sheddweller said..

SchobiHH said..


it is not faked. But it is meaningless in the hands of a non expert. Everbody with some decent knowledge can produce this colourful pictures. But to make them convincing there is much more to it some nice little pictures. And what makes it worth is, that Bourke throws smoke candles where ever he can. Decent research would result in a research paper, which explains what had been done and on what scientific basis the experimental setup has been developed. As this was only a student during I don't know how many weeks he spent, work, I highly doubt that he was able to produce proper research results. Unfortuantely. I would have loved to read what had been done, and how this could have been further developed. But it seems that the only reason why this had been done is to use it as marketing material and not to get any closer to the "truth". At least I have not read anything that convinces me that it is different.

I think you are maybe a bit behind the times with this.
FEA is now a standard design tool for non specialist engineers. They use it daily and they use it daily without the underlying mathematical understanding of the programs. They probably touched on the underlying maths in a couple of lectures as undergrads but that's about it. BUT the key is they do not solely rely on it, and it will go out to specialists in the field for critical parts, or specialist areas and most importantly of all functional testing of physical items. FEA ( inc fluid flow) modules are included in programs like solidworks, which is a farily low budget design suite. I think Delft University will certainly have the most expensive full on Software, with lecturers fully conversant in its use. My experience of such places is that the lecturers helped out a lot with these sort of interesting "fun" student projects, and particularly when the project is in collaboration with an industrial partner, like Bouke. So i would not expect the results to be completely micky mouse.
CFD is much more complex than basic FEA, but the trend is broadly similar. The tools are getting much easier to use for non specialists. The difficulty is the non specialist has no idea of the underlying assumptions or of the gross simplifications necessary to model an extremely complex environment.
But still i would say t is useful to test ideas, particularly in the case of windsurf fins where it is trivial and cheap to full scale test the results and verify. This is ( or should be) the overriding engineering approach when using it, be sceptical of the results and , verify verify verify.
also Toed n twisted n canted fins isn't cutting edge science, it isn't even new, so i dont see why anyone would be doing research papers on it- a product development project for an undergrad sure, but research papers? really?

FEA in this case would be good to estimate how much the fin actually twists under load. Having not done it on this myself or even hand calc'd it, I do wonder if the twist of the fin from the loading is on the order of the manufactured angle (0.1deg) here. So with manufacturing tolerances, twisting and flexure of the fins, a lot here can be lost in the sauce if you look at only the cfd. Which is why empirical results sort out the realities. Coupling cfd with fea is even more expensive (computationally, time consuming), and even harder to trust w/o test data...

Ola H 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.

You try to use theory to argue for the unimportance of toe in. I don't think it is very convincing. For example: why would bot the first 2cm of depth in fact matter quite a lot?
It's pretty simple for me, really. I reckon I know enough of the science and it has helped me think about issues, but in the end I just tested myself. I don't need to convince anyone else than myself. The people who ride my boards probably does not care about toe in, only if the boards feel good for them. I don't care if I'm right about toe in, I only care about if people like my boards (but to tell the truth, I care even more about that the boards I make for myself are good for me but I generally don't sell these boards to others...). Anyway... from simple testing... when increasing toe in you VERY clearly get to a point where the whole board starts getting draggy (in a straightline). I never felt 0 toe being draggy, even when using big front fins like on the first gen Starboard quad that was discussed. I think VERY few people could feel the difference in drag between 0 toe and a little toe, and probably no one will feel it with standard size (=small) front fins. Big fronts and no toe get quite twitchy in the bottom turn entry though. And in general, in relatively radical way riding, the difference to surfing is not that big. And just like toe in is a very sensitive aspect of surfboards, it is a sensitive aspect of windsurf boards IF you have relatively large front fins. I almost only run fcs front fins in my windsurfing boards I go between sets of different toe and difference cant. For me, it is FOR SURE a difference and toe in in particular has a quite radical effect on the bottom turn entry. Will most sailors notice? Not really and certainly not with small front fins. With big front fins it is a make it or break it issue to get toe in right though. As has been mentioned in the thread, this is probably why it has been so hard to get windsurfers to try fin setups with bigger front fins. I'm a bit intrigues byt R1ders's opinion that thrusters and quads need different front fin tuning. This is not AT ALL my experience. I go between quads and thrusters in the same board with the same front fins all the time. My belief though, is that this works because I have arrived at a quite forgiving setup for my front fins, both regarding positioning, toe and splay/cant. For example, I have found that with a bit of front fin splay, the placement of the rear fins are a bit less critical. I currently sail a lot "true" twin + trailer setups, is (for windsurfing) very large MR twins in the front and a small trailer.

