How does an icebreaker ship work? Icebreaker ships work by driving their bow up onto the ice and then using their weight to crush the ice. They don’t just smash straight through it. Icebreakers are not regular ships. They need several special features. They need a strengthened hull, they need to have a unique shape, they need to be heavy, and they need to have a powerful engine.
There are many types of icebreaker, and they serve different purposes, but the general reason to have an icebreaker is to keep trade routes open. In the far north of Europe, Russia, and Canada, they encroach on the Arctic circle, and winters are cold and long. Ports and trade routes get blocked in by sea ice. The choices are either to stop using those ports and routes or to find a way to smash through the ice. Although, as the global temperature climbs and seas warm up, there might not be as much call for icebreakers as there used to be. Recently, the Northern Sea Route, which is a 5,600 km long shipping route between Asia and Europe, has been free of ice and traversable in the winter months as well. This was previously unheard of. That is good because it means that ships can cut a significant distance off their route (roughly 7,000 km), which makes transporting goods faster and cheaper. It also means ships are travelling for less time, which is good for the environment. Although, as with most things, if ships can make the route more quickly, they will make it more often, so there will not really be any change. This is called the Jevons paradox. It also means that runaway climate change has reached a tipping point.
Sea ice is different to ice on a regular lake because of the salt in the sea. When you add salt to water, it lowers the freezing point of water so it is still liquid at 0℃. To get sea ice to form, the water temperature has to drop below -1.8℃, and not just on the surface, but at least 150 m down. If only the surface is that cold, then water from below could rise and prevent the ice from forming. The ice starts to form in small pieces, which ride up on top of each other and slowly start to stick together until sheet ice forms. This ice is not that thick and contains a lot of salt from the sea. When the warmer months come, this ice might melt completely, or it might just thin. If all it does is thin, then a lot of the salt will fall out of it, and when it refreezes the following winter, it will become much harder and stronger. Ice that has just formed is called first-year ice, and ice that has built on a previous year’s ice is called multiyear ice.
Icebreakers don’t have much trouble with first-year ice. It is not that strong, and their reinforced hulls can break through it pretty easily. They have much more of a problem with multiyear ice, which is where all their special adaptations come in. The first, and probably most obvious, is the reinforced hull. As we saw with the Titanic, ice can be more than a match for a ship. Icebreakers have a thick, strong hull that is made of high strength steel, reinforced with a support frame. They are also covered with a polymer that reduces the friction between the ship and the ice. The shape of the hull is also much different to regular ships. Some modern ships even pump air into the water from the hull, which produces bubbles and reduces friction even further. The shape of the hull is carefully designed as well. The bow of the ship points out further than a regular ship and slopes backwards. This design lets the ship drive through the ice and then pushes the broken ice down under the ship and to the sides. A lot of icebreakers also have a wide bow to make as wide a lane through the ice as possible.
For most ice, the icebreaker’s hull and shape has no problem, and it cuts a path easily. Sea ice is fragile and is easily broken and pushed out of the way. Multiyear ice forms more of a proble,m and this is where the ship’s power and weight comes in. If the ice is too thick to break through normally, the ship’s powerful engine forces it forwards, and its hull shape drives the bow up and onto the ice. Then the shape of the hull and the ship’s weight crush the ice below it. Sometimes, if the ice is very thick, the icebreaker has to repeatedly reverse and try again. How much longer we will need icebreakers is anyone’s guess. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/Icebreaker
https://en.wikipedia.org/wiki/Northern_Sea_Route
https://icebreaker.fi/how-do-icebreaker-ships-work
https://nsidc.org/learn/parts-cryosphere/sea-ice/science-sea-ice
Photo by paul: https://www.pexels.com/photo/ship-moored-and-frozen-10513171/