Select to expand quoteSubsonic
Didn't one of the sailmakers try for something like that once a few years back, with a a mast with an ultra flexi tip, and extreme luff curve at the top of the sail?
Are you talking about this one?
Select to expand quoteMark _australia said..
Welcome to the toe-in thread v2
This one looks like fun, how many armchair sailmakers can you fit into one forum thread?
Select to expand quoteWillyWind said..Subsonic
Didn't one of the sailmakers try for something like that once a few years back, with a a mast with an ultra flexi tip, and extreme luff curve at the top of the sail?
Are you talking about this one?
Yep, thats the one.
Select to expand quoteSubsonic said..sailquik said..choco said..Ben1973 said..
Yep going around in circles, hopefully this time they will stick with smaller sails and tighter leeches as that's just a better way to do things.
Twist and loose leach the same thing?
They absolutely DON't have to go together.
IMHO, it's a nice Dynamic twist of the upper leach that is ideal. Opens up to reduce power in the gusts and lower centre of effort. Closes up for better power and efficiency in the lulls. 
Also allows a smaller sail with less drag and weight.
Didn't one of the sailmakers try for something like that once a few years back, with a a mast with an ultra flexi tip, and extreme luff curve at the top of the sail?
Yes it might of been on some fanatic branded sails I think that hard a really soft top meter or so, that was 25odd years ago, there's also the gun sail above that did it more recently
Select to expand quoteSurferKris said..
The goal isn't a tighter leech, as I have understood it, but to remove any diagonal wrinkles in the sail between the battens.
Following his recommendations regarding sail changes, one would need at least two sails in the same size. Modify one until it is the best sail, then try to improve the other one to be even better, and so on.
He's removing the wrinkles by tightening the leech And I would add that any change in performance he's noticing is coming from that tighter leech and extra shape he's added and not from the reduced wrinkles.
Select to expand quoteSurferKris said..
The goal isn't a tighter leech, as I have understood it, but to remove any diagonal wrinkles in the sail between the battens.
Correct, main goal anyway.
But at 2'10 he says a lot of downhaul is required to give the required skin tension for stability. That can leave the top leech very open and flapping, which isnt efficient. So his goal, as well as a smooth sail, is also a non flappy one. A non flappy leech isnt the same as a tight leech.
A couple of things to think about.
Firstly we sail with our mast raked to windward so an open twisted leech will make the leech vertical ( so more forward drive versus vertical)
As shown by J2.0 below
Generally smooth constant twist is preferred. Any tight sections almost hook and create drag, slowing any accelerations.
Below is a proto which was too tight lower down, then a photo of two relief cuts which added a couple of cm each time.
The new sails are looking pretty smooth straight out of the bag, both fin and foil.
Select to expand quotePhilUK said.. That can leave the top leech very open and flapping, which isnt efficient.
There is a theory around, that the flappy leech, is preventing/reducing the tip vortex and thus decreasing drag. Also reduces lift of course. But maybe if it's optimised it's lift to drag ratio is improved?
Select to expand quoteSubsonic said..
other craft that carry tighter leeches also have a different way of managing/altering sail shape. they attach strings to everything, so they can adjust on the fly. They also sheet the mainsail in and out constantly to keep the boat flying on the correct amount of heel, and deal with gusts. Believe it or not, that's actually less efficient than having a leech with twist, that allows us to not have to sheet in and out. They are actually starting to put square tops on sailboats now (actually, they started the trend quite a number of years ago) because they've come to realise that it's better to be able to let the leech twist off and let the sail breathe, rather than constrict it with a tight hooky leech.
Sheeting a sail on a boat isn't "less efficient" than twist. Any boat can twist the mainsail as much as it wants, just by easing mainsheet and vang. They don't normally twist it off because it reduces power and pointing ability.
Twist and adjusting sheeting angles are different, because boats and boards are different. Putting a floppy, twisty leach on a sail means less power for the area, or more area for the same power. Adding more area to generate the same power increases cost, form drag, and weight. Whether that is worth it depends on the individual craft.
Windsurfers are different because the drag of the board (once planing) is very low and therefore the drag of the rig is critical. In most boats, the drag of the hull is very significant so they tend to want as much power as possible. They can have a higher-drag rig because the rig drag is minor compared to the hull drag. They also don't need to worry about back-hand pressure and fast boats have more righting moment than a board.