WRT "2cm of depth in fact matter quite a lot?" Does it really matter at lot? Assume the fin is toe in to be parallel to the flow near the bottom, but the flow 2 cm away is parallel. I.d. the rest of the fin is in the "right" direction, i.e. parallel to the flow. than it is reasonable to have the fin pointing in the direction where the majority of the flow points or somewhere close to it or am I wrong. 2nd reason this 2cm are in the boundary layer where the flow is highly turbulent i.e. therefore the lift generation is limited in this turbulent flow anyway.

As you said yourself. little toe on regular front fins someone will unlikely feel a difference.
All I say is that this is also what the theory tells you. (little we are talking 2?) Toe in or no Toe in doesn't matter.That is why you find good boards having toe in or no toe in. And therefore there is so much discussions and believe, because the difference issosmall that some believe in it and some don't. If the difference would be more noticeable then we would not have the discussion which goes on for years in the windsurfing community. The experimental answer,, i.e. the shapes which are out there, is non conclusive, and the theory also agrees withthesefindings then this is a win for science, i.e. the theory backs the experiment.

Your "surf" fin boards are very special. I always wonder if they are so good, why they are not in production or why these fins are not adapted more in windsurfing. Ifwindsurfingis so surfing like, it seems for me very obvious that this should be taken by storm in the wave rider community. Especially with so innovative brands like Quatro who also in the same time produce great surf boards, I wonder why they stick to the more conservative approach.
But even if you go bigger in the front fins, I wonder if surf fins are really the designs we can use in windsurf boards as these fins are made for lower speeds or am I wrong. At higher speeds then they might not be the right choice, but this is just a thought. I have no experience with surf fins.

Or might it be, that windsurfing is more different to surfing than you make us believe. For instance, I can not imagine that we will have windsurf bottoms similar to some of these very weird bottoms of some of these surf boards designs. Besides from that a windsurfing board must work also without a wave, we have much higher speeds than surfing. hydrodynamic forces have a much higher impact at higher speeds, which limits the space of variations dramatically, And this is why I believe that in surfing you have so much more variations in unusual shapes as the impact of hydrodynamic efficiency on the perceived quality of a shape seems to be less.
Probably that is why in windsurfing we still have this very "boring" bottom designs only with very little changes over the decades, because anything else seems to not work.

Also I would like to recommend a video serie from Thomas Traversa, he tested some old boards. Especially as his results show that "single fin" is not out of the game. So what has it to do with our discussion. It makes me wonder if because we all got used to multi fin boards our sensation is blured. As progressions come incrementally it can be deceiving and after some iterations the result can be worse the the base line, even if each increment felt as a progression.


The single fin design from 2008 was so impressive, you could see just from watching that this board was so much better then all the boards he had the years after.
He finally has asked Fabien to make him a replica with TriFin but I wonder if the TriFin is merely because any other board would not be good for marketing. But one thing for me was clear. The "hugh" advances with multi fin is not as "hugh" as so many want to believe. I changed my TriFin to Single in Cape Town this winter. It is different but the bottom turn had so much drive, I will keep the single fin in for a while.

Schobbi .... post some pics of your sailing ability ..... and convince us how yr scientific observations match with real on the water observations .... You have NO idea what you are talking about ---- and I suspect you have little / no idea what your doing on a wave board ...

Back in 2012 - I was having a 'ghost' moment in bottom turns on big waves sideshore/sideoff - was running a quad with TOED surf front fins ... at around 2.8deg ... everytime mid bottom turn the board would kinda 'disappear' when parallel with lip , then re-drive up the face ,.... It was happening at very fast speeds .... After talking to a shaper / and theorising myself - I added maybe half a degree to - 0.75 extra Toe - and the sensation completely went ..... and suddenly the board was driving all the way through , and importantly straight back up the face. This is how NUANCED the feel is .... And anecdotally - on the water EVERY production board IVE sailed , HAS another turning gear with toed (and for me CANTED fronts) .... Ive felt it - gone out several sessions trying to tune in symm stock fronts in - every other bottom turn mis-behaving .... then plug in some surf fronts or k4 Ezzy / AI fins - and it is night and day in feel .... and happy days - and maybe (for me ) the board is performing 30 % better ....

