Do longer skis turn slower than shorter skis? Where's the data?

[Horton]

You are just trolling me with this comment. Right?

@Horton Does the fin actually do that much relative to slippage in the turn?

 

[The_MS]

This is great

[JackQ]

I believe that as the rope gets shorter, the slide is critical to generating sufficient angle (direction of ski IE pointing cross course. Watch Regina at 38 and beyond, just as she completes her turn and is just starting to accelerate, her skis slides just enough to get a bit more angle. If she had that angle a bit earlier the load would be too much. A marvel to watch, but I am incapable of emulating.

[eleeski]

As a pilot, yaw, roll and pitch are needed to turn an aircraft in 3 dimensions. Uncoordinated turns (actual pilot language) result in a slip (more actual pilot language) that happens when the roll and yaw aren't balanced. Aircraft attitude changes if the pitch and yaw aren't balanced. Handling of an aircraft is quite complex.

 

Cars only move in a 2 dimensional world. Yaw and sliding are simple to understand and control.

 

On firm snow, snow skis tip, carve and skid (slide) and do it almost completely on the surface. (Note, in powder, skidding or sliding is minimal).

 

A waterski is in an unusual environment. It is constrained to a very small range of 3 d movement because of the surface of the water. So a pure aircraft model is not really valid. But it is absolutely moving in pitch, roll and yaw in 3 dimensions. So a car isn't even a close model.

 

A slalom ski is almost always at a significant angle relative to the surface of the water. Sometimes nearly 90 degrees tipped. If that ski is going to slide in a two dimensional manner, it has to slide over the water surface. When that happens to me, the ski skips out and I fall (Kjellander's slam dunk turn might have worked for him but nobody's coaching that style nowadays). Otherwise, the ski pushes the water mass out of the way. There's lots of resistance to this displacement due to the properties and weight of the water. A lot of force is involved - so a lot of ski movement and acceleration is possible. Regardless, it's nothing like a car sliding in a turn. In snow ski terms, it resembles a carve not a sliding skid. Minimizing any downcourse movement by the slalom ski when crossing the wake will improve the buoy count.

 

How does a ski turn? It certainly doesn't just tail slide flat to rotate (aircraft style pure yaw or a car's slide). It doesn't "bend" the ski to a pure carve (like snow ski instructors teach). There's some of an aircraft style turn - except there's no movable rudder and aileron. Instead, pressure on the tip of a ski rolled on edge will cause a rotation around the center of the ski and turn the ski. Sure, this is an oversimplification and there's a minor sliding yaw component to the turn but an elite turn depends primarily on tip pressure, ski tipping angle and the fore aft balance of the angled ski.

 

@bishop8950 's underwater picture shows more area ahead of the feet than behind (taking into account the width of the front vs the narrow tapered tail). This is driving the rotation. Note that the front of the ski has very little "slippage" and the tail is moving deeper underwater. How much do things anchored firmly in the water slide?

 

Alternatively, you can rear back on the ski, bury the tail until the tip is way out of the water and slam the tip sideways to generate angle (early LaPoint survival turns that ended with steep ski angles and huge turn angles). No yaw, just power and management of the fore aft balance of the ski.

 

Switching topics, how much slippage is there through the course? This is a variation of the aircraft crosswind problem. The plane doesn't slide but its speed toward the destination is a combination of the forward speed and the crosswind. Applying that logic, skier speeds have been measured at about 60mph. The boat is going about 36mph. That is about 48mph crosscourse component with a ski angle of close to 60 degrees off the boat's course. Mathematically, plenty to work with to get out to the buoy - as long as you're not sliding too much downcourse. Note, this is an imperfect model for skiing but it does illustrate that slippage is not required for the course. Also note, my skis with the experimental super flexible fins, that feel great, lose ground in the course - do they slide? Probably but it's not helpful.

