Dumb'n it down further, I like twinnies. Have other good boards but a good twin fin set up is the ducks guts for me.
Bouke I think it's great you did all that amazing costly research and share it.
But you're having a laugh with 0.1deg toe changes yeah?
That's 0.2mm over the length of the base on a side fin. A grain of sand in the box would change it.
It's also the thickness of a single piece of 4oz glass so if there was the tiniest error in sticking the box in you're off by 0.1deg.
Select to expand quoteBouke-Witchcraft said..Gestalt said..Bouke-Witchcraft said..Gestalt said..
Bouke
So here are my Questions.
Surely any foil with a 0 degree aoa should have zero lift which means zero lift drag.
When the side fin has zero aoa, it has about 2 degree toe. With zero aoa, the drag is lowest but not zero.
so this is the bit i'm hoping you can help me with.
why 2 degrees. is that a function of your asymmetrical fin or something else?
No, that is what we found in 2005 with the 4wfs and symmetrical fins to be fastest and give the most alround turning behaviour. Over the years this has been confirmed to be between 1.8 and 2.1 degrees, lateron also by CFD only that the 1.8 to 2.1 degrees was just the average, it is 3.7 to 4.1 degrees degrees at the fin base and zero at around 12 to 14 cm of depth. And the toe of 2 degrees was only correct at around 5 to 7cm depth so from the base and tip you still get excess drag with a symmetrical fin. The change in AoA over the depth is not lineair like it is with the blade of a wind turbine.
I have put these fins also on some surf boards over the last 10 years with amazing results. However the surfing fin industry is so powerful with their marketing that I am not even going to try. Plus that it is not suitable for the futures or FCS systems as they do not have enough room to twist the fin on the base. With the slot box it is just on the edge. So first you would need to get shapers to put the FCS or Futures systems with more angle before anyone would be able to try this and then they will not work with other fins, which will make people very hesitant and it will cost a lot of marketing investment to overcome this, sponsor a few Kelly Slaters, etc..
I forgot, you can also test the boards and sails in Sidi Kaouki, Morocco.
Ok thanks for being so open about something you have put a lot of time into.
Certainly looks like your system is producing results. Im still keen to see a comparison to a straight setup.
For me, the elephant in the room is the AOA. Whilst it might be possible to install a box at decimal point accuracy, the AOA of the water is going to vary well beyond that level of precision which would have an impact for sure.
Not to say you havent resolved the issue of toed fins being draggy caus i hope you have. Just saying there are still things that dont reconcile for me.
Select to expand quoteGestalt said..
Ok thanks for being so open about something you have put a lot of time into.
Certainly looks like your system is producing results. Im still keen to see a comparison to a straight setup.
Like I said, I left straight fins behind many years ago as even with straight fins, the result both for turning and drag was very very clear.Select to expand quoteGestalt said..
For me, the elephant in the room is the AOA. Whilst it might be possible to install a box at decimal point accuracy, the AOA of the water is going to vary well beyond that level of precision which would have an impact for sure.
Yes, off course, that is why we have been looking to see what is the average situation, the closer you get to that, the better it will handle a variation in the AoA. So if you see that for a V bottom shape the average situation needs 0.2 degree more toe over an inverted V bottom, it is easy for me to adapt to that. Besides I also look at where a board is aimed for, if it is aimed for tight turns at lower speeds, I may add a few tenths of toe. Not much but still it is easy for me to make such small variations by gut feeling. And with the mini tuttle fin set up, it is easy to modify the toe a tiny bit on a few pairs of fins to cross check every now and then. Plus we looked for a foil which can handle the widest variety of AoA without stalling and there is a lot to be gained as well when I look at most other "wave" profiles. There are data bases with thousands of profiles with all the data of their performance in air or water and they have a search function so it is not so hard to find what you are looking for and in the end you come to 3 to 5 profiles which are (visibly) very close to eachother and you can pick one from them.
Regularly I have interns who are studying engineering in various fields who help me with this research. In Europe they can get a Erasmus scholarship for going to do an internship abroad so they don?t cost me much and some do a really good job. Also the matter is often quite complex so they can learn a lot plus get to do a lot of sailing. Various of them have told me that they had been applying with various windsurf brands before contacting me and didn?t even get an answer.
