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Roo said..

Sparky said..
and that is seabreezer Roo on the left holding the board, and Pascal Maka in the middle

Someone mention Roo! Looks like a sail on a rig on top of a truck, wonder what that does? The twist was a byproduct of trying to reduce pitching moment in the sail. On a windy day when the trailing edge of the tip was pushed up with a stick the pitching reduced as the center of pressure moved down in the sail, the numbers being spat out by the computer showed it. Gaastra were the first to take advantage of it, they also owned Rushwind at the time. Here's a double surface wingsail we were also testing at the time.

You wanted reduce pitching moment because lowering COP will raised nose from water or you wanted reduce heeling moment to enable sailor to hold more power?
(basically its the same ,lower COP reduce pitching and heeling at the same time)

What is with wing and windsurfing,why wing is still not replace today race sail and why Gaastra do not go in production?
I never sail with wing,how it feels on gusty condition if it has not floppy leech/head.
Is it possible at all to sail with so rigid stuff?

Hi TurnBackTime, It's good to hear from a new comer who has such confidence and knowledge of sail dynamics. What is your background? Are you a designer? From a yachting background?
Maybe you are a nocturnal creature (a possum?) who likes to post on seabreeze at 3.39am Brisbane time?

Twist just looks cool, it changes the two dimensional bit of material & plastic we roll out into a living breathing thing

Sparky, its not me. Im no possum. 3.11am is my morning wake up call. Time for a quick read what the West Oz crew n Imax1 has been up to.

I'm never up at 3:11 am , I'm in bed at 9:00. I do however have a 3 am piss. But I can do that sleeping. In the toilet not the bed . But that could change any time soon , it's been close since I can remember

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Sparky said..
Hi TurnBackTime, It's good to hear from a new comer who has such confidence and knowledge of sail dynamics. What is your background? Are you a designer? From a yachting background?
Maybe you are a nocturnal creature (a possum?) who likes to post on seabreeze at 3.39am Brisbane time?

I have relative in Brisbane,I know to be in Qeensland 5months per year,but I am from Sylt,posts from different time zone.

I studied aerodynamics,I am not sail desinger(wish I am !!!)When younger, sail on laser,470 ,tornado but windsurfing is my passion.
Windsurfing is like sex or drug ,ones try -never stop.


Are there any of members sail desinger?
It would be nice to hear or talk abot sails desing etc..

(boards.uk is in my current zone,but I dont know what is happening with new forum,looks like unfinished version)

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mkseven said..



Twist just looks cool, it changes the two dimensional bit of material & plastic we roll out into a living breathing thing

I think you might have it there.

I allways admire to profi wsurfes what differences they are able to feel!!
He feels open or close clew system!( 2:00min)
Have someone of you this sail,if sail becom more power,open clew system gives more tight leech or give foot more shape/belly ?

I had similar clew system on gaastras, you could pull tension on it which tightened lower leach & yes it was noticeable.

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mkseven said..
I had similar clew system on gaastras, you could pull tension on it which tightened lower leach & yes it was noticeable.

But he said that he open clew system to have more power on light winds.
How open system gives tighter leech?this is not logical to me.

Sometime, way back in the early '80's as far as I can recall, I watched with fascination as a bloke called Lindsay Cunningham walked down the Sandy Point speed spit holding a long pole (with difficulty) with anemometers and wind vanes attached at a number of intervals up it's length. Being the curious type, I asked him what he was doing and why. He replied that he was trying to measure the wind direction and strength at various heights over the spit at the waters edge, so as to determine how much static twist to build into the wing for Yellow Pages.

He obviously thought it was worth doing. A year or two later, Yellow Pages broke the World Speed Sailing Record with it's rigid asymmetrical wing. (Which stood for over10 years) They later destroyed the boat when it hit an estimated 51 knots moments before flipping and disintegrating in an unexpectedly wild squall.

Apparently, this estimate of their top speed (from counting frames from a movie camera) gave them the confidence that they could rebuild the boat as Maquarrie Innovation, and that it should be able to achieve 50 knots plus (which it eventually did, but not until the outright record was taken even higher by others. (Kiter?)

I took quite a few pics of the MI wing to try to observe the extent of the twist built in. It actualy was not very much compared with a modern windsurfing sail.

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TurnBackTime said..

mkseven said..
I had similar clew system on gaastras, you could pull tension on it which tightened lower leach & yes it was noticeable.

But he said that he open clew system to have more power on light winds.
How open system gives tighter leech?this is not logical to me.

