sailquik said..

mr love said..
Subsonic...If you scroll back in the thread this is exactly why I said twist works on Windsurf sails. We physically hold the sail up, no stays, no mast mounted into a hull, if we let go the rig falls over. For us to be able to do that the sail needs to have the power low so we dont get pulled around or pulled over or exhausted after a couple of minutes. So high aspect rigs as efficient as they are just dont work in our situation.
To test this out go for a sail with less dowhaul than recomended, a tight leech and see how your rig feels when a gust hits. I will guarantee it is heavy , too physical and pulls you around.
The twist allows us to have a sail that is managable upwind but still has sufficient power to sail deep off the wind. If we used a smaller tight leeched sail upwind would be OK but we would be very underpowerd downwind. So the twist is effectively letting us go upwind with a sail that is effectively too big but perfect when we bear off and sail accross or downwind.
So regardless of any arguments about the twist and aerodynamics, a twisted sail works on a windsurfer because of the ergonomics.

Exactly this!!!

I would add - and I am shocked that no-one has even mentioned this directly, that what we need most is Dynamic Twist.

In my experience, static twist is very much less use than ideal! It really doesn't do what Martin Describes so well.

I have sailed some sails with very loose leech and almost NO dynamic twist, and they felt awful. No power to get going and then like and ON-OFF switch in the gusts and lulls.

The best sails I have used and seen have a twist that responds and adjusts to load. (and that is much more difficult to engineer!)

It's all about ergonomics, and bugger-all about aerodynamics.

Oh, Ok, maybe a little about aerodynamics.

+1

SchobiHH said..


Are there really any good comments in this thread? For me that is clearly a No. To many things mixed up.
The whole thing in my judgement is not so complicated. (Having a Physics and Math Masters btw shall qualify to add to the discussion)
There is a foil, i.e. the sail. The foil is mainly defined be the aspect ratio and the camber depth.
Aspect ratio is about efficiency of the foil. The higher the more efficient. Camber depth is about more lift with more camber. If you would have steady wind. We could stop the whole discussion here.

Many talk about the wind gradient is done here. But assuming a 90? course in 20knts of wind and assuming that you have 1-1.5 times the windspeed as boatspeed. The change of apparent wind angle is about 5? . So not really a deal when it comes to "twist".
But what is true is that the wind is stronger the higher it is, but also the wind is of higher quality i.e. less turbulence. That is why high aspect ratio sails are actually wanted. Get the wind from higher. Look the americas cup. These sails are crazy high (35m) now.

So next, what do you want as a sail designer. You want to have a sail that can "depower". Because we do not have steady wind.
Depower means 2 things: Angle of Attack change (i.e. twist ) as less AoA means less lift, and 2nd chamber depth change. As less chamber depth means less lift.
So the current approach in windsurfing foils, i.e. sails. is to have so much sail area outside the triangle of the sail to achieve that. That is all to discussion. We could stop here again.

This whole sail area allows for excessive AoA change and chamber depth reduction. And practice shows that you can achieve what you want. But if comes with a price. That you actually have much bigger sails than you actually need. The art of sail design is that you balance this properly for racing sails you make it much bigger as this allows to get the maximum effect. And with wave sails, you try to minimize it as size is always an issue.

So actually the whole thing is really boring. Because there is not so much physics behind all this. And that is also why sails haven'T really improved in the last 15 years. (The rdm Mast has made a change in the sail design, because it allows for higher bending curves) The magic comes from the fine tuning. And I hate if a sail designer changes a sail (just because marketing dept needs something new) . There are some really good years with some sails and some really bad ones. Just because of "little" changes,

Am I really missing something with that argumentation?

Agree with lots of it, but in one paragraph you said "Aspect ratio is about efficiency of the foil. The higher the more efficient" and later you said "what is true is that the wind is stronger the higher it is, but also the wind is of higher quality i.e. less turbulence. That is why high aspect ratio sails are actually wanted."

