Doug Lord

14' Stunt S9 Foiling Cat

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Wow, Doug, why do you write about stuff you are now so out of touch with?

 

Foiling in light air is a business decision for anyone building recreational foilers. Vast areas of the world and for sure the USA don't see much over 10k most of the time and usually significantly less. By allowing the customer the freedom to fly in light air there is no question that sales will be positively affected. Foiling in light air is simply designing a foiler whose primary purpose is not top end speed(necessarily) but is to allow the owner to foil in a much higher percentage of the wind range than most foilers are capable of now. Foiling in light air is an important marketing tool and a real advantage for any boat capable of it.

 

Really?. Did you know that downwind, A's now take off in less wind than any other foiler I have seen in action, and that includes Moths sailed by World class sailors. And with the right foils, you do not have to sacrifice early take-off for ultimate speed. You can have both. Admittedly, wand based systems do not lend themselves to efficiency over wide operating ranges, which is why top Moth sailors seem to have an array of foils to choose from. I thought we would head down the same route with the A's, but it seems we aren't - the best light wind take off foils are also the quickest top speed, but they do have other downsides.

 

You really do seem over fixated with early take-off. You quote the figure of 10 knots as the most wind many places see, but there are already foilers that take off in noticeably less wind than that. Upwind, there will always be an issue of foiling really early and even the best don't seem to get below about 7 knots of windspeed. Same is true downhill, so we are really arguing over a very small windspeed range. And there is a real problem that foil designers are always trying to overcome - light wind take-off needs higher lift foils which are higher drag and you end up at a point of diminishing returns. On top of that you have to add in many other factors. For instance, weight is a big differentiator - 10kgs of sailor weight can be the difference between 1 knot of take-of wind speed.

 

Another huge factor is whether you are talking about a one or two person boat. There is little to no evidence that you can get foiling out of a 2 person boat in the windspeeds Doug is talking about, while the single handers seem to be there already.

 

But all this still over simplifies the issues. I could start writing pages on the issues of designing rigs that perform across a wide wind range for foiling, but suffice to say that a rig designed to get a boat foiling early is usually sub-optimal once the boat is foiling.

 

I haven't seen the S9 system up close but given the quality of the boat and the design I imagine these systems will be well built and very low maintenance.

 

So you haven't seen it, but you imagine it is very low maintenance? Do you realise how ridiculous that sounds? While in no way wishing to be thought of as being negative towards a boat I think is seriously great, you only have to look at the systems employed to know what maintenance is needed, because it is a well tried and proven way of setting up wands. Having used bike cable connections, I know exactly the issues and how much maintenance is needed. Look at the way the cam works at the top of the board, leading to some sort of push rod down through the board. Yes, it is possible to design a virtually maintenance free wand system, but it will be nowhere near as good as this one and IMO, the maintenance needed is more than outweighed by the performance of the system.

 

Not only that but there is a MAJOR difference between the S9 foils and A Class or UptiP foils: the S9 foils don't just develop vertical lift they automatically develop righting moment when needed and this facility can allow a light weight person to sail with the same righting moment as a heavier person because the foils compensate 100% automatically for the difference.

The idea of making foiling easy and providing extra righting moment on-demand is something that a wand based multifoiler does extremely well-no other type of foils allow this.

 

Yet again, Doug plays with words. Sure, a wand system automates the development of righting moment, but so what? The A's can generate righting moment from their foils if they want to and this has been both discussed and played with within the fleet (something, yet again, Doug is probably unaware of). The real issue is how good this really is, how much it creates a differentiator and whether it is worth the effort. And Doug makes big claims for the S9 system, and I am not even convinced his claims are correct and that a wand system is the best one for creating extra righting moment

 

Simply, a wand system only starts to create righting moment when a certain ride height is reached, below that ride height, the system is either in neutral or is lifting. You can usually set that ride height through a number of different ways, but what is clear on the S9 is that you set the ride height the same on both tacks and cannot alter it "on the fly". Therefore, when a boat is foiling along dead level, the foils have to be producing the same amount of lift. It is only when the boat heels that the windward wand changes the flap to gain righting moment. So if you are sailing the boat level, which is usually the aim on a multihull foiler, the heavier person will have more righting moment. What the wand system does is help create a system that assists keeping the boat level, but it does that for everybody.

 

On the A, you can set the windward foil to a different AoA than the leeward one (if you have the systems), meaning that you always have some "pull down" working, irrespective of angle of heel. The debate is whether the systems needed, plus the requirement to adjust it for different points of sailing is worth the extra righting moment you can gain. While there are potential straight line speed advantages in certain conditions, many doubt you will be faster around a course once everything else is taken into account. Again, this picture probably changes on a 2 man boat, where extra hands make a difference.

 

Which brings us back to the ease of sail discussion. Doug argues that ease of sail, plus having some degree of automation of righting moment is a big winner. I think it misses the mark by a long way. To start with, for almost everybody who foils, the big buzz comes from mastering the boat, because the rewards are so great. I don't think I have ever heard somebody suggest it would be more fun if the boats are easier to sail. And it's not as if we have a problem of the boats being too hard to sail - in the A's you have guys well into their 60's sailing the boats and making the switch. We aren't seeing lots of people leaving the class because it is too hard. It's rather like the Moths - when that all began everybody said it was too tough for ordinary sailors, while we now know that most competent dinghy sailors can master a Moth.

 

Of course, all of this misses the point of the S9, which is a great little boat. For me, what makes it great is the size, price and the very fact it isn't too high performance. My guess is that anybody who can sail an S9 could also sail a foiling A, but I doubt they would want to for a number of reasons. First, it costs a lot more. Second, the extra speed is beyond many people's comfort zone. Third, they don't want to sail in a development class or have no class racing needs. If i wanted a foiling cat, and there were no A's around where I sailed, the S9 would be high on the list, because, as I keep saying, it is a great boat. How it would compete against a boat of a similar size using A class type foils or full on V foils is another matter, but as they do not exist, that discussion is mute and I am sure that the boat will do very well as it certainly seems to fill a hole in the market.

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Another huge factor is whether you are talking about a one or two person boat. There is little to no evidence that you can get foiling out of a 2 person boat in the windspeeds Doug is talking about, while the single handers seem to be there already.

 

 

 

The Quant 23 is a 2-3 person foiling scow keelboat and their new production boat is designed to foil in 5 knots at deck level, 8kts at the top of the rig.

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1) Simply, a wand system only starts to create righting moment when a certain ride height is reached, below that ride height, the system is either in neutral or is lifting. You can usually set that ride height through a number of different ways, but what is clear on the S9 is that you set the ride height the same on both tacks and cannot alter it "on the fly". Therefore, when a boat is foiling along dead level, the foils have to be producing the same amount of lift. It is only when the boat heels that the windward wand changes the flap to gain righting moment. So if you are sailing the boat level, which is usually the aim on a multihull foiler, the heavier person will have more righting moment. What the wand system does is help create a system that assists keeping the boat level, but it does that for everybody.

 

2)On the A, you can set the windward foil to a different AoA than the leeward one (if you have the systems), meaning that you always have some "pull down" working, irrespective of angle of heel. The debate is whether the systems needed, plus the requirement to adjust it for different points of sailing is worth the extra righting moment you can gain. While there are potential straight line speed advantages in certain conditions, many doubt you will be faster around a course once everything else is taken into account. Again, this picture probably changes on a 2 man boat, where extra hands make a difference.

 

 

 

1) what convoluted nonsense. The wands are automatic and once the boat starts to foil the dual independent wands start to work as required. As you say they wands cause the boat to develop extra righting moment when the boat starts to heel regardless of the weight on the boat when the boat is foiling. If the boat has a super light weight crew and starts to heel the wand controlled foils will generate extra RM until the boat is level. The windward foil can pull down and if it does, the leeward foil will provide extra lift. If the boat is sailed by a heavy person who can keep the boat level no extra RM will be required. The dual independent wands allow the light person and heavy person to sail nearly level regardless of the wind. In other words, the dual independent wands produce extra RM for the light person as needed to match the RM of the heavy person. They sail with EQUAL righting moment thanks to the downforce on the windward foil and extra lift on the leeward foil when it is needed. While a heavy person on a trapeze produces more RM than a light person on the trapeze the BOAT makes up the difference due to the dual independent wand controlled foils. Do you get it yet?

--

2) When you add downforce to the windward foil you have to add extra lift to the leeward foil or the boat will come off the foils. The wand system does this automatically .You didn't mention adding lift to the leeward foil on your A? Seems like a bitch to do this manually on any boat.......

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1) Simply, a wand system only starts to create righting moment when a certain ride height is reached, below that ride height, the system is either in neutral or is lifting. You can usually set that ride height through a number of different ways, but what is clear on the S9 is that you set the ride height the same on both tacks and cannot alter it "on the fly". Therefore, when a boat is foiling along dead level, the foils have to be producing the same amount of lift. It is only when the boat heels that the windward wand changes the flap to gain righting moment. So if you are sailing the boat level, which is usually the aim on a multihull foiler, the heavier person will have more righting moment. What the wand system does is help create a system that assists keeping the boat level, but it does that for everybody.

