In the search to acheive the magic 50 kts we consider board design, fins, sails and sail shape but has anyone done any work with the aerodynamics of the sailor and how that affects the speed. Should we be borrowing the aerodynamnic technology of the swimmers, runners and bike riders to acheive our holy grail?

Sorry guys just adding to the post - things like the bike riders have developed their bikes to have close to zero wind resistance. They wear a crazy tear drop shaped helmets to aid in wind resistance. Trucks have wind deflectors on the cabin roof. Cars are designed with stream lining in mind. Swimmers have special swim suits. The winged keel. Should we be looking at this to increase our speed or is it the drag on the water that is slowing us down?

Old Salty - personally hoping to build some better body aerodynamics into a life jacket / weight vest this year. The biggest problem I'm trying to get my head around is safety - you need to be able to swim if you come off - also how to design so that weeks of hard work is ruined from the first stack. Other problem is constantly changing shape of sailor whilst sailing. Whether to cope with both tacks too. My thoughts are that our bodies are a certain width that we can't change so to some extent we can minimise the drag by creating an aerodynamic flow over the body - I'd also like to generate a small component of lift as well and add to the drive of the board - Would almost have a slot effect like main / jib on a yacht. Will post pics if I get going on the build. Interested to hear of peoples opinion on slightly flexible watertight foam (ideally sandable / easily cut) also ideally not pre formed but mixed / sprayed into a mould. Any ideas???

My personal quest is to reduce my standing sideways profile to cut wind resistance. Plenty of room for improvement there.

On a slightly different note. If by 'Holy Grail' you mean the ultimate achievement then I don't think this is necessarily a healthy way of looking at it.
Back in the '90's my personal unattainable dream was just to crack 40 knots. To me that seemed like an insurmountable task, so much so that I almost lost interest, pretty much gave up, but it was also related to not having a practical way of measuring whether I actually got there.
Then along came GPS speed sailing. On almost my first run with a Garmin Foretrex I was amazed to find that I had cracked 40! Only just mind you, and not for 500m but suddenly that barrier didn't seem so unobtainable. My personal quest now is a 45 knot 500m and that seems a very high goal indeed for me. It will take a perfect wind on a perfect day with all the planets aligned if it ever happens. But I know if it ever does there will be a new challenge after that, even if it is to be able to repeat it to prove to myself that it was no fluke.

As for 50 knots..... well that has been done now in a number of different ways. Peak speeds from some of the best kiters is now considerably past that. They are probably looking at 55 knots and possibly 60 knots now. Martin, and then Chris have both shown that 50 is quite achievable on a windsurfer and now it is just a matter of getting the conditions to hold that speed for 500m. It really is only a matter of time. Yellow Pages, in all likelyhood cracked 50 way back on the early '90's when they caught a huge gust going through the start line and shortly after cartwheeled and disintegrated. By counting frames on the video camera the crew estimated it went through the line at about 51 knots. This is one of the things that has given them the drive to keep going at it for all these years, just the knowledge that the basic design could do it, even if there was a lot of work needed in the control department.

Personal goals and satisfaction with those is what it is all about for me.
Must be a slow day. I am getting all philosophical again.....

Good to hear that someone is thinking about the drag affect of our bodies on the wind. Trucks have a fuel saving scoop mounted on their cabins to reduce the drag on the body. Would small scoop shape deflectors mounted on the mast to channel the airflow past our bodies make a difference?
Would a small winged fin help to lift the board a little and reduce drag on the board?
Would a slot mounted on the board to fit the foot of the sail into assist?
Yellow Pages used a wing rather than a sail?
I guess what I am saying is the 50 kt barrier has been there for awhile and should we be looking outside the square at other areas to get the next jump in speed

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Old Salty said...