Also amongst my customers, I have various experts in various fields amongst which in hydrodynamics but also in composites, CFD, CNC or general engineering who also give me information, even if it is just where to look for, how to research something, they even may research something for me in a lab or where to get something made.
Yeah ive looked to get my own fins made. Finding someone with cnc facilities to do a one off that doesnt cost a fortune just killed the idea. Maybe some day in the future ill make it happen. I picked a few profiles but it stopped there.
In the mean time i tried getting handmade one off fins.
Doing my own boards from time to time and wanted to design matching fins plus just test my own ideas further.
All specifically for me of course.
I do love trying new fins. Am in the process of ordering some from flikka.
I am still hoping for an example of when 1 grain of sand in a slot box changed toe by 0.1deg (it would - I did the math, 0.17mm is enough) and somebody lost a heat in the PWA due to it.
Princesses with a pea under the mattress no doubt.
Until then I reckon I'm out of this one.
Select to expand quoteGestalt said..
Yeah ive looked to get my own fins made. Finding someone with cnc facilities to do a one off that doesnt cost a fortune just killed the idea. Maybe some day in the future ill make it happen. I picked a few profiles but it stopped there.
In the mean time i tried getting handmade one off fins.
Doing my own boards from time to time and wanted to design matching fins plus just test my own ideas further.
All specifically for me of course.
I do love trying new fins. Am in the process of ordering some from flikka.
Have a look at www.facebook.com/hans.robeers. Hans is a fin enthousiast who made a CAD program for surf and windsurf fins. I have had long discussions with him when he visited Fuerteventura and he bought an old flextail and a Slayer of me. Last year he adapted the program to make pre twisted fins. I do not use his program but if I had to start from scratch I probably would.
Select to expand quoteMark _australia said..
I am still hoping for an example of when 1 grain of sand in a slot box changed toe by 0.1deg (it would - I did the math, 0.17mm is enough) and somebody lost a heat in the PWA due to it.
Princesses with a pea under the mattress no doubt.
Until then I reckon I'm out of this one.
It?s what you call princesses....
Select to expand quoteShow me a guy who can pick 0.1deg toe on a side by side test.
I repeat - that is 1 grain of sand in the finbox. Has anybody be been able to feel that?
Which of those flash wave vids would not have been possible with a 0.17mm difference at the front of the finboxes?
Bouke I agree with much of your testing results but really saying U tweak 0.1deg toe and it's a difference that can be felt is plainly ridiculous man.
They're some pretty impressive aerials and glide how about some big hacks . That's what wave sailing is about isn't it
Select to expand quoteMark _australia said..Show me a guy who can pick 0.1deg toe on a side by side test.
I repeat - that is 1 grain of sand in the finbox. Has anybody be been able to feel that?
Which of those flash wave vids would not have been possible with a 0.17mm difference at the front of the finboxes?
Bouke I agree with much of your testing results but really saying U tweak 0.1deg toe and it's a difference that can be felt is plainly ridiculous man.
Off course you can?t consciously feel that unless you have laboratory like conditions. But that does not mean there is no difference. When I gave Will a set of fins with 0.5 degrees more toe in fairly big and clean conditions, he came back after half an hour and said the board felt less predictable. All the stuff we have done over the years clearly work and can be felt. And if you go from, for example, the straight paralel fins on the Pyramid to toed in asymmetrical pre twisted side fins, the result was visible from the beach. From one day to the next he went from a mediocre wave rider struggling to keep speed through his turns, to turning tighter with more speed and more precision, getting proper aerials, etc. And going upwind and getting more waves like the rest of us. As the owner said literally: Unbelievable. 
Select to expand quoteBouke-Witchcraft said..Mark _australia said..Show me a guy who can pick 0.1deg toe on a side by side test.
I repeat - that is 1 grain of sand in the finbox. Has anybody be been able to feel that?
Which of those flash wave vids would not have been possible with a 0.17mm difference at the front of the finboxes?
Bouke I agree with much of your testing results but really saying U tweak 0.1deg toe and it's a difference that can be felt is plainly ridiculous man.