Im not a witchcraft customer - there's alot of Bouke stances that I would disagree with... (you name it high booms , quads no good etc etc etc ) .,, but many moons ago I chatted with him on the beach - he's a super nice guy - passionate about what he does - and always trying to move forward , his construction methods are amazing - innovative ideas like flex tail amazing (again - not my cup of tea personally) , and you have to give him credit - he was running multifins a decade or more when everyone else was struggling with ****ty singlefins .... a bit like the delta designs back in the day (96/97 ish ) - that were ALSO using toed surf fronts and had some exceptionally talented sailors (Pat Redman , Blair Simpson ) ripping on their thruster shapes ....

so Schobbi / anyone else getting super 'negative' on here - post some pics of your sailing - and show us you have the skills to push your bottom turns past 10knots speed enough to show up the differences .... then you can talk science vs real world observations -

seabreezer said..
Schobbi .... post some pics of your sailing ability ..... and convince us how yr scientific observations match with real on the water observations .... You have NO idea what you are talking about ---- and I suspect you have little / no idea what your doing on a wave board ...

I reckon everybody has the right to a good board, regardless of level. But some of the finer aspects of turning that we are discussing here indeed require a relatively high sailor level to come into play.

Gestalt said..
just so it doesn't go unnoticed.

No one in this thread is saying that adding toe in to fins doesn't improve turning. A few have said it more than once. Not sure why you keep trying to argue that because pretty much everyone agrees with you

"Improve turning" is a bit too unspecific. I'd put it like: toe in is a very important tuning variable for how your turn will feel. My position is that (for symmetrical fins) 1.5-1-8 degrees is the safe space because you neither risk draggyness or twitchiness (if your customer decides to use bigger front that what it standard). If you run standard size windsurfing front fins (quite small) toe in does not matter a whole lot. If you run surf style fronts toe in gets quite critical and halv a degree plus or minus might matter a lot. For example, with K4 Ezzy 10cm, I feel 1 degree (in my 1.8 degree boxes) works but is a little too direct, but 2 degrees starts to feel a hunch draggy. My self made fins (fcs in slot bases) are 1.5, mostly. I think this sensitivity is probably also the rational for why we see so little of such setups, despite some people loving it. It's just too finicky

Just saw this:



He's using Ezzy fronts on the new 2023 ultra boards. He rides Quads and Thruster, quads with standard fins Thrusters with Ezzy sides couldn't see what angle they were.

Gestalt said..
If only I understood that using asymmetric fins on boards with toe in is only trying to undo the drag that the toe created in the first place.

That doesn't sound right, to me.

An asymmetric fin has a thinner profile and therefore less drag, that is the main purpose. But the angle of zero lift (and minimum drag) doesn't align with the centre line anymore, hence the base has to be turned towards toe-in, in order to have zero lift.

Gestalt said..

Well I have a quantum and it feels to me both draggy at the top end and twitchy when sailed in a straight line.... it has symmetrical fins and some toe in so go figure. that aside it's a great board. great acceleration and control when turning. in truth though my lack of high level ability probably doesn't enable me to understand the feel of the board correctly. Because it is true I do not consider myself a pro.

Which generation? I actually don't like the Quantum much myself (except for the first generation in some conditions). It is just too controlled and slow. That makes it sound like a terrible board, but another way of putting it is ease of use and predictability and this is generally what people like it for. . But I don't think it is a toe in issue as then if would be faster as a twin than as a thruster och quad. It is, but only to the predictable degree.

Gestalt said..
with all the pro level people in this thread you would think we could have a conversation around toe in and drag versus toe in and control and how the weighting of this choice biases the design. Or how fin availability effects design outcome.

I probably have over 50 different fins in my stash. Of all different varieties. I have some standards sets I use for testing of production boards (the original Simmer Blacktips in G10). It is indeed a good point that what fins you use when testing/designing will influence your design decisions. As mentioned, I work pretty hard with angles and placement to have the boards work with many different fin setups. It is a fundamental design choice for me to do this, rather than to try to fine tune a board with a particular fin set.

Gestalt said..
I am nuanced enough to have understood that t's ok for you to think a board is draggy if a certain toe with a certain asymmetry of fin goes too far and yet if I say it, I'm just not at a high enough level to feel what's actually going on.

That is not what I intended to say. I actually find it very important to get feedback from sailors of all levels and most peoeple buying boards are not of super high level, so in some way it i more important to get feedback from non pro-level sailors. You feel what you feel, usually (even though it is easy to fool yourself too, also for me). But to understand fin drag you HAVE TO sail different setups on the same board. It pretty much impossible to separate drag from outline curve, rocker, rail profiles and fins from each other from just feel.

A story: when testing he first Cortex proto the first time ever I first though it turned OK, but after a while though it perhaps was a bit slidey in the top turn. It felt very fast on the 500m downwind home from the reef though. When I got ashore I found out I had dropped both side fins, only sailing with a 16cm center fin.