With big boat campaigns running from $10mill to a few hundred million, they are enormously sophisticated, very well aware of the theory and what happens in boards, and they are certainly not behind boards in rig design.
The very fact that people here are interested when a top sailor modifies their production-line sail shows the difference between boards and boats. In top level open-design boats it's the norm to have a sailmaker on board or in the campaign, modifying the rigs to the individual crew's needs and desires. Even in singlehanded dinghies at the top level, no one would blink an eye if a sailor and sailmaker modified a stock sail; even in 7ft Optis the kids are sold a variety of different sails for different weights and conditions.
Select to expand quotejn1 said..
Yeah but, you wouldn't do this mod on a good sail. It would be something to try as a last resort on a disappointment that won't dial in; especially 2nd hand sails, where you have got nothing to loose.
Lots of boat guys, in campaigns that spend $90,000 on a single sail and may have multiple sailmakers on six figure salaries, take them back repeatedly to modify and tweak to change them from "good" to "even better". They'll take a few millimetres off the luff curve off a 20m tall sail, if I recall correctly, or a few mills off a seam or two.
It's also extremely common to adjust mast bend by easing the stays a few millimetres between races (in some classes) or using other adjustments to allow for different sailor weights and styles. The idea of just having one set of fast settings is a rather odd one given the complexity of the way sails work.
They will also provide stock sails that are aimed at the same class but are designed for different sailor weights. The idea that people should just buy one sail and use it as it is, unless restricted by rules, seems to be only a windsurfer thing.
Select to expand quoteChris 249 said..Subsonic said..
other craft that carry tighter leeches also have a different way of managing/altering sail shape. they attach strings to everything, so they can adjust on the fly. They also sheet the mainsail in and out constantly to keep the boat flying on the correct amount of heel, and deal with gusts. Believe it or not, that's actually less efficient than having a leech with twist, that allows us to not have to sheet in and out. They are actually starting to put square tops on sailboats now (actually, they started the trend quite a number of years ago) because they've come to realise that it's better to be able to let the leech twist off and let the sail breathe, rather than constrict it with a tight hooky leech.
Sheeting a sail on a boat isn't "less efficient" than twist. Any boat can twist the mainsail as much as it wants, just by easing mainsheet and vang. They don't normally twist it off because it reduces power and pointing ability.
Twist and adjusting sheeting angles are different, because boats and boards are different. Putting a floppy, twisty leach on a sail means less power for the area, or more area for the same power. Adding more area to generate the same power increases cost, form drag, and weight. Whether that is worth it depends on the individual craft.
Windsurfers are different because the drag of the board (once planing) is very low and therefore the drag of the rig is critical. In most boats, the drag of the hull is very significant so they tend to want as much power as possible. They can have a higher-drag rig because the rig drag is minor compared to the hull drag. They also don't need to worry about back-hand pressure and fast boats have more righting moment than a board.
With big boat campaigns running from $10mill to a few hundred million, they are enormously sophisticated, very well aware of the theory and what happens in boards, and they are certainly not behind boards in rig design.
The very fact that people here are interested when a top sailor modifies their production-line sail shows the difference between boards and boats. In top level open-design boats it's the norm to have a sailmaker on board or in the campaign, modifying the rigs to the individual crew's needs and desires. Even in singlehanded dinghies at the top level, no one would blink an eye if a sailor and sailmaker modified a stock sail; even in 7ft Optis the kids are sold a variety of different sails for different weights and conditions.
I probably should've said it in my post, but to be clear, I was referring to dinghies/skiffs and smaller performance yachts when I said boats sheet their sails in/out constantly. Big boats are very different machines in how they are operated and generally do less in the way of constant trimming, because they have much more righting moment on their side. but a sail that is sheeted in and out is always going to be less efficient than a sail that remains static. Every sail movement disrupts the air flow over the sail. Generally speaking, windsurfers keep their rigs very static compared to a sailing dinghy.
in any case, you've taken off on a tangent with an excerpt of what I said. I was doing a general reply to what a few others had said about tight leeches being better. They can be better, on the right kind of craft. Not necessarily on a slalom sail, where there are other factors that other craft don't face.
It sounds a little like the guy in the video prefers sails from early 2000's and course racing.
