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Principle and Development History of Propeller

Views: 8     Author: Site Editor     Publish Time: 2018-02-07      Origin: Site

Principle and Development History of Propeller

There are many ways of ship's propulsion. There was a period when the Ming Ship ruled the way of ship's propulsion just like the dinosaur ruled the earth. So the title of ship was established in that period.

Most of the "open ship" is exposed to the water. The machine drives the wheel's paddling, which produces high pressure on the front and low pressure on the back. The pressure difference between the front and the back generates thrust and pushes the ship away.

However, the structure of the Ming Ship is complex, and it is greatly affected by the wind and waves. If the ship encounters the wind and waves, it will sway left and right like a duck. The air and water density are 800 times different. The huge Ming Ship will enter and leave in and out of it, which is easy to be damaged. During the Crimean War of 1854, there were still many Ming Ships. The forts on the coast attacked the Ming Ships with heavy losses. The biggest disadvantage of the Ming Ship was its inefficiency. Some people were determined to change it. They thought of Archimedes.

Archimedes was a mathematician and physicist in ancient Greece. In order to solve the problem of water irrigation in the Nile River, he invented a cylindrical spiral water heater, which installed several blades on the rotating axis. Each blade had a certain angle of attack to generate lift. Like an electric fan, when the rotating axis rotated, it sent water out.

A steam locomotive was built at the age of 26. He had great interest in warships. In order to prevent enemy shells from firing, he first installed engines on the waterline of warships. In the year he developed propellers and obtained patents.

Eriksson later emigrated to the United States. On January 30, 862, he launched the USS Surveillance, a warship built for the Navy with full steam power and a propeller and armored rotating turret. Until the 20th century, the Surveillance was still a model of warship innovation.

Smith installed two-pitch wooden propellers on a small six-ton steamship. The effect was very poor. The ship could only drive about 4 sections. During repeated experiments, the wooden propeller encountered obstacles underwater and broke in two with a click. Smith was so anxious that he wanted to jump into the river with sweat that the ship unexpectedly accelerated its speed. Inspired by this accident, Smith turned his long screw into a short screw, and then the short screw into a blade, which is what today's propeller looks like, with several blades on one axis.

In 1843, the British Navy first replaced the Ming Ship with a propeller on the ship "Lettler" and then designed 20 propeller ships by Smith, who participated in the war against Russia. Smith became a famous figure.

There are many problems in propeller propulsion, such as terrible vibration on wooden hull ship, wear of propeller shaft bearings under water line, seal of propeller shaft, thrust bearing and so on. With the development of technology, the above-mentioned defects of propeller have been overcome one by one, and the speed of steam engine has increased. More and more propellers are replacing the open wheel on board. By 1858, the Great Oriental was equipped with the largest propeller in the world at that time. Its diameter was 7.3 meters and its speed was 50 revolutions per minute. At that time, the propeller standard was no longer authoritative. Because the propeller's propulsion efficiency was close to that of the open ship, and it had many advantages that the open ship could not compete with, the open ship gradually disappeared on the sea.

In the development of science and technology, the performance of many mechanical devices has been widely used when people are not very clear. However, it is difficult for these devices to achieve their best performance without fully understanding its physical laws and complete theoretical analysis. Propeller is no exception, until 1860, although it has become an outstanding ship, but its achievements are all based on years of accumulated experience. The progress of propeller depends on the intuitive reasoning of experts, which can no longer meet the needs of the development of ship technology. It requires scientists to make a complete explanation of its hydrodynamic characteristics, which promotes the development of propeller theory.

"Shut off the blade and propeller" has been tested on some ships, which has increased the speed of the ship, but more surprisingly, the vibration of the propeller has been greatly reduced. At that time, the Yangtze River 2000 horsepower tugboat and Chinese-character landing boat had achieved good results, which attracted many shipbuilders. In 1973, the open water test of "shut off blade and propeller" was carried out in Shanghai, and the design atlas was also provided. It is interesting to note that today's "large side-slope" propellers developed in the world's famous shipbuilding countries, such as the latest large side-slope propellers, 6.3 meters in diameter, 35 660 kW in shaft power, 32.8 knots in ship speed; the latest large side-slope propellers used on passenger and ferry ships, 5.1 meters in diameter, 15 640 dry watts in shaft power and 23.2 knots in ship speed. The latest chemical tanker uses a large skewed propeller with a diameter of 6.2 meters, a shaft power of 10400 kW and a speed of 16.7 knots. They are very similar to "turning off blade". Their important characteristics are vibration and low noise, which is also the characteristic of "turning off blade".

  Korean Daewoo Company processes bronze propellers for Dutch Maersk marine tankers using multi-axis CNC machine tools. Usually the bronze alloy is melted first, poured into the mould, then the sand layer is removed, and the layer is cut off by the NC milling machine, and finally the protective varnish is applied.

The propeller of the iced-sea wreck Titanic, the fastest passenger ship in the world at that time, has three propellers, one with four blades in the middle and three on both sides.

By changing the pitch angle of propeller blades, the adjustable pitch propeller can not only make the ship move forward, but also stop and retreat. There are very complex devices in the hub of the adjustable pitch propeller (part of the blade installed on the shaft), which can make the engine work in the most fuel-efficient state and change the speed by changing the pitch angle.

Propellers produce intense vibration and noise, which is a fatal threat to submarines diving under the sea. So people invented large sideways propellers with large bending angles. In fact, people who cook all know that we cut meat in the kitchen, not straight up and down, but up and down movement combined with horizontal direction. When the motion "cuts" down, the inclined angle of the large-sided propeller increases, which makes the propeller blade evenly "cuts" toward uneven water flow, delays the occurrence of cavitation and reduces the noise of submarines.

The repaired Soviet Akula-class attack nuclear submarine (Type 971) is the best silent submarine in the former Soviet Union and is a landmark volcano in the distance.

Nowadays, the design of propeller is very mature. The focus of consideration in the design process is our thinking process. For example, the vibration of large-sided oblique blade is reduced, but the efficiency is reduced, the blade with high disk ratio and the cavitation is reduced, but the cost is increased, and the efficiency is reduced. These design indexes should be considered comprehensively and balanced. Points to meet the use requirements.


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