Off course you can?t consciously feel that unless you have laboratory like conditions. But that does not mean there is no difference. When I gave Will a set of fins with 0.5 degrees more toe in fairly big and clean conditions, he came back after half an hour and said the board felt less predictable. All the stuff we have done over the years clearly work and can be felt. And if you go from, for example, the straight paralel fins on the Pyramid to toed in asymmetrical pre twisted side fins, the result was visible from the beach. From one day to the next he went from a mediocre wave rider struggling to keep speed through his turns, to turning tighter with more speed and more precision, getting proper aerials, etc. And going upwind and getting more waves like the rest of us. As the owner said literally: Unbelievable.
From there on, with a bit of technical insight it is easy to understand there is a difference in the flow with different bottom shapes. It is one more step in refinement and these steps indeed go smaller as you get closer to perfection. But why would you settle for something random when just tweaking that is a matter of changing a number once for a certain bottom shape? Costs absolutely nothing.
It wouldnt link the pictures of Facebook of the Pyramid but you can see more there under Koen Vandaele:
Will Ward is a local ripper. Some of the pics above are from him. Hes not a good contest sailor because he gets nervous and takes even more risks.
Proof that assy twisted toed fins work is not the same as what what I asked. Neither is a guy who once felt 0.5deg.
I said 0.1deg is ridiculous.
Yeah yeah bla bla proof is in the pudding show us some turns to warrant the radness
Select to expand quoteRango said..
You'll get bigger airs with a straight single fin.
it depends...that board (pyramid) works really well in trusther...in single fin it becomes very nervous..it's a very good board...i miss it
Select to expand quotesanti4 said..Rango said..
You'll get bigger airs with a straight single fin.
it depends...that board (pyramid) works really well in trusther...in single fin it becomes very nervous..it's a very good board...i miss it
Is that you in the photo?
Select to expand quoteIs that you in the photo?
no... I have long nails painted pink
Select to expand quotesanti4 said..Is that you in the photo?
no... I have long nails painted pink
That must be difficult to windsurf with
Select to expand quoteBouke-Witchcraft said..Gestalt said..
Yeah ive looked to get my own fins made. Finding someone with cnc facilities to do a one off that doesnt cost a fortune just killed the idea. Maybe some day in the future ill make it happen. I picked a few profiles but it stopped there.
In the mean time i tried getting handmade one off fins.
Doing my own boards from time to time and wanted to design matching fins plus just test my own ideas further.
All specifically for me of course.
I do love trying new fins. Am in the process of ordering some from flikka.
L
Have a look at www.facebook.com/hans.robeers. Hans is a fin enthousiast who made a CAD program for surf and windsurf fins. I have had long discussions with him when he visited Fuerteventura and he bought an old flextail and a Slayer of me. Last year he adapted the program to make pre twisted fins. I do not use his program but if I had to start from scratch I probably would.
I used his software very early on but it was too early in development. Kinda forgot about it. Looks fantastic now. Prob use it again. He's really developed it a lot further. Thx.
I just need a cnc contact now.
This is such a ridiculous discussion. Toe In is totally overrated with windsurf boards. I have a physics and math background and I have some insight about the physical principals.
1. You do not want to have 0 AOA, because then no fin generates lift
2. The flow sideways of water is just 1-2cm deep (called boundary layer) the rest of the fin still goes through still water. That is why Bouke sells his magic twist fin.
3. Because of these little angles little more or less simply doesn't create noticable drag. Thats a physical principle. Everybody knows this studing that subject. The drag only starts with higher AOA.
4. The reason why surfers have it is because they do certain different moves other than windsurfers can do where there is potential benefit but not with the radii we windsurfers turn.
But believe what you believe.
BTW you can start a discussion about sanding the bottom of the board. This also is one of this irrational myth in the windsurfing community.
Select to expand quoteSchobiHH said..
This is such a ridiculous discussion. Toe In is totally overrated with windsurf boards. I have a physics and math background and I have some insight about the physical principals.
1. You do not want to have 0 AOA, because then no fin generates lift
2. The flow sideways of water is just 1-2cm deep (called boundary layer) the rest of the fin still goes through still water. That is why Bouke sells his magic twist fin.
3. Because of these little angles little more or less simply doesn't create noticable drag. Thats a physical principle. Everybody knows this studing that subject. The drag only starts with higher AOA.
