Volumetric ski sizing

[JAS]

In today’s world of 3-D modeling has there ever been consideration of volumetric ski sizing. What if ski length was kept the same, binding/fin position kept the same, rocker location the same, and change only made to width to maintain similar base Psi. Maybe only Two lengths, but multiple volumes in each to adjust for skier weight, water temp, viscosity etc.

[BraceMaker]

Wasn't that basically the Goode Nano series?

 

But they then later added a long one which both Regina and Nick both rode the shorter one. Then they added asymmetric. And wide ride etc.etc.

[JAS]

Not sure about nano. Wide Ride seemed to be a different shape. I’m thinking more of a proportional volumetric with exception of length.

[aupatking]

There was the Goode 9900: Regular, Mid, and Wide. Were those shapes different? I know the nose was, but mostly to compensate for the width increase, I would think.

What about Radar’s Vapor, Senate lineup? Used to be Vapor, Senate, Theory, with only differing width. Was the extra width added to the outside, or is it proportionally consistent?

[Horton]

@BraceMaker no that is not the case with Nano

 

@JAS the geometry of a ski is all compound curves and radi. If you stretch a ski wider you essentially change everything. As an example the RADAR Senate is the Vapor with a tenth of an inch added just inside the bottom bevel on both sides (more or less). The Senate is a great ski but it is not interchangeable with the Vapor.

 

Ski designers spend a painful amount of time getting all the widths and radius and curves perfect. You have to realize that TINY changes make huge differences.

[Horton]

@aupatking those Goodes are 3 totally different designs

[Adam Caldwell]

@JAS That was exactly an objective of ours originally. We played with a single lenghth multiple widths.

 

Considering only weight, you can get away with only width changes. But when people start getting to be 6'2, 6'4 6'8, or at the other end of the spectrum, the ski needs to change length as well.

 

@scotchipman - surface area is only useful for skis of the same geometry. So, looking at the surface area of a 66 Nano vs a 67 Nano might tell you something. But comparing surface area between a 66 Nano and a 66 Radar is pointless. The shape of the surface is what is important.

Different tunnel geometry, bevel widths, radius etc control flow and impact lift/drag. Two skis could have the exact same surface area, but one creates 2x the lift and the other creates 2x the drag. Make sense?

[Horton]

@adamhcaldwell I should give you a panda for trying explain this to @scotchipman.

[aupatking]

Thanks @Horton. I’ve often wondered about the Radar width question. I can’t remember the last time I looked at a Theory, if there was a noticeable rail (flat area) outside the concave. I was trying to remember if the concave just seemed wider.

I would imagine that even if they were able to keep all things proportional, while widening the ski, it could still be a fantastic ski in its original shape, but total crap if “just made wider”. Anyway, the guys at Radar know what they’re doing. Having ridden a full line of the “same shape”; Strada, Senate, and Theory, they were all fantastic skis.

I also make assumptions about what they may or may not do with a CAD type program. Assumptions equal Pandas, I’m assuming.

[BraceMaker]

@Horton good to know, I just remember the marketing back in the day was that Nick Parsons and Regina were both on the "same ski" which I assumed in Goode world meant different amp, same length.

[BraceMaker]

@JAS I would be curious to see modeling of what effect on volumetric area change looks like with a boot location move.

[JAS]

@adamhcaldwell Thanks for your answer! Totally understand the complexity of modeling a ski that works the same for both Laurl and Hardy. Even with height/ weight curves being a bell shape,there are those way outside. Some it helps to be a world record holder, and others a steep uphill climb.

 

What got me thinking about this was our copy machine. Thought wow what if it was as easy as taking a 3-D CAD and enlarging or shrinking by 2% (or whatever). Relationship of curves would the same although as @horton mentioned slightly different (possible favorably different). Thought might be easier than designing another ski several inches different in length, moving binding 1/2 inch, and keeping a fin in same spot. Love what you guys are doing!

[Adam Caldwell]

@JAS -Scaling equally in each dimension is a great concept. But, reality is its not quite that simple.

[Horton]

@jas every factory handles different lengths of one model of a skis differently. Some do a straight scale. Some tweak the scaling so the ski is stretched longer and the additional width is a smaller increase. There have been instances in the past when one other factory has redesigned the shape for each size.

[JAS]

I really do understand and appreciate the complexity of advancing ski design. As skiers we owe a great deal of thanks to a relatively small number of minds. I’m sure few stones have been unturned, why I skied with a pretty good skier once who glued half of O’Brien Siege to half of a KD 7000. His ski boot was beyond description.

My interest in Tech/equipment is just part of my enjoyment of the sport. Thanks @horton for this forum and moderation, thanks @adamhcaldwell for your unselfish sharing of knowledge.

[disland]

why does a taller skier of the same weight need a longer ski?

[Sethro]

You beat me to it. I was hoping someone would explain that as well. So given the same 225lb weight, could a 5’11 skier want a shorter ski than the 6’5” skier?

[Adam Caldwell]

@Sethro @disland

 

 

YES. Most definitely. The way I think about it is pitch and roll stability.

 

Longer/wider skis being ridden by a short guy with a lower COM will have too much pitch and roll stability in the ski. Therefor making it take too long after the crossing the wakes for the attitude of the ski to initiate the preturn.

 

Shorter/narrower skis ridden by taller guys with a much higher COM will have tend to suffer from a lack of stability in roll and pitch, and enter the preturn too quickly and run out of speed prior to apex.

 

Those well versed in fin tuning can make either situations work -within reason. For example, I can ride a 64" or a 69" through my hardest pass. But, its not without moving out of the appropriate zone for fin and boot settings. From a given 'standard'. On the bigger skis I tend to run boot forward/fin:forward/shallower/longer. On the smaller skis I go boots back, fin back, deeper shorter.

 

Other big differences in ski sizes comes from pure hydrualics. In other words, the amount of reaction force generated by the bottom of the ski during high angles of attack.

 

Two skis on the same angle of attack at CL, both slipping downcourse at the same speed anc cross course at the same speed - with the same weight on top of it will develop significantly different reaction forces. The bigger ski can produce more lift which can act to increase load on the skiers body and in the rope. The smaller ski will generate less lift, and produce less load on the skiers body and rope. In a sense, the smaller ski is easier to pull and stay connected on.

 

In reality though, it comes down to the ability to build cross course speed into CL. The big question is how much cross-course speed was the skier able to bring into CL on the smaller ski versus the bigger ski, and how much load/energy did it require of the skier and the boat? Usually the smaller ski leaves you digging out of a hole without much energy, while the bigger ski will keep you moving better through the turn finish and make the acceleration slightly easier. Easy to see the differences in those scenarios and how that will play out in the downswing to CL.

 

This is one reason a lot of bigger guys like smaller skis. They can stay connected better through CL which lends itself to a better swing into the buoy. This is because they are strong enough or have enough leverage to handle the hydraulic forces produced by the ski. The bigger skis, albeit easier out of the buoys, can cause people to separate earlier if they do not have the strength or height to generate the leverage to resist the larger hydraulic force created by the bigger ski. Might be why you see the shorter guys at 200+ pounds opting for the smaller ski. They can keep it on edge through the wakes with less mechanical advantage of a lower COM as compared to the taller guy of equal weight. The taller guy might get into a deep lean, but the ski cannot produce enough lift to get him out of that deep lean early enough through CL.

 

This is why fin settings are so crucial. Having a 'big ski' advantage that you can still get a good preturn and finish with is awesome. But technically speaking, its harder to accomplish then just riding a smaller ski.

 

Hopefully that doesn't confuse the issue. The short answer is - its more complex then you might think.