Magnus effect - What is the idea behind it?

Dr. Gustav Magnus was the first researcher to observe and document this powerful Magnus effect.

Dr. Gustav Magnus was the first researcher to observe and document this powerful Magnus effect.

The Magnus effect was discovered around 1850 by the German physicist Dr.Magnus. It is the phenomenon that a spinning projectile from a cannon had a deviation upward or downward depending on the prevailing wind. That there would be a lateral deviation had been envisaged but the bullets also hit above or below the goal was something that everyone, including Magnus, did not expect.  He made a simple test setup with a rotating cylinder in a hinged construction to prove his claim. The cylinder was brought to rotate by pulling on a cord and placed it in the wind.
What appeared obvious during this run? There was a lateral force depending on the speed and prevailing wind direction. The discovery of this phenomenon was named after him: the Magnus effect.
Practical applications are clearly seen in soccer, golf and especially tennis. Here the "backspin" and "topspin" are a clear example of how the ball is “pressed” up and down respectively because the ball is rotating in different directions. Magnus not quantified his discovery; he realized the impact, but not the huge potential. We do this by now and know the tremendous forces generated by a rotating cylinder in air and or water.


The above diagram attempts to explain this. The ball or cylinder moves to the left and rotates clockwise. This will bent down the streamlines at the rear and front and creates an upward lift. It can also be argued that the streamline at the top have a longer way to go, so the speed is greater than at the top then at the bottom And we have to thank the physicist Bernouilly that we understand what this game does with the force, said very simplified: pressure times velocity is a constant. So the way over the top of the ball is a longer way to go; the streamline has to move faster. At the higher speeds on the topside, the pressure has to go down to keep the outcome constant and hence the resultant force is upwards. We call this force the "Lift”.

The Magnus effect brings stabilization to the next level of yachting comfort!

Click the button for more information about the Magnus effect

15 meter yacht with retracted rotors

Retractability means Safety

If your yacht needs to be lifted out of the water for servicing, the automatic retractability of the rotors will protect your yacht from potential damage.

This is in contrast with non retractable stabilizing systems such as the stabilizer fins!

This picture is a "fish eye view" of a 15 meter motor yacht with retracted rotors. Note that the placement for this rotorswing system is chosen to be mid-ships. We often try to place the rotors towards the transom to eliminate unwanted steering effects.  This is to show how flexible the RotorSwing system is in terms of placement!  RotorSwing Marine will provide you with the best calculated suggestions but you as yacht owner will make the final decision.

Compensation for Disadvantages

When deployed to their DRIVE position with the rotors at 90 degrees, the roll damping effect is optimal because the Lift force is largest. But the resistance (drag force) during the periods that the rotor is anticipating the next wave, is relatively high.
Therefore, RotorSwing Marine found a solution for this Drag Force issue and Patented it. It is called the RAKE function.

RotorSwing Marine always says: "Thanks for your discovery Dr. Magnus , we enjoy using it.  We hope you don't mind, since we felt compelled improving it!"

magnus stabilizer with rake

A technological breakthrough!

But beyond the use of a rotating cylinder for roll damping, we provide a technological breakthrough. We introduced the first electric stabilizer Magnus effect in the world. Not only electric but also swing away. No problems with assembly of hydraulic pumps, oil reservoirs and expensive high pressure hydraulic lines. No leakage and complex installations.

Yacht Service Erkens loved the products from RotorSwing so much that they are now integrated with RotorSwing Marine.

difference between fin stabilizers and RotorSwing Stabilizers

Let's discuss the differences between fin stabilizers and the Magnus RotorSwing stabilizers

The best known roll damping systems for motor yachts are fin stabilizers. They are effective and relatively simple in their design. They generate a force when moving CW or CCW and the generated Lift can therefore very well be used in roll damping.

There are two drawbacks:

  1. Fin stabilizers need a proper water velocity (at speeds below 5-6 knots they do not do very much).
  2. They protrude outside the hull so they can be easily damaged. To reduce the chance of damage often too small fins are installed that generate not enough stabilizer Lift.

These two disadvantages of the fin stabilizers are compensated by our RotorSwing system with the Magnus rotors.

The rotors are very effective at low ship speed (from 3-4 knots), there where the regular fins are useless. There is no need to sail at high speed to get optimum roll damping. This results in fuel saving!

Retracted stabilizer


When no roll damping is required, the Rotors will be placed in “Parked” position. This results in less resistance (drag) and less vulnerability.


At speeds above 14 knots, the Rotors will be automatically retracted to decrease drag force.  This is accomplished by the control system that measures the velocity of your yacht.  Naturally, the captain can maintain in control and override certain functions (unless they interfere with safety). 

Fin stabilizers

Comparing with Stabilizing Fins

Now we compare them with fins.

The basic version of the RotorSwing has the following dimensions: 140mm in diameter and 1000 mm in length. Thus a projected surface area of only 0.14 m². These rotors are relatively small but can be compared to fins of 1.2 m²!

This says something about the enormous safety features of these rotors and the absence of drag force (less fuel consumption compared to stabilizer fins).

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