Select to expand quoteMHSA said..
Fortunately the aerodynamicists that worked on the americas cup winning solid wings knew the importance of trailing egde twist to enable a water craft to smash top speed.
And I thought this was the speed forum.
In windsurfing not enough downhaul to match the designed luff curve and twist is so slow.
Its often over done in windsurfing. ..If the top cam looks flat and not producing any curve at all, what's the point of putting it there? ..Neither the America's Cup yachts nor any other speed focused sail craft exhibit anything like the amount of washout some windsurfers are using.
Select to expand quotePhromsky said..MHSA said..
Fortunately the aerodynamicists that worked on the americas cup winning solid wings knew the importance of trailing egde twist to enable a water craft to smash top speed.
And I thought this was the speed forum.
In windsurfing not enough downhaul to match the designed luff curve and twist is so slow.
Its often over done in windsurfing. ..If the top cam looks flat and not producing any curve at all, what's the point of putting it there? ..Neither the America's Cup yachts nor any other speed focused sail craft exhibit anything like the amount of washout some windsurfers are using.
There's a pretty strong surface gradient in windsurfing because the sail is right next to the water, so the wind speed (and thus apparent wind direction) changes rapidly up the mast.
The larger sail craft don't have their masts start right on the water where this effect is large...
Select to expand quoteaeroegnr said..Phromsky said..MHSA said..
Fortunately the aerodynamicists that worked on the americas cup winning solid wings knew the importance of trailing egde twist to enable a water craft to smash top speed.
And I thought this was the speed forum.
In windsurfing not enough downhaul to match the designed luff curve and twist is so slow.
Its often over done in windsurfing. ..If the top cam looks flat and not producing any curve at all, what's the point of putting it there? ..Neither the America's Cup yachts nor any other speed focused sail craft exhibit anything like the amount of washout some windsurfers are using.
There's a pretty strong surface gradient in windsurfing because the sail is right next to the water, so the wind speed (and thus apparent wind direction) changes rapidly up the mast.
The larger sail craft don't have their masts start right on the water where this effect is large...
Have you measured it?
Select to expand quotesheddweller said..aeroegnr said..Phromsky said..MHSA said..
Fortunately the aerodynamicists that worked on the americas cup winning solid wings knew the importance of trailing egde twist to enable a water craft to smash top speed.
And I thought this was the speed forum.
In windsurfing not enough downhaul to match the designed luff curve and twist is so slow.
Its often over done in windsurfing. ..If the top cam looks flat and not producing any curve at all, what's the point of putting it there? ..Neither the America's Cup yachts nor any other speed focused sail craft exhibit anything like the amount of washout some windsurfers are using.
There's a pretty strong surface gradient in windsurfing because the sail is right next to the water, so the wind speed (and thus apparent wind direction) changes rapidly up the mast.
The larger sail craft don't have their masts start right on the water where this effect is large...
Have you measured it?
I haven't but I would think Ezzy has? 
Select to expand quoteEzzy said..
How does twist stop the upper part of the sail from stalling?The wind angle at the top of the sail is different than at the bottom of the sail. This difference comes from a wind gradient that exists and causes wind strength to be less nearer the surface of the water and stronger higher up. So, the bottom of the sail experiences more apparent wind, which comes from the direction the board is travelling. The top of the sail, on the other hand, "feels" more of the true wind direction. If the top of the sail were set with no twist the flow of air would not stay attached to the surface of the sail and the flow would stop or "stall which would then have detrimental effects over the entire sail. In a sentence, a sail that does not twist is less aerodynamically efficient.
www.ezzy.com/rig-support/ezzy-basic-sail-design-theory/
I've never had a 4 cam sail destroy itself from bad sail rotation. In my experience with various sail brands, if you rig to the correct downhaul and are prepared to put in the time and effort to adjust the length of the cams either using spacers and even grinding the back of the cam if too long, to suit the bend radius of mast you use, then a 4 cam sail will rotate well.
Select to expand quoteaeroegnr said..sheddweller said..aeroegnr said..Phromsky said..MHSA said..