 

2)On the A, you can set the windward foil to a different AoA than the leeward one (if you have the systems), meaning that you always have some "pull down" working, irrespective of angle of heel. The debate is whether the systems needed, plus the requirement to adjust it for different points of sailing is worth the extra righting moment you can gain. While there are potential straight line speed advantages in certain conditions, many doubt you will be faster around a course once everything else is taken into account. Again, this picture probably changes on a 2 man boat, where extra hands make a difference.

 

 

 

1) what convoluted nonsense. The wands are automatic and once the boat starts to foil the dual independent wands start to work as required. As you say they wands cause the boat to develop extra righting moment when the boat starts to heel regardless of the weight on the boat when the boat is foiling. If the boat has a super light weight crew and starts to heel the wand controlled foils will generate extra RM until the boat is level. The windward foil can pull down and if it does, the leeward foil will provide extra lift. If the boat is sailed by a heavy person who can keep the boat level no extra RM will be required. The dual independent wands allow the light person and heavy person to sail nearly level regardless of the wind. In other words, the dual independent wands produce extra RM for the light person as needed to match the RM of the heavy person. They sail with EQUAL righting moment thanks to the downforce on the windward foil and extra lift on the leeward foil when it is needed. While a heavy person on a trapeze produces more RM than a light person on the trapeze the BOAT makes up the difference due to the dual independent wand controlled foils. Do you get it yet?

 

Yet again, you show your total lack of understanding.

 

Consider the S9 or, for that matter, any foiling cat. I think we can all agree that the optimum is to sail the boat level. If you sail the boat heeled, it will never be as quick as upright. In fact, sailing a foiling cat heeled really isn't a very good way to get around. When sailing the boat level, the windward foil cannot be providing righting moment because if it does, the leeward foil would be acting in the same direction, pulling the boat down and the boat would stop foiling. The alternative is you have some differential set up, so that the 2 foils work independently of each other and this is not present in the S9 or any other wand system that I am aware of. While the wand system might give assistance in getting the boat back to level when you start to heel, when sailing level and when max powered up or above, weight is what makes the difference, because if you are heavier, you can simply pull the sail in more and get more power. It's really rather simple, because you cannot change the science.

 

2) When you add downforce to the windward foil you have to add extra lift to the leeward foil or the boat will come off the foils. The wand system does this automatically .You didn't mention adding lift to the leeward foil on your A? Seems like a bitch to do this manually on any boat.......

 

Again, you haven't got a clue. With an A, as the boat rises up on its foils, the amount of lift they produce goes down, because there is less foil in the water. As it goes down, you get more lift. It's actually pretty automatic, maybe not quite as good as a wand system but still very effective. If you set your windward foil to provide righting moment, you have 2 options. First, you accept that you are not going to foil as high out of the water as you would do if it wasn't producing righting moment. The alternative is that you adjust the leeward foil so it produces more lift, which is no big deal because we adjust the AoA as we sail anyway. It certainly isn't a bitch to do because it is a single control to pull. All you need to do is set the difference between the AoA on both sides. Job done. Easy! What's funny about your comments is that when Nathan Outteridge talked about doing this on his A in a video, you got all carried away and excited even though at the time, the foils didn't really lend themselves to doing this. Now the foils have changed and it is potentially worthwhile but as it is me discussing it, you say something completely different. Yet again, we see your true colours.

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I have talked to a great deal of people about using the windward foil to pull down the hull. Everyone agrees that it's just not feasible for a 1 person boat and, as a matter of fact, it has yet to be proven it is even remotely possible on any real boat. I am 100% sure the s9 does to use its windward foil to generate righting moment. I don't even think it ever goes to 0 lift. The stability you see is just the product of having a very stable boat.

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In post #30 ita 16 says:

 

yes, the 2 foils can independently control, their lift control systems are separate

 

That doesn't mean the foils create down force (i.e. a downward force rather than creating less lift). To me it says they control lift, i.e. more or less, not that they generate a downward force. Ita 16 contributes to this thread but has not clarified this point, it would be very simple to do so.

 

To sail flat, at a constant height and have the windward foil producing down force requires the foils to have windward, neutral and leeward modes (in addition to gearing and height adjustment). It would be interesting to see if such a system has been developed and deployed anywhere.

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In post #30 ita 16 says:

 

yes, the 2 foils can independently control, their lift control systems are separate

 

 

To sail flat, at a constant height and have the windward foil producing down force requires the foils to have windward, neutral and leeward modes (in addition to gearing and height adjustment). It would be interesting to see if such a system has been developed and deployed anywhere.

If I remember correctly,phil s said this is how scow foiling moths work, and that it's pretty difficult to operate correctly

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I have talked to a great deal of people about using the windward foil to pull down the hull. Everyone agrees that it's just not feasible for a 1 person boat and, as a matter of fact, it has yet to be proven it is even remotely possible on any real boat.

You clearly haven't been talking to the right people. I think the first person to do it properly on an A was Nathan Outteridge and there is even a video of him talking about it somewhere. This year, almost the first thing he said when he came to put together his borrowed boat was that he hoped he had time to change the board AoA systems so he could get the windward board to either neutral or provide righting moment, if there was enough adjustment range. I honestly don't know if he did it in the end, but he was both convinced it worked and was practical. Since then, I know of a number of people who have been playing around with the idea. I can assure you that it is totally feasible.

 

Maybe the more interesting discussion is whether there really are any performance gains. With the A, we are talking about going upwind and with both boards down. Theory says that if you are able to reduce the lift from the windward board, you have to be reducing the drag, but is it worth the hassle? Then you get to the point where you are getting "negative lift", or righting moment. This poses a similar question - are the theoretical benefits enough in practice to worry about? I suspect this is a subject that will run and run.

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Hi Doug, reading carefully again Simon said 'the Stunt 9 is slower on the evidence he has', you replied 'I want to see that evidence'. So I'm getting the same concept.

 

But if you agree that you are not implying the S9 is faster than the A, so my due apologies.

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I have talked to a great deal of people about using the windward foil to pull down the hull. Everyone agrees that it's just not feasible for a 1 person boat and, as a matter of fact, it has yet to be proven it is even remotely possible on any real boat.

You clearly haven't been talking to the right people. I think the first person to do it properly on an A was Nathan Outteridge and there is even a video of him talking about it somewhere. This year, almost the first thing he said when he came to put together his borrowed boat was that he hoped he had time to change the board AoA systems so he could get the windward board to either neutral or provide righting moment, if there was enough adjustment range. I honestly don't know if he did it in the end, but he was both convinced it worked and was practical. Since then, I know of a number of people who have been playing around with the idea. I can assure you that it is totally feasible.

 

Maybe the more interesting discussion is whether there really are any performance gains. With the A, we are talking about going upwind and with both boards down. Theory says that if you are able to reduce the lift from the windward board, you have to be reducing the drag, but is it worth the hassle? Then you get to the point where you are getting "negative lift", or righting moment. This poses a similar question - are the theoretical benefits enough in practice to worry about? I suspect this is a subject that will run and run.

 

Sorry for the misunderstanding ... By feasible I didn't mean its not possible... I meant most people I've talked to... also from the a class, say it's not worth it and that it will never be worth it on a course racing boat.... Yeah looking at my phrasing from the original post I really fucked up :P whoops

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1) Simply, a wand system only starts to create righting moment when a certain ride height is reached, below that ride height, the system is either in neutral or is lifting. You can usually set that ride height through a number of different ways, but what is clear on the S9 is that you set the ride height the same on both tacks and cannot alter it "on the fly". Therefore, when a boat is foiling along dead level, the foils have to be producing the same amount of lift. It is only when the boat heels that the windward wand changes the flap to gain righting moment. So if you are sailing the boat level, which is usually the aim on a multihull foiler, the heavier person will have more righting moment. What the wand system does is help create a system that assists keeping the boat level, but it does that for everybody.

 

2)On the A, you can set the windward foil to a different AoA than the leeward one (if you have the systems), meaning that you always have some "pull down" working, irrespective of angle of heel. The debate is whether the systems needed, plus the requirement to adjust it for different points of sailing is worth the extra righting moment you can gain. While there are potential straight line speed advantages in certain conditions, many doubt you will be faster around a course once everything else is taken into account. Again, this picture probably changes on a 2 man boat, where extra hands make a difference.