That's not the case according to anything on aerodynamics I've ever read. Even in uniform inviscid flow (ie where the allegedly less turbulent wind up top is absent) high aspect foils are more efficient in terms of lift/drag ratio.

So high aspect sails aren't "actually wanted" to get less turbulent winds up top (although they can do that) but also because high aspect sails are more efficient in terms of optimum lift/drag ratio in uniform flow. They are also inferior in terms of lift for heeling moment aka root bending moment to a bell-shaped span load foil.

Luckily for us, we can get the benefits of a bell-shaped span load AND good gust response with a big flappy leach, but as you say that means carrying lots of extra material and weight and therefore it's often not the best method.

Roo said..
Today's sails are a lot more powerful than the ones from the late 1980s yet easier to handle so we go faster....pretty simple.

Is that "more power" as in more lift per square metre, or "more power" as in having lower drag and therefore more useful lift per square metre? Or is it measured against the size of sail that can be carried in the same windspeed? And at what windspeeds and angles is there increased lift?

I always thought that older sails, like the modern deeper and tighter-leached Raceboard sails, developed higher lift for their size at the cost of higher aero drag for their size.

Years ago a former speed sailor who now does tech work related to America's Cup boats etc was telling me that he was paid to be in a project where they put windsurfer rigs in a wind tunnel to get full size data. At the end of the time they said they may as well grab an original Windsurfer sail in the tunnel to show how much the sails had developed. When they saw the lift figures, they basically said "burn them all, and tell no one". :-)

Obviously the drag of the old-style rigs is much higher so they don't work well at high speeds, but every time we put a Formula or slalom sail on a longboard for whatever reason it was noticeable how slow they were for their size.

This is not being snarky about modern speed/slalom/etc sails but merely noting how different horses work on different courses.

Roo said..

Chris 249 said..

Roo said..
Today's sails are a lot more powerful than the ones from the late 1980s yet easier to handle so we go faster....pretty simple.

Is that "more power" as in more lift per square metre, or "more power" as in having lower drag and therefore more useful lift per square metre? Or is it measured against the size of sail that can be carried in the same windspeed? And at what windspeeds and angles is there increased lift?

I always thought that older sails, like the modern deeper and tighter-leached Raceboard sails, developed higher lift for their size at the cost of higher aero drag for their size.

Years ago a former speed sailor who now does tech work related to America's Cup boats etc was telling me that he was paid to be in a project where they put windsurfer rigs in a wind tunnel to get full size data. At the end of the time they said they may as well grab an original Windsurfer sail in the tunnel to show how much the sails had developed. When they saw the lift figures, they basically said "burn them all, and tell no one". :-)

Obviously the drag of the old-style rigs is much higher so they don't work well at high speeds, but every time we put a Formula or slalom sail on a longboard for whatever reason it was noticeable how slow they were for their size.

This is not being snarky about modern speed/slalom/etc sails but merely noting how different horses work on different courses.

More power from the fuller foil sections used in the sail compared with the flatter sails of the 1980s. Now we can use the power created because it is located in an position where we can maximise our leverage against it. More of the sail created power back then, it's just we couldn't use it as well. We carry up to 2m more sail area now but that extra material is used to control the lift distribution and make it easier to handle.

Ahhh, I didn't realise the foil sections were deeper now because I'm fixated on the floppy leach and I often carried too much depth way back when. That makes sense. Cheers.

Chris 249 said..

Roo said..

Chris 249 said..

Roo said..
Today's sails are a lot more powerful than the ones from the late 1980s yet easier to handle so we go faster....pretty simple.

Is that "more power" as in more lift per square metre, or "more power" as in having lower drag and therefore more useful lift per square metre? Or is it measured against the size of sail that can be carried in the same windspeed? And at what windspeeds and angles is there increased lift?

I always thought that older sails, like the modern deeper and tighter-leached Raceboard sails, developed higher lift for their size at the cost of higher aero drag for their size.