There's a difference between what I think of as a twisting leech, a loose leech and a floppy leech - all unscientific terms and you may classify them differently.
The Sailworks race sails, even with a LOT of downhaul, display a progressive twist under load but you wouldn't call it floppy - the whole sail fills but the top third is much more open than the middle third.
Point 7 and NP are good examples of a very loose leech, where the twist extends all the way down to the boom, but again, the whole sail fills and in smooth water there's no floppiness once powered up.
There's very little shape in the top of those three sails - the material is essentially flat with no camber.
Ezzy seems to like a pretty floppy leech - the area above the second batten really never fills with wind, even on very broad courses and even overpowered. It's as if he's using that section to create the shape he wants down below the second batten, and doesn't really care about the excess drag or weight (neither of which is all that substantial.)
I recut a 2012 or 2013 Ezzy Cheetah 8.5, taking a dart near the second batten, in an effort to convert it from a floppy sail to a twisting sail. The top of that sail, on the correct Ezzy Hookipa 490, really flopped around and bugged me, although the shape of the rest of the sail was excellent. It worked somewhat better after the recut, but eventually I sold it and replaced it with a heavier but much more efficient Sailworks NX 8.6.
The current owner of the Ezzy is on the forum and may chime in on how it's been working. The NX is great but then I'm mostly foiling now, on a progressively twisting Flyer FR.
Select to expand quoteSubsonic said..Chris 249 said..Subsonic said..
other craft that carry tighter leeches also have a different way of managing/altering sail shape. they attach strings to everything, so they can adjust on the fly. They also sheet the mainsail in and out constantly to keep the boat flying on the correct amount of heel, and deal with gusts. Believe it or not, that's actually less efficient than having a leech with twist, that allows us to not have to sheet in and out. They are actually starting to put square tops on sailboats now (actually, they started the trend quite a number of years ago) because they've come to realise that it's better to be able to let the leech twist off and let the sail breathe, rather than constrict it with a tight hooky leech.
Sheeting a sail on a boat isn't "less efficient" than twist. Any boat can twist the mainsail as much as it wants, just by easing mainsheet and vang. They don't normally twist it off because it reduces power and pointing ability.
Twist and adjusting sheeting angles are different, because boats and boards are different. Putting a floppy, twisty leach on a sail means less power for the area, or more area for the same power. Adding more area to generate the same power increases cost, form drag, and weight. Whether that is worth it depends on the individual craft.
Windsurfers are different because the drag of the board (once planing) is very low and therefore the drag of the rig is critical. In most boats, the drag of the hull is very significant so they tend to want as much power as possible. They can have a higher-drag rig because the rig drag is minor compared to the hull drag. They also don't need to worry about back-hand pressure and fast boats have more righting moment than a board.
With big boat campaigns running from $10mill to a few hundred million, they are enormously sophisticated, very well aware of the theory and what happens in boards, and they are certainly not behind boards in rig design.
The very fact that people here are interested when a top sailor modifies their production-line sail shows the difference between boards and boats. In top level open-design boats it's the norm to have a sailmaker on board or in the campaign, modifying the rigs to the individual crew's needs and desires. Even in singlehanded dinghies at the top level, no one would blink an eye if a sailor and sailmaker modified a stock sail; even in 7ft Optis the kids are sold a variety of different sails for different weights and conditions.
I probably should've said it in my post, but to be clear, I was referring to dinghies/skiffs and smaller performance yachts when I said boats sheet their sails in/out constantly. Big boats are very different machines in how they are operated and generally do less in the way of constant trimming, because they have much more righting moment on their side. but a sail that is sheeted in and out is always going to be less efficient than a sail that remains static. Every sail movement disrupts the air flow over the sail. Generally speaking, windsurfers keep their rigs very static compared to a sailing dinghy.
in any case, you've taken off on a tangent with an excerpt of what I said. I was doing a general reply to what a few others had said about tight leeches being better. They can be better, on the right kind of craft. Not necessarily on a slalom sail, where there are other factors that other craft don't face.
It's not a tangent; I was actually underlining the point you made in your last two sentences, but you over-stated the case when you said it's "better to be able to let the leech twist off and let the sail breathe, rather than constrict it with a tight hooky leech" and it's "better" to have a twisty leach - it's a matter of the sail area available, the righting moment, the conditions it's used in, the lift/drag of the entire vehicle, the angle of the course, the wind range, etc etc etc.
