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max speed to wind speed ratio |
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11/22/2003 11:57:05 AM |
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what is the max THEORETICAL speed to wind speed ratio for a sailboard, assuming real world frictions and average human dimensions (height, weight)?
Jim, Tiesda, I'm sure you two have already faced this question!
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cholo ( ) |
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11/22/2003 1:58:40 PM |
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Hi Cholo
I don't think anyone has worked out a unanamously agreed formula for calculating top speed per windspeed.
It changes with sailor, size, height, sails, rigs, boards fins, density of wind, direction, chop, and all too many real world factors to calculate, not to mention board bottoms and setups. |
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LeeD ( )
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11/23/2003 8:18:43 AM |
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LeeD,
I'm interested in theoretical maximum for given sailor height and weight. That means flat water and the best speed board and rig that can be built (doesn't have to be an existing one, I underline _teoretical_ )
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cholo ( )
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11/23/2003 10:58:54 AM |
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I kind of agree with LeeD. When you are modeling something as complicated as windsurfing, any "theoretical formula" is going to be based on some major simplications and assumptions. Depending on how you do it, you'll get different results.
Besides, I don't think we even have good theories to explain how current windsurfing equipment exactly works (mast flex, sail twist, fin behavior and planing surfaces), so there's no way to define a theoretical ideal.
It's a very "organic" sport, so development tends to be evolutionary rather than based on pure engineering science.
The best way to come up with an approximation would be to collect statistics and then try to fit those statistics to some formula that uses some input parameters that you specify.
But... it's known that on ice, a windsurfing rig can make you go really fast, so that means that the most important parameter is fin & board drag. Learn to minimize those and you can go a lot faster.
I think some of the current problems with breaking the existing speed records on water have to do with the low pressure side of the fin having such low pressure that the boiling point of water is reached and the water vapour causes spin-out. Now wouldn't that imply that faster speeds can be achieved in colder water, because the pressure has to be even lower for the water to boil? There's a neat theoretical problem for you. :)
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Juri Munkki (Starboard Team Finland) (jmunkki@cc.hut.fi )
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11/23/2003 10:59:45 AM |
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All the people involved with speed sailing seem to think a top speed of about 50 knots might be attainable, but I'm not sure how many of them think you can go much faster than that. As for speed to wind ratio, I think that one can travel on an order of about twice the wind speed in the lower wind ranges, e.g. 30 in 15. The thoeretical limit is set by the friction of the board and fin and not so much height and weight. For example, on ice one can travel much faster than the wind speed since the friction is so low. |
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wolfram ( )
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11/23/2003 11:37:31 AM |
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Juri,
Boat propellers generate lift without boiling water while moving through the water at speeds far in excess of 50 knots, so low pressure "cavitation" can be designed out. Fin "ventilation" from air passing under the board at the base of the fin may be more difficult to control. |
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Ray (rkuntz@ndak.net )
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11/29/2003 2:49:16 PM |
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Hi Juri,
Where would we be without independent thinkers like you?
These measurements are difficult. I agree.
Ken Winner devised a system one year with a series of sensors on our Gorge 100 meter course. There were three wind sensors, if I recall correctly.
I once got about a 265 or 280 in light 6.5 weather. That is 2.65-2.80 of measured wind.
BUT:
I had a specially prepared slalom board
Everyone was on the beach, it was morning, less chop,
There was a big puff 50 meters outside ( I was already hooked in)
There was another big puff, just as I entered the course, and wind faded rapidly, therefore the sensors got lower readings
The run was disallowed because of statistic variation from norm. But the above explains why.
We did get efficiencies of 220 to 230 pretty regularly, this in lighter wind. As the wind picked up ratios went down.
Juri, this is an example why the measurement is difficult. Your point is well taken.
I agree the sport is more about organic evolution. My experience with equipment designers supports this.
I do believe engineering is an essential complement, not a do all end all. Without precise engineering we could not have possibly added the major advancements in both our formula and slalom fins in the last months, this with special panel material for CNC and precision molded product. Computer aided design is an essential component as well. (Thanks, Dave Kashy for all the great engineering)
Given flex in fin will be stiffer in colder North Sea and North Pacific water , colder environments than warm water as in Maui or summer.
i am clueless about the boiling point stuff.
Special fins are the norm in speed sailing
Bill
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Bill Kline (bill@gsport.com )
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11/30/2003 2:01:23 AM |
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I'm pretty sure most cases of spinout are "ventillation" and have nothing to do with "cavitation" or "boiling water". But I saw an article somewhere that made a pretty good case that water vapour might be the problem at the very highest speeds, so I mentioned it here. I don't consider it a proven point, but rather something that might be looked into to, if it turns out that fins start to spin out without explanation at very high speeds.
One way to test it would be to have a high speed flow tunnel with no air inside. If you get bubbles on the fin at high speed, I guess it might be water vapour.
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Juri Munkki (Starboard Team Finland) (jmunkki@cc.hut.fi )
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11/30/2003 6:05:08 AM |
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That is why i think that a Hypersonic based design could be better than a traditionel speed needle.
Better grip to hold the right angle with less pressure on the fin.
70 cm wide, appr. 1,8-2m long, 2-3 deep concaves(sharp profile), flat profile, masttrack foreward on the nose.
Acceleration not so good, but maybe better top speed.
If the fin is the limitation, you have to support it with board design.
Ride the board flat on the surface.Less drag, better leverage, better angle-better board- to windspeed ratio
Just dreaming. No time or skill to try it out.
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LK ( )
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11/30/2003 10:00:20 AM |
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http://innovoile.free.fr/hydro_e.html |
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( )
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11 |
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11/30/2003 12:08:00 PM |
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I do not think that our speedboards have reached their true potential yet. Finian went 45 kts last weekend in 40 kts of wind. 1:1.125 true wind to boardspeed ratio. If he can manage the same in 45 kts then the 50 kt barrier will fall.
Juri, you are correct, cavitation only occurs at speeds of 45 kts and above. We will see if it is indeed a real problem for us soon enough.
I know that for yellow pages it is the main problem they have been incountering at around 46 kts. Of course for them cavitation does not result in an unexplanable spinout but the destruction of their boat ! Brave men those aussies.
Here in the south of France we have the best forcast for next week since the beginning of our record attempt. S. - S.E. winds forcast all week.
