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Ski Mapping


adamhcaldwell
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Holy Soft Ski Batman!

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I do super dig the white

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For those who have no idea what those numbers mean read this.

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@tap I bet it is light

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@Chef23 we got the same type of questions when we first started messing with fin shapes. We’re always looking for something better, or to try and learn something by trying new things. Most of the crazy stuff we’ve tried never makes it to a final product, but everything we’ve tried has taught us something. Hopefully the more we learn, the better our products.

 

As far as flex- does anyone have flex numbers on the old Schnitz skis? I believe those were super soft.

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@Tap - No, I did not run out of carbon.

 

@Horton - I setup a very high level flex tester last night to demonstrate what a 20# tail and 70# tip look like. If it wasn't for the fin hitting the floor, I could have gotten this thing to bend a hell of a lot more.

 

 

@Chef23 - I've always thought the way skis are traditionally constructed is not necessarily the 'best' way. This particular ski utilizes a much different construction technique. The super-soft flex was very intentional. The intent being to see how it would survive extremely high displacements under both longitudinal and torsional loads. The next step is to demonstrate the ability to control the flex and torsional progression of the ski. I built another one last night that has more ' normal flex values.

 

I have already learned a lot from this ski, but I can only disclose so much publicly. One thing is for sure- its more work and a bit more challenging to build the ski this way. But, mechanically, I believe its a much better way to build it. My hope is that it becomes a step change in terms of performance longevity.

 

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@adamhcaldwell interesting stuff, as you and I have discussed before, back in the day, I had Connelly build my skis with a softer than normal tail flex. I liked the way it allowed the ski to finish the rotation back across the wake. It worked for me, set the Alabama M3 record that has lasted 25 years on one of those skis.

 

Seems to me I remember Pat Connelly playing with the direction of laying the carbon also. But I don’t remember on which skis... And the amount of carbon was much less than new skis.

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@wawaskr - if you rely on the foam core as a significant part of your structural integrity, then obviously it will change with time. However, If the only demand on the core is just to keep water out of the ski and help improve impact toughness then it should be very consistent over time.

 

Hollow skis can be awesome.....until you pop it with a handle.....then it fills with water and sinks to the bottom of the lake. Not so awesome anymore.

 

@mmosley899 - I'm sure nothing I am doing hasn't already been done before. However, when you have no exposure, knowledge or data, you have to come up with it on your own. There were definitely some interesting things about this ski on the water.

 

 

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@adamhcaldwell- I love the scientific approach that your team at Denali uses for research and development. I agree that developing a data base for flex/stiffness (soft, stiff and in between) is fundamental for Denali to understand the effects on how skis perform. The industry standard uses this simple static test as that benchmark. I believe your intention was to show the readers that you need 'soft' and 'stiff' data in order to find the 'optimal' stiffness. Thanks for the video.

 

I have spent a good portion of my life working for a large scale assembly company in the Pacific Northwest posing as an aerospace composites engineer (thankfully retired). We were working with acres of relatively highly loaded thin skinned composite honeycomb structure as the most weight/cost efficient design. The design was driven by stiffness where composite plies were added for impact resistance. Waterskis are a perfect example of this structure.

 

You replied to "@wawaskr - if you rely on the foam core as a significant part of your structural integrity, then obviously it will change with time. However, If the only demand on the core is just to keep water out of the ski and help improve impact toughness then it should be very consistent over time."

 

Like it or not, foam core bonds well to the surface laminates.....initially. That is where the benchmark static stiffness numbers are generated. Then under dynamic loading over the life of the ski those bonds break down. Foam is basically non-existent in the commercial aerospace industry for parts used in vibrational environments becuase of this very reason.

 

IMO if core (foam, honeycomb, whatever) is used in the ski it is "required" to be part of the design analysis (stiffness map in these cases). Yes, it changes detrimentally with time. However, foam does more than simply keep water out and improve impact toughness. Foam is a very effective manufacturing aid to provide separation from the top and bottom skins during the manufacturing process. This allows cost to be manageable. Does Denali not include the foam as a bonded element of the structural analysis model for sizing purposes?

 

I believe that the stiffness map plays a major role in waterski designs today. Maintaining a relatively consistent stiffness after subjecting a dynamically loaded environment to the easily broken down foam core (mainly at the skin-to-core interface) is the major challenge. There are many ways to address impact without core (S2 glass, KEVLAR, more plies, etc). However, weight and cost would obviously need consideration.

 

Please don't take this wrong. I'm not suggesting I have the solutions. Designing cost effective marketable waterskis is not for the faint at heart. I'm only trying to clarify that the foam core has many proven functions in waterski designs that can be helpful and/or detrimental to performance. You people who have the skills (and balls) to actually design, market and sell waterskis are the masters at figuring out how to make a living at it!! Thank you for that! I have certainly opened myself up to beaten down.......but that can be the fun part!!