Years ago a former speed sailor who now does tech work related to America's Cup boats etc was telling me that he was paid to be in a project where they put windsurfer rigs in a wind tunnel to get full size data. At the end of the time they said they may as well grab an original Windsurfer sail in the tunnel to show how much the sails had developed. When they saw the lift figures, they basically said "burn them all, and tell no one". :-)

Obviously the drag of the old-style rigs is much higher so they don't work well at high speeds, but every time we put a Formula or slalom sail on a longboard for whatever reason it was noticeable how slow they were for their size.

This is not being snarky about modern speed/slalom/etc sails but merely noting how different horses work on different courses.

More power from the fuller foil sections used in the sail compared with the flatter sails of the 1980s. Now we can use the power created because it is located in an position where we can maximise our leverage against it. More of the sail created power back then, it's just we couldn't use it as well. We carry up to 2m more sail area now but that extra material is used to control the lift distribution and make it easier to handle.

Ahhh, I didn't realise the foil sections were deeper now because I'm fixated on the floppy leach and I often carried too much depth way back when. That makes sense. Cheers.

deeper than what? the old racing sails in the 80's that were size limited had a very deep camber ratio! they were also easy to handle for their job. ( 6m longboard racing sails) given the same restrictions of area i dont think you would design the sails very differently now.

I used to know this guy in the early 2000's who used to sail around on a 1980's high aspect tight leech 5 batten rotational and a 1980's very deep concave slalom board( think long hypersonic) at a local lake. In the short fetch he was as fast as anyone else, planed earlier and accelerated quicker. He could beat pretty much anyone on figure of 8 and that included national level racers. It was odd in many ways because we all just kind of ignored it and him, oh thats just phil, he does that! When that sail fell apart, must of been around 2008, he got a new one and he also got a new board, he never beat anyone again, and he looked just like the rest of us.

I think that for a lot( not all) of recreational sailors carrying an extra 2m of cloth for a bit of extra top speed or "easier" gust response is highly dubious. 2m extra? thats a ****load extra size weight and unwieldy ****. ( not to mention horrid great long booms that make handling awful)
Now i do not advocate a return to the 1980's, but also smaller sails that are a bit firmer, power up quicker and harder, can often be more fun. It actually feels like a sail, maybe not as quick ultimately- but most of us will never reach the speed potential of our kit anyway.
I think the market also agrees with me and that is why so many people have stopped fin sailing and gone firstly foiling and then winging, smaller easier lighter kit. We have pursued a type of performance that isnt that popular, those who remain are the self selecting group who will defend their decisions, the others have all buggered off to do something more fun.

I gave my 7.0 twin cam to a died in the wool big sail recreational slalom sailor a couple of years ago. It perfectly demonstrates the flappy floppy v tighter ( but still some looseness and dynamic twist). He sold his bigger heavier sails and purchased the smaller 2 cam after one session and still thanks me to this day. Another friend tried it and hated it, says it was too aggressive for him, he prefers the bigger sails as he says they don't react to the gusts, just sit there. His comfortable is my dead feeling. Like driving a caddilac or a go cart.

So yea horses for courses- but don't dismiss tighter firmer sails out of hand they have their place too

sheddweller said..

Chris 249 said..

Roo said..

Chris 249 said..

Roo said..
Today's sails are a lot more powerful than the ones from the late 1980s yet easier to handle so we go faster....pretty simple.

Is that "more power" as in more lift per square metre, or "more power" as in having lower drag and therefore more useful lift per square metre? Or is it measured against the size of sail that can be carried in the same windspeed? And at what windspeeds and angles is there increased lift?

I always thought that older sails, like the modern deeper and tighter-leached Raceboard sails, developed higher lift for their size at the cost of higher aero drag for their size.

