Author Topic: Float and Velocity and Equipment Choices  (Read 2259 times)

jbotti

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Float and Velocity and Equipment Choices
« on: September 10, 2011, 06:24:42 pm »
I started this as a different thread but it is clearly an adjunct to the thread we have had going about Rocker and skiing movements.

I learned something last year that is actually quite obvious so it's not surprising that it took me 9 years of skiing to figure it. When skiing 3-D snow the skis need to come up enough out of the snow so that they can release and so that the skier can tip the skis on edge to initiate the next turn (release, transfer and engage). The relationship between float and velocity is an important one. Most intermediate skiers that try to ski in powder on skinny skis find it very challenging. Many advanced/expert skiers don't find it very difficult at all. The reason why is speed or velocity. At a high enough speed, even the skinniest of skis will plane enough to allow release and transfer and re engagemnt onto the other set of edges. Having said that, if you are on thinner skis and you feel uncomfortable with skiing at a faster speed, then it is likley that you will not plane high enough to make RT and E free and easy and the skis will get caught up in the snow. Now add to this some other potential issues that intermediates may bring with them into 3-D conditions (like poor fore aft balance, or rotating the upper body) and without enough speed on thinner skis it can get ugly fast.

From a PMTS perspective (and those that don't care about this can disregard this) the goal is to get the bullet proof short radius turn bullet proof enough so that the skier can take the speed up to terminal velocity (the speed at which the skier will no longer be accelerating) and continue to make short radius turns. If you watch HH and Diana ski pow this is how they do it. Max has mastered this as well. I can do it on dark blue terrain for 15 turns but not on black terrain. So again from the PMTS perspective, the goal is to ski at terminal velocity using the bullet proof short radius turn. And this is a lofty goal for any skier. It took Max years and I am still working to get there.

So when looking at the issue of equipment when one is focusing on skiing this way, it is very simple. Sidecut and TR actually becomes more important than float!! I will say it again, when skiing at terminal velocity with BPSRT's sidecut is actually more important than float. The float is coming from the speed and at terminal velocity, almost anyone at any weight will have enough speed to plane high enough to RTand E all the way down the hill. No one is ever going to claim that this is easy, but it is the goal. And anyone that gets there (even if it is only for 15 turns at a time) will tell you that it is an amazing experience.

So it absolutely follows that if you can't or don't want to ski at terminal velocity. then you will need more float than the skier who is skiing at TV. This is why wide skis got popular in the first place. Speed will eliminate many issues that 3-D snow will throw at a skier. Without the speed we need more float. Add to this the issue of size and weight and 6 4" 220lb guys that don't want to go fast need a lot more float to be able to plane high enough in the snow to RTand E.

So there is no doubt that skiing on fatter skis makes things easier in 3-D snow. You can ski at a slower more lesiurely pace and not need to work as hard to get the skis to plane high enough to make turns.

It is also true that generally the longer and wider that you go, the wider the TR of the skis goes. What you gain in float you are losing in edging ability. So if you are skiing a 192cm ski that is 120mm underfoot and the TR is 36m, you have great float but you are also skiing on a plank and the natural TR is that of a super G ski. In PMTS we are trying to ski slalom turns in steeps in 3-d conditions (again at terminal velocity). This is very simply why Harald Harb has hated fat skis for so many years. He is giving up so much in TR and because he can ski fast he doesn't need the float. That's why he'd most times rather ski steep pow on his IM 78's than on a 30m TR ski. Can he ski it on the wide TR ski, of course, but he actually has to work harder because he can't use the sidecut of the ski to help him turn the skis.

So moving now to the issue of rocker. Does rocker give more float? Yes. So this makes it easier to ski at slower speeds and still be able to RT and E. But from a PMTS prespective rocker (especially rockered tails) come with another set of issues that complicates it for PMTS technique. Rockered tails make it incredibly easy to slip, pivot and steer the tails, so easy that this often becomes the default move for many skiers that are on them. Something that I haven't mentioned is the necesary component of counteracting forces and counter balancing forces in good PMTS skiing. When skiing SRT's at terminal velocity, there is no steering. There is only flexing to release and the CA and CB forces naturally move the skis to their new edge. This is the only that the a skeir can actuilly do slalom turns or BPSRT's at speed. Everything needs to be lined up with upper and lower body separation. It is hard or impossible to steer skis nto turns at these speeds. So when a skier skis on a ski that not only does not require proper CA and CB forces to initiate the edge change, but actually requires some modest amount of rotational force (that is what steering, pivoting, slithering, slarving and skarving require) this is why we will say again that rockered skis do not promote good PMTS technique and in fact promote the opposite. Again there is more than enough float available for any skier that wants a ski without rocker (at least at this point in time), but what attracts people to rocker is the amazing float and the ease with which the skis will pivot, steer, slither, slarve and skarve.

