Fins

" 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 !

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.

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 !

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 ...

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

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