4. The reason why surfers have it is because they do certain different moves other than windsurfers can do where there is potential benefit but not with the radii we windsurfers turn.
But believe what you believe.
BTW you can start a discussion about sanding the bottom of the board. This also is one of this irrational myth in the windsurfing community.
OMG! This is the best reply EVER! To this painful topic that occasionally rears it's ugly head. Well said!
Select to expand quoteSchobiHH said..
This is such a ridiculous discussion. Toe In is totally overrated with windsurf boards. I have a physics and math background and I have some insight about the physical principals.
1. You do not want to have 0 AOA, because then no fin generates lift
2. The flow sideways of water is just 1-2cm deep (called boundary layer) the rest of the fin still goes through still water. That is why Bouke sells his magic twist fin.
3. Because of these little angles little more or less simply doesn't create noticable drag. Thats a physical principle. Everybody knows this studing that subject. The drag only starts with higher AOA.
4. The reason why surfers have it is because they do certain different moves other than windsurfers can do where there is potential benefit but not with the radii we windsurfers turn.
But believe what you believe.
BTW you can start a discussion about sanding the bottom of the board. This also is one of this irrational myth in the windsurfing community.
I think you blew it on point no 1.
All your fins should have the same effective angle of attack all the time. Zero is the default because boards are symmetrical. When you're sailing you point your board at the required angles of attack for your fins.
No no. A really good shaper tweaks the fin toe in by 0.1 to 0.3 deg based on the board use and rider preference.
CAD allows this (under) 0.2mm difference in finbox placement so it must be good and sound tekonologicallyified and people will buy more.
Thankyou Schobi
Select to expand quoteSchobiHH said..
1. You do not want to have 0 AOA, because then no fin generates lift
That is where you go wrong right from the start. Sometimes you do have zero AOA, that is when you do not apply any pressure on the fins. And if you have zero lift every where when you do not apply pressure, the change is the same every where when you do apply pressure. Select to expand quoteSchobiHH said..
2. The flow sideways of water is just 1-2cm deep (called boundary layer) the rest of the fin still goes through still water. That is why Bouke sells his magic twist fin.
It is not lineair as Ive said but it goes waaay deeper then 2cm. It can clearly be seen in the underwater footage when you go in slow motion and pick the moments where you go DTL and straight.Select to expand quoteSchobiHH said..
3. Because of these little angles little more or less simply doesn't create noticable drag. Thats a physical principle. Everybody knows this studing that subject. The drag only starts with higher AOA.
BS, the drag very quickly is double. Even with a low AoA. That is a physical principle. Everybody knows this studying that subject. 
Just look at what lengths they go in F1 to improve the aerodynamics to gain one second. For sure the driver cant feel one second but it can be measured. Just that we cant measure it like that, does not mean it isnt there. With water having a 730 times! higher density, even very small things make a difference. Like having a small damage on a fin. Select to expand quoteSchobiHH said..
4. The reason why surfers have it is because they do certain different moves other than windsurfers can do where there is potential benefit but not with the radii we windsurfers turn.
Hmmmm not sure if the turns are much different......
Select to expand quoteBouke-Witchcraft said..SchobiHH said..
1. You do not want to have 0 AOA, because then no fin generates lift
That is where you go wrong right from the start. Sometimes you do have zero AOA, that is when you do not apply any pressure on the fins. And if you have zero lift every where when you do not apply pressure, the change is the same every where when you do apply pressure. SchobiHH said..
2. The flow sideways of water is just 1-2cm deep (called boundary layer) the rest of the fin still goes through still water. That is why Bouke sells his magic twist fin.
It is not lineair as Ive said but it goes waaay deeper then 2cm. It can clearly be seen in the underwater footage when you go in slow motion and pick the moments where you go DTL and straight.SchobiHH said..
3. Because of these little angles little more or less simply doesn't create noticable drag. Thats a physical principle. Everybody knows this studing that subject. The drag only starts with higher AOA.
BS, the drag very quickly is double. Even with a low AoA. That is a physical principle. Everybody knows this studying that subject.