As for myself I have been working like mad to tune my sails, adjusted the luff sleeves to let out the head, now have 45 deg of static twist instead of 30. Made some carbon asymetric booms as well which will help .
My Starboard speedguns are magic , I tried them all last sunday, the 30 cm (minigun) is fastest so far. The dyneema rails work great, no problems with the board picking up the vibrations of the mini chop , which at these speeds sounds like a distant machinegun.
More news as it happens,
Erik B. |
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erikbeale (Erik Beale@aol.com )
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11/30/2003 12:28:34 PM |
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Besides the weight room, what other workouts are you all doing to help keep the muscle mass alive and prepared for the big stuff? I've found bicylcing helps me hold down more sail. Just an idea. Of course, hoisting beers helps tons, right? |
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surfer ( )
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11/30/2003 5:39:48 PM |
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hi surfer
for all of us:
abs
www.healthforlife.com
incredible abs.. get to highest level, read insturctions carefully, follow to letter, get video
the difference from level 1 to 10 is incredible in your ability to hold the sail.
level 3: struggle with 12 meter at 14 knots level 6: piece of cake
in speed sailing, may add 10% or more,, or like adding 10 t0 20 lbs of weight, (depending on how long your limbs are)
ab work is not sexy, not good forum or magazine article
BILL
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Bill Kline (bill@gsport.com )
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11/30/2003 6:34:43 PM |
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Hi Juri,
I'm a little bored here at work trying to catch up with the work load and can't resist the on-line windsurfing distractions ;). The effect cold water has on the potential to cavitate is easily illustrated. To cavitate the water must be accelerated such that localized water pressure reaches the saturation water vapor pressure, which is 0.6 kiloPascals at 0C and 3.2 kPa at 25C. However, the potential is a function of the difference between the ambient (sea/lake level) pressure and the vapor pressure. So, temperatures theoretically don't mean much as water is accelerated and it's local pressure changes from from 101 kPa to 3.2 or 0.6 kPa.
I don't have a clue about how real world parameters such as dissolved gases, sand, salt concentrations affect cavitation potential. If anybody knows, please elaborate.
Check this really cool web site about cavitation, especially the photos in the second link.
http://cavity.ce.utexas.edu/
http://cavity.ce.utexas.edu/kinnas/cavphotos.html
Also check out the 2-dimensional hydrofoil pressure coefficient java applet (http://www.ce.utexas.edu/prof/kinnas/319LAB/Applets/Hydrofoil/). Based on this tool, simple calculations say that a 6% thick symmetrical NACA foil at 1 and 2.5 degrees angle of attack could begin to cavitate at 38.5 knots (19.8 m/s) and 22.3 knots (11.5 m/s).
This leads to a question for Bill Kline: What kind of foils are you guys designing for speed runs? What I'm really curious about is typical foil thicknesses of fins used for speed runs. How about the slalom or FW foils...what are their typical thicknesses?
Curious, |
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matt (hiker90@ )
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11/30/2003 7:20:51 PM |
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Hi Matt
Not Bill here, sorry.
My old Chuck Ames Speed Triangle from late '80's is very thick foil, much thicker than A box slot.
My Curtis Hesselgrave is also very thick, more like a swept low aspect pointer..not an H series, it's a custom speedtrial fin.
My Mike Lovell's are also thick, not quite as thick as above, it's shaped like an old low aspect Angulo Slalom.
None were made for really high winds, as someone my weight would need much smaller than 7" low aspect ratio to hold the tail upwind of the nose. |
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LeeD ( )
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11/30/2003 9:39:23 PM |
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Very interesting comments, Matt.
I haven't played with the java applet but it would be interesting to know what thickness ratio is most resistant to cavitation.
I guess one could eliminate cavitation by increasing the surface area of the foil and thus reducing the angle of attack, but the penalty in skin friction might be too great.
I had a look at a vertical foil on a formula 1 racing boat. It is a very narrow triangle cross section fabricated out of solid stainless steel, and the pointy part of the triangle points forward. My guess is that one entire side of the foil is permanently cavitated. There is no curvature in the cross section because it is desired to have a pressure gradient increasing along the length of the chord. |
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Greg (greg@ttcc.com.au )
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12/2/2003 10:41:18 AM |
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LeeD, Interesting stuff. What kind of speeds were you attaining with that hardware? I don't understand your comment about holding the tail upwind of the nose. It's my understanding and experience that the tail is a fraction leeward of the nose in order to generate lift and assuming the board is not railed, ie., the path sailed is slightly downwind of the direction the board is pointing and that's how the fin sees water coming at an angle of attack. This becomes more noticeable at slower speeds.
Greg, triangular cross section...cool....reminds me of the diamond foils used in the studies (undergraduate level) of supersonic flow. I too am curious to find out what type foils are now used. It appears that the java applet assumed a foil geometry with maximum thickness at about 25-30% chord length. According to the old NACA data, foils with same max thickness but located at 40-45% of chord length have a significant drag reduction at low angles of attack. I'd be curious what variations of this parameter are made for speed fins and how it affects cavitation potential. I reckon I could go buy a slalom fin and cut it up to take measurements :). Naah, I'd rather just sail and let somebody tell me.
Best, |
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matt (hiker90@ )
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12/2/2003 12:09:00 PM |
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I agree that the theoretical speed ratio might be pretty hard to calculate or model due to the big variety of variables. I do know that the best I have heard about and seen is 30 mph in about 14 mph winds. Just a smidge over 2:1. Not bad. I'm not all that good, but I can make 28 in 14 with my formula gear without too much trouble, using a 11.0 sail. I measure with a gps onboard.
One aspect of drag that nobody ever seems to talk about is the air drag on the human body. We have induced lift drag from fin, board, and sail, and parasitic drags from those again, but there is also parasitic drag from head, arms, torso, and legs. If we could design some sort of trailing-edge taper devices for our wetsuits, I think we could reduce body parasitic drag. A rounded leading edge and tapered trailing edge makes a rough airfoil shape. I don't think anybody has ever tried anything like this. Those guys in France should be experimenting with this.
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segler ( )
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12/2/2003 2:55:45 PM |
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Segler
I am with you on your idea of a "trailing edge wetsuit" for speed trial purposes.. I was thinking of such a thing back in about 1994 when we went through a patch of local speed trials and am still not convinced that it would not work..
Perhaps somebody else has thought of this an also tried it.. but I also haven't heard of anyone.. which sort of surprises me a bit..