The great news is that there are 3-D skis available that will fulfill the goals of most skiers. PMTS skiesr that want to learn how to ski at TV will be chossing skis that support this, with no rocker and tigher turn radii. The skis that come to mind are the Icelantic Shaman and the Ski Logik Ullrs Chariot (which I have yet to ski) or the Movement Pariah and Jam. Those that want the added flexibility to slither and slarve and pivot more easily have an even wider range of skis to choose from.

I hope this makes some of my comments and comments from Max clearer. There is a very specific goal for skiers to achieve in PMTS and it all revolves around the BPSRT and skiing at TV. There are skis that support this and ski that are detrimental to this. This is not about what is good skiing or about the right way to ski pow. Everyone should enjoy the snow in every way that suits them best.




 
« Last Edit: September 10, 2011, 10:45:45 pm by jbotti »

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Gary

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Re: Float and Velocity and Equipment Choices
« Reply #1 on: September 10, 2011, 07:58:30 pm »
WOW JB....really beautiful stated and absolutely understand what you are saying.

For me where I love to take my MX78's between playful turns along the edges to TV on a variety of terrain ..I don't feel that comfortable  doing the same in 3D terrain. That kind of speed in that kind of terrain just makes it all go by much to quickly and when that happens, my technique can get sloppy.

So I guess it's good to know what you like, what you capable of and to have a blast doing it!

I do know that I'm not a Terminal Velocity skier....I'm more of a PV skier...Playful Velocity with a shake of Terminal Velocity to spice things up once in a while.  :D

Best, G

LivingProof

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Re: Float and Velocity and Equipment Choices
« Reply #2 on: September 11, 2011, 07:00:20 am »
JB,

A major treatise on skiing 3D!

A question for clarity, when you refer to the "bulletproof short radius turn", my belief is that this is the "linked, brushed carve" PMTS technique and not a pure carved turn. If so, then "terminal velocity" would be reached when the resistance provided by the skis turning would offset the gravitational pull down the hill.

So, at my home hill, on a green trail, I work on linked brushed turns and just can't exceed a certain speed. When I try it on steeper terrain, my technique breaks down and I begin accelerating.

midwif

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Re: Float and Velocity and Equipment Choices
« Reply #3 on: September 11, 2011, 09:23:05 am »
OK, guys, I need some explanation.

In John's original post, he equates sidecut (and turn radius) with turns in 3D snow.  I had always assumed that there were two different forces that bent skis.  On a hard surface where the edge has something to hold onto, the edge causes the turn.  However, in soft snow (when the edge doesn't have anything to hold onto), isn't it the flex of the ski and the distribution of pressure over the bottom that causes the ski to bend?

Soft snow where you are skiing the firm surface underneath doesn't count, but off-piste you need a flex pattern that will allow the skis to bend into a curved shape so that when you tip them in the snow, that curved shape becomes the turn??  If you ski really fast, then you need a stiffer ski because there are greater forces against the bottom of the ski, to get started in 3-D you need a softer ski that will flex into a curved shape at slower speeds.

Help me out here with my education? What causes skis to turn when the edges don't have a gripping surface? How does sidecut come into play in 3-D conditions? And, concurrently, what is the real turn radius of a ski, since the sidecut measurement may be good for comparison, but really doesn't measure the turning radius of a given ski for a 180 lb skier at 15 mph?

Example. Jim's Ullr's Chariots are a pretty stiff ski on groomed surfaces, but off-piste he thinks the wide shovel has more pressure the greater amount of snow underneath, and therefore doesn't "feel" as stiff.

