Where does speed come from

[Orlando76]

I’ve never ventured into fin theory as it is a bit over my head and skill level. I feel I need to adjust myself before adjusting a fin .001. But Horton’s recent fin video got me thinking and spurred my question of where does speed come from? Of course ski materials and design determine this significantly as well as body position but what role does the fin play in speed if any? Wing angle?

[MISkier]

In my opinion, speed will occur and peak when more of the edge of the ski is in the water, with the skier leaning away from the boat in a balanced stance, and executing these in tandem at the moment that maximum centripetal force can be harnessed from the boat and rope configuration.

[Wish]

@Orlando76

 

https://www.denaliskis.com/gut-102

[Horton]

@Orlando76 It is all a bit of voodoo but generally you can think of the amount of leading edge and the amount of total fin as factors that make a ski faster or slower. The less fin the faster ..... sort of.

 

The more fin surface and fin leading edge there is the there more drag there is. Even the thickness of a fin makes a noticeable difference. If you replace a .085 fin with a .090 fin the ski will feel more stable but slower.

 

I like to think of a wing as not directly changing the speed of a ski as much as it changes the attitude of the ski in the water. A wing pulls the tail of the ski down and that does a lot of things including increasing the drag of the ski - the flatter the ski is in the water the less resistance.

[DW]

To back up a step, speed comes from geometry. The more angle one holds, the faster the skier will travel since the boat is basically holding a set speed. Once rope tension is released, deceleration will be a function of the ski setup, positioning in the water and skier inputs.

[thager]

Need!

[Horton]

@DW and there comes the rub. A bigger fin means more grip and less side slip but as grip increases and sideslip decreases the load in the skier's hands (and body) at the centerline increases.

 

I know at times I have had skis that turn Off Side (one ball) awesome because of a big fin. The amount of grip results in my losing connection at the center line and results in a crap On Side. The fix may be with DFT or with total fin area.

[ScottScott]

Theres an ideal angle of cross coarse direction, combined with COM forward, and combined with an ideal amount of lean, that gives maximum speed. If you try to take too much angle, you end up sliding sideways too much. Similar to trajectory when throwing a ball for distance, there is a perfect angle to maximize speed. But, even with that perfect angle, if COM is too far back, it puts too much of the resistance on the smaller back part of the ski that cant grip as much, so more slide. COM forward and stack puts the pull in the meat of the ski for maximum grip. I think fin settings all lead to getting you into that ideal position out of the turn for the cross without losing speed in the turn.

[adamhcaldwell]

My biggest revelation about speed happened when I stopped thinking about 'linear' speed.

 

Speed is initially generated by getting the boat and skier to move away from each other as fast as possible during the 'downswing' of the rope into center-line. Initial acceleration occurs when the rope is between 90 and 45 degrees to the boat.

 

The faster the boat can pull away from the skier in the first segment (90-45deg), the higher the potential for an increase in rotational acceleration of the rope moving around the pylon. However, the trick is to have body position, and attitude of the ski positioned to 'accept" the initial downswing energy that was created and not just act like an anchor against the boat as you pass through 45deg on the final approach to CL.

 

If you can effectively manage body position, ski attitude, connection, you can continue to accelerate the rope from 45deg all the way to CL.

 

After the initial downswing from 90-45deg, being too restrictive to the boats downcourse travel from 45deg to 0deg (or CL) causes rope-swing to decelerate. This guarantees very premature disconnection from the line.

 

Trying to RUSH yourself from buoyline to CL is a disaster, especially on the gate. The initial approach to CL (90deg to 45deg) must be methodical and controlled in order to reap the rewards during the final approach (45 to centerline).

 

To maximize energy received from the boat to accelerate all the way to CL, we want the following situation:

 

-On the buoy-line.

-High enough velocity to still be 'on-plane' and in an efficient body position to lead the ski into CL.

-Rope at a 45deg position to the boat - ALL AT THE EXACT SAME TIME.

