Vehicles brake by friction, what do ships brake by?

Braking devices are essential for the safe driving of any vehicle, both motor vehicles and non-motor vehicles.

Regardless of the type of vehicle, their braking principle is essentially the same, which is to use friction. Cars rely on brake discs, and the principle is relatively simple, which is to clamp the brake disc with a caliper, so as to use friction to stop the vehicle from moving. Since friction is used, the contact area between the caliper and the brake disc is particularly important. For example, the caliper of an F1 car is much larger than that of an ordinary car, so the braking ability is much stronger. An ordinary car with a speed of 100 kilometers per hour takes about 4 or 5 seconds from emergency braking to complete stop, while an F1 formula car with a speed of 400 kilometers per hour only takes 4 seconds. Cars rely on friction to achieve braking, and so do bicycles, which also use the friction between the brake pads and the wheels to brake.

Vehicles traveling on land have brakes, so do giant ships sailing in the ocean also have brakes?

Many people may think that there is no brake. If the ship also has brakes, how could the Titanic hit the iceberg? In fact, this is not the case. The ship does have brakes, but it takes longer for the ship to stop completely from emergency braking. Generally speaking, the braking time of a container ship is about 10 minutes, and it has to slide about 2 kilometers from the beginning of braking to complete stop. This braking time is too long, right? If compared with vehicles traveling on land, the braking time of the ship is indeed a bit longer, but it is completely sufficient, because on the vast ocean, there is almost no need for emergency braking, so a longer braking time is acceptable.

The long braking time of a ship is actually something that cannot be avoided.

On land, we only need to stop the wheels, and the strong friction of the ground will naturally stop the vehicle, but it is different in the ocean. The ship is surrounded by water, so even if the ship's power plant stops working completely, the ship can still sail forward for a long time and a long distance. It can be seen that simply stopping the propeller is not enough. If you want to stop the ship, not only must the propeller stop, but it must also rotate in the opposite direction to apply an opposite force to the ship, so that the ship can be stopped within ten minutes. So how can you make the propeller rotate in the opposite direction?

If we look at it from the perspective of the car's power system, it doesn't seem difficult to reverse the propeller, as it only requires the help of a gearbox.

Indeed, the propeller can be reversed by relying on a gearbox, but the problem is that large container ships are usually not equipped with gearboxes. As we all know, the main function of a gearbox is to adjust the speed, and the speed of a large cargo ship engine is very slow, so it is completely unnecessary to equip it with a gearbox for speed adjustment. Since the propeller of a large cargo ship is directly connected to the engine, there is only one way to reverse the propeller, and that is to reverse the engine. If this happens to a car, it would be a joke, because you can't turn off the engine and restart it every time you reverse, right? But it makes sense to put it on a ship, because ships use two-stroke diesel engines.

Simply put, the working principle of a two-stroke diesel engine is as follows.

When the diesel-air mixture explodes, it pushes the piston downward. When the piston drops over the air inlet at the bottom of the cylinder, the air pressurized by the turbine will enter the cylinder. At the same time, the exhaust port at the top will open and the waste will begin to be discharged. Next, the piston will move upward under the action of inertia. The upward moving piston continuously compresses the gas at the top, causing the temperature and pressure to continue to rise. At this time, the fuel injection device will open and spray oil inward, so another explosion will occur, and a new cycle will begin. From the working principle of the diesel engine, it can be seen that it is not difficult to reverse it. First, cut off the fuel supply, and then inject gas from the upper part of the cylinder to gradually stop the piston movement. At this time, adjust the cam responsible for exhaust and fuel injection to the opposite position, and then resume the fuel supply. The engine will rotate in the opposite direction to before. This process can be said to be done in one go.

The most common braking method for large cargo ships is to reverse the engine and thus the propeller. Are there other methods besides this? Yes, such as using a variable pitch propeller.

The braking principle of the variable pitch propeller is also very simple, that is, changing the angle of the blades while keeping the direction of rotation unchanged, thereby changing the direction of the propeller's power. This is similar to the electric fan in our home. If the angle of each blade is changed, it can change from blowing forward to blowing backward. However, this propeller has a complex structure and is too heavy and more susceptible to corrosion. Therefore, this method will not be used if the ship does not excessively pursue flexibility.

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