 

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@adamhcaldwell & @Shark: Great info, one thought on handle pops we use helicopter tape on the leading edge of race car wings for impact protection (stones, sand). Certainly not elegant but it is light and flexible. Composite noses get the Kevlar treatment for impacts (accidental and intentional ones).
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@Shark - I wrote a big reply...but then deleted mainly because its hard not to disclose to much about what I am doing...Maybe we ski together sometime and Ill give you my perspective. - Overall agree with you 100% and you're right....buut..theres more then one way to skin a cat....or a water-ski.
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Soft or Stiff does not necessarily equate to overall strength. Can make a super stiff laminate that can be brittle. Or one can make a super soft laminate that can be nearly bullet-proof and highly flexible. The opposite is also true.

 

A ski not only needs to be able to have the 'right' flex, but also needs to be able to handle all the compressive, tensile and shear forces as its warping and deflecting under load.

 

@thager, Isn’t there a myth that all white skis suck?

 

Has anyone skied on the MR skis? From what I remember seeing years ago, those were extremely soft skis.

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@adamhcaldwell MR crazy soft and HUGE bevels. I don't know anybody who's ever skied on one besides Herald

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@adamhcaldwell before there were CarbonFins there were Schnitz fiberglass fins. I don't know if he ever made them for sale but I know he used them to break at least one record. That dude played way outside the box a lot.

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I had one of the first Goode prototypes to the 9100 that had Bob Lapoint's name on the rear tail. The ski got tried by a lot of skiers and ended up with a lot of holes in it. I was out of skiing for 5 years (got a divorce and started back skiing!) and jumped on that ski (my former ski partner had it under his bed with about 7 other skis). I liked the way it felt so I tried it. It was really flexible but I do not think it was that flexible. Anyhow I immediately loved that ski EP'ed on it twice and made it to the Nationals in Destin in 1996. I bought one of the first 9100's because I thought that one could break to easy. I liked it too but that soft prototype did feel a bit better in the turn. I ran an EP at Nationals on that 9100. I was pumped. Dave Goode gave me a hat and a Goode bag. Still have the bag!
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Its been several years since I went back and looked at torsion data. Without giving away too much info, it might be interesting for some to see comparisons on torsional flex progressions between skis.

 

For Longitudinal flex, almost all ski companies fall with a very small bandwidth along the entire profile. For example, almost all skis today have a flex that falls within a 20% bandwidth at any given point from tip to tail.

 

However for torsional flex, this bandwidth is massive. Anywhere from 10% to 500% different. This is one of many factors in why skis feel so drastically different from one another.

 

I left off the Y-axis values on purpose as to not expose too much info, and I also made everything black as to protect the interests of other brands.

 

qvjdszn9hyx1.png

 

 

 

 

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@adamhcaldwell can you help me a bit with reading of the graph.

 

The X Axis is labeled DFT, so I am assuming that this device fixes the ski at a certain point and then twists the ski. Is the Y axis a unit of rotation to reach a certain force or is it a unit of force to reach a certain number of degrees of torsional stress?

 

Additionally is the unit always holding the tail of the ski and then twisting further and further down the ski? Or is the unit moved such that it is always applying a torsional load across 2 points a fixed distance apart (such as two sets of clamps 10CM spaced apart and then the center of that 10CM span moved along the ski to that distance from tail?

 

Would you be able to plot something as a reference such as a 1x6 poplar board.

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@BraceMaker - a 1x6 poplar board would be a flat line probably on the 2nd tick mark up on the Y-axis.

 

I did not disclose the Y-axis on purpose for the same reason I did not put data of Denali or a couple other skis.

 

I will say that I have built a few skis that tip to tail are off the top of the chart all the way across, and a couple that would be similar to that poplar board. :) A factor of nearly 25X the torsional stiffness between the two skis.

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@Than_Bogan I could be wrong but I would speculate that torsional Flex is most critical at the tail and progressively less critical as you move forward.

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For comparison, two additional benchmark/mapping skis are added to the plot. The "2019 Pool Noodle" is the white ski shown at the top of this thread. (These do not reflect the torsion of any production Denali skis)

 

For perspective, if you could theoretically twist the ski the to create 90deg of displacement between the tip and tail, the 2013 Denali max would required over 1100lb-ft of applied torque, while the 2019 Pool Noodle would need less then 100 lb-ft.

 

ru4yulhiz4aj.png

 

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@Than_Bogan - do you mean torsionally soft? The tail (behind 17" is remarkably soft on all skis posted.

 

@Horton, Yes and NO. Its crazy how sensitive the T-flex is with different construction methods & materials. We have the ability do make MASSIVE swings in T-flex with very little material.

 

A range of 25-50lbs (or 15-30% of nominal) in longitudinal flex is the norm for tip flex deviation across the board. My interpretation of that fact is clearly there is a significant amount of focus on L-flex by all brands.

 

However the torsional deviation between ski manufacturers can be 200-500% different. So, maybe your right and it doesn't matter, OR, its just not something few ski builders are paying much attention to in general.

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