I'm sure you'll agree that if you put a slalom-style big twisty leach on something like a Raceboard, LT, Laser, Formula 18 cat, Tasar etc and it will almost always be slower than a leach that actually does something. For the past century or more, boat sailors have often been able to dial in as much twist as they wanted. Over much of that time, the move has been towards tighter leaches most of the time because most of the time they are faster for boats and the courses and conditions they sail in. I can dial in a slalom-style twisty leach in all the above classes and it will almost always be slower than the leach tension they use.
One underlying point is that windsurfer sailors often seem to assume that their sails are more advanced than that of boats. That's just not true - they are different because the needs are different.
2- one point was that people seemed surprised that someone modified a sail, but that goes on all the time in many classes including dinghies and skiffs- and that's ignoring the fact that most of them can also modify the shape to their own preference by using rig tension etc. The idea that everyone should sail with the sail as designed for the sailmaker for someone else, in different conditions and with a different weight, is something that only windsurfers seem to do.
3- I'm not at all sure that it's correct to say that "a sail that is sheeted in and out is always going to be less efficient than one that stays static". For example, as Julian Bethwaite (who has done a lot of work in "automatic" skiff rigs says, in some boat (ie a 470) a "manual" rig that relies on the sheet being worked is better.
An "automatic" open-leach rig comes with its own bunch of issues, like extra weight for the lift. They're fantastic in their place but as we'd probably agree, that's not everywhere as some people claim.
Select to expand quoteChris 249 said..Subsonic said..
I probably should've said it in my post, but to be clear, I was referring to dinghies/skiffs and smaller performance yachts when I said boats sheet their sails in/out constantly. Big boats are very different machines in how they are operated and generally do less in the way of constant trimming, because they have much more righting moment on their side. but a sail that is sheeted in and out is always going to be less efficient than a sail that remains static. Every sail movement disrupts the air flow over the sail. Generally speaking, windsurfers keep their rigs very static compared to a sailing dinghy.
in any case, you've taken off on a tangent with an excerpt of what I said. I was doing a general reply to what a few others had said about tight leeches being better. They can be better, on the right kind of craft. Not necessarily on a slalom sail, where there are other factors that other craft don't face.
It's not a tangent; I was actually underlining the point you made in your last two sentences, but you over-stated the case when you said it's "better to be able to let the leech twist off and let the sail breathe, rather than constrict it with a tight hooky leech" and it's "better" to have a twisty leach - it's a matter of the sail area available, the righting moment, the conditions it's used in, the lift/drag of the entire vehicle, the angle of the course, the wind range, etc etc etc.
It is a tangent. My post was not about sail boats, it was about tight leeches on a windsurfing slalom sail. I referred to sail boats to demonstrate the differences, and why sailboats can or still do carry tight leeched mainsails. It appears I actually understated the case as to why a leech that can be made to open up can be better. Serves me right for trying to keep my post relevant to the op I guess.
I'm sure you'll agree that if you put a slalom-style big twisty leach on something like a Raceboard, LT, Laser, Formula 18 cat, Tasar etc and it will almost always be slower than a leach that actually does something. For the past century or more, boat sailors have often been able to dial in as much twist as they wanted. Over much of that time, the move has been towards tighter leaches most of the time because most of the time they are faster for boats and the courses and conditions they sail in. I can dial in a slalom-style twisty leach in all the above classes and it will almost always be slower than the leach tension they use.
Did you miss the first sentence of the paragraph of my post you're trying to pull apart? Here it is again for the sake of clarity:
"other craft that carry tighter leeches also have a different way of managing/altering sail shape. they attach strings to everything, so they can adjust on the fly." To clarify that further, that means they can in fact tighten the leech up as and when required, and loosen the leech up when it is required. Windsurfers generally don't have that option. We set the downhaul before we go out, and then have nothing but outhaul to make on the fly adjustments with. This is the main reason we carry a loose leech. I never inferred twisty leeches should be on everything else as well. Sail boats are not designed solely for going cross breeze/off breeze like slalom windsurfing gear is. It would be stupid to put an unadjustable super twisted leech on a boat that must perform upwind as well as downwind. But it's not such a stupid idea to give the sail a more reactive open leech design for when the Cunningham gets pulled on and the vang let off when the boat isn't aiming to point. That's part of where the square top main comes into the picture. They're higher aspect, but they can also give that flatter twisted profile to the top of the mainsail when required, to help lower the centre of effort of the sail, which makes for smoother off the wind sailing, with less sail adjustment required for trim.