 

 

 

1) what convoluted nonsense. The wands are automatic and once the boat starts to foil the dual independent wands start to work as required. As you say they wands cause the boat to develop extra righting moment when the boat starts to heel regardless of the weight on the boat when the boat is foiling. If the boat has a super light weight crew and starts to heel the wand controlled foils will generate extra RM until the boat is level. The windward foil can pull down and if it does, the leeward foil will provide extra lift. If the boat is sailed by a heavy person who can keep the boat level no extra RM will be required. The dual independent wands allow the light person and heavy person to sail nearly level regardless of the wind. In other words, the dual independent wands produce extra RM for the light person as needed to match the RM of the heavy person. They sail with EQUAL righting moment thanks to the downforce on the windward foil and extra lift on the leeward foil when it is needed. While a heavy person on a trapeze produces more RM than a light person on the trapeze the BOAT makes up the difference due to the dual independent wand controlled foils. Do you get it yet?

 

Yet again, you show your total lack of understanding.

 

Consider the S9 or, for that matter, any foiling cat. I think we can all agree that the optimum is to sail the boat level. If you sail the boat heeled, it will never be as quick as upright. In fact, sailing a foiling cat heeled really isn't a very good way to get around. When sailing the boat level, the windward foil cannot be providing righting moment because if it does, the leeward foil would be acting in the same direction, pulling the boat down and the boat would stop foiling. The alternative is you have some differential set up, so that the 2 foils work independently of each other and this is not present in the S9 or any other wand system that I am aware of. While the wand system might give assistance in getting the boat back to level when you start to heel, when sailing level and when max powered up or above, weight is what makes the difference, because if you are heavier, you can simply pull the sail in more and get more power. It's really rather simple, because you cannot change the science.

 

2) When you add downforce to the windward foil you have to add extra lift to the leeward foil or the boat will come off the foils. The wand system does this automatically .You didn't mention adding lift to the leeward foil on your A? Seems like a bitch to do this manually on any boat.......

 

Again, you haven't got a clue. With an A, as the boat rises up on its foils, the amount of lift they produce goes down, because there is less foil in the water. As it goes down, you get more lift. It's actually pretty automatic, maybe not quite as good as a wand system but still very effective. If you set your windward foil to provide righting moment, you have 2 options. First, you accept that you are not going to foil as high out of the water as you would do if it wasn't producing righting moment. The alternative is that you adjust the leeward foil so it produces more lift, which is no big deal because we adjust the AoA as we sail anyway. It certainly isn't a bitch to do because it is a single control to pull. All you need to do is set the difference between the AoA on both sides. Job done. Easy! What's funny about your comments is that when Nathan Outteridge talked about doing this on his A in a video, you got all carried away and excited even though at the time, the foils didn't really lend themselves to doing this. Now the foils have changed and it is potentially worthwhile but as it is me discussing it, you say something completely different. Yet again, we see your true colours.

 

 

Thats the key Simon: you're not aware of how a wand system creates RM. You've never sailed a wand controlled multihull with dual, independent wand based foil control systems!! The port and stb wands operate 100% independently of each other-that is why they can generate righting moment. They are able to do that effectively when the hulls clear the water and it is one of the great advantages of the S9 system.

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I have talked to a great deal of people about using the windward foil to pull down the hull. Everyone agrees that it's just not feasible for a 1 person boat and, as a matter of fact, it has yet to be proven it is even remotely possible on any real boat. I am 100% sure the s9 does to use its windward foil to generate righting moment. I don't even think it ever goes to 0 lift. The stability you see is just the product of having a very stable boat.

 

Boats like the Rave, Hobie trifoiler, Osprey, Skat, Whisper use dual,independent altitude control systems("feelers" on the Hobie, wands on the rest) that allow the windward foil to generate downforce. Greg Ketterman wrote a little piece on it-I'll find it.

 

This is something Greg Ketterman wrote about his system and it pretty much applies to the Bradfield system as well:

 

HYDROFOIL SAILBOATS IN GENERAL

"Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.

From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.

Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.

The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.

All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."

------

* On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors.

==========================

 

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I have talked to a great deal of people about using the windward foil to pull down the hull. Everyone agrees that it's just not feasible for a 1 person boat and, as a matter of fact, it has yet to be proven it is even remotely possible on any real boat. I am 100% sure the s9 does to use its windward foil to generate righting moment. I don't even think it ever goes to 0 lift. The stability you see is just the product of having a very stable boat.

 

Boats like the Rave, Hobie trifoiler, Osprey, Skat, Whisper use dual,independent altitude control systems("feelers" on the Hobie, wands on the rest) that allow the windward foil to generate downforce. Greg Ketterman wrote a little piece on it-I'll find it.

 

This is something Greg Ketterman wrote about his system and it pretty much applies to the Bradfield system as well:

 

HYDROFOIL SAILBOATS IN GENERAL

"Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.

From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.

Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.

The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.

All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."

------

* On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors.

==========================

 

 

I do not believe the the whisper generates rm with its windward foil. I would not consider any of the other racing boats

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Why? The principle is that the wands are independent and automatically increase windward foil downforce and lee foil lift as required. What part of that don't you get?

The Hobie Trifoiler Longshot set a speed record or two specifically because of the way its foil system works.Raves were raced as a fleet on courses all over the US.

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Why? The principle is that the wands are independent and automatically increase windward foil downforce and lee foil lift as required. What part of that don't you get?

The Hobie Trifoiler Longshot set a speed record or two specifically because of the way its foil system works.Raves were raced as a fleet on courses all over the US.

The windwad foil will decrease its lift but, mostly, never pull down. I am convinced it does not pull down on either the s9 or the whisper. This is because most racing boats are optimized for both slow upwind foiling and fast downwind. It's generally agreed that the compromise for designing a foil that can also pull down is too big to make the gain in rm compensate for the increase in drag.

 

PS: generating rm with a wand style system by pulling down would also create an impossible boat to sail in waves downwind... but this is just my opinion

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Did you read what Ketterman said about that? Did you read the posts earlier where SK specifically asked Michele if the windward foil pulled down and he answered "yes"? posts 29 and 30, I think.

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Did you read what Ketterman said about that? Did you read the posts earlier where SK specifically asked Michele if the windward foil pulled down and he answered "yes"? posts 29 and 30, I think.

You are quoting one person (should I say a fairly old quote made for a non course racing boat) just to prove your point while totally ignoring the fact that there must be a reason people have moved away from that concept in the sailing world. Posts 29 and 30 don't say the windward foil produces rm. they just say it can be set up to do so + you are also referring to a boat that does not concentrate on speed AND that is not quick compared to all other boats that use a different setup so even if the s9 did pull down with one foil it would not mean that configuration its faster than anything else.

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post 29--SK: "Does it have a system so you can use the windward foil to produce downforce, or less lift? "

--

post 30--Michele: "yes, the 2 foils can independently control, their lift control systems are separate ."

 

Joking, the key is that Michele said the two foil systems are independent. No one is arguing that the S9 is faster than any other cat only that it is easier to sail than most other foilers because of its dual, independent wand systems which simply make foiling automatic.

Its too early in the S9's development to talk much about speed-but I'll guarantee you there is more coming in that area.

---

You say "people have moved away from that concept in the sailing world". That doesn't explain ,then, why three* of the newest foilers use wand controlled foils?!

 

*the third being the Vampire which, while it uses wands, only uses one wand and one main foil at a time and therefore doesn't create RM with the foils like the S9 and Whisper do.

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post 29--SK: "Does it have a system so you can use the windward foil to produce downforce, or less lift? "

--

post 30--Michele: "yes, the 2 foils can independently control, their lift control systems are separate ."

 

Joking, the key is that Michele said the two foil systems are independent. No one is arguing that the S9 is faster than any other cat only that it is easier to sail than most other foilers because of its dual, independent wand systems which simply make foiling automatic.

Its too early in the S9's development to talk much about speed-but I'll guarantee you there is more coming in that area.

---

You say "people have moved away from that concept in the sailing world". That doesn't explain ,then, why three* of the newest foilers use wand controlled foils?!

 

*the third being the Vampire which, while it uses wands, only uses one wand and one main foil at a time and therefore doesn't create RM with the foils like the S9 and Whisper do.

Doug... let me rephrase it. No recent foilers use the windward foil to create negative lift or pull down. The negative lift, pulling down part of the concept was discarded by all recent wand controlled boats. I do not argue that they can get 0 or close to 0 lifting force from their foils. I just said they dont PULL DOWN

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You're dead wrong.........

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1) Simply, a wand system only starts to create righting moment when a certain ride height is reached, below that ride height, the system is either in neutral or is lifting. You can usually set that ride height through a number of different ways, but what is clear on the S9 is that you set the ride height the same on both tacks and cannot alter it "on the fly". Therefore, when a boat is foiling along dead level, the foils have to be producing the same amount of lift. It is only when the boat heels that the windward wand changes the flap to gain righting moment. So if you are sailing the boat level, which is usually the aim on a multihull foiler, the heavier person will have more righting moment. What the wand system does is help create a system that assists keeping the boat level, but it does that for everybody.

