Stephen Bové - Art, Technology, Right Action

Monday, October 23, 2006


Originally uploaded by sbove.
World's fastest sail boat.

33 knots avaerage speed while crossing the English channel. Top speeds of 40+ knots. Crew raised 15 feet above water level at maximum rise of windward outrigger.

You could catch this thing with a really fast motor boat, but not for long before your fuel ran out, and not at all in high seas.

Team is now building a Maxi version for circumnavigation speed-record bid...

Here's the physics behind the hydrofoil and its patented hydraulic "effort limiting dynamic angle of attack controller."

From the Hydroptere website:

"The bearing pressure P is given by a very simple formula:

P = ½ ρ e S V2

ρ is the density of water, e the angle of incidence, S the immersed surface of the Foil at V the velocity.

To obtain the bearing pressure necessary to make the sailing ship take off at a fairly low speed, a great surface of Foil is required. When speed increases, the Foil gradually gets out of the water, S decreases.

But, the incidence of the water on the Foil plus the combination of the orbital velocity in swells and movements of the pitching of the boat, cause the working surface area of the foils to vary continuously.

At high speed, the bearing pressure can thus dynamically reach values of more than four times the necessary value.

Such forces are disadvantageous, hence the idea of a shock absorber or rather, more precisely, of an effort limiter -- a system that allows the Foil to slightly fold up itself when the bearing pressure exceeds a given value, thus maintaining a stable bearing value.

The movement of the foil perpendicular to the water reduces the incidence and, therefore, reduces the bearing pressure.

The speed of the movement is regulated automatically to ensure this balance.

Obviously, this movement is inevitably limited (in the case of the Hydroptère, to approximately 60 cm at the end of foil). But calculation shows that it is quite enough for managing the bearing values in almost every situation on the sea."