 

While we are talking fins, I'm definitely not trolling @Horton . Nor has the Sierra Nevada Narwhal Imperial Stout that I'm sipping affected me @Bruce_Butterfield . Since the ski is at an acute angle relative to the water surface (and the direction of travel), the fin is not working as a rudder. It is more like an aircraft elevator stabilizing whether the tip raises or lowers. Due to the ski angle, the tail of the ski is working to stabilize rotation. In reality, I probably don't generate enough ski tipping angle to have the tail exclusively act as a rudder nor the fin exclusively as an elevator. Maybe I should make a Beechcraft style Vtail waterski?

 

Slippery slalom illustrates that a fin is not necessary. With the proper design, a dedicated slalom ski might not need a fin. There are already excellent skis with big bites taken out of the fin or big holes drilled in them. Current skis do require a fin so don't take your fin off on my advice (videos if you do!). Fins do add stability which is important as speeds increase. But there are ways to design in stability into a ski. Fins are getting smaller and less solid (some with big holes!). Who knows where it will end up? I doubt it will revert to the huge deep fins of banana skis of the past.

 

Slavishly sticking to misleading traditional thinking is limiting. Think with an open mind to make improvements - like flexible carbon fins.

 

Sorry about such a long post. I hope it's entertaining holiday fodder.

 

Eric

[Bruce_Butterfield]

@eleeski it seems to me that your descriptions require much more than a 6 pack or 2 of Sierra Nevada. Maybe a little more nog than egg in the eggnog, or have you been sneaking into Colorado for some of their legal pharmaceuticals?

 

Entertaining holiday fodder for sure!

[eleeski]

@Bruce_Butterfield Nice technical well thought out response...

[The_MS]

Now we have Beer in the thread

Awesome

Water is very heavy and hard to push around. With a fin and wing I would think that the ski pretty much stays on a path. Any movement in the tail area during the turn is more of a push movement and not sliding across the water.

[Bruce_Butterfield]

@eleeski its pretty hard to generate a well thought technical response to your comments. Most have a grain of validity, but are in reality non-sequiturs.

 

For example your comment that “Slippery slalom illustrates that a fin is not necessary.” Is completely true, but is analogous to “running a 1980 Yugo on a Formula 1 track illustrates that a $5M race car is not necessary.”

 

Maybe someday you or a closet genius will be successful in designing a top end slalom ski without a fin, but physics, human anatomy and build materials make that a looooong way off. If you can prove me wrong, I’ll gladly buy you a case of Narwhal.

 

Merry Christmas.

 

[Horton]

@Bruce_Butterfield

 

[eleeski]

Slippery slalom gets a lot of reasonably skilled (but not elite) skiers into extremely short line. The geometry of the rope's pull around the buoy is similar to "real" skiing at short line. Slippery slalom certainly models some aspects of deep shortline well. More than a "grain of validity".

 

Like cars have zero similarity to waterskiing, a Yugo has zero modeling validity in F1 racing (although you have the same chance to win a race in a Yugo as in a sprint car against an F1 car). How a "genius" tag is put on for a "non-sequitur" comment defies logic.

 

Perhaps logic isn't popular when it contradicts beliefs.

 

Sorry for going off topic but it seems to be personal, not technical.

 

Eric

[ROBOT]

@eleeski

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[thager]

Eric did you write to yourself? :)

[Than_Bogan]

Come on now people. Christmas spirit! Kindness to fellow man!

[BraceMaker]

In a wake crossing or really any time the skier is accelerating and decelerating doesn't the displacement of water have to be from slippage of the ski? Can someone provide me the physics of where else it comes from? Clearly it's not from some sort of thrust...

[dvskier]

@Horton Have you been visiting the Emerald Triangle up north?

[Horton]

@dvskier

100% no. You find my explanations illogical?

[liquid d]

Too much slippage=bad

Too little slippage=bad

We all strive for the perfect amount to help that tip get pointed in the right direction, engaged, and start the rocket to the other side! woooohoooo!

The tip and tail are going different speeds (and different directions) through the apex of a turn.