Likely it helps him when pumping. The pryde system there looks like it only has open or closed, i never paid attention to them at the beach but the gaastra system you could adjust velcro through loop, i preferred having it just done up with little tension. The whole concept was extra unnecessary thing to set up.

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mkseven said..

TurnBackTime said..

mkseven said..
I had similar clew system on gaastras, you could pull tension on it which tightened lower leach & yes it was noticeable.

But he said that he open clew system to have more power on light winds.
How open system gives tighter leech?this is not logical to me.

Likely it helps him when pumping. The pryde system there looks like it only has open or closed, i never paid attention to them at the beach but the gaastra system you could adjust velcro through loop, i preferred having it just done up with little tension. The whole concept was extra unnecessary thing to set up.

They are a pain in the ass , the year after they dropped that idea . Gimmic ???

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sailquik said..
Sometime, way back in the early '80's as far as I can recall, I watched with fascination as a bloke called Lindsay Cunningham walked down the Sandy Point speed spit holding a long pole (with difficulty) with anemometers and wind vanes attached at a number of intervals up it's length. Being the curious type, I asked him what he was doing and why. He replied that he was trying to measure the wind direction and strength at various heights over the spit at the waters edge, so as to determine how much static twist to build into the wing for Yellow Pages.

He obviously thought it was worth doing. A year or two later, Yellow Pages broke the World Speed Sailing Record with it's rigid asymmetrical wing. (Which stood for over10 years) They later destroyed the boat when it hit an estimated 51 knots moments before flipping and disintegrating in an unexpectedly wild squall.

Apparently, this estimate of their top speed (from counting frames from a movie camera) gave them the confidence that they could rebuild the boat as Maquarrie Innovation, and that it should be able to achieve 50 knots plus (which it eventually did, but not until the outright record was taken even higher by others. (Kiter?)

I took quite a few pics of the MI wing to try to observe the extent of the twist built in. It actualy was not very much compared with a modern windsurfing sail.

Interesting! I never realised that MI had built-in twist.

Your observation that the twist in MI was small compared to a windsurfer sail makes perfect sense since the maths and geometry show that wind shear becomes less important as boatspeed increases.

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Chris 249 said..

sailquik said..
Sometime, way back in the early '80's as far as I can recall, I watched with fascination as a bloke called Lindsay Cunningham walked down the Sandy Point speed spit holding a long pole (with difficulty) with anemometers and wind vanes attached at a number of intervals up it's length. Being the curious type, I asked him what he was doing and why. He replied that he was trying to measure the wind direction and strength at various heights over the spit at the waters edge, so as to determine how much static twist to build into the wing for Yellow Pages.

He obviously thought it was worth doing. A year or two later, Yellow Pages broke the World Speed Sailing Record with it's rigid asymmetrical wing. (Which stood for over10 years) They later destroyed the boat when it hit an estimated 51 knots moments before flipping and disintegrating in an unexpectedly wild squall.

Apparently, this estimate of their top speed (from counting frames from a movie camera) gave them the confidence that they could rebuild the boat as Maquarrie Innovation, and that it should be able to achieve 50 knots plus (which it eventually did, but not until the outright record was taken even higher by others. (Kiter?)

I took quite a few pics of the MI wing to try to observe the extent of the twist built in. It actualy was not very much compared with a modern windsurfing sail.

Interesting! I never realised that MI had built-in twist.

Your observation that the twist in MI was small compared to a windsurfer sail makes perfect sense since the maths and geometry show that wind shear becomes less important as boatspeed increases.

Purpose of twist in windsurifng is reduce power in upper part of sail,lowerd COP,thus sail more controllable and reducing catapults ,stable etc etc....

You are talking all the time that twist is here to adapt angle of attack of upper part of sail to apparent wind, because of wind shear,but if you do that, then you will increase power in upper part! Now you have opposite effect !

Twist reduce power ,not increase ,in windsurfing.

In proper tunnning sail ,top one or two panels are aligned directly into apparent wind,angle of attcak is 0,no lift,reduce induce drag and lowerd COP.

Roo nicely explain why twist was introduced.

If it was just about reducing power in the head of the sail, a battenless pinhead would be the best sail. If having no angle of attack was always better in windsurfing then the Raceboard sails would not have tight leaches. Raceboard sail designers are NOT morons - they have tight leaches because they work in some situations.

Twist for control can work hand-in-hand with twist for wind shear. There is no reason that twist cannot BOTH work for control and to reduce drag by allowing for wind shear.