Years ago a former speed sailor who now does tech work related to America's Cup boats etc was telling me that he was paid to be in a project where they put windsurfer rigs in a wind tunnel to get full size data. At the end of the time they said they may as well grab an original Windsurfer sail in the tunnel to show how much the sails had developed. When they saw the lift figures, they basically said "burn them all, and tell no one". :-)

Obviously the drag of the old-style rigs is much higher so they don't work well at high speeds, but every time we put a Formula or slalom sail on a longboard for whatever reason it was noticeable how slow they were for their size.

This is not being snarky about modern speed/slalom/etc sails but merely noting how different horses work on different courses.

More power from the fuller foil sections used in the sail compared with the flatter sails of the 1980s. Now we can use the power created because it is located in an position where we can maximise our leverage against it. More of the sail created power back then, it's just we couldn't use it as well. We carry up to 2m more sail area now but that extra material is used to control the lift distribution and make it easier to handle.

Ahhh, I didn't realise the foil sections were deeper now because I'm fixated on the floppy leach and I often carried too much depth way back when. That makes sense. Cheers.

deeper than what? the old racing sails in the 80's that were size limited had a very deep camber ratio! they were also easy to handle for their job. ( 6m longboard racing sails) given the same restrictions of area i dont think you would design the sails very differently now.

I used to know this guy in the early 2000's who used to sail around on a 1980's high aspect tight leech 5 batten rotational and a 1980's very deep concave slalom board( think long hypersonic) at a local lake. In the short fetch he was as fast as anyone else, planed earlier and accelerated quicker. He could beat pretty much anyone on figure of 8 and that included national level racers. It was odd in many ways because we all just kind of ignored it and him, oh thats just phil, he does that! When that sail fell apart, must of been around 2008, he got a new one and he also got a new board, he never beat anyone again, and he looked just like the rest of us.

I think that for a lot( not all) of recreational sailors carrying an extra 2m of cloth for a bit of extra top speed or "easier" gust response is highly dubious. 2m extra? thats a ****load extra size weight and unwieldy ****. ( not to mention horrid great long booms that make handling awful)
Now i do not advocate a return to the 1980's, but also smaller sails that are a bit firmer, power up quicker and harder, can often be more fun. It actually feels like a sail, maybe not as quick ultimately- but most of us will never reach the speed potential of our kit anyway.
I think the market also agrees with me and that is why so many people have stopped fin sailing and gone firstly foiling and then winging, smaller easier lighter kit. We have pursued a type of performance that isnt that popular, those who remain are the self selecting group who will defend their decisions, the others have all buggered off to do something more fun.

I gave my 7.0 twin cam to a died in the wool big sail recreational slalom sailor a couple of years ago. It perfectly demonstrates the flappy floppy v tighter ( but still some looseness and dynamic twist). He sold his bigger heavier sails and purchased the smaller 2 cam after one session and still thanks me to this day. Another friend tried it and hated it, says it was too aggressive for him, he prefers the bigger sails as he says they don't react to the gusts, just sit there. His comfortable is my dead feeling. Like driving a caddilac or a go cart.

So yea horses for courses- but don't dismiss tighter firmer sails out of hand they have their place too

Mate, I'm probably the very last person to dismiss tighter and firmer-leached sails - in fact I've become quite unpopular here a few times when I've promoted them because I prefer them personally. That's one of the reasons I showed pics of tighter-leached dinghies earlier, because as we both agree tight leaches work better in many situations.

Most of the '80s raceboard sails weren't size limited to 6m; they were either one design, limited to 6.8 to 7.3m (D2 sails) or unlimited (raceboard sails). Yes, for Raceboards or longboards I agree you wouldn't change the shape much these days - the fact that deeper but smaller sails give more power for the metre and therefore work better for longboards etc is something I've said repeatedly in this thread as far as I remember, and Roo's post confirms it.

