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Thread: Toe-in 2017, what we know now.
6th February 2017, 01:30 PM #1
Toe-in 2017, what we know now.
There have been some massive discussions about fin toe-in – and some heated arguments – over the years since windsurf wave boards went to multi-fin set-ups.
Maybe it's time to talk about what we know now. I'm in Cape Town surrounded by windsurfers using multi fin kit, and I've been looking at various set ups and asking what people prefer.
So I'll kick this thread off with my own thoughts, and please feel free to disagree.
I was in a windsurf shop this morning (with a number of well-known windsurfers) and a guy came in to buy some thruster fins for his Quatro wave board – and his question was: what should he buy? What size, and what style and what toe in angle. The first thing we did was to measure the boxes in his board. The boxes had no toe in. Three of us measured them three times, to be sure.
If you want to measure your own board's toe, then use the simple formula on the K4 fins site.
You measure the distance between the pair of boxes at the front, and then at the back. You then need to mere the box length to calculate the true toe-in angle. The K4 formula does that for you if you enter the figures.
You'll find that many windsurf boards have no toe in for their boxes, whereas others have up to, say, 2 degrees.
I might dare to list a set of things 'we' or I think I know.
1) Surf boards and SUP boards usually have tow in for their thruster fins, but they do not perform as windsurf boards do, so our shapes don't always need toe in. The windsurf rig puts sideways load on fins, plus we also plane in a straight line when not on a wave face. We can therefore ignore what happens with fins in surfing and in the SUP world.
2) In windsurfing, there is often a trade-off between having neutral toe-in for better straight line speed, and more toe-in in for better turning on the wave. If you jump and blast about more than you properly ride waves or if you need early planing to get out, then having no toe-in or less toe-in will probably help.
3) All our boards are different shapes – and some board shapes might suit toe-in and others not.
Put simplistically, a board with Vee might part the wake at the board tail in a different way than a board with double concaves. What works in one board is therefore not transferrable to another.
4) The more fins you put in a board the more draggy it becomes for early planing, and the slower the top speed is. Adjusting fins for size, shape and toe in may help reduce this problem but won't change that basic fact.
5) Following on from the above, it seems you can generally put more toe in with a tri fin/thriuster set up than you can with a Quad. Increasing toe in on a quad may make it very draggy. (If you find your quad is a bit 'draggy' when getting going, my tip is to reduce the size of the fins you use – as a lot of quads come over-finned.)
6) Increasing toe-in on a tri fin or quad may slow down your early planing but should improve the board's potential to turn on the wave. This then becomes a matter of personal preference.
7) Asymmetric fins HAVE to be offset with 1 or more degrees angle just to set them in neutral. To have toed-in asymmetric fins you need 2 or more degrees offset or else increased toe-in for your boxes. It's handy that offset fins are available for experimentation (K4 Ezzy fins, for example).
8) Plastic fins can soften the ride of your board and a set of them are a lot cheaper to buy than G10 sets. Softer, twisting fins can also adapt to different water flow angles, which may or may not be good.
9) A lot of crap and strange claims are made for different fin sets ups and for and against toe in. This basic finding means you have to watch out when you read or hear something.
10) If you have a board then I'd say: sail it as it comes, and then experiment with different fins if you want to. What you find for yourself is what counts, more than what people like me might write on here.Main boards: Flare 101, NuEvo 86, UltraKode 80, Reactor 82, NuEvo 73. Powered by Severne Blades and S1s.
9th February 2017, 09:26 AM #2
So far still no one has taken the effort and do some CFD research and from there continued to develop. We have done a CFD research program twice, in 2010 and in 2015, using the latest CFD software with pretty similar results. And we have been using an underwater camera to film the fins.
I know you would prefer to avoid to discuss this since your brand does not use it but you have agreed before that it is logical that the water deflection is greatest directly below the board and will fade away the deeper we go. This requires the side fins to be pretwistet, right? And you will agree the amount of pretwist that is needed will vary on the speed. Still, again, taking the average speed as a starting point, designing the amount of pretwist for this speed will be ideal a lot of the time and still close if the speed varies, right? Even if that means that the ideal pretwist at an average speed on an average board shape is around 4 degrees, with no other brand even supplying pretwisted fins. For sure for a continuing development other brands should go this way but off course it complicates things and also increases costs of the fins a bit.
Now, if you get the toe-in right with a symmetrical fin, you allready have it right in the centre of the fin and are "only" 2° off at the base and the tip. So getting the toe-in right is the first step, pretwist and then further fine tuning.
Last edited by Witchcraft; 25th February 2017 at 10:05 PM.Bouke
Witchcraft Windsurfing Fuerteventura
9th February 2017, 09:42 AM #3
i watched this the other day and it does show how CFD is now coming into the board design arena for surf-boards interesting to hear you have looked into this for your boards Bouke
9th February 2017, 10:22 AM #4
- Join Date
- Aug 2008
10) If you have a board then I'd say: sail it as it comes, and then experiment with different fins if you want to. What you find for yourself is what counts, more than what people like me might write on here.
So what did he buy then and what impact did the well known windsurfers have on it?
9th February 2017, 04:51 PM #5
We did similar stuff but including the flow direction under the board and the influence this had on the fins. They did not do that so far where as you have to see the board and fins together. I wonder if they took the round shape of a wave into account as surfboards only travel on a curved surface.
We also simulated bottom turns as well as lift when planing along and trim angle with a certain weight on the board.
Here are some images, CFD delivers a lot of different pictures, pressure distribution, flow direction and speed, turbulances and reality images plus data sheets of the lift and drag of each fin and the board, but I can´t show that all here.
Witchcraft Windsurfing Fuerteventura
9th February 2017, 08:03 PM #6
9th February 2017, 08:33 PM #7
Here 3 images from 2014 showing the effect of asymmetry, one without camber and zero AoA, giving zero lift and 6.46N drag, one with 2% camber and -2.08 degree toe in, giving a very tiny bit of negative lift and 4.606N drag and one with 4% camber, -4.14 degree toe in, giving zero lift and 8.689N drag. So I have opted for 2% camber so that the inner fin in a turn has less drag (more drive). Adding a bit of camber makes that the inner fin also can handle a bigger angle of attack.Bouke
Witchcraft Windsurfing Fuerteventura