A Deeper Dive into Foil Matters

In recent years, the foil has conquered the world of water sports. When presenting the operation of the Syroco Speedcraft, the concept of "inverted foil" is often mentioned. As explained in the article on the aile d’eau concept, during our exploratory phase, the Syroco team studied the work of one of its technical experts Luc Armant and its main element, the foil.

The foil is therefore one of the decisive areas the team had to look into when designing the speedcraft. We asked Olivier Taillard, CTO of Syroco, to provide more detail.

How would you define a foil?

A foil is a generic term for a device that acts like an airplane wing, but into the water. When this wing is moving forward, it generates a force. It is this force which makes it possible to sail upwind, to windward (the daggerboard on a dinghy), and as we see it more and more often, to lift a boat off the water.

Why is Syroco's foil reversed? What does that mean?

The foil of the Syroco speedcraft is not used to lift anything, its role is to counteract the effort of the kite, which pulls windward and upwards. We therefore use the foil in the opposite direction of the wing, that is to say leeward and downwards. It avoids skidding and flying away. This opposition of forces enables the craft to accelerate.

What are the challenges encountered on the foil?

Due to the concept of our speedcraft, the team is facing several challenges:

Its depth must be stable and constant, which allows safe navigation.

This implies having a dynamic control of the foil. We use flaps, like on the wings of an airplane. It is important to be able to adjust the yaw and the lift of the foil. These mechanisms are integrated in the very small volumes of the foil itself.

It does not cross the surface of the water, which allows us to avoid the formation of spray (making waves consumes a lot of energy).

It is connected to the capsule by an element in tension, which can be assimilated to a thin cable. This allows us to greatly reduce the section of the element that goes through water and therefore its resistance.

And to cap it all, the wing of the foil moves at such a speed underwater that it will operate in a supercavitating regime: its extrados will no longer be in contact with the water but in a vapour bubble. To evolve in this supercavitating regime, we have had to completely rethink the profile of our foil.

We have designed and sailed with roughly twenty versions of our foil to date and also tested profiles in a cavitation tunnel. The shaft also had its share of experimentation with a dozen versions so far. We know how to be perfectly stable on our runs in remote control but also in automatic pilot now.

Several foil architectures have been considered, produced and tested. We now have a design that works at our maximum experimental speed and that generates the necessary efforts to run our prototype, with all the required stability.

A new validated step which brings Syroco closer to the world sailing speed record!