One underlying point is that windsurfer sailors often seem to assume that their sails are more advanced than that of boats. That's just not true - they are different because the needs are different.
in some aspects they are, in others they aren't. I never stated they were better, only that we are able to maintain a static sail, and there are benefits to that. I referred to the twisted leech as it's a design point (that is specifically needed by windsurfers) that has given us the ability to hold the sail static. They are in reality a different line of design. I haven't met any windsurfers that see windsurfing sails as superior to other sails.
2- one point was that people seemed surprised that someone modified a sail, but that goes on all the time in many classes including dinghies and skiffs- and that's ignoring the fact that most of them can also modify the shape to their own preference by using rig tension etc. The idea that everyone should sail with the sail as designed for the sailmaker for someone else, in different conditions and with a different weight, is something that only windsurfers seem to do.
Windsurfing sails are far more of an over the counter product than a performance sailboat sail. You walk into the shop and purchase then and there a sail that has had years of specific design experience poured into it, alongside professional sailor input, specifically to that design, for what it is designed for, and you rig it on masts designed specifically to suit the sail. Not at all trying to take away from the vast experience that sailboat sailmakers have, but unless they're making a one design sail, they are almost always making a one off for a specific boat with its own design quips. That generally means sail alterations are part of the game. Wotjek being a sailmaker can make the alterations himself, when he wants. Most windsurfers don't have a want or need to visit a sailmaker for every sail they purchase. The sails are generally very well performing straight out of the bag, no alterations required.
3- I'm not at all sure that it's correct to say that "a sail that is sheeted in and out is always going to be less efficient than one that stays static". For example, as Julian Bethwaite (who has done a lot of work in "automatic" skiff rigs says, in some boat (ie a 470) a "manual" rig that relies on the sheet being worked is better.
Certainly proven true in light winds, when there is a more likely chance less sheeting action will be required in the first place, but even he and his father Frank came to the conclusion after vigorous testing and observations that a rig that responds to gusts in an "automatic" fashion, with less adjustment required from the crew is superior in much more typical gusty/windy conditions.
An "automatic" open-leach rig comes with its own bunch of issues, like extra weight for the lift. They're fantastic in their place but as we'd probably agree, that's not everywhere as some people claim.
True
Automatically reacting sails does not have to mean flappy leech sails with loads of twist.
Massively oversized sails, downhauled to take all the power out with mega twist and flappiness is just using an unnecessarily bigger and heavier sail than you have to.
It's changing away from it slowly, it takes time, but catalysts are reacting.
Select to expand quotesheddweller said..
Automatically reacting sails does not have to mean flappy leech sails with loads of twist.
Massively oversized sails, downhauled to take all the power out with mega twist and flappiness is just using an unnecessarily bigger and heavier sail than you have to.
It's changing away from it slowly, it takes time, but catalysts are reacting.
That came from the formula era where they needed the maximum sail size to go dead downwind but still had to carry it going upwind.
Select to expand quoteSubsonic said..Chris 249 said..Subsonic said..
I probably should've said it in my post, but to be clear, I was referring to dinghies/skiffs and smaller performance yachts when I said boats sheet their sails in/out constantly. Big boats are very different machines in how they are operated and generally do less in the way of constant trimming, because they have much more righting moment on their side. but a sail that is sheeted in and out is always going to be less efficient than a sail that remains static. Every sail movement disrupts the air flow over the sail. Generally speaking, windsurfers keep their rigs very static compared to a sailing dinghy.
in any case, you've taken off on a tangent with an excerpt of what I said. I was doing a general reply to what a few others had said about tight leeches being better. They can be better, on the right kind of craft. Not necessarily on a slalom sail, where there are other factors that other craft don't face.
It's not a tangent; I was actually underlining the point you made in your last two sentences, but you over-stated the case when you said it's "better to be able to let the leech twist off and let the sail breathe, rather than constrict it with a tight hooky leech" and it's "better" to have a twisty leach - it's a matter of the sail area available, the righting moment, the conditions it's used in, the lift/drag of the entire vehicle, the angle of the course, the wind range, etc etc etc.
