Old Tweakers Posts Fin Thickness

HortonHorton Posts: 23,366 Administrator
edited June 2007 in Other Stuff
Thinner? John Taylor Horton <!--EZCODE ITALIC START--><!--EZCODE BOLD START-->An up and coming pro skier contacted me this week and asked for a thinner fin. Below is my response. <!--EZCODE BOLD END--><!--EZCODE ITALIC END-->



Stiffness in any one direction is roughly proportional to the number of layers of carbon in that direction. The order of the layers per direction is also a big deal but is a long explanation. My two best selling materials (Stiff 106 & extra Stiff 116) are just under .1”. These materials ski well because they have the right balance of stiffness vertically and horizontally. My newest material (116) is stiffer vertically then anything else I have ever made but is slightly less stiff horizontally then my bread and butter “Stiff” (106). Remember that my whole concept is that by offering a range of stiffness I give skiers a wider choice of performance.



Asking for a thinner fin is like asking for a lighter jump ski. You have to take something away to get thinner or lighter. I have made stiff fins as thin as .075” but there is always a trade off. I wish I could find some of that material (114). It was super fragile and unstable horizontally until you put it in a fin box. Once in your ski and supported by the fin clamp it was as durable as anything I can make. I was afraid that skiers would hand flex the fin before they installed it and spring a carbon splinter in their eye. If money was no object I am pretty sure that I could get thinner but it would require a much more expensive grade of fiber and some additional R&D. At my current sales levels and costs that R&D is out of the question without outside funding.



The importance of thinness is debatable. Kris, Wade and Andy have all told me that they think that thickness affects lift at the tail of the ski. All three of these guys have told me that they prefer thinner. I have also heard that various theories regarding thickness and speed. My argument is that since aluminum fins get stiffer as they get thicker and vise versa. So when they go thinner is it the change in speed & lift or the change in stiffness that they like. I assume that is a combination.



I have thought about tapered fins with .07” edges and then .1” an inch in from the edge. I suspect that that would achieve the same thing as a thinner fin of the same thickness.


 




ezOP

Posts: 815

12/5/06 11:47 am

146.23.4.22

Reply | Edit | Del All

ezSupporter




SS did this with alum. MS He had given me a fin for my 9500 that was thinner then stock. The problem I had was the Goode Finbox would not clamp and hold the fin into position. I tried to shim it, but it always had that hollow sound and would vibrate when tou tap the back of the ski. I was never able to get it to work. He was sold on the thiner fin for the Goodes. I am not sure what he uses today. After trying your 106 and 116, I would think the 114 would really be nice. If I dont loose an eye, I would be willing to try one.

 




Unregistered User

12/5/06 12:42 pm

12.40.178.65

Reply | Edit | Del


Schnitz did this with alum. John Taylor Horton ( MS is talking about Schnitzer. )



I assume that Steve’s idea about thin fins is the reason that the Fischer fin is so thin. It is somewhere around .075”.



What is cool about the Fischer that I have seen is that slot is super narrow so the fin is a really tight fit. That way the fin flexes starts at the bottom of the ski. If the slot was wider the fin would not be supported by the ski and would flex from the clamp. This shorter distance of flex means that the super thin Aluminum does not over flex. (If the slot was wider and the fin flexed from the clamp the additional flex could be a problem. )


 




ezOP

Posts: 817

12/5/06 1:57 pm

146.23.4.22

Reply | Edit | Del

ezSupporter




The Fish wing MS leaves a bit to be desired. I think the wing may be a bit to thin. But the fin box is sweet. When I tried my friends fish, I used a HO wing on it. The stock one looked like paper.

 




Unregistered User

12/6/06 6:54 am

12.40.178.65

Reply | Edit | Del


Boron? eleeski John, would boron fibers add enough stiffness that you could thin the fin and keep the stiff flex? Can you get the stuff?

Eric

 




Unregistered User

12/6/06 3:35 pm

207.200.116.70

Reply | Edit | Del


Re: Boron? John Taylor Horton I worked on getting some HyBor fins made that last year. WAY too much $. There are higher grades of Carbon that are way better then the Boron but the cost is beyond my budgets.

 




ezOP

Posts: 819

12/6/06 3:38 pm

146.23.4.22

Reply | Edit | Del

ezSupporter




fin variables eleeski Did you ever try the tapered fin?

Or even a smoothly blended edge?

Note that aircraft designers do not want a rounded trailing edge. Leading edges rounded but trailing edges sharp or squared off (after tapering substantially). Minimum drag in air is a teardrop shape. I'm sure similar work has been done in water.

Or is it that flex matters more than shape?

Eric

 




Unregistered User

12/7/06 12:41 pm

152.163.100.197

Reply | Edit | Del


Re: fin variables DW One must think about all the variables that you are adding to the equation: the correct shape hydrodynamically would be a tapered shape with the correct bullet nose front surface with some taper, not as much as a wing in air, just enough to minimize separation and as mentioned a sharp trailing edge.



The other variables you are playing with is stiffness and surface position relative to the surface and water side of the fin. Perhaps the affinity to a thin fin and the thought that the ski rides deeper is that the fin thickness displaces a certain amount of water and since it is incompressible, you can't displace any towards the bottom of the lake but you can upward (on the air side), therefore causing the ski to ride at a different height. The stiffness element certainly can be tuned with different materials, and you can break down the experiment with equal thickness fins of different materials therefore changing stiffness, or, different materials at different thickness' keeping the flex the same (one hell of a math model to get that one right!).

 




Member

Posts: 52

12/7/06 4:26 pm

198.208.159.19

Reply | Edit | Del


<< Prev Topic | Next Topic >>

Support BallOfSpray by supporting the companies that support BallOfSpray

Babe's /Connelly / DBSkis /Denali Goode / HO Syndicate / Mapple / Masterline / O'Brien /
MasterCraft / Performance Ski and Surf / PTM Edge / Stokes / Reflex / Radar / Wakeye

 

This discussion has been closed.

Not sure how to deal with a long link?