I'm not sure where you sail, but many of us aren't sailing around trying to stop catapulting and increasing stability all the time. Lots of us want more power a lot of the time.

I think you'll also find that Sailquik has proven his knowledge of high-speed sail trim on the water, time and time again.

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Imax1 said..

mkseven said..

TurnBackTime said..

mkseven said..
I had similar clew system on gaastras, you could pull tension on it which tightened lower leach & yes it was noticeable.

But he said that he open clew system to have more power on light winds.
How open system gives tighter leech?this is not logical to me.

Likely it helps him when pumping. The pryde system there looks like it only has open or closed, i never paid attention to them at the beach but the gaastra system you could adjust velcro through loop, i preferred having it just done up with little tension. The whole concept was extra unnecessary thing to set up.

They are a pain in the ass , the year after they dropped that idea . Gimmic ???

I agree with you.
dont worry for few years they will bring back again,in the name of "big aerodynamics improvements".
they are waiting people to forget ,it must take a few years..
(just like in boards shape,pin tail,fish tail.....cycle)


marketing stuff

One of the best designers of Windsurfing riggs once said : " Anything above 3 meters is just a pop-off valve ..."

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NelsonFoils said..
One of the best designers of Windsurfing riggs once said : " Anything above 3 meters is just a pop-off valve ..."

For sure,but some people dont understand that...

His name is?

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NelsonFoils said..
One of the best designers of Windsurfing riggs once said : " Anything above 3 meters is just a pop-off valve ..."

Righto then you two, please explain how i fit external turbo wastegate on a sail?

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olskool said..

Righto then you two, please explain how i fit external turbo wastegate on a sail?

(When you lift up gas pedal, throttle butterfly valve close(only on gasoline engine) ,then air with cca 1bar stay trap beetwen butterfly and compressor wheel.Then this air goes backward in compressor wheel which is still spinning because of inertia,and make nice sound but also slow down wheels in (compressor-turbine)
Or you can put blow off valve between compressor and throttle valve,now blow off release traped air ,stop air to go backwards in compressor wheel and now wheels are no more slow down so much...


Maybe you can cut hole on second panel (15cm radius) to release gust pressure!

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TurnBackTime said..

NelsonFoils said..
One of the best designers of Windsurfing riggs once said : " Anything above 3 meters is just a pop-off valve ..."

For sure,but some people dont understand that...

His name is?

Would you care to explain why what we are failing to understand, using (1) aerodynamic theory and (2) showing real-life examples?

So far your entire justification has been based on your claim that lowering the COP makes you faster. That claims rests on the assumption that everyone always sails around generating as much righting moment as they can. That's just not correct. That would only be true if, for example, every sailor was always carrying the biggest sail they could possible carry and is always maxed out with it. That's not what happens. We are often sailing around without being fully powered up.

We also know that in dinghies and yachts, people try to induce extra twist in light winds. They are doing that when they are underpowered. If your claim was correct, they wouldn't need to do that. Are you claiming that all the dinghy and yacht sailors are morons who are sailing wrongly?

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TurnBackTime said..

olskool said..

Righto then you two, please explain how i fit external turbo wastegate on a sail?

(When you lift up gas pedal, throttle butterfly valve close(only on gasoline engine) ,then air with cca 1bar stay trap beetwen butterfly and compressor wheel.Then this air goes backward in compressor wheel which is still spinning because of inertia,and make nice sound but also slow down wheels in (compressor-turbine)
Or you can put blow off valve between compressor and throttle valve,now blow off release traped air ,stop air to go backwards in compressor wheel and now wheels are no more slow down so much...


Maybe you can cut hole on second panel (15cm radius) to release gust pressure!

Blow off valve ain't a wastegate, but i suppose both could be considered pop off valves in generic terms.

& so the marketing goes re blow off valves but in truth they are as much of a gimmick & more of a pain in ass than the clew closure system.

Digression aside you can't compare yachts, Yellow pages/MI/Sailrocket to shortboard sail (not referring to sailquiks post which makes sense).

Chris what is the thinking behind boaties inducing twist in light winds & what point of sail are they doing this?

(@Chris I said everything in my past posts,I will not repeat myself...)


One more evidence why twist is so important in windsurfing sail;

Here is Neilpryde(Robert Stroj& Bjorn Dunkerbeck) attempt to bulid wing sail:

link:
www.wsurf.net/docs/Speedseeker.pdf

in short:

1)
First they try with a light foam that was moulded into a full wing-like shape and then given a laminated coating.