Good to hear that someone is thinking about the drag affect of our bodies on the wind. Trucks have a fuel saving scoop mounted on their cabins to reduce the drag on the body. Would small scoop shape deflectors mounted on the mast to channel the airflow past our bodies make a difference?
Would a small winged fin help to lift the board a little and reduce drag on the board?
Would a slot mounted on the board to fit the foot of the sail into assist?
Yellow Pages used a wing rather than a sail?
I guess what I am saying is the 50 kt barrier has been there for awhile and should we be looking outside the square at other areas to get the next jump in speed

In answer to your questions. Maybe, nope, possibly, you have got to be joking!
Not necessarily in that order.

All sorts of stuff is available to the hard men of speed but wind under the board is probably not their greatest desire.
I see Dave trying a solid sail, one sided boom and wind pipes. Then he gets a record run with none of these.
Hard to tell from pics taken with long lenses, but from his board angle, it looks like Antoine is learning to sail with a cavitating fin. The answer may be as simple as sailing with back foot behind the fin.
Go for it..

Yep, windage is DEFINITELY a factor. For cycling they say drafting another rider at 40 kph removes ~30% of the overall resistance. If that's true at 40, and wind resistance increases geometrically (square?) with speed, how much greater is the wind drag on a big lump of sailor going twice as fast.

One of the subtler reasons big heavy guys are faster is that they have a better drag to mass ratio. They have proportionally less cross sectional area.

The things that make a difference as I understand it are 1) cross sectional area i.e. area presented to the air stream, 2) shape, 3) surface. Nothing that surgery cant fix.
Realistically you should be able to make small but appreciable improvements with small changes to fairing.

A lot of people have been trying to think of ways to do this safely for a long time. Don't let that discourage you though. Go for it. If you find a practical and safe way to do it I will be the first in line to try it.

Did anyone ever take a photo of Dan's speedsuit? I heard it wasn't very practical.
Once I tried stuffing bits of foam down my wetsuit but I almost died of heat exhaustion, maybe not such an issue at Sandy point as is in WA but it was obvious that with a variable apparant wind something adjustable would be better.

But I think at max speed (ie 50 knots) you have to run so deep that the apparant wind is from abeam and streamlining is not so critical as you would think.



Have to agree with an earlier post. Antoine seems to sailing with a partially cavitating fin. Though the forshortening of the telephoto may exaggerate the angle .

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yoyo said...
But I think at max speed (ie 50 knots) you have to run so deep that the apparant wind is from abeam and streamlining is not so critical as you would think.

Of course! Apparent wind is nothing like 50 knots. Maybe it doesn't matter. I'll ask Stewie.

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NotWal said...

yoyo said...
But I think at max speed (ie 50 knots) you have to run so deep that the apparant wind is from abeam and streamlining is not so critical as you would think.

Of course! Apparent wind is nothing like 50 knots. Maybe it doesn't matter. I'll ask Stewie.

Less than 50 knots. Hmmm. That was my first thought, and then when I got my brain percolating I realised that I don't know. My Physics is not good enough. If one was going at 90 deg to the wind the apparent wind would be 50 knots PLUS a component of the real wind at, say 40 knots. When one is going at 135 off the real wind direction my gut feeling is that the apparent wind would be slightly less, but it would still have to be right up there I recon.

Geeeze the internet is a wonderful thing. I typed 'apparent wind calculator' into Google and got a beauty.

At 50 knots speed, in 40 knots of true wind and 135 off the true wind angle:

The direction to the apparent-wind is 52.48 degrees off the bow!!
The speed of the apparent-wind is 35.66 knots!!

That is considerably less than I would have guessed!

Have fun with this: http://www.sailingusa.info/true_wind_calculator.htm

Of course this also explains why when there is 40 knots of wind I am in all sorts of trouble beam reaching into the speed course but as soon as I get to 130+ off the wind it all becomes a lot easier.

This calculator is lots of fun.

Here I am beam reaching into the speed course at 30 knots board speed in 40 knots of wind (90 deg):

The direction to the apparent-wind is 53.13 degrees off the bow!!
The speed of the apparent-wind is 50 knots!!

No wonder I am struggling to keep the sail under control!!!
Notice the apparent wind direction is not much different from the first scenario.

