hi guys . a lot of people started to use carbon fins with flex but what difference does the flex make ?

you can only have flex with an uprite fin, the further you go back with the rake the stiffer the fin has to be

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markaru27 said..

hi guys . a lot of people started to use carbon fins with flex but what difference does the flex make ?

This question is much too complicated, to cover all aspects, even if I was completely clued up on them.
But basically, as keef says it all depends on the fin rake, with a vertical fin flex will give the fin a component of vertical lift. As the fin is raked back the vertical component reduces and at some stage all most becomes negative.

Whether this component of lift is beneficial to you depends on how the board is tuned to your weight. As the lift is behind you, it can push the nose down if you're too light to sink the tail. If you're heavy and sink the tail, it can help to flatten the board out. But this effect varies with fin load, and can make the fin unpredictable. Being light, I prefer a fin as stiff as I can get it. Other more skilled people prefer a bit of flex, it can help to "fly the fin".

a stiff fin and a simple delta wedge/wing with 2" span, probably less, would be much better and easier to control the hydrofoil effect, you would only need a 1 degree angle of attack, maybe even less when you are on a windsurfer. i guess the only trouble with this is you need to introduce bulbs to break up the flow as it hits the intersection of vertical/horizontal sections. bit of a head F**K. But for anyone with fin shaping experience and some time on their hands (mike I'm looking at you!) could be the next craze.

the great thing about this is it creates a self leveling system as well as generating lift to help 'fly the fin.' for example: when the nose of the board lifts up the angle of attack increases on the wing and creates more lift at the back of the board, thus pushing the nose down and returning to the point where sailor weight vs fin lift creates overall lift.

it has been done before on yachts like the moth, hydrofoils were placed on the rudder and it instantly made the boat more stable through waves.
also the international 14 has a foil on the rudder and when you watch a 14 sail upwind the skipper and crew all get to the back of the bus and the boat still sails level because the foil keeps generating lift pushing the nose of the boat back down and in turn generates overall lift.

now that i think of it using flexy tips is just plain stupid and asking for a ridiculously unstable ride. load changes with every wave/ripple/gust/lull and thus changes lift coefficients and drag etc.. god my head hurts just thinking about how much would be going on under there with that sort of flexy setup.

The only trouble with the winged fin, is weed! and we have lots of it.
The other thing is most people don't want much lift behind them, I for one can't get my weight back far enough to counter balance it. Ideally max lift should be directly under the rider, but bringing the fin that far forward is asking for cavitation.
2cm instead of 2" may be a good start. Maybe if I've got a lot of time on my hands one day.

agreed, weed sucks, and frankly there is bugger all wetted surface area on a well set up board that reducing it even further will come at a massive loss of stability. still, something cool to try i guess.

When I work Rake 30? fins for speed, I look only for flex. To work flex and twist thats not so good. I speek from carbon. If you work twist,so works it against flex. Thats not so good for speed,thats a brake. I found that flex near the base is a good way. For one way worked I a fin in an angle of
10? to the other side of leeward. I have no word for the other side. So I have flex in the fin,it works earlier and need not so much power for
bending. 10? are only at the base. Why cut out at the base.? For wide base fins a good way to make the blade smaller ,for a better flex. I work
the cut out from 3-5cm.To make better flex,is only one of three points,why I work cut outs. Wolfgang

Just a thought for an alternate material decrepit ?
www.seabreeze.com.au/forums/Kitesurfing/General/First-Basalt-Fibre-Kiteboard/

Yes, yoyo has been talking about basalt fibre, looks like it would be worth an experiment.