Basically you would have to have a series of lightweight flexible triangular shaped closed cell foam blocks on the sailors "trailing edge".. perhaps these could be attached to the wetsuit with velcroor glue.. They would have to have cutouts to allow a certain amount of flex at joints (elbows, knees etc) and could then be wrapped entirely in some of that drag reducing lycra.. (like they use for speed skating).
Further improvements could be made by contouring blocks and fitting them to the sailors upwind leg so that when in the straps the gaps between the legs was filled and air could flow in a "smoother" path than it does at the moment.
Also as you suggest (and in spite of our limbs already being vaguely rounded) a more pointy leading edge could be added to the wetsuit in the direction of travel.
Cap this off with a similarly treated helmet.. and I'm sure the overall drag coefficient could be considerably reduced by a margin that would allow an extra few knots..
If it was all structurally sound enough the "Foilshape" that was produced by a sailor could possibly be used to generate a little bit of positive lift to counteract a bit of the pull from the sail, effectively allowing a larger sail to be used by the sailor..??
A few drawbacks are that in it's most "perfect form", such a wetsuit (well speedsuit reall) might not be totally practical to use from the sailors point of view. i.e. it might get in the way a bit.. but I think a bit of practice and a few design compromises would ultimately produce a suit that was useable and still delivered improvements..
Another little drawback could be that it can only really be used on a single tack.. maybe not such an issue as lots of other speed equipment seems similarly designed.. and if you don't have to sail back to the start is not really an issue...!
Guess it was something that I thought through pretty thoroughly at the time.. but like so many of the things I think about, just never really had the time to get about to trying.. It's good to see that other people sometimes think along the same track and that perhaps one of them will give it a try... and maybe surprise the world...!
;-)
PS.. For a post about maximum speed/ wind ratio.. this thread has also become a really good one about fins.. just far too technical and scientific though for me to really be able to contribute too.. but really good reading anyway..
I like the stuff about cavitation.. but apart from my own opinion that although the water pressure is much reduced on the upwind side of the fin, I'm not sure it gets as low as boiling.. probably more so that dissolved gases are liberated and then expanded in quantities that facilitate cavitation.. Got no scientific evidence of course.. just a laymans gut feeling from observation of how the bubbles in beer works.. further backed up by putting a small quantity of it in a syringe and subjecting it to even lower pressure than it is outside the can..
Maybe though this is not very scientific and only relevant if sailing in beer?
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Graham ( )
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12/2/2003 4:04:06 PM |
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Graham Ever try to hold a 70cm fin upright in 50 knots of wind? Turn it one direction or another and it will amost pull out of your hand. Imagine how a sailor's neck will feel after "flying" his head? :)
-Dan |
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Dan ( )
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12/2/2003 4:07:37 PM |
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I like the idea of using beer to demonstrate the effect of lower pressure on evolution of dissolved gases.
Matt, I agree it is getting too complicated. Still, while I am work musing about sailing is interesting. A while ago I suggested somewhere on this forum that thicker foils would have only a marginal drag penalty. The universal response was that they are SLOW. I had based my comment on looking at published data on NACA foils but forgot to take into account that the Re number of sailboard fins is extremely low. So there is a further complication. |
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Greg (greg@ttcc.com.au )
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12/2/2003 4:24:13 PM |
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Dan..
Like I said....
.....there might have to be "a few design compromises"!
(sorry.. but I can't think of anything else sensible to say.. I'm laughing so hard at your reply...)
Maybe human evolution could play a part in eventually resolving the flying ones head at 50 knots issue..
;-)
I think I'm going to go to sleep laughing tonight!!! ha.. ha.. ha...
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Graham ( )
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12/2/2003 9:33:49 PM |
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Hi Matt
I was talking speed trials, where you are heading well off the wind, in windspeeds well over 20 mph.
Fastest production board speed is Sailboard Maui 9', a slow slalom board with tail rocker and soft rails..with 5.0 Gaastra Racefoil, Custom Curtis, winds 17-24, 39 mph on radar gun.
Fastest custom board speed is US Open Speedtrails at Klickatat, with Haut 15" speed single concave, Ames triangle fin, Gaastra Speed Foil with top 3 battens reversed, Serfiac Gold mast, 200 meter course, 46.22mph for equal 7th place.
First place was Mike Delahante, the US champion, at 49 something.
Spin out wasn't my problem, the problem was excessive lengthening of waterline on the smooth course due to board pitching the nose down. Any setting that allowed comfortable sailing outside in the rough waters was completely wrong for the smooth course with land just upwind. |
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LeeD ( )
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12/2/2003 11:22:46 PM |
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ok Graham, I laughed, too!
LEE:
Lee, you must really have an old fin. I have quite a few speed fins and all but two are thinner. When did you do 46? From what I recall Charlie Escher was the fastest lightweight. At 155 he went through hell getting over 42. The water was always rough outside up to 50 meters to the entry. Or, is that a missprint?
I know Segler well,, he has a point with regards to drag, but how to do?
We have done speed fins over the years, a number of records have been set on Curtis. We have some fins being used as we speak.
I can say in general, the designs are thinner than referred to above.
Also have used and tested Assymetrical fins. We have special foils for them.
Much work has been done,, more to do. Those who compete plan far ahead with rigs, boards and fins.
Hope this answers questions.
Bil Kline
www.gsport.com
Curtis fins
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Bill Kline (bill@gsport.com )
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12/3/2003 5:20:55 AM |
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Why are wedges used on offshore power boats instead of foiled fins? Obviously, leading edge forward. I believe the sponsons on those inshore boats are wedges too. Has anyone applied that technology to speed boards? |
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surfer ( )
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12/3/2003 1:28:40 PM |
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A method I have thought about for making airfoil shapes out of our body and wetsuit is this.
Get some flexible sheet material. Heck, I don't know what kind, just make sure it is flexible and gluable. Cut it into lengths that are about 2 feet wide. Glue pieces of it to the front and back sides of a wetsuit so that the glued edges are located on the "corners" such as hips and shoulders. Do this on both the left and right sides of the wetsuit. Cover torso, arms, and legs. On each side (left and right) at the outer edges of the sheets glue them together with a thin glue line to form a triangular cross-section trailing edge, then trim the excess.