Fortunately the aerodynamicists that worked on the americas cup winning solid wings knew the importance of trailing egde twist to enable a water craft to smash top speed.
And I thought this was the speed forum.
In windsurfing not enough downhaul to match the designed luff curve and twist is so slow.
Its often over done in windsurfing. ..If the top cam looks flat and not producing any curve at all, what's the point of putting it there? ..Neither the America's Cup yachts nor any other speed focused sail craft exhibit anything like the amount of washout some windsurfers are using.
There's a pretty strong surface gradient in windsurfing because the sail is right next to the water, so the wind speed (and thus apparent wind direction) changes rapidly up the mast.
The larger sail craft don't have their masts start right on the water where this effect is large...
Have you measured it?
I haven't but I would think Ezzy has? Ezzy said..
How does twist stop the upper part of the sail from stalling?The wind angle at the top of the sail is different than at the bottom of the sail. This difference comes from a wind gradient that exists and causes wind strength to be less nearer the surface of the water and stronger higher up. So, the bottom of the sail experiences more apparent wind, which comes from the direction the board is travelling. The top of the sail, on the other hand, "feels" more of the true wind direction. If the top of the sail were set with no twist the flow of air would not stay attached to the surface of the sail and the flow would stop or "stall which would then have detrimental effects over the entire sail. In a sentence, a sail that does not twist is less aerodynamically efficient.
www.ezzy.com/rig-support/ezzy-basic-sail-design-theory/
Well yes, it does occur.
But how much? And what are the variables?
I would argue that topography and water state are going to be hugely impactful of the effect, and so the amount of twist needed to counter this specific phenomenon will be very variable. As such using more or less twist( reducing or increasing the downhaul) is completely valid, which is kinda what the guy was saying before.
Select to expand quoteJohn340 said..
I've never had a 4 cam sail destroy itself from bad sail rotation. In my experience with various sail brands, if you rig to the correct downhaul and are prepared to put in the time and effort to adjust the length of the cams either using spacers and even grinding the back of the cam if too long, to suit the bend radius of mast you use, then a 4 cam sail will rotate well.
For John 340. ..The measurements on the sail are often wrong, and in a very significant margin! ..But anyway, I'm normally rigging all my sails within a 2 centimetre margin. My favourite sail size is 7.0 with 4 cams, and depending on the wind I'll normally rig between 30% and 50% washout in the top few panels. And I definitely prefer the feeling of the sail this way.
On the occasions when I've rigged washout all the way into the head the sail has felt worse for it to me - twitchy, less stable and underpowered - And actually if you turn the sail over so that its camber is uppermost and watch what happens to the leading when you rig this amount of downhaul you'll see the curve in the leading edge collapsing centimetre by centimetre which is bound to be killing the bottom end of the sail.
The two sails I'm currently most irritated with (7.0 & 6.8) were bought new by me over the internet just a few weeks apart and from different manufacturers, the second because I was really pissed off with the first, and I actually got unlucky with both of them! ..they were both bad news right out of the bag and rigging first time on my lawn, and ultimately with all spacers removed. ..Buying a brand new sail and then having to grind the back of a cam/s down is too much, in fact its ridiculous!
Select to expand quotePhromsky said..John340 said..
I've never had a 4 cam sail destroy itself from bad sail rotation. In my experience with various sail brands, if you rig to the correct downhaul and are prepared to put in the time and effort to adjust the length of the cams either using spacers and even grinding the back of the cam if too long, to suit the bend radius of mast you use, then a 4 cam sail will rotate well.
For John 340. ..The measurements on the sail are often wrong, and in a very significant margin! ..But anyway, I'm normally rigging all my sails within a 2 centimetre margin. My favourite sail size is 7.0 with 4 cams, and depending on the wind I'll normally rig between 30% and 50% washout in the top few panels. And I definitely prefer the feeling of the sail this way.
On the occasions when I've rigged washout all the way into the head the sail has felt worse for it to me - twitchy, less stable and underpowered - And actually if you turn the sail over so that its camber is uppermost and watch what happens to the leading when you rig this amount of downhaul you'll see the curve in the leading edge collapsing centimetre by centimetre which is bound to be killing the bottom end of the sail.