So I had always assumed that a good ski for me would have lots of sidecut for the groomed, be fairl soft so that it bends in the powder at the speeds I ski, and have good lateral stiffness so that the sidecut didn't wash out at slightly faster speeds.
« Last Edit: September 11, 2011, 09:33:52 am by midwif »
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midwif

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Re: Float and Velocity and Equipment Choices
« Reply #4 on: September 11, 2011, 11:22:17 am »
........ For a traditional design, the more sidecut the more the ski bends.
So is that the reason JBotti was referencing soft snow skis with lots of sidecut, that it is an approximation of the flex of the ski??
I am very satisfied with my Fischer Muanga's (and also like the Ski Logik Rave's that I demoed at Jeannie Thoren's shop), was mostly just curious from a conceptual point of view as far as the difference in turns in soft vs hard.  Clearly, both are tipping of bent skis (or the alternative of twisting a flatter ski), but wanted to make sure my understanding of the forces that cause the ski to bend was correct. With modern materials, would indicate that you could also have a wide but still soft flexing ski or a narrow but still pretty stiff ski???

Interestingly, the Muanga is MUCH softer than the Rave, but I liked the two almost equally (maybe the Rave slightly more on the groomed). A paradox?
« Last Edit: September 11, 2011, 11:25:05 am by midwif »
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Liam

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Re: Float and Velocity and Equipment Choices
« Reply #5 on: September 11, 2011, 11:36:41 am »
Assuming a ski is long enough to get a critical amount of edge metal on the snow, would an early rise ski with traditional camber work with your stated goals?  I can see where tail rocker in inimical to your pursuits, but I don't see why early rise/ modest front rocker (again, assuming the ski is long enough to have a meaningful on snow running length) wouldn't work. 

My time at the end of last season on the Blizzard Bonafide and Rossi experience line tells me different.

Also, though the Icelantic doesn't refer to the Shaman's boat hull tip as 'rockered' but it sure ain't standard issue either..when I've laid them down next to my Nomads (which have a corpulent 145mm tip) the Shaman's tips go way higher-there is an early rise aspect to that ski.  The tip is definitely designed to add extra flaot where a standard tip does not-just like early rise.  And, those unique tips when coupled with a twin tip tail, ample side cut, and a fairly stiff construction, make it the deep snow world-beater that it is.

Terminal Velocity...isn't that the speed at which a falling mass can go no faster until another force acts on it??...Maybe Critical Velocity (the minimum speed required to get float on traditional skis) is a better term.  Just working with the basic word, I'm not sure 'terminal' is ever something I want to achieve on skis :o






jbotti

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Re: Float and Velocity and Equipment Choices
« Reply #6 on: September 11, 2011, 11:40:52 am »
Not sure you need to bend a ski in Pow but the sidecut helps the ski turn. If you just ride the sidecut there is a big difference between a 15m and a 30m TR. As well most turns in pow are brushed carved turns and the bend that one gets on hard snow, pressuring the tips in an edge locked carved arc is not happening. But again sidecut and TR is key to doing slalom brsuhed carved turns in soft snow.

The softness of a ski is a factor in float. the more the skis bends at the waist the higher the tips come up. But also the deeper one sinks from ski bend the more one has to flex to release the skis. So yes wider and softer helps float and potentially ease of use, but it is really width and speed that keeps a ski planing. . The faster you go the less need for soft and wide. What Max said is also a key point, too soft and you may get slightly better float but you will ge bounced and tossed in chop, crud and smaller bumps (that you can ski through with a stiffer ski). I also find that where soft skis really fail is when you get back on groomed terrain where they haven't groomed that day and you have a lot of harder chop. Soft skis just get tossed in this stuff and it is generally plentiful on powder days at most resorts (getting back to lifts).

jbotti

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Re: Float and Velocity and Equipment Choices
« Reply #7 on: September 11, 2011, 11:49:06 am »
Liam, for me the main thing I don't like about early rise tips is that the tips flop all over the place and when you do get on harder snow where you wantt to pressure the tips and bend the ski more, early rise and or rocker makes this much more difficult. I will say that I have been on some modest early rise tips that don't flop much and where you can get some tip pressure to help bend the ski. I do wonder what they (ski co's) are accomplishing with this other than selling more skis. I'm not sure there is much reason for it. It doesn't help float that much (again in minimal ER) and it definitely detracts from the skis performance in crud, chop and harder snow.

jbotti

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Re: Float and Velocity and Equipment Choices
« Reply #8 on: September 11, 2011, 12:11:53 pm »
The term terminal velocity was chosen by Harald and I think it is apt for the way he uses it. Essentially he is talking about doing SRT's on steeper terrain where the skier will gain speed for the first several turns and from there as long as the turns stay constant and at this same radius, the skier will no longer gain speed, hence hitting "terminal velocity".