Say you are sailing on starboard tack. If the material is flexible, on the windward right side this material will conform to the rounded leading edge shape of the body parts, while the trailing left side edge will feather out from the body parts forming an aero shape for reduced drag.
Then, when you switch over to port tack, the left side sheets conform to the body parts while the right side sheets feather out to form a trailing edge.
I have no idea whether this would work, but it be fun to try.
--Segler
Boeing Engineer
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segler ( )
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12/3/2003 4:44:55 PM |
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To Eric Beale,
What were your experiences with the wing mast sail? No mention of it anywhere so it would apear that it didnt worked out? Hard to control or just slower?
Very curious, hope you dont mind sharing..
wh |
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( )
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12/3/2003 5:32:27 PM |
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Segler,
I can't quite see what would make your material 'fill out' at the trailing edge, but it could be possible to use the 'ram air' principle being tried in paragliding harnesses, as you can see quite well at www.airwave-gliders.com (select ram race progress from the news items on the left for photos). But I am sceptical of the practicalities for speedsailing, although a cycle time trail helmet would at least look radical for the photos !
I don't see there is a theoretical speed/wind limit, as such. But I do think it will be necessary to make (soft) wing sails work well on boards to acheive significant progress. This is supported by seeing how efficent (solid) wing craft have proven (C class cats 20 knots in 7/8 of wind , and of course YP still above 2.25 at record speeds) . So it is good to see NP edging in this direction, and I suspect a high twist full wing sail will be sucessful one day.
Paul M |
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Paul M (pmorley@spammed.co.uk )
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12/4/2003 1:37:22 PM |
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Yes, I think the research being done on the full-wing sails will bear fruit. That's fine for sails.
However, we still have these big human bodies that we have to streamline, too.
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segler ( )
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12/4/2003 9:19:13 PM |
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Surfer,
I am almost certain that wedges are used on high speed power boats because of cavitation. The forces on fins, wings etc increase as the square of the speed so obviously the forces (or pressures) on the fins of these boats will be extremely high. In fact the low pressure side of the fin will be in full cavitation as soon as the boat attempts any sort of cornering. If a curved cross section was used there is the risk that some cavitation would occur even on the high pressure side.
I don't think these fins would be very efficient, and I think they are operating in a different speed realm to be of any interest for sail boats. |
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Greg (greg@ttcc.com.au )
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12/5/2003 2:46:50 AM |
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I had a discussion with some high speed boat designers. They are in a different realm. It was a half dozen years ago at the New York Boat show.
I also had some brief discussion with Mario and Michael Andretti at his warehouse sale two years ago about wings and wing settings on the racers. Mario , with Colin Chapman were pioneers in that area
I have researched reducing sailor drag and an number of other issues not yet published
All these circumstances require a power sources that can be controlled at high speed. A lot of this work ,including some we do is highly confidential.
But, with the race boats, they have budget to add power
In sailing our finish preparation in general is more precise, because our power source, useability there of is limited by budget and biomechanics.
With race cars, they keep wing setting in design from view and in America s Cup sailing the leels from view.
In speed sailing the water adds soooo much drag relative to our ability to get a good power source we can harness and control
If there is anyone out there who would like to get serious and fund such an effort, please conjtact me. The pieces are there. It needs funding and coordination form different disciplines.
Bill Kline
Gorge Sport USA
www.gsport.com |
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Bill Kline (bill@gsport.com )
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12/5/2003 5:00:25 AM |
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Matt how did you do the calcs?
"Also check out the 2-dimensional hydrofoil pressure coefficient java applet (http://www.ce.utexas.edu/prof/kinnas/319LAB/Applets/Hydrofoil/). Based on this tool, simple calculations say that a 6% thick symmetrical NACA foil at 1 and 2.5 degrees angle of attack could begin to cavitate at 38.5 knots (19.8 m/s) and 22.3 knots (11.5 m/s)."
Would this suggest 50Knots is possible at 1/2 degree AOA without cavition??
This 15% foil is cavitating at only 16 knots with an AOA of 8.5 degrees
[img]http://www.fluidlab.naoe.t.u-tokyo.ac.jp/Research/CavPictures/Cloud.birdseye1.jpg[/img]
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david ( )
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33 |
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12/5/2003 10:59:10 AM |
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LeeD: I thought the production sailboard record was set on a Bic Adagio (Mudshark) by Serge Greissman? Anyway, lots of windsurfers have beaten the 39mph mark on production boards. For example in 1998 at Sotovento, Christoph Prin-Guenon, went over 39 on his Fanatic Hawk 268. I probably mnisunderstood, maybe you were talking about a specific event at Klikitat? |
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Dan ( )
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34 |
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12/5/2003 7:40:59 PM |
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Hi
Yes, my mistake, as I was thinking about Jeff Bayles's speed, while typing about my speed, which is much slower.
Bill, I've been working the last 6 days in a row as a laborer, and you caught me. Thanks...equal 7th yes, but in lightweight, 40 mph, not 46. If I was even close to 46, I'd have my head up my butt even MORE than it is right now.
Dan, I was only talking about my personal speed, wih a production board, during qualifying at Hood River Marina, with the 7 logs out into the river. Out of more than 20 paid entrants who tried to qualify, I got highest speed. There were already more than 35 guys who prequalified for the trials when they moved across the river to Klickatat. |
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LeeD ( )
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35 |
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12/6/2003 12:43:38 PM |
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Hey LeeD,
You wrote, "I was talking speed trials, where you are heading well off the wind......"
Duh! LOL. Some folks do it and some folks spend too much time sitting on their arses thinking about it. Guess which one I am:). Nevertheless, I'm still intrigue by the physics of speedsailing and fin cavitation. Eric Beale's comments about Yellow Page's cavitiation at 46 knots triggered a realization that I had no idea about the orders of magnitude involved in cavitation. Hence, my simple hand calcs to try and put things in perspective.
Best,
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matt (hiker90@ )
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36 |
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12/6/2003 1:45:26 PM |
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Sorry 'bout that last post....synapses misfired yet once again.