 

2)On the A, you can set the windward foil to a different AoA than the leeward one (if you have the systems), meaning that you always have some "pull down" working, irrespective of angle of heel. The debate is whether the systems needed, plus the requirement to adjust it for different points of sailing is worth the extra righting moment you can gain. While there are potential straight line speed advantages in certain conditions, many doubt you will be faster around a course once everything else is taken into account. Again, this picture probably changes on a 2 man boat, where extra hands make a difference.

 

 

 

1) what convoluted nonsense. The wands are automatic and once the boat starts to foil the dual independent wands start to work as required. As you say they wands cause the boat to develop extra righting moment when the boat starts to heel regardless of the weight on the boat when the boat is foiling. If the boat has a super light weight crew and starts to heel the wand controlled foils will generate extra RM until the boat is level. The windward foil can pull down and if it does, the leeward foil will provide extra lift. If the boat is sailed by a heavy person who can keep the boat level no extra RM will be required. The dual independent wands allow the light person and heavy person to sail nearly level regardless of the wind. In other words, the dual independent wands produce extra RM for the light person as needed to match the RM of the heavy person. They sail with EQUAL righting moment thanks to the downforce on the windward foil and extra lift on the leeward foil when it is needed. While a heavy person on a trapeze produces more RM than a light person on the trapeze the BOAT makes up the difference due to the dual independent wand controlled foils. Do you get it yet?

 

Yet again, you show your total lack of understanding.

 

Consider the S9 or, for that matter, any foiling cat. I think we can all agree that the optimum is to sail the boat level. If you sail the boat heeled, it will never be as quick as upright. In fact, sailing a foiling cat heeled really isn't a very good way to get around. When sailing the boat level, the windward foil cannot be providing righting moment because if it does, the leeward foil would be acting in the same direction, pulling the boat down and the boat would stop foiling. The alternative is you have some differential set up, so that the 2 foils work independently of each other and this is not present in the S9 or any other wand system that I am aware of. While the wand system might give assistance in getting the boat back to level when you start to heel, when sailing level and when max powered up or above, weight is what makes the difference, because if you are heavier, you can simply pull the sail in more and get more power. It's really rather simple, because you cannot change the science.

 

2) When you add downforce to the windward foil you have to add extra lift to the leeward foil or the boat will come off the foils. The wand system does this automatically .You didn't mention adding lift to the leeward foil on your A? Seems like a bitch to do this manually on any boat.......

 

Again, you haven't got a clue. With an A, as the boat rises up on its foils, the amount of lift they produce goes down, because there is less foil in the water. As it goes down, you get more lift. It's actually pretty automatic, maybe not quite as good as a wand system but still very effective. If you set your windward foil to provide righting moment, you have 2 options. First, you accept that you are not going to foil as high out of the water as you would do if it wasn't producing righting moment. The alternative is that you adjust the leeward foil so it produces more lift, which is no big deal because we adjust the AoA as we sail anyway. It certainly isn't a bitch to do because it is a single control to pull. All you need to do is set the difference between the AoA on both sides. Job done. Easy! What's funny about your comments is that when Nathan Outteridge talked about doing this on his A in a video, you got all carried away and excited even though at the time, the foils didn't really lend themselves to doing this. Now the foils have changed and it is potentially worthwhile but as it is me discussing it, you say something completely different. Yet again, we see your true colours.

 

 

Thats the key Simon: you're not aware of how a wand system creates RM. You've never sailed a wand controlled multihull with dual, independent wand based foil control systems!! The port and stb wands operate 100% independently of each other-that is why they can generate righting moment. They are able to do that effectively when the hulls clear the water and it is one of the great advantages of the S9 system.

 

Surely you cannot be this confused and as such, you are just being obtuse.

 

I am ot talking about them being 100% independent, which of course they are. I am talking about a differential system, where the ride height settings of one side are different from that on the other.

 

However, just in case you really don't get it, I will try to explain it again as simply as possible.

 

As said above, and apparently understood by everybody but you, these beach cats foil noticeably better when being sailed flat than when heeled. This has been found to apply with all systems and certainly applies to T foils powered by wands. This is why you see the sailors of foiling beach cats always working hard to keep the boats sailing flat and why you can see the ride height drop (sometimes to the point of touchdown) when the boats heel. For a boat like the S9, leeward heel is a killer, just like it is on a Moth, and for the same reasons.

 

Now, if you accept the boat needs to be sailed flat, consider what happens with the ride height system on a wand foiler, and in particular, the S9. While the wands do operate independently, for any given height above the water, the wands are in the same position on both sides of the boat, meaning the flap is in the same position and both foils are producing the same amount of lift. So when you are sailing the boat properly (flat), there is no way that the windward foil can produce any righting moment, unless you have a system that sets the ride height differently from one side to the next.

 

Taking this further, as the boat begins to heel, what happens is that as the windward hull rises, the wand reduces the amount of lift to that foil. At some point in time, the amount of lift becomes zero and then, if you heel more, it would reach the point of the foils producing righting moment. What we need to consider is at what point that happens. A number of factors influence this, such as the gearing of the wand system, boat speed, foil section, flap design etc. The really important part is that on a foiler, to lower the ride height, you don't need to go into "pull down"mode with your foils but you simply have to reduce lift. Now, I am sure that if you heel the S9 enough, you will reach a point when the foils start to pull down (create righting moment), but that point has to be beyond what most would consider an acceptable amount of heel.

 

So, when sailed properly (as close to flat as possible), it is highly unlikely that a conventional wand system on a beach cat, like the one seen on the S9, will provide righting moment.

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I'm afraid you don't understand at all. The main foils are already set at a positive angle of incidence. When the boat reaches the design flight altitude, the flaps are in neutral with the main foil angle of incidence providing around 80% or so of the lift required to fly the boat. The instant the boat heels to leeward-even a little bit- the wands respond by raising the windward flap and lowering the leeward flap which creates a righting moment to restore each hull to its design flight altitude.

That mechanism allows the boat to fly with no crew or with a light crew or with a heavy crew and ensures that the boat is sailing at all times with its designed righting moment whether that moment is supplied by the crew, by the boat alone or by a combination of boat and crew. It's automatic,it's proven and it works very well.

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Well Doug what you are saying is actually very different to what you started with. You are saying that the foils changer the righting monent! Ok we get that. So the lift distribution can go from say 50 50 on each hull to 90 10 when the boat is heeled, bringing the boat back to flat position.

What you were saying at the start was that the load can be -20 on the windward hull ( pulling down) and 120 on the lee hull. This does not happen except in some special boats (sailrocket or whatever).

This means that the dual wand boat will not produce more rm that the vampire (a speed machine) but will be more stable.

Is this what you are trying to say?

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I have no idea where you got the -20 and 120? I have been saying since I first responded to Simons nonsense that these boats have dual INDEPENDENT wand systems. I tried to explain that the windward foil is capable of downforce(matched by upforce on the lee foil).

This boat could , theoretically, develop RM until something breaks but because it is designed to be sailed with a crew on a wire that is unlikely.

There is no relationship between this boat and the Vampire-the Vampire does not use the single main foil to develop righting moment- only vertical lift. On that boat RM comes only from the distance of the CG from the center of lift of the lee foil(incl. crew), whereas on the S9 the foils can add as much RM as becomes necessary.

A dual wand foiler the same length and width as the Vampire would be capable of much more RM than the Vampire but not necessarily more speed.

From a speed standpoint, the foils on cats using dual, independent wand systems are relatively close together compared to a Rave or an Osprey(18' LOA X 22' wide) so they are less efficient in developing RM but no less capable of developing tremendous force. In other words, the further the foils are separated side to side the less drag they will develop when creating righting moment.

Post 122 says it the best I can say it about how this type of system works. The system is automatic and always provides the boat with the designed RM(if it needs to). The wand system is so sensitive that it will respond to gusts as well. Whatever it takes to keep each hull at its designed flight altitude.

So to try to answer your question: in my opinion the S9 could probably be described as more stable than the Vampire because the S9 system is automatic always providing the needed RM if the crew doesn't(or can't). Which helps to make it an easy to sail ,fast foiler.

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Why? The principle is that the wands are independent and automatically increase windward foil downforce and lee foil lift as required. What part of that don't you get?

The Hobie Trifoiler Longshot set a speed record or two specifically because of the way its foil system works.Raves were raced as a fleet on courses all over the US.

 

 

"Increase the windward foil downforce". To me this implies that the windward foil is constantly producing downforce, or pullling down to increase rm ( which is not happening on any racing foiler) and that it can increase it's downforce to generate even more RM if needed.

This is simply not happening.

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Doug

Joking is spot on. You have completely changed your tune. Up until now, you have been clearly arguing that the windward board pulls down, creating righting moment.

 

by way of example, to quote you

 

Post 103 - The windward foil can pull down

 

Post 120 in reply to the comment "they don't pull down" - you are dead wrong

 

You also quote Ketterman on the subject, highlighting the "pull down" part of his comments.

