High-Speed Sailing

Vessel Name: Sailien
Vessel Make/Model: Experimental/custom
Recent Blog Posts
28 September 2013

The America’s Cup

I watched, with interest, the videos of the 34th America’s Cup. At last we have fast sailboats engaged in a competition that is fun to watch. The virtual images (such as course boundaries, distance grid lines, separation between boats, etc.) overlaid on the real images really helps to keep the race [...]

31 August 2013

100 Knots for Hydroptere?

The latest news from Hydroptere is that they have plans for a 100 knot sailboat. This was posted on 26 Aug 2013, so look for that date at this address. http://hydroptere.com/en/the-news/last-news/

17 November 2012

Aptly named Sailrocket, blasts off!

While yet to be ratified, Sailrocket posted an average speed over 500 meters of 59 knots. I will not be surprised if they increase their record into the 60 knot range during this record attempt.

02 January 2012

More drag for VSR2?

I want to start by pointing out that the whole VSR2 team has done a stellar job and has demonstrated conclusively that the forces that drive a sailboat can be aligned for roll stability without using ballast and without using any down-force. (Trifoiler achieved roll stability by using down-force, but [...]

18 December 2011

My analysis of Sailrocket

I copied a diagram of VSR2 (wing doesn’t show well) and added in the major force arrows that apply. Be aware that these arrows are not correct in terms of scale (length) and some of their locations are guesses, however I believe I’m correct enough for us to learn something about what VSR2 has been [...]

23 October 2011

60 is within reach, what’s next?

I have been watching Sailrocket’s progress with great interest and there’s no question they have a winner. I fully expect to see them reach 60kt in the near future. Sailrocket has now demonstrated what I first learned with my models and again with my full-sized prototypes, that if you get the forces [...]

Sailloons and Fliptackers

03 November 2008
A few days ago Hydroptere broke the mile record and the Class D record. Those runs were at about 1.5 to 1.6 times the true wind speed. See "news" on their website for more info.

Here is a link to the Gizmag page, showing a model of the Wing-Borne Hydrofoil. http://www.gizmag.com/go/3272/ (Thanks Alan for the tip).

I want to discuss weight and how it affects sailing. The title of this post is in reference to Bernard Smith's inventions following the Aerohydrofoil. Use the link "Mr. Smiths Amazing Sailboats" for more on this.

One of the biggest problems with hydrofoil or planing sailboats is low wind-speed performance. Both hydrofoils and planing hull shapes add drag at low wind-speeds and are therefore slower than conventional sailboats until they get enough wind to get up on the foils or plane the hull. This is one of the reasons cited by Hobie for discontinuing production of Trifoiler.

In "The 40 Knot Sailboat" Smith reasoned that with buoyant foils supporting the craft, any increase in speed would cause the foils to generate lift, raising the foils which would decrease the wetted area, lessening the drag. (I bought this until I learned differently with my full-sized prototypes.) What happens is: when you move an object through the water at the surface, it makes waves. It takes energy to make those waves and your craft is supplying that energy; in fact displacement boats get trapped by the waves they make. Shorter craft get trapped by shorter length waves, which move slower than longer wavelengths. So the main way to go faster in a displacement boat is to build a longer hull (clipper ship, anyone?) Well, those buoyant hydrofoils are very short and hit their maximum wave drag at low speeds, this results in the craft being slow in light winds until there is enough wind to force the craft past that point. With sufficient wind, the foils lift the craft, the drag drops and the craft takes off.

Windsurfers know all about this problem, the small fast boards can't even be sailed until there is enough wind to get them up on a plane. Kiteboarders need enough wind to fly the kite and get the board planing. So we either design a boat to be efficient at low speeds (America's Cup anyone?) or we design for efficiency at high speeds. I believe Bernard Smith was trying to solve this problem with his 1980 patent and I know Ned Snead was with his design, because he discussed hull drag in his patent. (See my post of 28 April 08 for more info.) By the way, those who plan to use aerodynamic lift to support the weight of the craft, have the same problem - it will take a certain amount of wind to get the craft supported.

Now let's look at how weight affects this. Weight causes the craft to sit lower in the water, which results in a larger wave being generated, resulting of course in more drag. It also takes more force to support more weight, no matter the method of support. From this we can see that a lighter craft will be to our advantage. Smith went all out on this with his helium filled "Sailloons". To be continued...

Bob
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