Robert Stroj words ;
"All this particular prototype really demonstrated was that windsurfing sails require a high degree of twist, and this foam wing simply couldn't accommodate this, so we soon realised that it was almost unsailable"

2)
Then they try with fully double soft surface wing...hoping they will increase twist/make sail sailable

Robert Stroj words;
"Our first prototypes were fully double surfaced, but we quickly learned that these too lacked the necessary degree of twist that a windsurfing sail requires. Essentially the two surfaces of the sail began to fight against one another once the sail was in motion and this restricted the natural twist of the sail and began causing drag"

3)
Then they decide to go on 25-30% double surface leading edge(similar with today race sail),rest area is conventional sail..

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Chris 249 said..
If it was just about reducing power in the head of the sail, a battenless pinhead would be the best sail. If having no angle of attack was always better in windsurfing then the Raceboard sails would not have tight leaches. Raceboard sail designers are NOT morons - they have tight leaches because they work in some situations.

Twist for control can work hand-in-hand with twist for wind shear. There is no reason that twist cannot BOTH work for control and to reduce drag by allowing for wind shear.

I'm not sure where you sail, but many of us aren't sailing around trying to stop catapulting and increasing stability all the time. Lots of us want more power a lot of the time.

I think you'll also find that Sailquik has proven his knowledge of high-speed sail trim on the water, time and time again.

Sail-trim is everything - be it big boats or little ones...It is not just "reducing power in the head" -> it is to dynamically-react-to-the-current-gust in a way which allows the sailor to maintain efficient control of the rig.In the case of windsurfing -generally speaking, you want to shed some of that power -> if you can keep yourself locked-in, then you can will go faster.

You could choose to sheet-in/out, but most people's reaction time is not fast enough (they dont "feel the gust").... The result is that a gust pulls you onto your toes (a lull rocks you onto your heels), and thus you are not as fast as you be otherwise.

Twist is another way to have reaction control.

You do want to have static-twist for height based wind-sheer - as explained previously, it isn't clear whether this is significant or not. ... it definitely depends on the venue... somewhere like Sandy Point probably has wind almost down to the water level, vs elsewhere it is likely to be higher off of the water-surface.

You also need to build in dynamic-twist so that gust-reaction can occur. The panel-layout needs to suit the mast-reaction due to wing-loading, so that the sail-deformation works in your favour... ie: so that gusts cause the CoE to reduce-sail-lift from above the boom and/or move the CoE forward/down to counteract the corresponding increase in sail power. In either case, the sail needs to comeback to optimal when the gust has subsided, and thus allow you to be stable and locked-in.

Alternatively, you could have the power move backward along the boom so that it automatically causes you to sheet-out. Tat is how we used to build windsurfing sails, but mostly have moved away from that.

Either way you want shed some of that extra power to keep your body stable -> if you can keep locked-in, then you get to use a bigger sail for the same wind-speed and thus have more *usable power* [ and more apparent-wind when hitting top speed ].

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TurnBackTime said..
(@Chris I said everything in my past posts,I will not repeat myself...)

One more evidence why twist is so important in windsurfing sail;

Here is Neilpryde(Robert Stroj& Bjorn Dunkerbeck) attempt to bulid wing sail:

link:
www.wsurf.net/docs/Speedseeker.pdf

in short:

1)
First they try with a light foam that was moulded into a full wing-like shape and then given a laminated coating.

Robert Stroj words ;
"All this particular prototype really demonstrated was that windsurfing sails require a high degree of twist, and this foam wing simply couldn't accommodate this, so we soon realised that it was almost unsailable"

2)
Then they try with fully double soft surface wing...hoping they will increase twist/make sail sailable

Robert Stroj words;
"Our first prototypes were fully double surfaced, but we quickly learned that these too lacked the necessary degree of twist that a windsurfing sail requires. Essentially the two surfaces of the sail began to fight against one another once the sail was in motion and this restricted the natural twist of the sail and began causing drag"

3)
Then they decide to go on 25-30% double surface leading edge(similar with today race sail),rest area is conventional sail..

You didn't refer to "everything" in your earlier posts. You completely ignored the effects of induced drag, spanload, the fact that a lower COP and lower catapulting are irrelevant to many of us who are not fully powered up all the time, and other factors.