 

 

Now you are clearly agreeing with both Joking and myself. We both have said that what is happening is the reduction in lift from the windward foil, which is very, very different from it pulling down. It now appears the penny has finally dropped with you and you have stopped talking about "pull down".

 

However, what you don't seem to realise is that you get the same effect with the A Class Z foils, if maybe a little less pronounced. As we know, the Z foils self level because as the boat flies higher, they produce less lift. Therefore, as you heel, the windward board comes out of the water more and like the wand controlled board, it produces less lift. The leeward hull reduces ride height as the leeward board needs to provide more lift and that is achieved by having more foil in the water. It's also totally automatic.

 

So, having established that the wand controlled windward board does not contribute to righting moment by pulling down with a conventional wand system, we can look at whether this could be achieved some other way, and the answer is yes. If you change the gearing/ride height of the windward board in relation to the leeward one, you could potentially reach a point where, when flying level, the windward board did pull down. Of course, you need a system that you can "tack", and you have to assume that the leeward board is capable of providing the required lift to compensate, but, theoretically, it is possible.

 

Creating extra righting moment through the foil pulling down is far simpler with the A Class Z foils, so long as you have the right board section (not too asymmetric which some are and some aren't) and you can adjust the AoA of each board separately. It really is a pretty simple system to set this up.

 

Finally,there is the issue of whether the wand system can compensate for a lighter crew and on this, it should be very clear that in performance terms, it can not. For any given angle of heel, exactly the same thing happens irrespective of weight of crew. So the "self leveling"properties that Doug keeps going on about are there irrespective of crew weight. And while the lighter crew might heel more and therefore use those properties more, the very fact the boat is heeled means it is slower than a boat sailed flat, so therefore you only get the benefit when you are sailing slower compared with a boat sailing flat. The only way you can give a lighter person some help to overcome the advantage of being heavier is to allow them something the heavier person is not allowed. If the system is available to both, the advantages or disadvantages of being a particular weight stay the same.

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Why? The principle is that the wands are independent and automatically increase windward foil downforce and lee foil lift as required. What part of that don't you get?

The Hobie Trifoiler Longshot set a speed record or two specifically because of the way its foil system works.Raves were raced as a fleet on courses all over the US.

 

 

"Increase the windward foil downforce". To me this implies that the windward foil is constantly producing downforce, or pullling down to increase rm ( which is not happening on any racing foiler) and that it can increase it's downforce to generate even more RM if needed.

This is simply not happening.

 

 

As required is the key point. The two foils work together to provide righting moment as required. The windward foil most certainly does create downforce if required. And it surely does work on a race boat if and when required.

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Simon, you never have read well and your reading comprehension is notoriously bad. I've been saying what I'm saying now since post 93 and once before then.

I've always said that if(and when) the windward foil pulls down creating downforce the lee foil automatically matches it in the opposite direction.

 

That's the way it works. I've said it repeatedly throughout this thread -you simply didn't see it or , I guess, comprehend it.

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OK then we both agree the windward foil does not pull down on the hull for the purpose of constantly obtaining more righting moment when sailing flat.

All cleared up.

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Finally,there is the issue of whether the wand system can compensate for a lighter crew and on this, it should be very clear that in performance terms, it can not. For any given angle of heel, exactly the same thing happens irrespective of weight of crew. So the "self leveling"properties that Doug keeps going on about are there irrespective of crew weight. And while the lighter crew might heel more and therefore use those properties more, the very fact the boat is heeled means it is slower than a boat sailed flat, so therefore you only get the benefit when you are sailing slower compared with a boat sailing flat. The only way you can give a lighter person some help to overcome the advantage of being heavier is to allow them something the heavier person is not allowed. If the system is available to both, the advantages or disadvantages of being a particular weight stay the same.

You still don't get it: the wand system responds instantaneously-it never lets the boat heel significantly- it immediately corrects for anything that changes the flight altitude of the hulls -quickly and completely. The wand system is automatic-if the crew falls overboard it will continue to stabilize the boat keeping it foiling!!

The dual independent foils respond to any change in the flight altitude of the hulls immediately-virtually instantaneously. Including response to gusts as required.

And the system will compensate for crew weight, crew movement etc and do it right now! That's one of the major advantages of this kind of wand system. And that's one of the major reasons the boat is easy to sail!

And in doing this if required, the windward foil can and will pull down and will be matched by the increased lift on the lee foil. Automatically. Quickly.

 

PS -you apparently didn't understand what Ketterman said which is virtually the same thing I've been saying: he referred to the windward foil pulling down but also to the increased induced drag of the lee foil when that happens. His way of saying the lee foil matches the windward foil when it pulls down!

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OK then we both agree the windward foil does not pull down on the hull for the purpose of constantly obtaining more righting moment when sailing flat.

All cleared up.

 

What I just said........the windward foil CAN pull down for the purpose of obtaining more righting moment BUT if it does it will be matched by increased lift from the lee foil-the two foils together creating the required righting MOMENT...... On the S9 this is automatic and instantaneous.....

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This is getting stale.

 

The point is that Doug thinks the S9 foils produce down force, no one else thinks they do. The guy who could clear this up hasn't.

 

So in the interest of trying to move on, can someone please post the design for a flapped foil that providse say 100kg lift at 20kn with the flap in neutral, and have enough flap range to provide say 50kg of downforce. A Bladerider flap has about 10 degrees of up flap and it does not produce downforce, so it will be interesting to see how much flap (size and range of movement) is required.

 

To produce down force, the flap has to overcome the lift from the main part of the foil, which is still producing its full allocation of lift, and create further downforce. Without stalling.

 

Then look at the drag produced as a result. Also, the other foil is now producing 150kg of extra lift to compensate. What is the penalty in drag for that?

 

Once such a foil is designed, or even just considered, I think it's pretty clear that any such system needs to incorporate an AoA control, otherwise the flap has way too much work to do.

 

But I'm happy to be proved wrong about that.

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You are moving into the requirement of relatively poor performance symetrical foils fitted with both a flap and aileron. Look at aerobatic gliders for such designs and just look how complex the control movements and linkages are to be able to operate these and then compare their best L/D against the best performing gliders with assymetrical foils ( wings ), 12:1 compared to over 50:1.

 

Interesting that some of the modern design thinking in gliders is using flexible wing shapes and materials to create what ever shape ( within limits of course ) you need at any one moment in time, by computer controlled shaping of the active foil. Now we really are talking complexity.

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This is getting stale.

 

The point is that Doug thinks the S9 foils produce down force, no one else thinks they do. The guy who could clear this up hasn't.

 

 

 

Rob, the guy that could did in response to a direct question. posts 29 & 30.

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Once such a foil is designed, or even just considered, I think it's pretty clear that any such system needs to incorporate an AoA control, otherwise the flap has way too much work to do.

 

 

The Rave had a set up on some racing boats that would allow the angle of incidence of the windward foil to be changed underway from +2.5 degrees to zero degrees to get more downforce(or the same with less drag). Of course, that would have to be changed back before every tack or gybe.

 

---

In terms of the penalty in drag for the windward foil downforce and increased lee foil induced drag read what Ketterman said:

 

"Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides."

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This is a Rave(and Osprey and Skat) foil control animation video just to give some idea of what happens to the flap as altitude changes. This is not the S9 system but the two work in a somewhat similar way. Note that when the flap is neutral(neither up nor down) the boat has reached its design flight altitude. If I remember correctly the flap moved 30 degrees down and 20 degrees up.

 

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Have I understood this right?

 

As the wind increases, the boat accelerates and the leeward foil generates more lift, so the boat rises a little, the wand responds to the extra distance down to the water and it adjusts the angle of the foil flap to generate less lift, thereby causing the hull to lower back down a little, but not back as low as it started (as that would lead to the foil flap angle returning to its original state). This means the boat is flying slightly higher than it was before.

 

To keep the boat level, you either need to get your weight further to windward or change the lift from the windward foil, or a combination of both. Because the boat is now flying slightly higher, the windward wand too will respond to the water being further down and will reduce lift from the windward foil's flap, so that will either reduce or eliminate the need to move weight to windward, and if it doesn't eliminate that need, it will at least lead to the crew having more time to react and not having to make such a big adjustment to their position, thereby resulting in the boat being easier to sail than if the windward foil wasn't there.

 

If you're on an A-cat though, a similar thing happens: the hull is flying higher, so there's less of the leeward foil in the water, but there's less of the windward foil in the water too, again either reducing or eliminating the need to move weight to windward. The two systems are thus exactly the same, unless you adjust the windward foil to produce less lift at all flight heights.

