BMW Technologie Story Foiling

FLYING PLEASURE.

The fastest boats.

FLYING PLEASURE.

The fastest boats.

FLYING PLEASURE.The fastest boats.

FOILING.

The fastest racing yachts in the world.

The revolution began at the 34th America’s Cup in San Francisco: catamarans started to “fly”, enabling them to reach incredible speeds. The secret lies in the hydrofoils, wing-like rudder blades, on which the yachts are able to lift themselves out of the water, thus reducing water resistance to a minimum.

What may look both easy and spectacular presents a major challenge in many regards. On the one hand, foiling demands innovative technology and design. This is where defending champions ORACLE TEAM USA can count on the support of Technology Partner BMW, who bring to the table a wealth of expertise from the automobile sector, and particularly from the pioneering BMW i project and BMW EfficientDynamics technology.

 

On the other hand, foiling also requires extraordinary instinct at the helm. Keeping the balance is a task that puts both man and machine through their paces. However, the result is extraordinary. “It is an incredible feeling,” says ORACLE TEAM USA skipper Jimmy Spithill. “Foiling is one of those things that you have to have experienced to really feel it.”

Video: It's all about efficiency.

THE PRINCIPLE.

Why do catamarans “fly”?

Hydrofoils work exactly the same way as wings on an aeroplane – the only difference being that the necessary lift is not generated by the air, but from the water. At just two metres in length and 70 centimetres wide, the foils, like a wing, have a convex upper surface. This makes the distance the water must travel on the upper side longer than on the lower side. As such, the water must flow faster. This, in turn, generates negative pressure. This negative pressure sucks the foil upwards, creating the desired lift. 

 

If the catamaran has achieved a high enough speed, it will lift completely out of the water. Like every other sailing boat, catamarans also heel in the wind. This results in only one foil and a rudder being in contact with the water, thus reducing water resistance to a minimum. This means that the displacement caused by the hull no longer hinders the speed – this is no less than a sailing revolution and has made aerodynamics and the reduction of air resistance a key factor in achieving maximum performance. No wonder, then, that the BMW Group’s aerodynamic test centre in Munich and the BMW specialists’ expertise play a major role in the design of ORACLE TEAM USA racing yachts.

EFFICIENCY.

Drag vs. lift.

The crucial efficiency criterion for yachts is the relationship between lift and drag. Above the water, the wing sail on AC catamarans generates a huge lift. Under the water, meanwhile, the foils generate the lift that minimises water resistance. 

This combination has dramatically increased efficiency, along with other progressive factors, such as the reduction of weight through the use of the very latest lightweight technology – another area, in which BMW provides a valuable technology transfer for ORACLE TEAM USA. The pioneering automotive achievement of putting a carbon chassis into production plays a key role in the realisation of the fully-electric BMW i3 and the BMW i8 plug-in hybrid sports car. The weight saved by using carbon fibre allows the pioneering efficiency and dynamics of the BMW i models.

STEERING.

Balance is everything.

To allow the catamaran to fly continuously, helmsman Jimmy Spithill must adjust the angle of both foils and the rudder blades every second to suit the course, direction of the wind, speed and opposition. He needs absolute sensitivity for this task – and an intelligent steering mechanism. This is being developed by BMW Motorsport engineers, who are transferring technology from automobiles to competitive sailing. The constant readjustment is immensely important, as sailing on foils is extremely unstable – and if the hull hits the water, the boat loses an awful lot of speed.

DRAG.

Revolution through multihulls.

The drag of a classic monohull is proportional to the water displaced by the hull – this dramatically limits the speed potential. By using multihull boats and the boost from foiling in the America’s Cup, it has been possible to triple the top speed. 

 

A glance at the history of the America’s Cup shows just how profound the change of paradigm has been: between the very first America’s Cup and 2007, the maximum speed of the boats increased by just four knots. Since then, the speed has increased by an incredible 30 knots.

Multihull
BMW Technologie Story Foiling

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