So I'll cherry pick the latter and run with that

why not ?
confirmation bias, the flavour of the thread! ( for me to)

Ola H said..

Gestalt said..
just so it doesn't go unnoticed.

No one in this thread is saying that adding toe in to fins doesn't improve turning. A few have said it more than once. Not sure why you keep trying to argue that because pretty much everyone agrees with you

"Improve turning" is a bit too unspecific. I'd put it like: toe in is a very important tuning variable for how your turn will feel. My position is that (for symmetrical fins) 1.5-1-8 degrees is the safe space because you neither risk draggyness or twitchiness (if your customer decides to use bigger front that what it standard). If you run standard size windsurfing front fins (quite small) toe in does not matter a whole lot. If you run surf style fronts toe in gets quite critical and halv a degree plus or minus might matter a lot. For example, with K4 Ezzy 10cm, I feel 1 degree (in my 1.8 degree boxes) works but is a little too direct, but 2 degrees starts to feel a hunch draggy. My self made fins (fcs in slot bases) are 1.5, mostly. I think this sensitivity is probably also the rational for why we see so little of such setups, despite some people loving it. It's just too finicky

You mean you can feel 0.3 degree? Only joking. Yes, like you say, with bigger side fins, tuning the toe becomes a lot more sensitive/fickle. The thing is that even if I use a lot of toe in the base, going down there is less and it ends with zero. What you could do with your 2 degree Ezzys is make them warm/hot (80-90 degrees celcius) and twist the tips back and let it cool off like that. Plastic is thermoformable.

R1DER said..
I'm out! I'll leave this to Ola and Bourke to spruke their products and greatness.
K4 assym toed in fronts felt they gave better turning for me only on a thruster, but I think the flexibility of the plastic has a huge influence.
Just leaving this here do yourselves a favour and ........
keep the front fins on a quad parallel.

Happy wave sailing.

what about the back fins?

SchobiHH said..

sheddweller said..

SchobiHH said..


it is not faked. But it is meaningless in the hands of a non expert. Everbody with some decent knowledge can produce this colourful pictures. But to make them convincing there is much more to it some nice little pictures. And what makes it worth is, that Bourke throws smoke candles where ever he can. Decent research would result in a research paper, which explains what had been done and on what scientific basis the experimental setup has been developed. As this was only a student during I don't know how many weeks he spent, work, I highly doubt that he was able to produce proper research results. Unfortuantely. I would have loved to read what had been done, and how this could have been further developed. But it seems that the only reason why this had been done is to use it as marketing material and not to get any closer to the "truth". At least I have not read anything that convinces me that it is different.

I think you are maybe a bit behind the times with this.
FEA is now a standard design tool for non specialist engineers. They use it daily and they use it daily without the underlying mathematical understanding of the programs. They probably touched on the underlying maths in a couple of lectures as undergrads but that's about it. BUT the key is they do not solely rely on it, and it will go out to specialists in the field for critical parts, or specialist areas and most importantly of all functional testing of physical items. FEA ( inc fluid flow) modules are included in programs like solidworks, which is a farily low budget design suite. I think Delft University will certainly have the most expensive full on Software, with lecturers fully conversant in its use. My experience of such places is that the lecturers helped out a lot with these sort of interesting "fun" student projects, and particularly when the project is in collaboration with an industrial partner, like Bouke. So i would not expect the results to be completely micky mouse.
CFD is much more complex than basic FEA, but the trend is broadly similar. The tools are getting much easier to use for non specialists. The difficulty is the non specialist has no idea of the underlying assumptions or of the gross simplifications necessary to model an extremely complex environment.
But still i would say t is useful to test ideas, particularly in the case of windsurf fins where it is trivial and cheap to full scale test the results and verify. This is ( or should be) the overriding engineering approach when using it, be sceptical of the results and , verify verify verify.
also Toed n twisted n canted fins isn't cutting edge science, it isn't even new, so i dont see why anyone would be doing research papers on it- a product development project for an undergrad sure, but research papers? really?

CFD is a totally different beast compared to FEA.

As with every tool you use, you have to calibrate it to the circumstances. That is what you usually do with CFD. You have some data from a water tank experiment, or where ever you got it from and use it as a base and you compare the data with your model and calibrate, so that the model calculates the same experimental data. Then from that you can make changes and know you are close to known numbers, than your results of simulation are likely realistic. Without that you have no idea of how close you are to the truth. Especially with planning hull experiments and simulations I think there is not so much experience and the advances are still big. This is quite a difficult area in fluid dynamics. As it is on the boundary of the fluid. And the governing laws make it quite complex.