David,
The java applet calculated the coefficient of pressure for both the high and low pressure sides of the foil and was the basis for my hand calcs:
Cpx = (Px-Pinf)/(0.5*rho*Vinf*Vinf)
where,
Cpx = coefficient of pressure of high or low pressure side of foil at x location along the foil chord
Px = fluid pressure at x location on the high or low pressure side of the foil
Pinf = fluid pressure at infinite distance from foil, ie, ambient pressure, sea/lake level pressure, I assumed 101.33 kiloPascals (N/m2)
rho = fluid density (997 kg/m3 for h2o)
Vinf = straight line board speed
We want to know the straight line board speed at which the water is accelerated around the fin such that water pressure on the low pressure side reaches the water vapor pressure. Therefore, rearrange the above equation for Vinf while including a sign change to account for negative Cp's on the low pressure side:
Vinf = square root [ -2*(Pinf-Px)/(rho*Cpx) ]
Px =water vaport pressure (3.2 kiloPascals for 25C water) since cavitation is assumed and Cpx equals the minimum value calculated by the Java applet. For the two cases, 6% thick symmetrical NACA foil at 1 and 2.5 degrees angle of attack, the minimum Cpx on the low pressure side per the Java applet was -0.5 and -1.5, respectively.
Best, |
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matt (hiker90@ )
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37 |
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12/7/2003 9:04:18 AM |
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I think I'm missing some basic informations to follow the topics here...
What is the sailing angle where you look for your best speed? The guys with a GPS must know very well !
Another thing: is Finian or any other at the Canal using asimmetric fins? And what was the sailing angle for the record?
Just worndering...
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cholo ( )
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38 |
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12/7/2003 1:02:41 PM |
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Cholo,
I'm referring to the water-fin angle of attack required for the fin to generated lift, not the board direction-true wind angle. I don't know what the optimum board direction-true wind angle is, something greater than 90 degrees. LeeD and others more knowledgeable could help here. The MOS website didn't have enough info to figure out Finian's board direction-true wind angle.
Best, |
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matt ( )
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39 |
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12/7/2003 3:08:15 PM |
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Matt,
The fastest angle for windsurfers running in speed trial conditions (high ambient windspeeds) is about 120-125 off the (true) wind.
The MOS course at St Marie is (intentionally) aligned accordingly to the prevailing strong wind directions
For Yellow Pages (now “Macquarie Innovation”) running in lower winds (~20kts) it’s closer to 110.
The YP Course at Sandy Point is long and slightly curved, allowing for more variance in true wind direction.
Cheers :)
Ian Fox ~ StarBoard Team
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( )
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40 |
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12/7/2003 4:05:14 PM |
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Hi
Ian is absolutely correct.
However, in lightwinds, say 15mph steady, fastest course is not well off the wind, it's slightly down from true 90 (across the wind).
Reason is that with such light winds, if you run farther off the wind, you are going much faster than the wind, equaling less wind.
That's why we can all power right out of our jibes in 22 mph winds, but when we plane at 10mph winds, we mostly break off a plane. |
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LeeD ( )
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41 |
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12/7/2003 7:16:46 PM |
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Suggesting that “if you run farther off the wind, you are going much faster than the wind, equaling less wind”
can be misleading, or maybe indicates a less than thorough understanding of the complexities of “apparent
wind” sailing downwind. Even in the lightest winds. Take that to the limit – ice yachts !
If you held a speed trial in steady 15mph winds and ideal water etc (cholo) would the fastest times be set
closest to 90’ or 120’ (??)
Most of us understand that the apparent wind moves back towards beam reach as we reduce our total velocity,
but the discussion was really about maximum speeds in optimal conditions (cholo).
And that’s why the comparison of windsurfer Vmax (~50 kts in 50 kts true wind at 120’-130’) is quite relevant to YP/MI Vmax (~50kts in less than 20kts at 100’-110’).
The fastest angle/course for lightwind actually also depends then on the equipment plus rider skill / technique.
In modern windsurfing, there is a considerable range of “performance” variables at a steady 15mph true wind.
In a steady 15mph a fully powered and well driven FW or modern light wind slalom gear will still be at it’s fastest running closer to 120’ than 90’. Not so a waveboard with 5m.
Obviously a rider only just powered up (sailing on small sails for the conditions – won’t be able to maximize their boards theoretical maximum speed in light winds as they need to stay up tight (close to 90’-beam reach) just to get moving (displacement speed) with that sail. They simply don’t have enough power to have the speed to be able to bear away, increase board speed and in doing so increase the apparent windspeed vector that is the result of true wind plus boat speed.
It’s all about the ability of the rider to maximize power over drag; you increase the power (and thus speed) further by leveraging the vector of apparent wind which increases power exponentially (square of speed increase) whilst the increase in drag of a planing hull (fully planing !) is basically linear (doubles at twice the hullspeed).
Time for sailing..
Cheers :)
Ian Fox ~ StarBoard Team
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( )
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42 |
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12/7/2003 11:25:39 PM |
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Thanks Matt, for Cholo, you coul dgo to the Chalkwell site. They have been running speed trials on very flat water for the last 10 years and have the speeds,wind velocity and direction logged.
I thought about putting all the info into graph form but would rather spend my time sailing.
go here and click on the dates on the left
http://www.chalkwell-windsurfing.fsnet.co.uk/contents3.html |
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david ( )
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43 |
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12/8/2003 4:30:06 AM |
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It's true guys, 1 hour from London is a speed strip about 6 miles long, but we have so little wind from the right direction in the last few years. But when it's good, it's very, very good. |
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Chalkwell Sailor ( )
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44 |
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12/8/2003 4:47:07 AM |
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I still miss the influence of the hull design in this interesting discussion. Sounds like the only important thing is the fin.
Can you design a fin that can take 80 knots on the same board that can take 46,24 knots ?
Read Finians report on Masters of Speed, he had mega spinouts in his fastest runs, cost him the world record.
I think you have to run too deep en angle because of the fin.
So the sail does less work as a wing as deeper you go.
This must be one of the reasons why they only sail 46 knots in 40+ knots wind.
I am maybe totaly wrong, I am Just a Chemist who loves to windsurf.
If you could sail on a reach, or clouse to, the speed would be higher ??
Regards |
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LK ( )
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45 |
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12/9/2003 10:04:25 PM |
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at 46 knots the hydrdynamic lift is so great there is almost no board in the water. That's why it is the fin which is the critical aspect...at least on the flat water of the canal. |
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david ( )
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46 |
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12/10/2003 3:57:51 AM |
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The Rider and the Sail is out of the water all the time and are very important parts anyway. People discuss the Riders aerodynamics.
The board connects the Rider/Sail to the fin. So the way the power is put on the fin is very important.