 

If you can produce enough lift from the leeward foil alone to fly the whole boat, you don't want to generate lift from the leeward foil, so whichever foil system you're using it should be advantageous to reduce the lift generated on that foil for a given flight height to a lower value than the leeward foil. Where the key difference between the two systems come in is that the wand controlled version can be designed to generate downforce, and an increasing amount of downforce as the flight height inches higher while the boat speed goes up. That cannot be done with static foils, because even if you angle the windward foil to generate downforce, the amount of downforce generated will go down as the boat goes faster and rides higher.

 

If I've got all of that right, the big question remaining is whether the S9 and the Whisper are actually designed to produce downforce in this way or if they simply reduce lift from the windward foil to zero once the flight height is above a certain level. If the latter, then there is still an advantage over the A-cat system in that the windward foil can be set to generate some lift at some speeds while reducing automatically to zero at others (without the crew changing any of the settings), whereas on the A-cat there will either be no lift from the windward foil throughout the same speed range or there will be a range of lift values which does not go down to zero (because zero would only be reached with the foil right out of the water, which isn't going to happen with the boat level unless the leeward foil is completely out too).

 

So, that's a difference that will make the S9 and Whisper easier to sail than an A-cat even without generating downforce. However, further gains could be made by generating downforce if that allows a light crew to sail the boat level in strong winds where they couldn't do so otherwise. If someone reading this thread owns an S9, it should be easy to clear this issue up for that boat, because if the wand isn't actively powered down against the water by a spring, it isn't going to be capable of generating downforce from the foil flap because the water will simply keep the flap level and hold the end of the wand off the water.

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If I've got all of that right, the big question remaining is whether the S9 and the Whisper are actually designed to produce downforce in this way or if they simply reduce lift from the windward foil to zero once the flight height is above a certain level. If the latter, then there is still an advantage over the A-cat system in that the windward foil can be set to generate some lift at some speeds while reducing automatically to zero at others (without the crew changing any of the settings), whereas on the A-cat there will either be no lift from the windward foil throughout the same speed range or there will be a range of lift values which does not go down to zero (because zero would only be reached with the foil right out of the water, which isn't going to happen with the boat level unless the leeward foil is completely out too).

 

So, that's a difference that will make the S9 and Whisper easier to sail than an A-cat even without generating downforce. However, further gains could be made by generating downforce if that allows a light crew to sail the boat level in strong winds where they couldn't do so otherwise. If someone reading this thread owns an S9, it should be easy to clear this issue up for that boat, because if the wand isn't actively powered down against the water by a spring, it isn't going to be capable of generating downforce from the foil flap because the water will simply keep the flap level and hold the end of the wand off the water.

 

Read from post 93 again. A wand controlled foil system is automatic and will provide all the RM it needs to based on the design flight altitude.

It can provide no downforce on the windward foil all the way up to max downforce and as much lift on the lee foil as it takes to match the degree of "downforce".

"downforce" can be anything from a slight reduction in lift to enough force to cause the windward foil to pull down.(all matched by the lee foil with extra lift)

This is done 100% automatically by the wands moving the flaps in response to any deviation from the design flight altitude and it is done instantly.

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Doug - you cannot design in a single flight height and have the boat stick to that as the wind increases. If it rises and the wands adjust the foils to bring it back down to that same height, the wands will then have no option other than to go back to where they were before and the foils will return to their original angles too, just as if the wind has not gone up at all. You need to change your description of things to take that into account: the flight altitude has to change and stay higher than it was before if the wind is higher.

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Geez, David-after all this you make a statement like that??!!

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I missed one factor. The higher wind doesn't just try to lift the windward hull by tipping the boat over, but must transfer more downward force onto the leeward hull in the process, so it needs to generate more lift to balance that, but then the higher speed of the boat will generate more lift, and I don't know how to calculate which wins out, but it's just possible that the flight height ends up being exactly the same afterwards even though the foil is generating more lift, but if that's the case then 100% of that extra lift would have to be down to the extra boat speed and with 0% being due to any change in flap angle because there cannot be any difference in flap angle if the flight height is unchanged. The windward hull's foil flap angle would also have to be unchanged if the flight height is the same as it was before, so that means the higher boat speed will amplify its lift if it's still set to positive lift or will amplify its downforce if it is already set to negative lift. Either way, if the flight height doesn't change, the flap angles don't change and the wands serve no useful purpose.

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David, you may need to consider that with the flap on a T foil arrangement set at neutral, regardless of the speed, the foil shouldn't go up or down vertically.

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David, you may need to consider that with the flap on a T foil arrangement set at neutral, regardless of the speed, the foil shouldn't go up or down vertically.

 

How do you set it to neutral? If it's still connected to the wand and the hull drops, the flap will be pushed down and it will generate lift. If you've disconnected it from the wand to make it neutral though, then that won't happen and it becomes directly equivalent to a windward A-cat foil being angled for zero lift.

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This is all getting a little boring and repetitive..........

Doug believes that if he endlessly repeats the same stuff without addressing the flaws in his logic that he'll win the day. So far he has zero to support his case, he can't point to a single system that relies solely on wand and flap that produces both lift and down force and doesn't change the angle of incidence. Certainly systems like the S9 control RM by reducing the lift on the windward foil, but there is nothing to show that it generates down force (once again Doug, the comments in #30 only refer to changing lift, not creating down force). The only known systems that produce down force change the angle of incidence of the main foil, because that's the only sensible way to do it.

 

Doug has also made no attempt to show a foil that can go from 250kg of lift to 50kg downforce by flap alone, without changing the AoA, but he has no answer (he just ignores the question).

 

No doubt it's possible to effectively produce downforce on an A Class with symetric (or very nearly symetric) foils, and that is likley where a contemporary version of such a system may come from. But it will need to be tacked with the sail and will need very careful setup for specific conditions to get right, so will require quite a bit of skill to use effectively. A starting point will be to set the foil for zero lift.

 

Some in the Moth world have tried dual wands and independent starboard/port flaps, but they have not been successful.

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David, you may need to consider that with the flap on a T foil arrangement set at neutral, regardless of the speed, the foil shouldn't go up or down vertically.

 

How do you set it to neutral? If it's still connected to the wand and the hull drops, the flap will be pushed down and it will generate lift. If you've disconnected it from the wand to make it neutral though, then that won't happen and it becomes directly equivalent to a windward A-cat foil being angled for zero lift.

 

Haven't you answered your own question, afterall the whole point of the excercise is for the wand at some point of vertical travel of the hull, to have the flap set at neutral, which should mean the hull neither rises or falls. But that is in an ideal world and theres a whole dicussion on just how that wand mechanism achieves a smooth transition from course travel ( lots of movement of the flap at the extremes ) to tiny incremental movement just either side of the ideal hull height to prevent oscillation where the hull starts a harmonic up and down moment ( which the DNA video above was showing just before the end of the video, with its bow down and up motion getting larger with every loop, it would interesting to have seen the next minute of vid ).

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This is all getting a little boring and repetitive..........

Doug believes that if he endlessly repeats the same stuff without addressing the flaws in his logic that he'll win the day. So far he has zero to support his case, he can't point to a single system that relies solely on wand and flap that produces both lift and down force and doesn't change the angle of incidence. Certainly systems like the S9 control RM by reducing the lift on the windward foil, but there is nothing to show that it generates down force (once again Doug, the comments in #30 only refer to changing lift, not creating down force). The only known systems that produce down force change the angle of incidence of the main foil, because that's the only sensible way to do it.

 

Doug has also made no attempt to show a foil that can go from 250kg of lift to 50kg downforce by flap alone, without changing the AoA, but he has no answer (he just ignores the question).

 

No doubt it's possible to effectively produce downforce on an A Class with symetric (or very nearly symetric) foils, and that is likley where a contemporary version of such a system may come from. But it will need to be tacked with the sail and will need very careful setup for specific conditions to get right, so will require quite a bit of skill to use effectively. A starting point will be to set the foil for zero lift.

 

Some in the Moth world have tried dual wands and independent starboard/port flaps, but they have not been successful.

 

 

Rave, Osprey, Skat, S9, Whisper-all of which produce downforce from the windward foil when required, automatically. The systems automatically increase the lift from the lee foil to match downforce from the windward foil. This is not a "belief" system: it is physics and science. If you don't "believe" it, its because you don't understand it and have no experience with the systems. I've tried to explain it as clearly as possible and that's all I can do.

I've worked with wand systems for over twenty years including sailing, designing and building them. I learned much of this stuff from Dr.Sam Bradfield and from lots of work.

The Rave system was so powerful that there was a "never exceed" speed posted in some cockpits because exceeding that speed would take the chance of breaking the single crossbeam. That actually happened due strictly to the forces developed by the foils.

Thats why Greg Ketterman referred to the limit of the forces developed by the foils as structural on the trifoiler.

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Wasn't the Trifolier a fixed symmetric single foil on either side, without flaps and the whole foils angle of attack was changed to get both positive and negative lift of equal amounts ? if so then we are speaking of a whole different setup to the S9.