 

[TacoMan]

I'd like to throw skiing technique out the window for a second and focus on pure physics for a second because ultimately physics govern the world we live in. Ultimately what we have is a ski in contact with the water at an arbitrary angle during a turn or while holding a straight line cross course. Now keeping that angle constent for this duscussion (45 degrees for example for which is the ski rolling around the long axis). This generates an incline plane which allows the water to gain a mechanical advantage on the skier. Keep this thought in mind now. Now how does this effect the length of the ski?

 

In theory you are going to need a specific surface area of your ski in contact with the water to generate enough force or "holding power" to keep you on your path or "hold your angle behind the boat". This is independent of the length of the ski because surface area is a function of width and length. Now how come you cant run 38 off on a short and wide wakeboard or trick ski at 36mph? Due to the fact that the water has the mechanical advantage on you due to the incline length, you physically cannot get the ski deep enough in the water at speed and the result is sliding forward down course.

 

Now how do you generate the surface area needed for the proper "hold" in the turn or cross course action when you are essentially constrained in the width direction? Answer: increase the length. This is also a double edge sword in your favor as well. Think of the surface area in contact with the water (as it remains constant). A long and skinny incline surface vs. Wider more square incline plane (while of course keeping the inclination constant). With this you are decreasing the horizontal and vertical components of the vectors representing your inclined plane and with that you are effectively reducing the mechanical advantage the water has on you and your ski requiring less work (force x distance) on your end.

 

Now bringing it all together. On a short and wide ski, due to the resistance generated by the thick viscous nature of water (causing lift effectively) you are not able to get the ski deep enough to generate enough surface area for the proper hold. Thus, increasing the length knowing the ski will only ride so deep at cross course at angle will generate the needed surface area for "hold". Now for a 36mph skier there will be a point at which additional length beyond "x in." will allow for even more surface area then required for the hold needed on a set path cross course. The result is a increase in cross couse speed due to reduced drag via increased lift, and increasing the width only results in more ski out of the water. So in theory a longer ski will allow for a skier to gain mechanical advantage on the water, thus making cross course more efficient. However, due to length and scaling design as @horton mentioned, this generally means you or binding connectionat the ski (the applied force) will be at a greater distance from the fin (the applied load) and closer to the ski (the fulcrum just ahead of the bindings). In physics terms of a 3rd class lever this means you will be at a greater mechanical disadvantage making the ski harder to turn.

 

 

Now for relationship of the skier height and relation of their center of mass while keeping the mass value (skier weight) constant:

 

The taller the skier, the higher the center of mass is above the ski while keeping their weight constant between skiers. The skier in relation to the ski is a 2nd class lever. That means the ski surface is the fulcrum, the resistance is at the width of the feet and lateral binding pressure points, and the center of mass is the applied load. In the scenario of the 2nd class lever increasing the distance between the applied load and the fulcrum will increase the mechanical advantage the skier has on the ski making it easier to turn. That being said a 6'3 skier 180lbs (skier A) will be able to turn a given ski much easier than a 5'3 180lbs (Skier B ) skier. Now when you sum the total work done from our entire descussion with mechanical advantage in mind, skier A will be able to ski a Longer ski and generate more speed and turn the same radius as skier B with the same overhall input work of the function.

 

Take that with a grain of salt because putting that all together only works if you the skier can put it together with proper technique to mirror the physics needed. Technique then with that in mind will have a huge effect on how a given skier may perceive how a longer or shorter ski may help them, and the world we live in is not perfect either and is filled with anomalies.

 

I apologize for any spellimg or grammer in that long post, i went into engineering because i hated English class in school haha.

 

I hope this helps with topic insight, but at the end of they day we'll be right back where we started with the gold standard "try it before you buy it".

 

 

 

 

 

 

[hammerski]

And then there’s tail rocker. I recently tried a 67” ski that I hadn’t tried before(190 lbs) The tail rocker was pretty flat compared to other skis I’ve ridden. Bottom line, no matter what fin/binding settings I tried, could not get it to finish the turn. So a longer ski with more rocker will still turn, then there’s how much flex the tail has. I rode a 68” HO A1, one of the best ski seasons of my life in 2010. It had a lot of tail rocker in comparison. My .02, longer skis that still turn are easier on the ole back.