It is a tangent. My post was not about sail boats, it was about tight leeches on a windsurfing slalom sail. I referred to sail boats to demonstrate the differences, and why sailboats can or still do carry tight leeched mainsails. It appears I actually understated the case as to why a leech that can be made to open up can be better. Serves me right for trying to keep my post relevant to the op I guess.
I'm sure you'll agree that if you put a slalom-style big twisty leach on something like a Raceboard, LT, Laser, Formula 18 cat, Tasar etc and it will almost always be slower than a leach that actually does something. For the past century or more, boat sailors have often been able to dial in as much twist as they wanted. Over much of that time, the move has been towards tighter leaches most of the time because most of the time they are faster for boats and the courses and conditions they sail in. I can dial in a slalom-style twisty leach in all the above classes and it will almost always be slower than the leach tension they use.
Did you miss the first sentence of the paragraph of my post you're trying to pull apart? Here it is again for the sake of clarity:
"other craft that carry tighter leeches also have a different way of managing/altering sail shape. they attach strings to everything, so they can adjust on the fly." To clarify that further, that means they can in fact tighten the leech up as and when required, and loosen the leech up when it is required. Windsurfers generally don't have that option. We set the downhaul before we go out, and then have nothing but outhaul to make on the fly adjustments with. This is the main reason we carry a loose leech. I never inferred twisty leeches should be on everything else as well. Sail boats are not designed solely for going cross breeze/off breeze like slalom windsurfing gear is. It would be stupid to put an unadjustable super twisted leech on a boat that must perform upwind as well as downwind. But it's not such a stupid idea to give the sail a more reactive open leech design for when the Cunningham gets pulled on and the vang let off when the boat isn't aiming to point. That's part of where the square top main comes into the picture. They're higher aspect, but they can also give that flatter twisted profile to the top of the mainsail when required, to help lower the centre of effort of the sail, which makes for smoother off the wind sailing, with less sail adjustment required for trim.
One underlying point is that windsurfer sailors often seem to assume that their sails are more advanced than that of boats. That's just not true - they are different because the needs are different.
in some aspects they are, in others they aren't. I never stated they were better, only that we are able to maintain a static sail, and there are benefits to that. I referred to the twisted leech as it's a design point (that is specifically needed by windsurfers) that has given us the ability to hold the sail static. They are in reality a different line of design. I haven't met any windsurfers that see windsurfing sails as superior to other sails.
2- one point was that people seemed surprised that someone modified a sail, but that goes on all the time in many classes including dinghies and skiffs- and that's ignoring the fact that most of them can also modify the shape to their own preference by using rig tension etc. The idea that everyone should sail with the sail as designed for the sailmaker for someone else, in different conditions and with a different weight, is something that only windsurfers seem to do.
Windsurfing sails are far more of an over the counter product than a performance sailboat sail. You walk into the shop and purchase then and there a sail that has had years of specific design experience poured into it, alongside professional sailor input, specifically to that design, for what it is designed for, and you rig it on masts designed specifically to suit the sail. Not at all trying to take away from the vast experience that sailboat sailmakers have, but unless they're making a one design sail, they are almost always making a one off for a specific boat with its own design quips. That generally means sail alterations are part of the game. Wotjek being a sailmaker can make the alterations himself, when he wants. Most windsurfers don't have a want or need to visit a sailmaker for every sail they purchase. The sails are generally very well performing straight out of the bag, no alterations required.
3- I'm not at all sure that it's correct to say that "a sail that is sheeted in and out is always going to be less efficient than one that stays static". For example, as Julian Bethwaite (who has done a lot of work in "automatic" skiff rigs says, in some boat (ie a 470) a "manual" rig that relies on the sheet being worked is better.
Certainly proven true in light winds, when there is a more likely chance less sheeting action will be required in the first place, but even he and his father Frank came to the conclusion after vigorous testing and observations that a rig that responds to gusts in an "automatic" fashion, with less adjustment required from the crew is superior in much more typical gusty/windy conditions.
An "automatic" open-leach rig comes with its own bunch of issues, like extra weight for the lift. They're fantastic in their place but as we'd probably agree, that's not everywhere as some people claim.
