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 [...]

Tip stall?

18 October 2009
Mark has made a couple of interesting comments about tip stall in connection with forward sweep. I'm sure that windsurfers have experienced the problem he described and I have been trying to understand what the cause might be.

I've been surfing with vertical fins on my surfboards since 1969 (only exception is if I surf in kelp). By vertical I mean the leading edge is 90deg. to the bottom. Usually the trailing edge angles or arcs forward making the tip narrower than the base. I have tried fins with the leading and trailing edge parallel (rectangular plan shape). I have even tried fins with forward sweep (yes, the tip leads the base!) I got on to that idea by reading about a US fighter jet that was built with forward sweep to the wings. It was done for faster response in dogfights. The article also stated that forward sweep required very stiff wings or they would twist adversely.

My experience with forward sweeping fins is that they are unstable, same as conventionally swept fins and for the same reason I describe in my book on surfboard design. This is a different problem than tip stall. My guess is that if the windsurfer has a problem with tip stall, caused by the tip leading, it's actually a problem of the tip flexing and possibly twisting, thereby increasing the angle of attack at the tip. The tip might be stalling or cavitating. A stiffer fin should eliminate the problem.

With the tip trailing the base (rear sweep) fin flex will decrease the angle of attack at the tip. This will also decrease the lift a bit but it will be gradual.

Bob
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