Pulling The Wind – Science Behind Rotor Sails Explained

As a new type of propulsion device, the rotor sail can adjust the speed according to the wind direction at any time and make full use of the wind force; compared with the traditional sail, the rotor sail occupies a small deck space, is not affected by severe wind conditions, and has the greatest effect on the lateral wind. obvious.

In recent years, due to the advantages of maritime transportation cost and volume, maritime transportation has become an important way of global trade, but at the same time, the emission of pollutants from ships has also increased year by year, which has a huge impact on the global environment and climate.

With the continuous improvement of environmental protection standards for ships, the development and utilization of green energy such as wind energy to reduce fuel consumption have become an important way to save energy and reduce emissions in the shipping industry.

325,000-ton super-large ore carrier
Image Credits: cssc.net.cn

From this, it is not difficult to see that the background of rotating sails is the requirement of low carbon and environmental protection. The emergence of tumbler sails has greatly improved economic benefits, reduced carbon emissions, and improved the atmospheric environment while reducing operating costs and overall fuel consumption.

When it comes to the energy-saving principle of rotor sails, we have to mention the Magnus effect.

The Magnus effect is common in ball games. Take a rotating sphere as an example. When the direction of rotation of the sphere is the same as the direction of the airflow, low pressure is generated on one side of the sphere and high pressure is generated on the other side. When the advancing sphere rotates in a clockwise direction since its lower side is opposite to the direction of airflow, the air velocity is slower, so that the pressure on the lower side of the sphere is greater than that on the upper side, thereby generating an upward lift, and the sphere is in The phenomenon of deflection of the motion trajectory under the action of lift is called the Magnus effect.

According to the Magnus effect, the rotor sail generated by the engine has friction, which will drive the surrounding gas to rotate together.

When a side wind blows, the air velocity on one side of the wind duct will increase, and the velocity on the other side will slow down.

The rotor sail system has a simple structure and low self-weight. It only needs a small motor to generate significant thrust, and by adjusting the rotational speed and lift of the rotor sail, it can achieve reasonable energy distribution and reduce shipping costs.

Afros
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Unexpectedly, after the Magnus effect “cross-border”, it showed its skills on the ocean, and the small figure turned in a circle, converting wind energy into kinetic energy.

As early as 2018, the 64,000-ton bulk carrier “AFROS” designed by Shanghai Shipyard, a subsidiary of China State Shipbuilding Corporation for Greek shipowner Victoria Steamship, has successfully applied rotor sails.

Four rotor sails are installed on the deck of the ship as auxiliary propulsion power units.

In 2021, the 325,000-ton super-large ore carrier designed by the Shanghai Shipyard will be delivered. The vessel is the world’s first ore vessel to be equipped with rotor sails, and the installation of five rotor sails will increase energy efficiency by up to 8%, thereby reducing emissions by up to 3,400 tonnes of carbon dioxide equivalent per year.

Although rotor sail technology has been available in the 19th century, it was not until the 1980s that it was more effectively applied, and the application of this technology to large ships is a matter of recent years.

The modern giant ships are once again equipped with sails, which not only reduces the energy consumption cost of the ship and reduces the carbon emissions to the environment, but also reduces the load power of the ship’s engine, thereby effectively prolonging the service life of the equipment.

It is wonderful that a wise shipbuilder sings the old song of the sail, an ancient device.

Reference: cssc.net.cn

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