The board design has influence on the aerodynamic at these speeds. When it toutches the watersurface there is fluiddynamic to think about.
So, isnt it true that we couldt get a better boardspeed to windspeed ratio on a better angle ?
A better angle gives more pressure on the fin = more spinouts.
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LK ( )
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47 |
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12/10/2003 5:41:30 AM |
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Again, do you think fins are, perhaps, the wrong design for those types of speeds? The wedges used on high speed power boats are the precedence from their world. Considering how long they've been above 40knots, maybe they know something? Who has tried one of these? Anyone? |
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surfer ( )
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48 |
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12/10/2003 5:55:25 AM |
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David, at 46 knots the lift is exactly equal to the total weight of the board, sailor and rig minus the vertical component of weight taken by the sail. In other words there is not much more lift at 46 knots than at 15 knots. That lift is almost all hydrodynamic lift created by the planing hul. Given that the fin is very short (and therefore not very flexible) and that the board is essentially flat, there will be no lift (1% perhaps) provided by the fin. The lift due to the planing hul is proportional to the square of the speed times the wetted area times the angle of the board viewed from the side. Thus the real reason why so little of the board is in the water is because not much surface area is needed to support the sailor at that speed. A good example of the importance of speed on lift is that it is possible to water ski barefoot.
I have also wondered why sailboards are running such broad angles from the wind. It seems that they must be a lot less efficient than MacQuarie Innovation. Sure the relative wind speed is higher on a reach than a broad reach but the direction of the force on the sail becomes closer to a right angle to that of the direction being sailed. Thus both the rig and fin need to have a better ratio of lift /drag.
I would be suprised if aerodynamic drag on the sailor would be very important only because ice yachts aren't a lot better in this respect and yet travel much faster. |
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Greg (greg@ttcc.com.au )
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49 |
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12/10/2003 2:08:00 PM |
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Greg -As a non-scientist, I have one (actually, two) words for you, and please take it FWIW: hydrodynamic drag. If such a term is scientifically recognized I feel lucky, but I think you know what I mean and what the speed sailors mean when they say that above 40 kts the water gets very sticky. Water is many, many times more dense than air and, unlike air, does not compress under pressure. I'd imagine that this lack of compression contributes to the "stickiness" of the water as one goes that fast (and why cavitating foils are used by speed boats).
The only way to increase the speeds we now see in a given wind strength is to make faster fins that operate in smaller ranges. The risk is that they are not fast all the way down the 500m course. This balance is, of course, nothing especially unique to speedsailing. We see examples in other sports all the time (e.g., auto racing, rugby, tennis, -whatever). I would bet that if Bjorn took his gear from Fuertoventura and plopped it into the canal he would not have gone as fast as Finian -assuming that Dunkie's gear was more all-around for the sea conditions than Finian's was for the ditch. But that's just my assumption.
Stable sails we have. Great rocker lines we got. Fast fins with just enough lift? -I'm not so sure.
-Dan |
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Dan ( )
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50 |
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12/10/2003 3:40:05 PM |
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guys,
it's all about the balance of the forces.
there are obvious limitations in the goemetry of a windsurfer.
the righting moment [length outboard and weight] of the sailor has to be balanced by the power of the sail and the fin. if it doesn't you get pulled over the front or fall backwards into the water.
the force of the sail could be visualised by differnt vectors into a forward component and a sideways component.
the more you bear away the more forward force you have and the lesser force [and thus drag] you have on the fin.
bear away too much and the apparent wind [and your powersource for the sail] drops. if you sail too tight the sideways component takes too much of the available righting moment of the rider.
a heavy rider of 100kg and hiking out around 1m has a righting moment close to 1000Nm.
the crew pod inclusive the crew on MI is somewhere around 200kg heavy and hangs out around 10m from the center of bouyancy when the pod is slighty lifted out of the water, that comes to 20,000Nm.
they have 20 times the sail carrying power of a windsurfer.
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boogie ( )
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51 |
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12/10/2003 6:37:58 PM |
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As Mr Boogie pointed out, the sail force vector has a forward and a side force components - and you can lessen the side force by sailing downwind but your power drops. The fin lift must counter the side force and if the fin lift is high, its also generating lots of induced drag and when the low pressure gets too low and "boils", big problem.
So bearing off the wind reduces the sails side force componenet but I cant help but think that running the sail more upright will do the same thing. The more you rake a sail, the higher the angle of attack it needs to operates at and on a board, this moves the sail force vector more to the side. If you could operate the sail more upright, it "in theory" will operate at a lower angle of attack and the force vector moves forward and the side force (for a given angle off the wind) should be reduced and put less lift demands on the fin - possibly reducing induced drag and delaying the onset of boiling.
It could be just "an illusion" and certainly hard to tell but it sort of looks like Finian does operate his sail more upright than a lot fo the other guys.
wh |
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wh ( )
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52 |
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12/11/2003 1:01:19 AM |
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wh, I am not quite sure what you mean by raking the sail. Do you mean raking it aft or raking it to windward? The direction of the force from the sail is dictated by the direction of the relative wind, the angle of attack of the sail relative to the wind and the lift/drag ratio of the sail. One thing I notice from the photos is that the sail is raked aft significantly and that there is a huge amount of twist in the sail. The implications of this are that the lift/drag ratio will be low and that therefore the direction of the force will not be as far forward as it could be. MI is presumably far more efficient - it gets a similar speed in half the wind strength.
I think induced drag on the fin could be made quite low - certainly much lower than the induced drag on the sail which really has a very low aspect ratio. I wonder if cavitation could be prevented just by going to a slightly bigger fin. This would however increase skin friction.
(I apologise to the guys who are building and sailing these boards because they have probably tried anything I have thought of and found that it doens't work!) |
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Greg (greg@ttcc.com.au )
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53 |
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12/11/2003 1:51:55 AM |
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greg,
due to the sideways bend of the mast the actual twist in the sail is not that much. just cut the loaded rig into cross sections and look at the angle of attack for each section.
a lower aspect ration is not necessarily bad for high speed.
the induced drag on a fin is highest when you go slow and relatively small when you go fast.
a lower aspect ratio sail enables you to carry more power in the sail as the center of effort [COE] is lower. that is the main reason why MI has gone to a shorter sail compared to YP.
there are plenty of dots in the picture... keep filling in.