 

This will ensure the boat is giving you energy over the most amount of time/distance possible. Just need to be standing on the ski and controlling the attitude and direction of the ski such that it will reward you after accelerating through CL.

 

 

[Horton]

That's exactly what I said :- )

[adamhcaldwell]

Thanks @Gloersen - hard to keep that one short!

 

This is why you see so many skiers can ride just about anything. The are not relying solely on the ski for production of speed. They take advantage of the global system.

 

This doesn't mean ski setup and design isn't important though. Getting a ski dialed in with optimal acceleration and deceleration characteristics is huge.

 

Ski setup is what gives us the opportunity to stay in harmony with the pendulum swing around the pylon and simultainuousky be synchronous with the slalom course.

 

 

 

 

 

 

[Deke]

My biggest revelation about speed happened when I stopped thinking about 'linear' speed.

Ski setup is what gives us the opportunity to stay in harmony with the pendulum swing around the pylon and simultainuousky be synchronous with the slalom course.

Hey guys!
Remember when pendulums weren't cool? B)

@adamhcaldwell thank you for some great explanations.

[Drago]

@Deke I never swayed from the pendulum theory, when I had kids and put them on swingsets, it increased my belief to religious status

[rfa]

I am not nearly a good enough skier to contribute to this discussion in terms of knowledge or advice. My engineering background does help me understand the physics and technical parts of this topic. Even so, I agree it is sometimes difficult to grasp all the concepts when described in writing without visual aids. Well, this week, I had the privilege to spend 3 days with @adamhcaldwell at Trophy Lakes. You can tell just by how well he's able to describe his concepts in writing, how much he knows this "stuff". But 3 days of drawing diagrams, showing videos, discussing the physics with 3-D visuals, watching him ski (practicing what he preaches...), seeing some of his ski/fin technology development, etc. was a real treat. If I can only put in practice some of what I learned...

Thank you @adamhcaldwell

[A_B]

Speed comes from resistance. There is a best fin setup for every ski and skier. Just because a skinny strong kid from Indiana runs a specific setup into 43 off, doesn't mean it will work for an old fat guy. It comes down to tradeoffs and balancing a fin that rolls up and holds edge behind the boat, to one that can turn on both sides of the course, and what the particular skier can handle or push around in the turns when the need arises.

 

To not play with fin setup is leaving balls on the table if you ask me. Make changes, take good notes, and try pushing an adjustment to the limit, then back it off to the sweet spot. They stopped making fixed fins a long time ago for a reason!

 

[Horton]

Just because a skinny strong kid from Indiana runs a specific setup into 43 off, doesn't mean it will work for an old fat guy.

that Mr @AB is wisdom that needs to be heard

[bko]

Thanks @adamhcaldwell!

I am looking forward to implement these thoughts into my "concepts" when the winter is over.

 

But I have to admit I don't understand the actual description of the how-to:

 

"On the buoy-line."

Does that mean the desired starting point is at the buoy-line?

 

"High enough velocity to still be 'on-plane' and in an efficient body position to lead the ski into CL."

This is clear (I think).

 

"Rope at a 45° position to the boat"

?

 

"ALL AT THE EXACT SAME TIME."

I don't get this at all. Can the skier be at the buoy-line at the same time the rope is at an angle of 45° (if the rope is shorter than, let's say, 22 off)??

 

 

 

 

[adamhcaldwell]

@bko - Come ski with me in Charleston some time.

 

I want to run 41 in a tournament before I give all the secrets away for free on BOS.

[Andre]

There's also the Jeff Rodgers's way.

Put ski on.

Ski.

[bko]

@adamhcaldwell

Once you have run 41 off your advice must become more expensive ;)

 

If I ever make it across the big pond again, skiing with you and/or Cord is on top of my bucket list.

So far I only have had glimpses of your coaching through Austin Abel here in Austria. He was also the one who introduced me to the Denali

[Horton]

@andre love Rogers but he plays like a good old boy who just skis. I don't buy it.

[adamhcaldwell]

Agree!