The two sails I'm currently most irritated with (7.0 & 6.8) were bought new by me over the internet just a few weeks apart and from different manufacturers, the second because I was really pissed off with the first, and I actually got unlucky with both of them! ..they were both bad news right out of the bag and rigging first time on my lawn, and ultimately with all spacers removed. ..Buying a brand new sail and then having to grind the back of a cam/s down is too much, in fact its ridiculous!
You are just describing the exact reason you have rotation problems. Forget loose leech for a second, and focus on mast bend vs luff curve.
All that depth forward when you have with sail flipped over isn't good.
It just means you have no where near enough mast bend to match the designed luff curve. Not enough mast bend for the luff curve kills the rotation and as you say, eventually destroys the sails.
The sail wasn't designed to with that much depth at the cams in mind. Maybe you like it like that, and that's fine. But as long as you keep rigging like that you'll keep damaging sails.
You can't really fight the designed luff curve of a cammed sail.
If you want cams with a tighter leech why not try a foil sail or go back to a race board sail?
Rather than under downhauling a race sail made with ****loads of downhaul, bend and loose leech in mind.
Select to expand quoteMHSA said..Phromsky said..John340 said..
I've never had a 4 cam sail destroy itself from bad sail rotation. In my experience with various sail brands, if you rig to the correct downhaul and are prepared to put in the time and effort to adjust the length of the cams either using spacers and even grinding the back of the cam if too long, to suit the bend radius of mast you use, then a 4 cam sail will rotate well.
For John 340. ..The measurements on the sail are often wrong, and in a very significant margin! ..But anyway, I'm normally rigging all my sails within a 2 centimetre margin. My favourite sail size is 7.0 with 4 cams, and depending on the wind I'll normally rig between 30% and 50% washout in the top few panels. And I definitely prefer the feeling of the sail this way.
On the occasions when I've rigged washout all the way into the head the sail has felt worse for it to me - twitchy, less stable and underpowered - And actually if you turn the sail over so that its camber is uppermost and watch what happens to the leading when you rig this amount of downhaul you'll see the curve in the leading edge collapsing centimetre by centimetre which is bound to be killing the bottom end of the sail.
The two sails I'm currently most irritated with (7.0 & 6.8) were bought new by me over the internet just a few weeks apart and from different manufacturers, the second because I was really pissed off with the first, and I actually got unlucky with both of them! ..they were both bad news right out of the bag and rigging first time on my lawn, and ultimately with all spacers removed. ..Buying a brand new sail and then having to grind the back of a cam/s down is too much, in fact its ridiculous!
You are just describing the exact reason you have rotation problems. Forget loose leech for a second, and focus on mast bend vs luff curve.
All that depth forward when you have with sail flipped over isn't good.
It just means you have no where near enough mast bend to match the designed luff curve. Not enough mast bend for the luff curve kills the rotation and as you say, eventually destroys the sails.
The sail wasn't designed to with that much depth at the cams in mind. Maybe you like it like that, and that's fine. But as long as you keep rigging like that you'll keep damaging sails.
You can't really fight the designed luff curve of a cammed sail.
I understand perfectly well what you are saying about mast bend versus luff curve. That maybe the mast was too stiff, but I bought the brands recommended (top end) mast with the sail. ..No doubt a PWA racer can go handpick his preferred mast, but an ordinary guy can't.
..As a matter of coincidence I was just watching Dunkerbeck go down that strip in Namibia. And it was really quite noticeable that he had a lot of twist off going on, but at the same time he also had plenty of curve in his leading edge and all the way up to his top cam.
But anyway there's a lot more to this issue than mast bend alone. The quality of engineering/manufacture in the batten/cam interface is not pretty, its not anything an engineer worth his salt would be proud of. ..Meanwhile I've discovered the stiffness of the main batten can also be an aggravating issue in respect to rotation, ..and as a matter of fact is entirely different in the two iterations of this sail that I have, and both are 7.0's - In the newer problem sail the front portion of the main batten (before it broke) was driving the main cam on to the mast much harder than in the earlier iteration of the sail.