[TacoMan]

@hammerski that is true, the point i was trying to make was when length is your only unconstrained variable with a pure physics definition. When you change the rocker in one and not the other you're now comparing an apple to an orange. But that is a good point. There's more than one way to skin a cat. Im sure the Denali guys can jump in on tunnel design as well. Effectively we have a infinite variable expression with a semi infinite solution. Good luck finding the absolute optimization.

 

But back to the original post question on deciding length between 2 otherwise identical skis. Physics will always win.

[Stevie Boy]

Is length irrelvant, how much of say a 67" ski is in contact with the water, is surface area what we should be talking about.

If you cut the front 3" off of the front of the ski, would you still be skiing on a 67" that was 64" ?

Interesting to see if the Denali concept of one length of ski , stands the test of time, obviously cost and the lack of opportunity to Demo, will affect the amount of feedback that is available, but I find it interesting that they work with surface area and not length.

[thager]

@TacoMan @Stevie Boy @hammerski I like how you guys are thinking! It's a surface area thing for sure but widening a ski has its limitations for grip as speed increases, unless we go to extremely deep fins at some point the fin would lose contact with the water. Same for length at some point also since more edge in the water would decrease turn efficiency, but I think one could compensate by moving the bindings back. I had a 68" Razor 2A (stiff) that I could not get to turn no matter what factory fin settings I used. On a lark I moved the front binding back 1/4" from factory which shortened the wheelbase and reduced stability. Ski was twitchy but it sure turned quick! Windshield wiper turn then drop the tip back in the water and rocket to the other side. Wasn't pretty but it worked for me. Tied my PB on it.

[Deanoski]

Not sure if a big ski turns slower but a bigger ski has a bigger turning radius

 

 

[TacoMan]

@thager absolutely moving your bindings back helps the turn due to a gain in mechanical advantage but now you've opened another can of worms. Your CG is now farther back on the ski relatively. Its like solving a rubics cube that wants to fight back.

 

Im curious now to see if anyone has ever experimented with a ski that was say 1 or 2 sizes too large or "long" with their bindings on the extreme end of backwards form the neutral or stock position. In theory i would think if its possible by a less than conventional skier form modification in this scenario to have a larger center of mass shift nack and forth while skiing, unlike skiing a more conventional ski reccomended for your size where the optimal CG locations may be more closely aligned in turn and cross course.

 

Also let's not neglect to recognize scenarios where your ski may be flat and not on edge where width or length in excess will always help here to maintain speed by causing the increase of surface area (for example during the split second you're changing edges). Let's face it your chain is only as strong as your weakest link.

 

Maybe the Denali guys have it right with their design. The shorter length and increased width may provide more benefit from second wake to ball an in the turn than you could gain from ball to second wake with an increase in length of the ski in contact with the water would do knowing that there will be a slight negativeimpactat the ball.

 

[Horton]

 

[eleeski]

@TacoMan I have done your experiment with ski sizes. Often. I sometimes build a ski that is too long and too wide. I am willing to take a massive binding move, a sawzall or a grinder to the ski until it works well. (Yes, I have chopped over an inch off the tail of a ski and improved it!) Horrifying to watch the process but I have gotten good results.

 

Length is just one factor in making a ski work well. Area is another. Rocker might be the most important. Edge shape a close second. Tunnel next. Binding placement, fin setup, shape and even weight - all must be balanced to make a ski work. Since everyone is different, no one ski will be perfect. Demo as many skis as you can.

 

Eric

[Roger]

@jrs who weighs about 155lbs skied on a 70 inch HO CDX for a while and didn't seem to have any problems executing tight turns. Someone above mentioned that Nate rides a 67 which is true, but for the first couple of years (and several wins), he rode a 68 (IIRC).

[Blofeld]

https://www.instagram.com/p/B8MBvuGJhZU/?igshid=1qf8vr90gb3r3

[Horton]

Haaaa Haaa Haaaaa