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joe windsurf said..
n

joewindsurfer.blogspot.com/2012/03/fins.html




have asked similiar questions on iwindsurf forum:
www.iwindsurf.com/forums/viewtopic.php?t=31100&highlight=soft+fin

"Manufacturers are not getting away from G10 except maybe in the larger fin sizes. On the larger fins carbon will be much lighter, not so much on smaller fins. As stated earlier, carbon fins can be made with different flex patterns

" There are giant formula fins like in this image. Rarely have I seen such flex or asymmetry on land."

How about that! I've initiated a Chinese whisper. Don't believe everything you read on the web. The fin is not at all flexy on land. I've just dug out the original. It was an experiment. I forget what we were trying to prove. But I recall it sailed reasonably well in both directions. The message is if you're reboxing a fin didn't get too pedantic about it being exactly 90 degrees. A degree or two off you won't notice the difference.

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Imax1 said..
Am I invisible ? Has anybody read my original post ? I'm looking for some honest advice ! Everything is going around in circles . The question was ...... As a heavy 115hg rider IS IT BETTER TO HAVE A FLEXY OR STIFF FIN ? , that's all I want to know , I kinda got a grip on most things , this is one grey area I could need some help !

Theory aside here is my experience.

I use tectonics talon 44cm on 73 cm wide board with a grunty 8m sail. The talon is not an overly stiff fin, probably in the the middle of the range. This works nicely from 12 -20 knots. I'm around 85kg.

if the wind is really marginal or dying I'll use 46cm course race fin, super stiff. This is an old fin I picked up in a specials bin

Using good technique i feel I can get either of those fins planing about the same time. What the stiff 46cm will do is help me stay on the plane easier. It's almost impossible to spin out. I'm just barely planing and this thing still holds on. So in the 10-14 knot range if I can get the board planing the stiff fin will allow me to stay on just a little longer, giving me more time to catch the next gust.

The stiff bigger fin will top out earlier and be less comfortable in the chop. However with your extra weight it may not be an issue.

the best bet will be to borrow a couple of fins to try. Some fins will be a better match for your skill level so may give you a better result.

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Imax1 said..
Am I invisible ? Has anybody read my original post ? I'm looking for some honest advice ! Everything is going around in circles . The question was ...... As a heavy 115hg rider IS IT BETTER TO HAVE A FLEXY OR STIFF FIN ? , that's all I want to know , I kinda got a grip on most things , this is one grey area I could need some help !

Haha, you poor bugger, you've become lost in a brain surgery style discussion.
Ain't forums great for that!
I reckon that you, at 115kg, will make a stiff fin feel like a soft fin to somebody like me (74kg).
I think that twist/bend stiffness is determined by the riders weight and power.
I believe you will need what are referred to as stiff fins.
I make fins.
Speed and Slalom.
For me and my mates.
Have been doing them for 10 years or more.
I pay to have good, accurate CNC molds made.
I don't try to reinvent the wheel, instead I use proven foil sections using as my guide, your (Oz) best fin designer.
I make them with carbon, calcite, graphite, glass and kevlar to modify their deflection behaviour.
I measure their twist and bend behaviour with jigs I have made for the purpose.
While testing, I've made 11 different layups for my 40cm fins this season.
#11 feels real good to me at 74kg bare weight.
Along the way I made some stiff (in bend) ones which felt way powerful but too lifty for me.
They felt controllable in flat water but not in choppy water.
I was being controlled by the fin.
#11 is always under my control.
I gave one of the powerful (stiff) ones to my 100kg mate and he thinks its the best fin he ever used.
He says it's slippery, fast, controllable, planes real early, smokes upwind.
Not at all what I felt when using it. I felt it was fast, lifty, not controllable in chop.
He's one of the best sailors locally, big, heavy, loads of experience, fast racer etc, so good evaluation.
During my testing I have found that.....lots of twist, feels great in light wind /flat water but the brakes come on as the speed goes up and the chop gets bigger.
Feels to me like the tip twist works like a brake as the speed/chop rises and the twisty tip slows things down.
I now make my fins stiff in twist with plenty of bend depending on the riders weight.
Lots of bend gets the fin planing early.
They bend so far at low speed/lots of load that they lay almost horizontal under the board and give lots of lift, then as the speed rises/load reduces they straighten up to a more normal orientation and become controllable.
The degree of bend at planing threshold depends on the sailor weight/strength.
Most of the bigger slalom G10 fins I have measured are too twisty to be great IMHO.
Building with G10 and its possible to get the bend stiffness right but usually by then, the twist is excessive.
Material limitation.
Composite materials can give any behaviour you can imagine.
Making shorter fins in the same mold (ie cutting the length) requires completely different layup.
Chop a 40cm to 37cm and its too lifty, uncontrollable in chop.
Lots of testing and layup change was needed to get the 37cm and 34cm versions working well.
Fascinating project.
So much brain surgery........stiff fins for a big fella.

As said by a fin designer.all fins bend .I reckon grab a stiff fin off the rack .
Dont know if this picture of my collection will help choice a fin .Im just your average free rider .
30,33,34,36,36,38,38,40,42,44,48, All great fins for different conditions and sail sizes.

Thanks Te
I think I will go a stiffer fin at 55cm a straighter parallell type that doesn't look too twisty. Still wondering if a heavy guy could hold down a bending lifting fin ? I'm using a solid as a rock fin but it feels like its got a plastic bag wrapped around it . Mabee it's too solid . I think I'm going mad !

Try a jp56 slalom, the stock one that comes with the super light wind board. Works for me, trucks upwind, fast, doesnt spin out, gets board on the plane early. I am 105kg.

i am almost afraid to comment here any more nothing i say or post is gospel !! just gathering info and commenting
hoping some of it approached "the truth"

the first fins that came with the JP SLW92 were considered "too soft" and were improved upon ...

Yep Joe, from an Aussie it's kind of ironic that a Kiwi was knocking intelligent information gathering ............... but still offered some good information nonetheless.

He's right ............. "aint forums great for that"

Keep contributing Joe, the whole idea of public forums is that you get a full spectrum of information that could be sourced from the dude at the pub right through to a scientist.

My problem is my enquiring mind, when a guy says "use this, it's better" I say "how/why?"

Hello,

I read a bit on the link to the forum and they all have pretty accurate accounts. Bigger guys in general should have stiffer fins than lighter sailors. But still all fins should have some give relative to the sailors weight. The better the sailor you are, the more you will begin to understand how flex can help in all aspects of sailing. For intermediate sailors it is not that big of an issue because you are learning how all of your equipment comes into play and works together. The most important thing is to have all parts of your rig work together and properly balanced! Then you can fine tune with fin flex or not!! Yes George Greenough did have a super flexible VERY HIGH aspect fin!! BUT #1: he is an incredibly good and efficient sailor and (he could Pump onto a plane like nobody else!) #2: he weighs in at 135lb (61.5kg).

Chuck Ames

True Ames Fins

Te, what fibre orientation due you use to reduce the tip twist? I've been achieving it by just packing in as many layers of carbon at 90x45x90x45 as a can get in the mold.

Hi Yoyo,
It was quite a mission to get rid of the twist.
PM me and I'll give you the story.

In case anyone has been wondering , I have bought a VMG E 66 that I plan to cut down to 56cm . Hopefully that might be right for a heavy guy like me on a 83cm wide , 8.7 , 9.5 combo