..And as I've said earlier in this thread I always thoroughly enjoyed sailing with the older version of the sail and it always rotated for me as well as I expected - As evidenced by the fact my best hour (19.2 knots) was with it and included approx. 40 gybes, I fell in one of them at the 45 minute mark and scrambled back on fast as I could. ..But the point is what I just described would have been a physical impossibility with the newer iteration of the sail.
It's great you bought the manufactures best specified mast.
But it's wasted and actually the suboptimal mast to choose if you aren't bending it to the manufacturers specification for a given sail.
And bending it properly in a race sails case means a loose leech
We're talking about 1 - 2 cms of downhaul here ?????? ..and the sail doesn't actually come with any instructions at all
Select to expand quotePhromsky said..
and the sail doesn't actually come with any instructions at all
If you need written instructions to rig and tune a race sail for optimum performance you are probably better off saving some $$$ and purchasing a freerace 2-3 cam sail and enjoy yourself. Rather than trying to reinvent the wheel with gear that doesn't suit your needs. Reckon you could improve the hour PB if you did
The OP doesn't want a solution to his problem.He is not listening, he just wants to rant and blow off some steam.
Select to expand quoteMr Keen said..Phromsky said..
and the sail doesn't actually come with any instructions at all
If you need written instructions to rig and tune a race sail for optimum performance you are probably better off saving some $$$ and purchasing a freerace 2-3 cam sail and enjoy yourself. Rather than trying to reinvent the wheel with gear that doesn't suit your needs. Reckon you could improve the hour PB if you did
Has your hour got 40+ gybes in mate? ..as in forced to gybe every 700 metres? ..and I'm 67 and only 66 kilos into the bargain
Select to expand quotePhromsky said..
Has your hour got 40+ gybes in mate? ..as in forced to gybe every 700 metres? ..and I'm 67 and only 66 kilos into the bargain
You do realise ....
- you are arguing with people older than you, whom have no problem with cams
- arguing with people whom hold distance records
- arguing with some of the fastest sailors on the planet, for their age bracket
- some even have input into sail designs to make them faster and easier to use
... ?
"I am intrigued by your expert opinion. Can I subscribe to your newsletter?"
Just to back up Mathew.
Here's my hour and distance attempt as a 75 year old.
www.gpsteamchallenge.com.au/sailor_session/show?date=2020-01-21&team=2
Admitedly good conditions and 1km runs. Only 34 gybes with two stuffed up
My biggest sail is a 6.6 koncept, rotation is great when set properly.
For Mathew, I have stated exactly what I believe to be true in accordance with my experience of 37 years windsurfing. I also have relevant knowledge of aerodynamics on account of being a pilot. And so I stand by every single word I've written above.
..And its been very well known for a very long time that camber induced sails (especially 4 cams) often exhibit poor rotation or worse.
Select to expand quotePhromsky said..
For Mathew, I have stated exactly what I believe to be true in accordance with my experience of 37 years windsurfing. I also have relevant knowledge of aerodynamics on account of being a pilot. And so I stand by every single word I've written above.
..And its been very well known for a very long time that camber induced sails (especially 4 cams) often exhibit poor rotation or worse.
That knowledge of aerodynamics isn't really as helpful as you think unless you have designed and tested aircraft. Pretty much every aircraft ever built is compromised aerodynamically for any number of reasons, you make one thing better then something is worse etc. e.g. a shape with less drag may weigh more or bend more, a better shapes may have undesirable control issues, etc endless permutations.
The same with sails, 4 cams slalom races sails are designed to be used in slalom boards on a slalom course, not even on a foil. Foil race sails typically have a higher aspect ratio and less twist for a reason! Its a good example, because a foil race sail, can handle a stiffer mast setup with a tighter leach, for better performance when apparent wind speed is high. A low aspect ratio can give better acceleration in combination with a railed slalom board, and the twist can assist in giving the required softness so the nose sit where it needs to be.
