Hydrofoil

Yale Sculling Hydrofoil Project

Video of Hydrofoil in action - ipod M4V format (~24 MB)

Video of Hydrofoil in action - .mov format (~170 MB)

(when we play this video at home, we use Tom Petty's "LearningTo Fly" as accompaniment)

Frequently Asked Questions

So the video is cool to watch but why do we need rowing hydrofoils?
Well, it’s not clear that we do. However, going fast while using the human body to its fullest potential usually teaches us something about humans as well as energy transmission and transportation. Given that energy may be one of the biggest problems facing engineers for the foreseeable future, it seems like it is worth studying any form of human-machine locomotion.

Second, boats are fun [1]. In the course of rowing and paddling many miles, John Morrell has often pondered the quoted efficiency for rowing (60%-70%) [2]. A colleague at Segway, Jeremy Lund, and Morrell kicked around the idea of a rowing hydrofoil after seeing the foil kayak designed by Einar Rasmussen (www.foilkayak.com).

Recently, Andy Ruina and David Cabrerra at Cornell measured propulsive efficiency of rowing and also developed an improved analytical model that shows rowing can be up to 84% efficient (as good as many propellers)[3]. Given that rowers can recruit more muscle fibers for power generation, we believe a world record on water is possible with a single scull and probable in a double scull.

Hasn’t this been done before?
Well, no. There is a hydrofoil kayak (Flyak) and numerous cycling based hydrofoils (Decavitator, Flying Fish), but to our knowledge, no one has built and successfully “flown” a hydrofoil based on rowing for propulsion.

Is this legal?
To our knowledge, no one is likely to arrest the operator of a rowing hydrofoil. However, sliding riggers and foils are certainly banned from most rowing competitions.

Is this practical?
We don’t know. Hydrofoils can hit submerged objects with catastrophic results so the seaworthiness and/or practicality of this hydrofoil is probably limited. Still, most people thought airplanes were impractical in 1910 and today we rely heavily on them.

What foil section are you using?
We use the HQR/2.5 – 12 section. This was chosen based on the relatively low Reynolds numbers and the structural requirements for carrying the weight of the sculler and shell.

Why is there a sliding rigger apparatus?
Sliding riggers result in a more constant boat speed since the rower does not move relative to the boat. This is desirable so that the weight distribution on the foils is more constant than if the seat were to move as it does in traditional rowing shells.

Isn’t it unstable up on the foils?
Remarkably, no. The foils have fairly high roll stability and are more stable than some rowing shells. In addition, the skilled rower can use the oars to adjust the roll attitude of the boat continuously, restoring it to level when it begins to deviate.

Why isn’t there a surface follower like I’ve seen on Decavitator and Flying Fish?
The first question we wanted to resolve was whether rowing with a sliding rigger and balancing on the foils would be possible for a skilled rower. The oars provide a lot of control for the pilot to adjust the boat orientation as well. This prototype shows us it is possible.

The propulsion force is periodic and we would like to be able to fly at a variety of speeds so we will put some kind of active depth control on the hydrofoil to keep the foils at an efficient depth over a range of speeds and rower weights. We will also experiment with electronic control strategies “during flight” to see what opportunities exist for managing changes in propulsion power (i.e. fatigue) as well as disturbance rejection from waves, oar and body movements.

What’s the boat’s name
Slip Velocity. This term is used to describe the losses incurred by the blade moving backward in the water during the stroke.

Who was involved in creating this hydrofoil?
John Morrell and Kyle Washabaugh built the first prototype between July 2007 and May 2008. Yale Lightweight Crew coach Andy Card, an accomplished sculler and expert in the mechanics of rowing, provided feedback and demonstrated the capabilities of the hydrofoil. Since those videos were taken in May/June 2008, James Schulmeister and John Scrudato (Yale students) have fabricated a higher speed foil and surface following mechanism that will be tested in 2009.

What's next?
Tow testing with our new high speed wing, a new sliding rigger mechanism and a surface follower for depth control. The boat is presently in storage for the winter.

[1] The Wind in the Willows, Kenneth Grahame "There is nothing- absolutely nothing- half so much worth doing as simply messing about in boats."

[2] Human Powered Vehicles, editors Allan Abbott and David Gordon Wilson, 1995 , p. 78.

[3] Propulsive Efficency of Rowing Oars, David Cabrera and Andy Ruina, 2006.