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 [...]

More drag for VSR2?

02 January 2012
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 it added too much drag to get past the low 40 knots.)

Now some of you are going to protest and say "Bob, the force from the main foil (inclined keel, etc.) is pointing down on an angle." True, but the "up-force" on the airfoil and the "down-force" on the main foil are equal, opposite, and cancel out (in the plane viewed from fore or aft). There is no net down-force acting on the craft (if it's properly set-up).

I also want to point out that VSR1 had roll stability as well, however many of you may have been tricked by Paul's magnificent aerobatic show. Paul's "airs" were not due to the main airfoil's inclination but rather to a slight miscalculation in pitch control.

In looking over Paul's comment to my last post, I saw another area that appears to be causing un-needed drag. The top section of the main foil is set at a low inclination with the purpose of lifting the tail of the craft clear of the water. The purpose is correct (to get the aft plane out of the water and eliminate its drag) but a low angled foil at the surface is a problem. The problem is that anything we run at the surface generates waves and that causes drag. I've run into this problem with foils quite a bit.

I'd like to offer this as a solution: place the top (lifting) section of the main foil straight up, then angle the anti-drift foil off the bottom of the vertical section. The profile is up to the fluid dynamicist but the part near the bend should probably be cavitating. To avoid a deep foil, the top would need to be low aspect, and should be sized for low speed control (eliminating any supplementing rudder aft) it should taper to the bend where the anti-drift foil starts.

I've included a sketch showing the forces between the airfoil (blue line and arrow) and the upper (vertical) section of the main foil (green line and arrow). Note the resultant red arrow - that'll get the tail up.

I adjust my own craft (inclination of airfoil and hydrofoil) by which end goes up or down, until it's neutral.

Bob
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