You mentioned Bjorn at Luderitz, he is using sails cut especially for Luderitz style sailing, not traditional slalom sails suitable for open waters.
The cams are designed to be used in a very limited range of downhaul settings, as a compromise, some allow more tuning than others in respect of downhaul. I look to tune no more than .5cm in any direction with downhaul, and make other adjustments instead.
outhaul,
mast stiffness (shorter mast, softer top, softer mast)
choice of clew,
mast foot position.
boom height
harness line length etc.
fin size,
footstraps
Perhaps you should look at raceboard sails, with an adjustable downhaul, or maybe you should try a foil sail instead, or make/modify your own.
IMHO it all comes down to weight, we are already using exotic materials, if weight wasn't an issue other trimming adjustments might be possible without compromising the primary performance criteria.
Select to expand quotePhromsky said..
For Mathew, I have stated exactly what I believe to be true in accordance with my experience of 37 years windsurfing. I also have relevant knowledge of aerodynamics on account of being a pilot. And so I stand by every single word I've written above.
..And its been very well known for a very long time that camber induced sails (especially 4 cams) often exhibit poor rotation or worse.
Facts are facts, your belief is not required. Stating an opinion, is not a stating a fact. You need to provide actual evidence to support your claim.
Select to expand quotePhromsky said..
For Mathew, I have stated exactly what I believe to be true in accordance with my experience of 37 years windsurfing. I also have relevant knowledge of aerodynamics on account of being a pilot. And so I stand by every single word I've written above.
..And its been very well known for a very long time that camber induced sails (especially 4 cams) often exhibit poor rotation or worse.
Hahahaha! Good one!
I know a few taxi drivers, no way do they know anything much about the design of cars, and bus drivers and train drivers.
Select to expand quotesheddweller said..Phromsky said..
For Mathew, I have stated exactly what I believe to be true in accordance with my experience of 37 years windsurfing. I also have relevant knowledge of aerodynamics on account of being a pilot. And so I stand by every single word I've written above.
..And its been very well known for a very long time that camber induced sails (especially 4 cams) often exhibit poor rotation or worse.
Hahahaha! Good one!
I know a few taxi drivers, no way do they know anything much about the design of cars, and bus drivers and train drivers.
Well, i'm quite sure a pilot by necessity must learn things about aerodynamics that the rest of us don't, but the aerodynamics that apply to a plane wing don't necessarily transfer across very well to a race sail. Theres more than a few key differences.
The way I figure it is this 
:
If I could afford to trash a light aircraft. As in saw off the starboard wing at the wing root (which would likely be around 7 to 8 square metres) and then attach a windsurf boom and a board to it. Meanwhile also teach a Silverback Gorilla to windsurf in a straight line. ..Then I could send him off sailing down that strip in Namibia with my aircraft wing and he just might beat Albeau.
In the same vein:
I think it would be eminently possible to make a flyable hang glider, out of two 7.0 windsurf sails bolted rigidly together at their bases and rigged with 4 degrees of washout at the tips. ..The best choice for such an experiment would have to be a similar pair of wide luff four cam sails. ..By far the most dangerous choice would be a pair of no cam sails.
..Ultimately I'm just saying that I believe the latter (hang glider concept) is actually feasible - "but I am absolutely not recommending it to anyone"
The thing is, flying and sailing/windsurfing are very similar indeed.
To me, windsurfing is vertically banked flight at the interface of two fluid mediums, one of my wings flies in air, whilst the other flies in water, and my board seals the interface.
Select to expand quotePhromsky said..
The way I figure it is this :
....
The thing is, flying and sailing/windsurfing are very similar indeed.
To me, windsurfing is vertically banked flight at the interface of two fluid mediums, one of my wings flies in air, whilst the other flies in water, and my board seals the interface.
I agree, pretty much every aircraft could be improved aerodynamically very easily, certainly any light aircraft, by simply changing the aspect ratio, and other tricks. Why isn't this done in the first place? Because the shape whatever it is a comprise to reach the required strength, rigidity (resistance to flutter), weight, stability and control, speed and probably a few other things I can't thing of right now...