Personally I completely agree about carrying a lot of extra weight just to get "better gust response" isn't normally worth it - in fact I LIKE having to respond to gusts. To me that is part of the fun of sailing. If the rig does most of the work I get bored, which is one reason I fall asleep after 20 minutes on slalom or B&J gear now that I no longer sail it for top-level competition. But for the guys who like blasting or like the automatic feel the gust-responsive sails do work better in many ways and as we both said that makes it a case of horses for courses.

A smaller sail rigged with less downhaul has similar if a little less power than a sail a metre larger but is massively more fun to use provided you are not underpowered.

For your average 75 kg person i recommend using max 7m unless you are planning on sailing in really marginal days.

For 85 kgs and above a 7.5 to 7.8 might be more fun in the lighter days.

I remember maybe 25 to 30 years ago at the Swan River in a westerly front that dropped to 10 to 15 knots Neil S and another going out planing both on their large 290 Windtech boards and massive 6.7m sails.

The other 50 or so were on the grass waiting for the wind to fill in.

Chris 249 said..

SchobiHH said..

I totally agree with you. As I said in the beginning, I phrased it not correctly, what I wanted to say, wrt to the wind gradient. But it is obviously one aspect that the wind is stronger (better quality) in higher altitudes and therefore you want to take advantage of that benefit if possible. But it is just a side note. Sails are actually a boring topic. And to much is interpreted into the topic. That is a very windsurfer-community like thing. We like to believe there is some magic with the gear. (e.g. 100% mast vs less carbon, toe-in discussion, sanded vs. polished bottom drag, etc...) Unfortunately this is rarely the case.

Sounds great, and I agree with you. Cheers.

As we both seem to like "tighter" leeches. I recommend this video. Take the time to watch it to the end.

Chris 249 said..

SchobiHH said..

I totally agree with you. As I said in the beginning, I phrased it not correctly, what I wanted to say, wrt to the wind gradient. But it is obviously one aspect that the wind is stronger (better quality) in higher altitudes and therefore you want to take advantage of that benefit if possible. But it is just a side note. Sails are actually a boring topic. And to much is interpreted into the topic. That is a very windsurfer-community like thing. We like to believe there is some magic with the gear. (e.g. 100% mast vs less carbon, toe-in discussion, sanded vs. polished bottom drag, etc...) Unfortunately this is rarely the case.

Sounds great, and I agree with you. Cheers.

As we both seem to like "tighter" leeches. I recommend this video. Take the time to watch it to the end.

Manuel7 said..
Why are factory sails not properly cut then?

Why did the universe start with a big bang? Seriously: There is too much blind believe in the industries marketing especially in the windsurfing community. "they" have to rush from year to year with new products. Because the last years products are only worth 50%, ie. can be sold with big discounts..... A Hobby 16 is the same already since 40 years. Why do customers in the windsurfing industry still believe this innovation myth. "We" are really stupid, when it comes to equipment. Like junkies always the next kick. Do you really need to know more to understand, that each evolution cycle is not always better.....

Hey there for what it's worth in the unrestricted sail/rig design on 12ft skiffs we all moved to square top bigger roached looser leeched sails. Partly from looking at windsurf sails I think!
My remembering is they are better for a variety of reason:
drag profile (less tip vortices)
better twist characteristics and gust responsiveness
more sail area up high in better breeze allowing flatter lower drag sails
More automatic in their responses to gusts and chop so easier/less frequent tuning required

In pin top sails the loss of laminar flow behind the mast means the top of the sail is very inefficient and mostly just increases drag

Of course there is a point at which some of the square tops just got too big??

Doggerland said..
interspecies transmission on all that flopping around/loose material in the leech
the architects of the ocean have spoken

Clearly the grey suits do not approve of any kind of floppy/flappyness at all.

In 80s had 5m with floppy luff and tight leach, was terrible :-). Floppy leaches give better freeride and wave sailing, tuning to conditions via down and outhaul helps.
I'm sure if you sailed a single bearing with uniform wind a tighter leach is more efficient. Speed sailors get closest to this.