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boogie ( )
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54 |
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12/11/2003 12:01:10 PM |
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Just curious about the induced drag - is it the coeficient of induced drag that is lower at high speed or the actual induced drag force?
On rake, I was refering to forward and backwards rake.
Interesting about sail carrying power and the height of the CE. Boats like YPE have a lot of leverage to hold a big sail but as the CE of the sail gets higher, this puts a larger down force under the sail and unless the boat sinks from this force, it must accelerate water downwards as it moves over the water and any component of this acceleration in the forwards direction is drag. On ice or a dry lake bed, you have almost no drag penalty from this down force and to some extent, it helps keep the boats from sliding sideways - ie, its somewhat of a good thing. Not true on water and lowering the sail ce would be better. |
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wh ( )
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55 |
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12/14/2003 2:41:29 AM |
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Greg , I thought it so obvious when I said "lift is so great" that I felt I didn't need to add "per unit area".... but what the heck..
Surfer wrote... "The wedges used on high speed power boats are the precedence from their world. Considering how long they've been above 40knots, maybe they know something? Who has tried one of these? Anyone?"
Yep... built myself a wedge ala high powered hydros ...but it was a big disappointment . Sounded like a vacuum cleaner on steroids and made a nice roostertail but had no capacity for side loads though it jibed nicely.. sort of the opposite of what I expected. I suppose if I had thought more about it it should have been obvious. In yaching the major forces are sideways which you try to resist so the smaller forward componant can be utilized. In powerboating it exactly the opposite. Made an interesting talking point on the beach tho' :-) |
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david ( )
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56 |
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12/14/2003 4:56:28 AM |
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Dave, I am sorry I misunderstood your comment.
The fins used on high speed power boats are in fact for used for taking extremely high sideways loads when cornering - up to about 4g I believe - thus your point about high force per unit area is useful. The problem is that the force per unit area is so high on these boats that the low pressure side boils the water (cavitates). One could design a non cavitating fin for such a power boat but the skin friction drag also increases in proportion to speed squared and it is apparently more efficient to have a cavitating fin than a larger fin that doesn't cavitate. It would be interesting to know whether this is really true for high speed sailboarding.
wh, Boogie is right that a high aspect ratio fin is not important for high speed - total induced drag diminishes in proportion to speed squared. i.e. double the speed = 1/4 the induced drag. |
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Greg (greg@ttcc.com.au )
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57 |
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12/14/2003 10:13:43 PM |
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I see now.. if you hold lift constant (you apply the same sheet force going fast or slow), the 1/v**2 relationshiip for induced drag falls out.
Thanks and regards,
wh |
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( )
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58 |
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12/15/2003 8:34:56 AM |
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I have been saying to anyone who will listen (few) for years that we need LOWER aspect sails to go fast. Lower the C of E and you can hold more power! Simple! (Of course there are design trade offs for stability etc.)
Modern speed sails achieve this by very flat upper foil and lots of twist - keeps CofE low. I am not yet convinced this is better.
Macquarie Innovation has a much lower aspect wing and wider beam (distance to the crew pod) than YP. The crew explained that the gains for developing power far outweighed the slight added drag/loss of efficiency.
The limitation in windsurfer speed sailing is not the rig. It is not the drag of the sailor. Put your rig and yourself on wheels or Ice and you will easily double your speed in less wind.
The limitation is the drag/resistance of the board and fin in the water. Simple really
The trick is to work out how to reduce it! Sounds like there are a lot of good minds out there working on it.
By the way: MI (and YP) use asymmetrical foils on the fins.
Not only that they have 'Fences' on them that must increase drag a LOT!
They also have a concave foil on the trailing edge of the leeward side.
They are also quite low aspect - and there are 8 of them - four on each of the leew'd hulls.
And MAN! The humming, wailing noise this thing makes as it screams towards you at 35 k + just HAS to be heard. Awesome!
Like everyone else it seems, they have had amazingly bad luck with the weather. EG. Their current attempt period ends on the 19th apparently. Guess what the outlook is for the 20th. Yep. SW change. First one for weeks. Murphy’s Law again!
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Andrew (sailquik@hotmail.com )
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59 |
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12/15/2003 2:20:28 PM |
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hi andrew,
you can go faster by either increasing the power relativ to the drag or decreasing the drag realit to the power you have at hand.
MI has chosen the first way and unfortunatly windsurfers are stuck with the second option.
if you look at what boards and fins the speed guys using and how small the actual area is that touches the water at speed... not much to reduce there.
to create a jump in performance, we will have to think a bit more outside the box.
cheers
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boogie ( )
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60 |
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12/15/2003 5:15:19 PM |
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Daffy,
You play in a special place.
There are few places on earth that we found yet that reward low drag tuning like that.
We knew it back then, it still prevails in modern racing there today.
MI will do it easy in the right conditions and we are both lucky to know that.
Finian is also lucky it wasn’t 12 hrs after his..
Cheers :)
Foxy
(Hey, ring me…demo centre, right ?)
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( )
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61 |
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12/15/2003 5:39:40 PM |
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Andrew's point may be particularly relevant to speedsailing very broad since low aspect aerofoils apparently work relatively well there (eg from aerodyn.org " At aspect-ratios 1 < AR < 2 the most evident effect is the shift of the angle of attack at which maximum lift is reached. This angle increases progressively and easily reaches 30 degrees"). And as I understand it sailing broader reduces the water/fin angle of attack & delays the speed at which cavitation starts to occur.
But as Boogie says increasing the L/D ratio also allows more power to be carried. I haven't seen any claims for single surface sailed craft going much above 2*wind on water (Longshot & Boards).
Perhaps a lower drag fin hull combination can be found but to resist cavitation too that must be tough: whatever lets hope the effort improves the gear we all get to use |
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PaulM (pmorley@spammed.co.uk )
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62 |
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12/15/2003 6:59:17 PM |
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http://www.nyteknik.se/bilder/bildarkiv/drivankare.jpg
http://www.trampofoil.com/speedsailing/
??? |
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( )
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63 |
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12/16/2003 11:13:17 AM |
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Somebody want to know, if one on the canal in SM used
asymmetrical fins. Yes , Rüdiger Lotz used a 27cm fin.
2 concaves and a cut out on the base.39,05 knots, german
best result of the year. The board is to long and 13 years old.