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The trifoilier* was an incidence(see post 112) controlled foiler where there were long "feelers" sticking out in front of the boat connected directly to the foils.The feeler would change the angle of incidence of the symmetrical foil to control both lift and righting moment. And the wand controlled foilers have the wand move a flap to accomplish the exact same thing.

---

But the basic principle is the same: changing the lift of the foil using a surface sensor. Both can create enormous righting moment.

 

*In about 2012 Greg Ketterman patented a new version of the trifoiler using trailing wands with large "paddles" on the ends, rather that "feelers" to actuate the foils.......

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So yes you could have both rates of negative and positive lift then on the Trifoiler, but we were talking about the S9 which has tiny itsy bitsy teeny little flaps on the back of an assymetrical foil. Sort of apples and oranges isn't it.

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This is getting really really boring.......why don't the main protagonists of this thread message both the S9 (and Whisper) designer to get the definitive word on all maters relating to righting moment and foils affect on that so we can move on?

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A-- I wrote to Thom at White Formula about the Whisper-this is his response:

Hi Doug

The foil system is active so it uses AOT (angle of attack) to constantly re-adjust the foil position, the crew are able to adjust the foil heigh whilst sailing and adjust the overall rake, for fine tuning.
Thom
White Formula UK
============

B--I've talked to Michele about this thread he's satisfied with my responses.

 

So we're done, right?

 

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No doug you aren't......please ask them to respond to confirm or deny the windward foil creates a downward force such that it has an affect on rm.........simple question really.....

 

I have no stick in the fire in this discussion, but all this discussion about this point is getting very boring.......please get them to answer this question.......I know you have the contact details of the Whisper designer (rather than builder) so please contact him and the S9 designer and ask them to respond in person on this thread......

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You may be bored, Nacraman, but it might just be reaching a crunch point. I think Doug may have been misleading people like me about this downforce thing for a very long time, and he hasn't been taken to task over it properly. A question I was planning to ask has just been answered: the Rave generates downforce by rotating the entire foil, and that means that the water can't push it back level again in the way it will with a flap. The Osprey was half a mile wide and probably never needed to generate downforce, so I'm now wondering if it ever really did. Is it possible that Doug's Fire Arrow can't generate downforce either, but he merely thinks it can because when he moves the wand down the flap goes up to an angle for negative lift? Does he actually have a mechanism to stop the water holding the flap down and lifting the wand off the water?

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Maybe Michele and the owners of the S9s have given up on this stupid thread, but if they are still there can they please say if the flap is connected to the vertical pushrod, or is it still only able to push down as I saw it in 2014? If it still can not pull the flap up, there is no way that down force is possible. This simple fact will settle this stupid argument.

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Phil, I asked Michele about that and he said from 2015 the pushrods were connected to the flaps. And the wand system can cause the flap to pull up......

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You may be bored, Nacraman, but it might just be reaching a crunch point. I think Doug may have been misleading people like me about this downforce thing for a very long time, and he hasn't been taken to task over it properly. A question I was planning to ask has just been answered: the Rave generates downforce by rotating the entire foil, and that means that the water can't push it back level again in the way it will with a flap. The Osprey was half a mile wide and probably never needed to generate downforce, so I'm now wondering if it ever really did. Is it possible that Doug's Fire Arrow can't generate downforce either, but he merely thinks it can because when he moves the wand down the flap goes up to an angle for negative lift? Does he actually have a mechanism to stop the water holding the flap down and lifting the wand off the water?

 

David, the Rave does NOT rotate the whole foil!!!

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Come on Doug - I want to hear about your mechanism to keep the wand on the water when a couple of tons of pressure are trying to hold the flap level.

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Oh, I got the wrong name: when I said the Rave, I meant the Trifoiler, but you should have guessed that from the context.

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Doug keeps telling the same old story about this downforce going up and up until it breaks the beam, but that was actually on a boat where the whole foil rotated to generate downforce. I always got the impression from him (perhaps by misreading what he said) that the same applied to systems using a flap, but the more downforce you try to generate with it, the more strongly it will work against the foil, trying to lift it off the water, so it should be dead easy to design in a point where the pressure against the flap overpowers the wand to protect the boat from extreme forces. I've never heard him mention that idea. I haven't yet ruled out the possibility that a wand is heavy enough, has enough leverage and can be geared in such a way that it can tilt the flap against the power of the water that's trying to flatten it to generate significant amounts of downforce without the wand lifting off the water, but I want to see the numbers to show that the mechanism can work. He should be able to tell us straight off what the maximum amount of downforce is that his foils can generate before the wand lifts off.

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Doug keeps telling the same old story about this downforce going up and up until it breaks the beam, but that was actually on a boat where the whole foil rotated to generate downforce. I always got the impression from him (perhaps by misreading what he said) that the same applied to systems using a flap, but the more downforce you try to generate with it, the more strongly it will work against the foil, trying to lift it off the water, so it should be dead easy to design in a point where the pressure against the flap overpowers the wand to protect the boat from extreme forces. I've never heard him mention that idea. I haven't yet ruled out the possibility that a wand is heavy enough, has enough leverage and can be geared in such a way that it can tilt the flap against the power of the water that's trying to flatten it to generate significant amounts of downforce without the wand lifting off the water, but I want to see the numbers to show that the mechanism can work. He should be able to tell us straight off what the maximum amount of downforce is that his foils can generate before the wand lifts off.

 

David, you need to read more carefully and, well.. more. The story about the main beam breaking was told to me by Dr. Sam and happened on a RAVE!(with........flaps!)

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You're a serious designer, Doug. You must have the figures on weight, leverage, gearing, etc. You must have diagrams or photos. You must have explanations. Quit with the short diversions and show me how this downforce with flaps thing actually works.

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It's all falling to pieces in my head, Doug. The force on the flap pushes the wand down against the water hard when the foil's generating lift - on the Moth you can tell it's not just the weight of the wand doing the work from the way it judders like crazy against all the little wavelets, so it clearly can't just be gravity doing the work. If water pressure against the flap powers the wand down so strongly, then when you reverse the angle and have downforce instead of lift, the pressure's going to power the wand straight off the water after the first few grams of downforce have been applied. You're going to need a ruddy great spring to outgun the levels of downforce you've been talking about and to hold the wand down. And if you do use a powerful spring, that's going to hold the wand right down underwater at low speeds, isn't it? Please tell me I'm wrong. Please show me I'm wrong.

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Will it is getting rather boring, I suspect that what is really going on is an argument over literal meaning vs connotation.

 

To start with, when you have a foil system like the S9, I think everybody agrees that as the boat heels and the wands move, there is a change in righting moment.

 

The problem is what causes that change in RM. Again, I think that everybody agrees that initially, that change happens because the windward foil produces LESS lift while the leeward foil produces more lift.

 

The key is that Doug argues that the windward foil changes the direction lift is generated from upwards to downwards, and that this contributes to the increase in righting moment. What everybody else is questioning is whether that really does happen, or whether windward foil only contributes to the change in righting moment solely due to a reduction in lift.

 

Consider the simplest situation (theoretical) for a foiling wand controlled cat, which would be symmetrical foils with a flap, with the foisl set at a zero (neutral) AoA. The direction of the flap from neutral determines the direction of lift. This might be very crude, but this is for initial illustrative purposes only. Now, if this cat was foiling, it would be because the flap was being forced down, creating a foil that would lift upwards. For simplicity, lets say the flap has a positive angle (vs neutral or negative). Easy so far!! Now, if the cat heels, the wand controlling the flap would change the flap angle. On the windward board, there would be a period between the position of the flap when the boat was foiling level (positive angle) and the point where the flap is neutral, so that the foil overall gives no lift at all. In that situation, the windward board goes through a range from a certain amount of upwards lift to neutral. the change in RM is due (ignoring leeward board) to reduced lift and not due to the foil pulling down, negative lift or any other such term. We could then reach the point where the flap goes negative and the direction of lift changes, creating pull down or a change in the direction of lift.

 

So far, so good. In this case Doug's argument stands up. But let's add some real world factors to it. To start with, in the real world, foilers set their lifting foils to having a positive AoA. In the case of the foils described above, that means when the flap is neutral (to the rest of the foil), the foil is still producing lift. This only changes when the flap goes negative. Now we begin to run into a number of issues, such as range of adjustment that can be made by the wand and also the fact that if you apply too much negative flap, you can stall the section.

 

Then you get to the absolute real world situation. In this we have asymmetrical foil sections set at positive AoA. The flap solely controls the amount of lift. RobG give the case of the Bladerider foil which never reaches the point where the flap can change the direction of lift, despite having a very large flap ranges.

 

Looking at pictures of the S9 and Whisper, it appears that the foils are not symmetrical and are not set at a neutral AoA. What we need to know is whether the flap, at its maximum range, can change the lift direction with the foil at its operating AoA. To be clear, this a very different question to one about changes in RM.