At the other extreme. When Chris did 45 recently at SP in a broad westerly which he thought was at least 150 degrees you find that with a true wind gust of 45knots at 150 degrees when you are doing 45 then the apparant is only 23.5 knots at 75 degrees off the bow. Almost directly abeam. The drag in rearward direction must be minimal... don't think I will bother with an aerosuit.

One of the interesting questions is wind shear and what the true wind is at different heights over water level. When fully maxed our bodies do lower toward the water a bit - especially legs. True Wind at water level is supposed to be 0 knots. I think it increases faster in higher winds due to turbulent layers etc etc but in a true wind of 40 knots measured I suspect that the wind at body level will be something a bit less - particularly close to shore - not entirely sure of this though. So when you are going 45 knots your calf muscles should be seeing close to that in apparent wind from straight in front and the apparent wind will twist as you move up the body to more beam like and lower strength (depending on your heading but talking about 135deg here). What I find enticing is not whether the drag on my body will reduce my speed by acting against the board - but whether the wind that needs to make its way around my body could actually contribute more forward thrust for the same amount of drag I'm already resigned to. higher angles of apparent wind make this all the more interesting due to the forward thrust that could potentially result. I'll try and see if I can have a go at some fairing ideas - I'll look like an idiot on the water thats for sure....

some ideas for going more aero?

shape all trailing edges aero to reduce the Cd. ie head, torso, arms and leg(s). Im sure a bit of shaped polystyrene and some velcro could do the job as a trial. Would make the catapults more spectacular visually!

Get rid of all dangly bits, ie harness straps etc, neaten the whole lot up.

Reduce skin friction of the wetty, maybe something like a tri suit? (bloody expensive though)

How about filling the gap between the legs to minimise turbulance- for all those cross dressers out there it could be similar to a long tight stretchy dress, from the hips to the ankles. Maybe you could use thin stretchy wetty material like rip curls E3 neoprene (or latex if your inclined that way)? When you eat it you may need to modify your swimming technique a little...

seahorse - sounds like you are talking about the slot effect that occurs between a main and headsail on a yacht- yeah why not! If properly done sure the shape of the rider could complement the sail- it would be a pretty bloody expensive suit though!

Strangely enough you've got the same ideas as myself - there's certainly some opportunity for a skirt for the upper legs thats for sure.

True Wind at water level is supposed to be 0 knots

Looking at the way the sand blows off the ground at SP it appears this supposition is incorrect.

shape all trailing edges aero to reduce the Cd. ie head, torso, arms and leg

Look at the photo of A2 above. Wind is sideon on his head. His torso & hips are elliptical and upper legs & rear arm horizontal to air flow. Aero gains would be awkward for little benefit.

A full skirt aerosuit making a bi-plane arrangement with the sail might work ..but in 40 knots?



Or go the full hog...



And hope you don't drown!

YoYo - understand your point but would like to point out that due to the nature of the boom and that A2 has his body parallel to the boom his torso is actually more or less in line with the angle of attack of the sail. With a slot effect this angle would be slightly different to the actual apparent wind angle too. I could be totally wrong about this but I reckon there's something in it. I'll have a go and then we can all laugh about it afterwards - will need to get someone to take a photo.

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True Wind at water level is supposed to be 0 knots

Looking at the way the sand blows off the ground at SP it appears this supposition is incorrect.

The wind over the sand spit and water at Sandy Pt is more laminar than some other places but the basic principle still holds I think that it is less close to the surface. Wow, the way the surface water gets ripped into spray on the big days makes you wonder what the wind speed is at 3m above the surface!

It's a matter of scale as to how close you have to be to a surface for the wind to drop to zero. Closer than the height of a grain of sand it seems. Part of the deal with windblown sand is the strong vertical velocity gradient. Some sort of curve ball effect holds them up for a while until they get closer to the speed of the wind and fall down. And then there's the avalanche effect going on. And electrostatics as well. It's pretty busy down there.

http://www.weru.ksu.edu/new_weru/multimedia/movies/dust003.mpg