True
SS, I'm not attacking your comments in general as you seem to believe. I do however stand by the comment that it's not "less efficient" in general to have a sail with a tighter leach - it's horses for courses as you actually seem to agree.
I'll still also stand by the comments that it's odd that some windsurfers are surprised when someone modifies a sail. Even in top one design classes using identical spars, top sailors will often have their sails tweaked to match their style and weight, while in the very strict one designs were all the gear is identical (ie a Laser, which is more of an over the counter product than a windsurfer sail) the top sailors can carry different sail settings to the average sailors because their superior ability allows them to sail in a different way and to fit their style. The point was that there's nothing surprising about someone modifying a sail as some other people had implied, as in the thread title "WTF?"
Re Julian's comment about the 470; he was talking about the tight leach less automatic rig as being more efficient overall in that type of boat. I first met Julian and Frank in the '80s and he was making the comment to me in response to a direct question in a chat we were having.
2 to 3 degrees for everyone in every situation and all the manufacturers have it wrong.
Select to expand quoteMark _australia said..
all the manufacturers have it wrong.
Not at all , they have it right, they are selling fashion products. Fashion is a dominant thing and you should not underestimate its influence in the market.
In my experience, the expectation of what something should look like is very important to windsurf purchases, even if that look means it is not as good functionally. Often its just easier to sell them what they want than persuade them that the "strange looking thing" is better. Combined with Inertia and limited development time means the wheels turn slowly, but turn it does.
For the twist non believers you may want to read about why Nasa have spent 30 years studying Prantl lift distribution theory and developed a flying wing using the principle......LOTS of wing twist....result...way less induced drag and better stability.
www.nasa.gov/centers/armstrong/news/FactSheets/FS-106-AFRC.html
Select to expand quotemr love said..
For the twist non believers you may want to read about why Nasa have spent 30 years studying Prantl lift distribution theory and developed a flying wing using the principle......LOTS of wing twist....result...way less induced drag and better stability.
www.nasa.gov/centers/armstrong/news/FactSheets/FS-106-AFRC.html
Sorry to correct you @mr love but I think you mean Prandtl! It's been around since 1933 and the Horton brothers used it to good effect during the 2nd World War. Al Bowers at NASA used it to build a number of flying models. We, my son and I, reverse engineered their figures, Al provided some guidance, and used it to build some 3D printed flying drones. It's also being used on the new B21 bomber that Northrup Grumman are building. I've tuned my Neil Pryde EVO race sails to have the same characteristics when fully loaded.
Select to expand quotemr love said..
For the twist non believers you may want to read about why Nasa have spent 30 years studying Prantl lift distribution theory and developed a flying wing using the principle......LOTS of wing twist....result...way less induced drag and better stability.
www.nasa.gov/centers/armstrong/news/FactSheets/FS-106-AFRC.html
Are there any "twist non believers" here, ML? Isn't it just a few people who think that some people overdo it some times?
As Tom Speer (America's Cup and Boeing wing designer) pointed out year ago, that paper is completely wrong in its claim that Prandtl's second spanload model is "virtually unknown". The fact that a bell shaped spanload is better in some cases (ie where things like the best lift/drag ration for root bending moment must be maximised) has been very well known for many decades; Robert T Jones did a paper on it in 1950 and apparently Max Munk was aware of it about 1913. At the "popular" level, the same thing was pointed out in the old Australian Sailing magazine in the 1980s, and elsewhere. Wing designers have been using washout (twist) for eons; there were wingless designs from 1913 using studies of high-washout foils from the 1800s.
The stuff in the paper is very well known by guys like Prof Mark Drela (aero guru from MIT, world record holder in man-powered aircraft and boats) but they note that increasing rake and twist don't come without their own penalties.
The fact that the bell shaped spanload is often better has been used as an explanation about why pinhead shapes with LESS twist (or negative twist) are much more efficient in some situations than many people would think.
Agree that some sails go overboard with twist but I don't concur with the arguments that tight leech sails are more efficient in the case of downwind windsurf slalom racing. I used to race Tasers back in the dark ages and if you want to go fast downwind you trim in twist and let the top tell tails stream...way faster..... Windsurf Slalom sails are designed with twist as that is what works the best for that format of racing, always planing, you can pump to get on the plane, you can use massive sails and the courses are downwind...but sure they wont work on other boats with a whole different set of criteria.
