How are they different from regular ships?
What makes them be able to plow through ice where others aren’t?
In: 4586
well the trick is, they actually don’t plow through ice. They “beach” themselves onto the ice until their weight is to much for the ice to bear and it breaks off. Then repeat. Think of you falling into the water on a frozen pond. You try rolling onto the ice to pull yourself out of the water, but everytime you’re halfway up there, the ice beneath you breaks and you’re back in the water.
edit: spelling
Normal ships is made with a more or less straight wedge bow which is designed to push the water to the side out of the way of the ship. And that is fine because water will just rise up in a bow wave and get out of the way. However if you take such a ship into ice it will encounter problems. Ice is quite hard and when you try to push it aside it will just crash into more ice and be prevented from moving.
So icebreaker bows are not straight wedges but angled forward. So it does not push the ice outwards but rather down and out. When an icebreaker hits the ice it will climb up onto the ice forcing it down into the sea breaking it apart and then the wedge will force the ice flakes under the surrounding ice. It works kind of like an inverted snow plow.
In addition to this the bow is heavily reinforced with lots of internal structures distribute from the bow through the ship and into the propeller as well as thick hull plates to avoid any damage from ramming into the ice.
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It’s just because of design. Ice breaking ships are built specifically to do that. So their hull is stronger and shaped differently. They don’t do it on other ships because it’s really not needed. They have strong hulls and can go through some, but not as strong as ice breakers. They prioritize efficiency in design for more speed less fuel usage.
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I spent 2 years on the USCGC Polar Sea. At the time one of only 2 polar icebreakers in the fleet. As somebody mentioned elsewhere in this thread, the ship was designed to ride up on top of the leading edge and then break the ice due to the forward/downward pressure. This wasn’t always the case due to ice thickness where it was more ramming than riding up on. Going by memory but I think we could make steady progress through ice up to 4’ thick and could get through ice up to 24’ thick if we used a process called “backing and ramming”.
At one point in Antarctica we spent 24 hours “backing and ramming” only to advance < .25 miles. We moved a bout 6 feet on one 4-hr watch. Somebody also mentioned engines. We had 6 main Diesel engines and 3 gas-powered turbines. I wasn’t on the mechanical side but I think the turbines provided 30,000 horsepower each.
It was a fun duty station and going to the poles and actually breaking ice was a memorable experience. What was also memorable, and what many don’t know, is how goddamned loud it was inside the ship while ice breaking was occurring. The noises you hear as the ice grinds past your only shelter is not exactly comforting.
Icebreakers have really big an thick hulls with a very specific sharp geometry. Most ship’s bottoms are basically flat ([picture](https://images-global.nhst.tech/image/UVowQXJqcWJ1SGRkWG5na01OeUU3d0M5UWMzdEJOL3o3bnd1WS9sYm42cz0=/nhst/binary/71cd4425d526697adb5ed3b78975c6df)), but icebreaker’s bottoms are sharp ([picture](https://rmcfinland.fi/wp-content/uploads/2017/10/Referenssit_otso_1-2000×1500.jpg)). So what icebreakers do is that they push themselves on the with their engines, so that the sharp edge of the hull rests on the very edge of the ice. This creates immense amounts of pressure due to the sheer mass of the ship resting on very small surface area. Pressure is simply force/area.
Now it is important to keep in mind the verb being used, they are ice**breakers**, only thing they do is break the ice. This is actually rather simple all things considered, take an ice cube and a butter knife of similar not sharp utensil. Place it on the edge of the cube and push against it. You notice that the ice doesn’t neatly split in half, little bits of it fly off on the sides until suddenly it snaps in to two without you even needing to push the knife thought. This is what ice breakers are doing but on a bigger scale and another dimension. They go on the ice so that there is lots of force on the edge of the sheet so it break in to smaller pieces, then the wide hull pushes these pieces under the ice sheet. If the ice is thin enough they can also force the ice to basically break around the ship by basically bending the ice sheet. The two primary methods are going slow, which causes the described effect of pressure on the ice, and under it from the sea pushing against it. Or they can go fast, and basically ram the ice shattering and flipping it.
Would a normal ship with a bottom like this be able to do this? No. Ice is really hard and an ice sheet has a lots of tension and force in it. Normal ship¨’s hull ranges from 12-30mm in thickness depending on where in the hull it is, average being somewhere around 20mm. This simply is not enough to handle the force of the ice, due to the sheer mass of the ship and the ice pushing against each other. This can easily lead to situations where the tensile strength of the steel (Usually 235-300MPa) is exceeded. Ice ranges in 5-25MPa, however you can’t compress ice once it has reached it’s maximum compression, after that it starts to behave more like a viscous liquid; if it can’t escape somewhere it’ll start to transfer force directly in form of pressure and in that game the ship’s hull will lose.
However there are *normal* ships that can act as icebreakers, these are called *double acting ships*. Basically the back of the ship is equipped to do ice breaking. So the same mechanism apple. They push the ship on to the ice with the engines, and the mass and leverage forces of the ship exceed the ice’s strength breaking it apart.
A modern icebreaker however has other tools in it’s use than just the powerful engines, shape of the hull and outrageous mass. There are all sorts of clever mechanisms like forcing pressurised air under the ship so it bring up water to act as a lubricant and barrier between the hull, along with wearing the ice on the edges. They can oscillate the ship from back to front or sideways to basically do what you you do when cutting something tough. There are also some kind of design for hulls that can vibrate which basically agitate the ice to turn slush under it, I’m not familiar with this.
Now a bit of fun trivia about the mechanism in action. The basic principle used to break ice is the same we use to break rock while tunnel boring with a TBM. The disks on the TBM force so much pressure on to the rock that it shatters under it ([picture](https://www.herrenknecht.com/fileadmin/user_upload/Main_Website/03_Produkte/01_Tunnelling/09_Einfachschild-TBM/02_Content/04_content_einfachschild.jpg)).
Now about the future of icebreakers. There are designs being made for icebreakers that go sideways. The same mechanism in action, but they can break wider paths for the ever growing cargo ships.
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To add: it’s a popular misconception that ice breakers thrust THROUGH the ice because that’s how we see ships go over water.
Ice breakers don’t. They are designed to ride up on top of the ice and then their weight collapses the ice under them. They then ride up again and repeat.
It’s why they are rated for various thicknesses of ice, by how much weight they have and by extension how much the ice will carry before it gives way.
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