weight, may seem like a very big hammer to throw at the ice. However, to the command and crew of the cutter, the vessel is a precision tool, that, when coupled with skill and appropriate tactics, can be a formidable weapon against the ice.
“The whole concept behind icebreaking is you have to have a place for the broken ice to go,” said Master Chief Petty Officer Gregory Zerfass, qualified ice pilot and command master chief aboard the Polar Star. “To plan for this you have to think in advance, to consider all of the different ice movement scenarios during favorable conditions.”
All of the preplanning comes together by researching the types of ice that may be ahead, the capabilities of the ship design and the appropriate tactics that can be used to tackle the elements and help make each situation work in the favor of the mission.
Ice conditions are vastly different when comparing that found in the Arctic versus the Antarctic. In the north, the ice forms large floes that are in continual movement from the influence of wind and currents. However, the ice found off of Antarctica in the south is predominantly “fast ice,” or ice that is held fast (anchored in place) by surrounding land mass.
Fast ice can be new or single-year ice, or it can be older and tougher multi-year ice, or a combination of both. When these types of ice form together, ice ridges interact with one another, creating a formidable barrier to the progress of icebreaking. For the icebreaker to traverse an ice ridge, it may have to back and ram the ridge multiple times in an effort to create weaknesses in the ice, eventually allowing the vessel to form a navigable path.
Additionally, fast ice that is being held or pinched into place by two land masses can be placed under immense pressure, squeezing the ice and causing friction between the ice and the cutter that slows the breaking process.
An icebreaker can be designed with attributes to overcome the variance of ice conditions. Built more than 40 years ago, the Polar Star and its sister ship, the Coast Guard Cutter Polar Sea, were built with top-of-the-line design features, including the hull shape, strength and weight. The rounded hull design of the Polar Star allows the vessel to pivot on its bow and swing the stern to port or starboard, helping facilitate freedom of movement when working under fast or anchored ice conditions. Another design feature of the Polar Star is the hull’s ice horn. This ice horn is what allows the vessel to continuously break ice up to 6-feet thick and back and ram ice up to 21-feet thick.
The ice horn acts as a saw blade that allows the cutter to rise up onto the ice, creating pressure that allows the vessel’s weight to cut through the ice. Once the cut is made, the cutter’s rounded hull helps push the broken ice to the right and left of the ship, forging a navigable path.
“The ship’s design allows us to cut the ice, but it is not so much weight and force, but much more about the management of the broken ice,” said Zerfass. “We have to be aware of how the broken ice is behaving behind us. It is possible that it can accumulate and cause a blockage in the channel, becoming a whole other concern.”
To help guard against the broken or brash ice from clogging a channel, the vessel’s crew uses several different techniques to help facilitate breaking and the movement of the ice.
These are the tools that a knowledgeable ice pilot will use to create the width and angle that is desired when establishing a clear channel through the ice.
“We will try to use these techniques to take advantage of conditions, such as wind, to help move the ice we are breaking,” said Zerfass. “Our ultimate goal is to have the channel ready and prepared for the arrival of commercial vessels and help them with a safe transit through the ice.”
Source & Image credits: USCG