Just look at what lengths they go in F1 to improve the aerodynamics to gain one second. For sure the driver cant feel one second but it can be measured. Just that we cant measure it like that, does not mean it isnt there. With water having a 730 times! higher density, even very small things make a difference. Like having a small damage on a fin. SchobiHH said..
4. The reason why surfers have it is because they do certain different moves other than windsurfers can do where there is potential benefit but not with the radii we windsurfers turn.
Hmmmm not sure if the turns are much different......
The diagram below shows the correlations between drag / lift vs. AOA. If you can read it you know what I am talking about. But you have have a different opinion on it, because your whole sales story is based on it.I don't want to discuss this with you. That is already obvious from your picture of the airfoil app and your argument that you can see this in any picture of some CFD picture that any physical and mathematical argumentation is pointless. Just one point your fin is ridiculous 20x10cm in size. In single Fin terms a 24cm single fin. But using this information calculate backwards the drag of a typical thruster which is 1/3 in size and then having the effect of the boundary layer also only to 1/3 of the deepth. Then as a result you have 1N force of drag which is the equivalent of 100g in gravity. If this is not neglectable I don't know what is. Especially if nobody really knows what the right angle should be. Assume that you have a toe in so that the AOA is 0 at the base, then if you consider that 2/3rd of the fin flow not in the boundary layer then therefore with the wrong AOA which should be 2N of force so eventually it is bad to have a toe in which is 0 at the base, so what is then the right angle? But you have found the holy grail. You promote your twisted fins. Congratulations! And you can measure forces of 1N. Again congratulation. Because nobody needs them because nobody can feel 1N. But I forgot, you have these nice colourful CFD pictures. Your CFD arguments are in my opinion silly and show only one thing that you do not have the necessary respect for the complexity of the physics that is related to it. None of it is conclusive but merely shows nice colourful pictures. It might have been possible to discuss this with the original creators of that work. But that you assert to be able to judge the meaning of it without the academic background tells everything. Finally I have to answer to the silliest of sentences I have read wrt to argumentation. "Just look at what lengths they go in F1 to improve the aerodynamics to gain one second. For sure the driver cant feel one second but it can be measured. Just that we cant measure it like that, does not mean it isnt there." EXCACTLY, the F1 would never invest a cent in it if they couldn't measure it. Because then they don't know if it is even there. But you know that it is there. 
Select to expand quoteGasHazard said..SchobiHH said..
This is such a ridiculous discussion. Toe In is totally overrated with windsurf boards. I have a physics and math background and I have some insight about the physical principals.
1. You do not want to have 0 AOA, because then no fin generates lift
2. The flow sideways of water is just 1-2cm deep (called boundary layer) the rest of the fin still goes through still water. That is why Bouke sells his magic twist fin.
3. Because of these little angles little more or less simply doesn't create noticable drag. Thats a physical principle. Everybody knows this studing that subject. The drag only starts with higher AOA.
4. The reason why surfers have it is because they do certain different moves other than windsurfers can do where there is potential benefit but not with the radii we windsurfers turn.
But believe what you believe.
BTW you can start a discussion about sanding the bottom of the board. This also is one of this irrational myth in the windsurfing community.
I think you blew it on point no 1.
All your fins should have the same effective angle of attack all the time. Zero is the default because boards are symmetrical. When you're sailing you point your board at the required angles of attack for your fins.
That is the wish but not what I was trying to say, I simply wanted to say that you need an AOA for the fin to work. There will be no same effective AOA for all fins because the fins are going through different water depth and with it the AOA changes. Also leeward are windward fin are different. So you always have a compromise. The question is, is the effect dramatic or neglectable? I have this discussed with some aerodynamics professor who also is a windsurfer a while ago and he clearly agreed with my master knowledge on that subject that this is on the neglectable side. Anybody else stating the opposite should have real physical arguments.
Select to expand quoteMark _australia said..
No no. A really good shaper tweaks the fin toe in by 0.1 to 0.3 deg based on the board use and rider preference.
CAD allows this (under) 0.2mm difference in finbox placement so it must be good and sound tekonologicallyified and people will buy more.
Thankyou Schobi
CAD is fun. CNC is not. It is quite difficult to index the board properly on the machine.I have seen assymetrial and to thick or thin boards all coming from the CNC.
