High-Speed Sailing

I've wanted to talk about fundamentals for about two weeks - here goes. I'm going to separate sailboat design into two areas; fundamental and exotic. This is my own arbitrary division for the purpose of simplification. By fundamental, I mean the design factors needed to have a successful sailboat and by exotic, I mean "fancy stuff" that makes it more efficient, etc. such as Paul's cone-head helmet (Sailrocket).

From what I've seen so far, every major problem, crash, etc. has been a problem with fundamentals. Now some might say that a wing (Sailrocket, Innovation, etc.) or hydrofoils (Hydroptere, Wotrocket, etc.) are exotic, but you need an airfoil (wing or sail) and a hydrofoil (keel, centerboard etc.) just to have a sailboat that can sail at some angle to the wind. I will class wings and hydrofoils as being fundamental in their function; however we could class their shape as being exotic.

The fundamentals that have to be accounted for are pitch, roll and yaw (which I discussed in a post of that name on 14 June 08). The forces that act on a sailboat have to be balanced in order to maintain control. The greater the velocity of the wind or the craft, the more critical this balance becomes. Anytime there is an imbalance of these forces, the craft will deviate from its intended motion. If the imbalance is great enough, control will be lost. It doesn't matter how exotic the shape of the airfoil or hydrofoil may be; the problem is how to maintain a balance of forces at all times.

I definitely classify Wotrocket's super-cavitating hydrofoil shape as being exotic, but the craft flipped because control of the force balance was lost. Actually, from their statements, they were unable to de-power or steer, indicating the problem was not actually a sailing design problem but a mechanical design problem of the controls.

While we don't actually have a description of Hydroptere's crash, I'm assuming that the description I posted is what happened (roll to port, then pitch forward). No matter how exotic we might consider its hydrofoils to be, control of the fundamentals was lost and the craft flipped. Essentially, their means of control was inadequate to maintain proper force balance in the gust that accelerated them to 61 knots.

Sailrocket's flip was due to a loss of pitch control. That the cross-arm airfoil was designed to "fly" the lee pod to reduce drag could be called exotic; the fact that too much lift was generated, flipping the craft, is a fundamental pitch control problem.
While all the craft we are watching chase the record are quite exotic in appearance; their limits in speed are still being hindered by the fundamentals. Once a designer gets the fundamentals fully under control, craft efficiency (exotics), the true wind velocity, and possibly surface conditions, will dictate top speed.

There is one area that we really don't want the forces to balance, that is: forward acceleration. However, when the driving force is equaled by the total drag, the craft is at its top speed for the existing true wind. Only by an increase in efficiency, will the craft go faster for that true wind velocity. At this time Macquarie Innovation is the efficiency king, per the true wind speed compared to boat speed numbers they posted.

Once the fundamentals are fully conquered, I expect to see a significant increase in boat speed.

Bob