He get anew. |
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Lessacher Wolfgang (Wolfgang.Lessacher@t-online.de )
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64 |
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12/16/2003 3:01:11 PM |
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Hallo LK message number 9
I saw in Netherland the new generation of speedboards. They
are based on the Hypersonic,are shorter ( 2,20m- 2,00m) and
65-45cm wide. The buttom 3 concaves. The concave in the
middle is in front 35-40cm wide, at the end 12-15cm. In front
3-4cm deep,and at the end the last 40cm flat. The boads are
in front not round, they look like an M ,or two waves.
Stephan van den Berg and Martin van Meurs.
Stephan and his crew make the boards,and Martin van Meurs
make the speed. Dutch record 40,85 knots.It was no time to use
the small board.
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Lessacher Wolfgang (Wolfgang.Lessacher@t-online.de )
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65 |
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12/17/2003 8:54:14 AM |
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Hi Boogie,
You are quite right of course when you point out the very small area of the modern speed board that contacts the water. The area of the fin can be larger than the area of the board in contact. It is very hard to see how this drag can be reduced, but I recon that is still the area (sic) to work on as it has the potential for the most gain. May be some form of small hydrofoils...... who knows.....?
To me it seems that Starboard are on the right track with the new 100 and 110 sonics with shortening the length and widening the tails to create virtually a higher aspect planing area. (same or less area but shorter and wider). The new boards being tried by Robby N Bjorn D and Finnian M seem to follow the same idea. Shorter and wider than traditional speed needles. The narrow old needles seem to disturb the water a lot if you look at the wake. If you are game to look back :-) . This indicates to me that there can be less drag if we can smooth out this disturbance.
I have an untouched old speed blank (pretty hard to get these days) in my shed that is earmarked for a new speed board. I just havn't settled on the final shape yet. Watching...learning. Got to try it soon though!
Might be good to get together and throw around a few ideas one day Foxy?
The more I look at that Tandem speed board that Mal and you built, the more I recon you were on the right track with its rounder wider tail than ours.
My experience speed sailing in a "very low drag location" is that as you get really far off the wind the weight comes back onto the front foot and the lateral pressure comes off the fin. Its really interesting to see how your speed keeps increasing as you go broarder, when you would swear you are going slower but for the evidence on the speedwatch or GPS. As the weight goes back onto to front foot though, it tends to put more of the hull back on the water. This is the riddle I am trying to figure out for the new board!
Paul: I could not have put it better. Come to think of it. I could not have put it anywhere near as well! :-) |
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Andrew (sailquik@hotmail.com )
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66 |
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12/17/2003 6:42:50 PM |
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I thought it might be interesting to estimate the skin friction drag on a fast sailboard. I assumed that the contact area would be 0.8 x 0.25 m. Have I over estimated? It looked about this size on a photo of Finian at near 46 knots.
Anyway, using formulae from an old text book the drag is about 150 N (equivalent in force to a 15 kg weight). There were different formulae to use and they all came out at about the same force.
One can also estimate the drag force due to the fin. If the board was sailing on a reach I estimate that the sideways force from the sail is about 800 N. Some people might be able to better estimate the fin L/D (Boogie are you there?) but I took as a rough estimate 20:1. Thus the fin drag is 40 N.
I then estimated the required planing area from some course notes for a naval architecture course. At 46 knots a sailor could easily be supported on the heels of his feet!
It seems that the biggest gains on this crude analysis would be to further reduce the surface area of the board in the water. |
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Greg (greg@ttcc.com.au )
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67 |
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12/18/2003 6:06:20 AM |
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greg your first assumption is way off...as are all the others based on it...as you noted yourself, at 46k the heels of your feet have enough area to support your weight. |
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david ( )
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68 |
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12/18/2003 8:12:37 AM |
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so it is all about the fin and the sail, right? |
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surfer ( )
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69 |
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12/18/2003 9:24:01 AM |
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In my opinion apart from the shorter length not much has changed in speedboard design when looking at the photos and film footage of the boards Bjorn used in Arinaga. Yes, he had wide tailed boards but seemed to fly on the old fashioned ones. Finian was using boards that have pretty much the same one foot of width as 10 year old speedboards. There will be a refinement in scooplines, but on the canal you are sailing on the tail only.
So the major changes have been the sail/mast combination and fins (length, profile, flex and twist). The consensus for the perfect speedboard set up seems to lie around 20 to 22cm. one foot off, boardlength 200/230cm. with fins between 20 and 22,5 cm.
It will be very interesting to see if the current board designs allow the very best to break the record by a fair margin.
It's all about logistics, like Barry Spanier pointed out already. Take a production race sail and a whole lot of guts, weight, skill and strength and we will find out how far the wind to speed ratio has improved in blistering winds. The MOS attempt is a perfect example how things should be organised and with a little more luck we will see where it ends.
The one thing we are forgetting here is overall progression. We are talking about a record that stood for ten years. Just look at the records in athletics and you will see there has also been a leap in the evolution of sportsmen in general. You have to count in that factor as well.
So far the biggest gain seems to lie in more moderate winds. Finian is capable of doing an outright record for sure but it seems to me Boogie is right when he is claiming we have to think outside the box to create a jump in perfomance.
Or....we should get the magic day with 55-60 knotts winds, the right angle with totally flat water. Then we can use the advantage of the development that Formulasails have given us. The best can hold on to sails that will stay stable in windspeeds that would have torn apart the profile of every sail available back then. If the canal doesn't flood in a SE hurricane we will know. |
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Martin van Meurs ( )
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70 |
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12/18/2003 10:54:41 AM |
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Get a bigger sailor too. No offense smaller people, but more glutious maximus seems to hold on better in this aspect of the sport. |
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surfer ( )
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71 |
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1/14/2004 4:29:25 PM |
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I heard a rumor “that Dunkerbeck is going to try to break the speed record with Elite Select fins”, but I think I know there where some contacts with Lessacher and could it be that Jeff Fagerholm also is involved? Does any body know more? |
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Fred ( )
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72 |
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1/17/2004 1:44:49 AM |
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Hallo Fred .
Worlcup Sylt, 1 week later Danmark, Björn was there, I asked him to show me his
Aluminium fins. He did it. No contact with my fins. The aluminium fins are made by
Mr. Jeff Fagerholm. At that time was no wind in Danmark, for heavy weights.
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Lessacher Wolfgang (Wolfgang.Lessacher )
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