A race sail, and they do vary is a compromise to achieve its design goal. Recently they have changed to be more foil friendly along with other features, as world cup level slalom no longer seems to exist 
If the goal was tunebilty or ability to pump, or the most grunt for smallest area, they would be designed differently. Instead the goal seems to be biggest sail that can sensibly controlled by an athlete, simple really.
Select to expand quotePhromsky said..
The way I figure it is this :
If I could afford to trash a light aircraft. As in saw off the starboard wing at the wing root (which would likely be around 7 to 8 square metres) and then attach a windsurf boom and a board to it. Meanwhile also teach a Silverback Gorilla to windsurf in a straight line. ..Then I could send him off sailing down that strip in Namibia with my aircraft wing and he just might beat Albeau.
No, he would not. Not even close.
Select to expand quotesheddweller said..Phromsky said..
The way I figure it is this :
If I could afford to trash a light aircraft. As in saw off the starboard wing at the wing root (which would likely be around 7 to 8 square metres) and then attach a windsurf boom and a board to it. Meanwhile also teach a Silverback Gorilla to windsurf in a straight line. ..Then I could send him off sailing down that strip in Namibia with my aircraft wing and he just might beat Albeau.
No, he would not. Not even close.
Aircraft wings are a lot more efficient than windsurf sails. A wing off almost any light training aircraft could easily be used to land sail at speeds far in excess of 60 knots. ..The limitation on water would be fin/foil cavitation, as it is for other sailing craft.
Select to expand quotePhromsky said..sheddweller said..Phromsky said..
The way I figure it is this :
If I could afford to trash a light aircraft. As in saw off the starboard wing at the wing root (which would likely be around 7 to 8 square metres) and then attach a windsurf boom and a board to it. Meanwhile also teach a Silverback Gorilla to windsurf in a straight line. ..Then I could send him off sailing down that strip in Namibia with my aircraft wing and he just might beat Albeau.
No, he would not. Not even close.
Aircraft wings are a lot more efficient than windsurf sails. A wing off almost any light training aircraft could easily be used to land sail at speeds far in excess of 60 knots. ..The limitation on water would be fin/foil cavitation, as it is for other sailing craft.
1- we are not landsailing when windsurfing on the water.
2 - if you place a "conventional" windsurf sail on a landyacht it will achieve a greater speed than it does on the water, not 60 knots but still quick(er) ( sail size will be highly influential to maximum speed, and I agree less twist the better)
3. Solid wing windsurf sails have been used in windsurfing, they have proven sub optimal compared to flexible membrane conventional sails. This is due to dynamic shape variation under load being proven superior to fixed geometry in our specific circumstances.
4. Your understanding of wing design is informative( to you) but it is misleading you in terms of sail design, there are similarities, but there also (big) differences.
5. Whatever you design for windsurfing, the overriding first principle is that it must be useable, we are not flying by wire with avionics.
6. Soft Landyacht sails with narrow luff tubes, circular section masts and no camber inducers are good for 50 mph on a decent landyacht chassis.
I could go on, but you get the idea. In some ways I would like you to prove your ideas, maybe try building a solid wing based on a chopped off wing and taking it to cavitation speeds? make me eat my words?
just rig your 4 cammed race sail like its a 4 cammed race sail. its not hard.
your cams will rotate, youll go fast.
Select to expand quotesheddweller said..Phromsky said..
The way I figure it is this :
If I could afford to trash a light aircraft. As in saw off the starboard wing at the wing root (which would likely be around 7 to 8 square metres) and then attach a windsurf boom and a board to it. Meanwhile also teach a Silverback Gorilla to windsurf in a straight line. ..Then I could send him off sailing down that strip in Namibia with my aircraft wing and he just might beat Albeau.
No, he would not. Not even close.
What a dumb conversation.
Silverback Gorillas are notorious for wobbly windsurfing. There is no way of getting one to go in straight line. They just won't.
This is the classic topic where the OP posted because he wanted to share his view on race sail cam rotation but is not interested in learning why this view is unreasonable. The best thing is to ignore him and he will go away.