If the student was there doing this as part of his university career then he will have created some paper which described what he did.

But anyway, if you want to make anybody believe in the results of this work you will need to explain what you did in detail and what are the results and what is your conclusion. So that others can evaluate your work. Just using "pictures" with some arrows are nothing else than some pictures with some arrows.

I would like to state the paper "Towards CFD guidelines for planing hull simulations based on the Naples Systematic Series" from 2017:
Due to their higher motion amplitudes and instabilities, numerical simulations of planing hulls using Computational Fluid Dynamics (CFD) codes are more difficult than that of displacement ships. Indeed, for an accurate evaluation of the hydrodynamic performances of planing craft, the high-fidelity estimation of the pressure field around the hull is crucial. For this reason, validations and comparisons with experimental data are still important to identify the guidelines for both simulation settings and mesh generation

upcommons.upc.edu/bitstream/handle/2117/332155/Marine-2017-89_Towards%20CFD%20guidelines.pdf

Yes, off course there were papers, various with very good grades. Another student also used FEA to see how the fins flex and we used that in CFD. Also both the simulations we did with 5 years in between gave very similar results. But they are confidential.

Hey Ola ....

A sideways pic of your large fronts / small rear - would be great - to see how your lining up fins vs screw plugs back strap .... Are you running fronts trailing edge on front screw - or more middle of fin to front screw .... and how is the small rear lining up ? Super curious ... Ive played around with larger fronts set-ups ..... thanks

Bouke-Witchcraft said..

Mark _australia said..

Bouke-Witchcraft said..

I understand that in Australia you hardly ever get to see a Witchcraft as we do not have a world wide distribution and a limited production capacity. And as a result this information is all new to you and I can imagine it is all a bit much to process all of a sudden.

Yes sorry I live in a backwater where windsurfing is never seen and no development happens here. We are cognitively limited and can't process all this information over such a short 15yrs that you have been educating us.

I'm out.

I could have known, my mate Tim from Dongara said Ozzies could be sensitive if you touch their waves.... He is (or was) a crayfisher and explained me how it works there. Actually I did not say you have bad waves but it isn?t the only place with good wave sailing, I had some good waves and videos clearly show you have good waves, if anything there isn?t much in it. BUT one big thing is the distances. Here if conditions turn up, in half an hour we are on the water and 2 hours later back at work. But WA is different, especially the continental shelf makes it different. It filters out the big (huge) winter swells (You have a lot more ocean south to generate swell, it would be like if north of Africa, Europe and North America would not exist.) Still the Atlantic ocean also produces good swell (See Nazaret) and Fuertes north shore is quite good in picking up swells. Swell does come in unfiltered at Margaret River and Gnaraloo and Ningaloo. The best sailing I had was at Ningaloo, various very user friendly breaks, some good for both jumping and riding, the light house bommie was a nice point break (but the wave somewhat unpredictable) and the best sail was at Yardie Creek. Thats a 4km off shore reef where the wave wraps around and becomes cross of and super clean and pretty hollow. Tim had a small dinghy with a 3HP to anchor off the reef just in case of a broken mast. Gnaraloo was good but less userfriendly, quite crowded and you had to take care not to get closed out and end up on the shallow corral reef (I was told it was lower tides than usual) Then the whole area around Geraldton is good, loads of wind but quite choppy and less predictable waves. Also sailed Spot X . 7 mile beach was terribly choppy. Dongara/Point Leander was quite good and right in the end of the day after sun set the wind turns more off shore. I can see why boards developed in WA have the shapes they have. There is plenty of wind, hardly any rip and no crowds (2 is a crowd, I saw Glen Alexander sail Green Head on a reef about 1km off shore on his own.) so planing or up wind is not a priority. Many waves are off shore reefs so the wind blows directly through it so it is quite choppy. Pozo is cleaner as various of the spots I sailed in that area. As a result, boards have a fairly paralel outline with round rails to have control and a tail kick to turn. Is that a reasonable analyses?

Oh my. You don't see how condescending your statement was?

Bouke-Witchcraft said..

Yes, off course there were papers, various with very good grades. Another student also used FEA to see how the fins flex and we used that in CFD. Also both the simulations we did with 5 years in between gave very similar results. But they are confidential.

That is excatly what I was talking about. I do not understand why you make them confidential. The only reason I can see is, that you fear that it has not the convincing results as you mention.

And when I see the pic from above as part of the results then I have some idea of the quality.