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I think you will find that most if not all assymetrical foil shapes with 30% / total area flaperons will create such inefficient foil shapes when the flaperon is moved negative to any great degree, that the whole foil begins to not work as designed and begins to stall and thus lose any potential of downward force . With water being such a dense medium then probably anything beyond 10 - 15 degrees negative will create a total failure of foil efficiency and will instead just produce added drag.

 

I do sypathise with Doug in someways though on how distructive flaperons can be to the supporting structure. A lot of the early composite gliders ( we're talking 60's and 70's designs ) had such poor understanding of forces that you could smash the wings off at high speed by simply moving the flaps into the wrong position. I'm not sure but I suspect the early Trifoilers and such boats were probably in the same infancy of understanding of the forces involved.

 

Things have moved on in our knowledge, but rest assured get the forces wrong and our knowledge is still not advanced enough, that foils will continue to break under the force they can produce.

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Don't you guys do ANY research! This pointless debate was solved over 10 years ago.

Read the Rave and Trifoiler info, NOT skim! if you want the truth.

As far as real world experience check out the A cat forums there is plenty.

My personal experience with a foil test in dingy at 5mph set for +5 and -5 degrees, could not hold it down and worst yet could not hold it up and spent the next hour finding it in the weedy bottom!

Go to the A cat forums.

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Those interested should read this site-carefully: http://www.s9team.eu/

 

"The wand system link to a flap on the main foil allows auto control flight stability".

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Don't you guys do ANY research! This pointless debate was solved over 10 years ago.

Read the Rave and Trifoiler info, NOT skim! if you want the truth.

As far as real world experience check out the A cat forums there is plenty.

My personal experience with a foil test in dingy at 5mph set for +5 and -5 degrees, could not hold it down and worst yet could not hold it up and spent the next hour finding it in the weedy bottom!

Go to the A cat forums.

Jim

Thanks for your contribution, but it doesn't really help. We aren't talking about 10 year old designs and the A doesn't have a wand and flap!

 

Those interested should read this site-carefully: http://www.s9team.eu/

 

"The wand system link to a flap on the main foil allows auto control flight stability".

Seriously, Doug, what are you trying to tell us? Has anybody denied that the flap allows for automatic flight stability? Is there anything on the site that advances the debate?

 

Surely this is just another example of you totally avoiding the questions directed to you. You do this time and again whenever you are unable to support your previous comments. You have been asked to provide evidence by a number of people and you have't done so.

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Don't you guys do ANY research! This pointless debate was solved over 10 years ago.

Read the Rave and Trifoiler info, NOT skim! if you want the truth.

As far as real world experience check out the A cat forums there is plenty.

My personal experience with a foil test in dingy at 5mph set for +5 and -5 degrees, could not hold it down and worst yet could not hold it up and spent the next hour finding it in the weedy bottom!

Go to the A cat forums.

Jim

Thanks for your contribution, but it doesn't really help. We aren't talking about 10 year old designs and the A doesn't have a wand and flap!

 

Those interested should read this site-carefully: http://www.s9team.eu/

 

"The wand system link to a flap on the main foil allows auto control flight stability".

Seriously, Doug, what are you trying to tell us? Has anybody denied that the flap allows for automatic flight stability? Is there anything on the site that advances the debate?

 

Surely this is just another example of you totally avoiding the questions directed to you. You do this time and again whenever you are unable to support your previous comments. You have been asked to provide evidence by a number of people and you have't done so.

 

 

That's just bullshit, Simon!

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The tension on the bungee/spring was greatest when the flap was up: water pressure on the wand keeps the flap down(vertical lift) but keeping it up for downforce requires tension from the bungee/spring to overcome water pressure on the wand......

 

 

That's a quote from Doug found in a thread on another forum, so he clearly does understand that you can't get downforce from a flap without some kind of spring pushing or pulling either the flap or up or the wand down. I apologise to him for doubting him on that point (and I still hope he'll turn out to be right about most of this).

 

The best I can find on the Rave is a diagram 2/3 of the way down this page: http://www.sailingbreezes.com/sailing_breezes_current/advertisers/rave/rave_redefining.htm . It doesn't explain how the flap is held up for downforce, though clearly it is designed to produce downforce as well as lift, and by the look of it it can produce equal amounts in both directions. I can't find out how it does it, and I still can't work out why the force from the water against the flap can't overpower the spring before the boat breaks. In the quote at the top, Doug says that the tension is greatest when the flap is up, but that doesn't make sense as it's the wrong way round - the tension would only go higher as the flap rises if the spring is trying to pull the flap down rather than up (and the same applies if the spring's powering the wand down to achieve this: it should apply less force the further down the wand goes).

 

I can't get anything better out of Google (half the results lead to Doug who provides lots of facts without the evidence) and I'm fed up of hunting through all the empty s**** in PDFs that look as if they might answer the questions but never quite do.

 

Edit: Found another Doug quote:-

 

So regardless of what is done to the flap the spring/ bungee must be arranged so it has greater force on the wand when the wand is forward and down.

 

Whatever trick is used for that, it must show up in the hardware. Does the S9 (and/or Whisper) have such a system for applying force in this way (and can the flap be angled upwards)? That's all that needs to be known to settle this.

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Don't you guys do ANY research!

 

Yes. This discussion continues because there is one person who believes that not only is it practical for a flap alone to produce downforce, but that the whole world is in denial for not believing him. There is zero evidence to support the notion, it all indicates otherwise.

 

It's well known that A Class cats are at least considering (and likely trying) generating down force using flapless foils and AoI adjustment. But that's a different discussion since there's no doubt they can generate downforce, for them it's just a question of whether it's practical and faster than other approaches. In theory more RM makes more speed possible, but do drag, higher forces, tacking the foils and so on make it slower around a course? Only experimentation will tell since theory and computer analysis only gets you so far.

 

But in regard to flapped foils generating down force, first it needs to be seen if a practical main lifting foil can be designed or developed that transforms from useful lift to downforce solely by adjusting the flap. No one, not even the concept's chief supporter, seems to have done that (or even designed that) yet.

 

PS @David Cooper

 

The wand return spring only needs enough tension to keep the wand on the surface, which isn't a great deal. For Moths, 1m of 4mm bungee stretched to 1.5m and attached to a 100mm lever on top of the wand provide sufficient force (of course there are a huge number of variations on that, both in magnitude and implementation, so consider it a very rough guide). Pushing the flap down takes a great deal more force, made possible by the wand's big mechanical advantage.

 

But your point is valid. Where the flap is required to overcome lift from the rest of the foil (set at say 2.5° AoA) and provide additional downforce, it must be pulled up with a similar force as is required to push it down to provide lift. It's a significant factor that encourages adjusting AoI if downforce is desired and must be addressed in a system where the flap produces the downforce.

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Don't you guys do ANY research!

 

Yes. This discussion continues because there is one person who believes that not only is it practical for a flap alone to produce downforce, but that the whole world is in denial for not believing him. There is zero evidence to support the notion, it all indicates otherwise.

 

 

 

Thats 100% false. You have been presented "evidence" that you choose to ignore.

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More "evidence": http://smalltrimarans.com/blog/jim-brown-article-on-sam-bradfields-hydrofoil-trimaran/

 

"For very high speed aircraft, and now for hydrofoils, “symmetrical” sections – cambered both top and bottom – (convex/convex) are used by Bradfield and others. When fitted with an articulating aileron or flap, these foils can create lift in either direction, up or down, and so can exert a profound stabilizing influence on a sailing trimaran. Heeling effort in the sails, which would normally depress one side of the craft and elevate the other, is resisted absolutely by the downwind foil lifting up and the upwind foil pulling down. The craft stays dead flat, the mast stays plumb vertical, the usual spilling of wind from heeling is converted instead to thrust, and the power of the sails is fully utilized to propel a craft that is now largely relieved of the age-old drudgery of hull drag."

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But Doug, symmetric foils are yester year, they are just too draggy to make their case in todays efficiency driven boats. The A's are the ones leading the mass development now and they are only interested to fly the boats in the most efficient way, to obtain the fastest time around a course. Do they need more RM with the limited amount of sail area they have, no their crew weight will do that. Do they need more draggy foil shapes, been there, done that and now moved on.

 

The boats Bradfield designed were good in their day, sadly they wouldn't be able to compete now, such is the development pace. Doug you need to be more open to information that is being passed to you on the likes of these pages, the amount of time you spend defending your beliefs, would be far better off getting your models sailing and proving or disproving your theories.

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But Doug, symmetric foils are yester year, they are just too draggy to make their case in todays efficiency driven boats.

 

 

 

Wayne, sorry, but you simply don't know what your're talking about. This is about the S9 and other wand based foilers, not A class cats-totally different foil systems,totally different foils.

 

The Osprey was launched in 2011 and is still a state of the art Bradfield foiler.

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