Gary

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Re: Float and Velocity and Equipment Choices
« Reply #9 on: September 11, 2011, 12:29:08 pm »
Liam, i n my opinion I can not agree with JB is saying about rockers or early rise skis not performing in crud and chopped snow.

My typical hard snow ski is a 168. My rocker ski is 178. even though when the skis are flat and tips are rising,  there's enough edge connected to the snow and enough sidecut to bring the skis around nicely. The shovels ride up and over the nasty stuff and the skis perform superbly for me. I do think it is important to note that they should be skied longer than your everyday carving board. AND yes, on edge when the ski is tipped on it's side, rocker shovels and tails do hook up....There is no shovel flopping on my Rossi S3's and I've been told it's non existent on the DPS....test will tell.

If  the words Terminal Velocity means being able to set a turn shape and speed on any steep and maintain that rhythm, turn shape and speed all the way to the bottom of the run...I like it and I preach the same thing...it's all about control and edge finesse.

G




« Last Edit: September 11, 2011, 12:30:39 pm by Gary »

jim-ratliff

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Re: Float and Velocity and Equipment Choices
« Reply #10 on: September 11, 2011, 12:56:24 pm »
Terminal Velocity...isn't that the speed at which a falling mass can go no faster until another force acts on it??...Maybe Critical Velocity (the minimum speed required to get float on traditional skis) is a better term.  Just working with the basic word, I'm not sure 'terminal' is ever something I want to achieve on skis :o
Liam:
I had the same word reaction since it is usually used if reference to free falling objects of various mass and surface area; followed by the "well, yeah, at the speed these guys ski it would be terminal for me."

But since terminal velocity is the speed at which the resistance (wind in the case of free falling objects) is equal to the acceleration (gravity) and the body in motion ceases to accelerate, I can see Harald and John's usage. It's the speed at which the slowing effects of the turns and the snow itself equal the force of acceleration (gravity), i.e. the speed at which you stop accelerating as long as you keep making the same turns.
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jbotti

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Re: Float and Velocity and Equipment Choices
« Reply #11 on: September 11, 2011, 01:29:34 pm »
Gary, I have never been on the S3 or the DPS 112 RP (?) so I can't comment on those. I have been on many rockered tip skis and on all the tips flapped and on all you could not get solid tip pressure on harder snow.

jim-ratliff

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Re: Float and Velocity and Equipment Choices
« Reply #12 on: September 11, 2011, 01:54:17 pm »

Ok, so this is a little off topic, but maybe only a little. What role does sidecut really play when making turns in powder. My gut tells me none. What causes the skis to "carve" in powder (probably an oxymoron, lets call it a non-rotated turn)). I say it's the basic flex of the ski bending into a rounded shape and, when tipped, following that arc through the snow. And the more weight or force you can apply to the ski, the more it will bend and the sharper it will turn. ??

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jim-ratliff

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Re: Float and Velocity and Equipment Choices
« Reply #13 on: September 11, 2011, 01:59:34 pm »

And Liam, I see your point. If you take Gary's Kastle '78 and add 2 inches (10mm) of early rise on the front, they should still ski the same when on the groomed? Makes sense to me.

WOW, I am enjoying this whole thread. Thanks to all. I can't ski it, but I love understanding the physics behind it.
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jbotti

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Re: Float and Velocity and Equipment Choices
« Reply #14 on: September 11, 2011, 02:06:19 pm »
Jim, the answer to your question is that it really depends on how you are turning the skis. If you are pushing tails on a flat ski with little or no tipping forces, then yes perhaps the sidecut does not matter (or probaly it matters less). However if you are doing PMTS style brushed carved turns in powder where the skier is forward and pulls back the feet in every trun and engages the tips while tipping the skis, then sidecut matters a ton even in powder. You are still producing a brushed turn but you are getting the sidecut to do some good percentage of the work. As well, when I get on less steep terrain in powder sometimes I am brushing little and actually close to edgelock carving in the pow. Here sidecut matters a ton.