Referring to Bjorn and a speed sail is misleading, because what works for speed sails doesn't work for all sails. Speed sails don't accelerate from low speeds. They don't go upwind. They don't have to be used at the bottom of their range much. Bjorn also sails very differently from the usual sailor - I know, I was his training partner at a world championships when he was a kid. Even around that time he used lots of twist, but that's because he sails in a very different way to most windsurfers.

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mathew said..


Sail-trim is everything - be it big boats or little ones...It is not just "reducing power in the head" -> it is to dynamically-react-to-the-current-gust in a way which allows the sailor to maintain efficient control of the rig.In the case of windsurfing -generally speaking, you want to shed some of that power -> if you can keep yourself locked-in, then you can will go faster.

You could choose to sheet-in/out, but most people's reaction time is not fast enough (they dont "feel the gust").... The result is that a gust pulls you onto your toes (a lull rocks you onto your heels), and thus you are not as fast as you be otherwise.

Twist is another way to have reaction control.

You do want to have static-twist for height based wind-sheer - as explained previously, it isn't clear whether this is significant or not. ... it definitely depends on the venue... somewhere like Sandy Point probably has wind almost down to the water level, vs elsewhere it is likely to be higher off of the water-surface.

You also need to build in dynamic-twist so that gust-reaction can occur. The panel-layout needs to suit the mast-reaction due to wing-loading, so that the sail-deformation works in your favour... ie: so that gusts cause the CoE to reduce-sail-lift from above the boom and/or move the CoE forward/down to counteract the corresponding increase in sail power. In either case, the sail needs to comeback to optimal when the gust has subsided, and thus allow you to be stable and locked-in.

Alternatively, you could have the power move backward along the boom so that it automatically causes you to sheet-out. Tat is how we used to build windsurfing sails, but mostly have moved away from that.

Either way you want shed some of that extra power to keep your body stable -> if you can keep locked-in, then you get to use a bigger sail for the same wind-speed and thus have more *usable power* [ and more apparent-wind when hitting top speed ].

Sure, I agree that using leach twist for gust response works well, and I never said it didn't. I've gone to sailmakers for custom sails myself, and specified a bigger roach for better gust response.

What I'm objecting to is that TBT is claiming that twist has no other purpose. We often want it to allow for wind shear.

I'm actually fairly sure that TBT and Wing 11 are probably just the sock puppets of our aggressive wingsail maker, the one who insults and abuses all the other sailmakers.

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mkseven said..

Digression aside you can't compare yachts, Yellow pages/MI/Sailrocket to shortboard sail (not referring to sailquiks post which makes sense).

Chris what is the thinking behind boaties inducing twist in light winds & what point of sail are they doing this?

Yes, the emphasis you put on various aspects of trim does change enormously between boats and boards, but the aerodynamics are the same.

In boats twist is induced upwind and down in light airs. It's done because boaties are very aware that the wind is normally stronger higher up the rig, which shifts the vector of the apparent wind aft at the top of the mast. If you don't twist to sail to allow for the different apparent wind angle up at the masthead, the head will be over-sheeted or the foot will be under-sheeted. We notice this even in Laser Radials, which have a mast about 5m long.

Boats also use more twist to allow for choppy water, partly because their mast tips go back and forth as they go over waves, and that further affects the windspeed over the top of the rig and therefore the apparent wing angle and the required twist.

The ideal twist can vary probably 10 degrees during one race. If it's light, choppy and you're trying to accelerate you will twist more. If you get into flat water, in medium breeze and you're trying to point, you will have the leach poking back to windward. Two minutes later you may be over-powered and going for speed rather than trying to point high so you'll have the leach flopping to leeward. And on top of that the amount of wind shear can vary day by day.

I tend to think many windsurfers aren't aware of it because they tend to be interested more in top-end speed on a reach in good breeze, rather than trying to cater for a wide range of windspeeds, boat or board speeds and angles.

How can I be socket puppet of "wingsails maker" if I just said that wing is unsailable because it is too stiff,no twist,no control ,nothing...???????????????????????
How much is your IQ,if you make these conclusion!

Keep talking about foken wind shear and leave me alone

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olskool said..

NelsonFoils said..
One of the best designers of Windsurfing riggs once said : " Anything above 3 meters is just a pop-off valve ..."

Righto then you two, please explain how i fit external turbo wastegate on a sail?

Could you imagine if sails made the same noise , wooo,woooo,wooo. We could have FULLY SIK sails. All we would then need is a sound system wiff sub woofers , ( what do u call a small dog ? ...a sub woofer ) , that echo for miles like with the wake boarding crew. Or just buy a jetski .