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Float, how fast, how deep?

post #1 of 23
Thread Starter 
How fast do you need to ski to "float" in powder? How deep does the powder need to be to truely "float"?
post #2 of 23
At 185# I can ski on less than 5 inches of "regular Colorado freshies" and not touch bottom. that is on 188 cm Volkl Explosiv! (a pretty wide ski) Hard turns might press to the base however.

"Floating" in soft dry pow up to the hips is not too unusual. (Special though ;-). Waist deep can be termed
"bottomless" in most cases, even at speeds of 3-5 meters per second.
Narrow skis ski powder just like wide skis do, only they require higher velocities to "float". A "force per unit area" kind of thing. Slow is good! It allows time to enjoy! No two snows are the same!

CalG
post #3 of 23
Let's see...

OK, I've run the numbers (W / SA x V) and (MC / G) through NASA's supercomputer and the results are:

Q#1- depends.

Q#2- depends.

Hope this cleared things up.
post #4 of 23
Quote:
Originally Posted by Cgrandy View Post
Narrow skis ski powder just like wide skis do, only they require higher velocities to "float". A "force per unit area" kind of thing. Slow is good! It allows time to enjoy! No two snows are the same!

I'm going to have to disagree with this. I can get a 110mm waisted ski to float almost as well as I can a 136mm waisted ski, once you get up to speed.

The reason I like the bigger ski more in pow is because it is more stable, and more maneuverable.
post #5 of 23
Quote:
Originally Posted by Whiteroom View Post
Let's see...

OK, I've run the numbers (W / SA x V) and (MC / G) through NASA's supercomputer and the results are:

Q#1- depends.

Q#2- depends.

Hope this cleared things up.
And this year's Nobel Prize goes to Whiteroom!

That's pretty funny
post #6 of 23
Quote:
Originally Posted by steveturner View Post
How fast do you need to ski to "float" in powder? How deep does the powder need to be to truely "float"?
depend on how thick the powder is and how big the ski is.

my thugs will mostly stay on top of any snow at speed Id say 15ish mph
me at :30 seconds
post #7 of 23
I would argue that some skis require some float to function. If the area under the ski is moving, the ski is no longer carving on a solid. Its floating on a fluid of soft rolling snow.

This is the case with most rockered or reverse cambered skis.

Michael
post #8 of 23
I think it's the Skier not the skis. I tried to float with a 91mm waist and it didn't work for me.
post #9 of 23
About 4 times as fast as Bushwacker if I'm on 68 mm SGs.
post #10 of 23
Quote:
Originally Posted by steveturner View Post
How fast do you need to ski to "float" in powder? How deep does the powder need to be to truely "float"?
Don't listen to any of these guys.

The real answers are: 58 mph and 2.3 feet.
post #11 of 23
Quote:
Originally Posted by Whiteroom View Post
Let's see...

OK, I've run the numbers (W / SA x V) and (MC / G) through NASA's supercomputer and the results are:

I work for NASA and can barely get time on the supercomputers! I think Tom/PhysicsMan made a thread on this topic at one point. I didn't completely agree with the fluid/aerodynamics analogy he used, but the basic gyst of the thesis was decent.
post #12 of 23
Yeah, there were a couple of interesting threads on this a while back. Use PM's calculator to figure SA, divide it by your weight, to get a rough idea of how different skis stack up. If you want something fancier, go calculate lift for your skis. (Yep, I know not everyone buys a fluid model, but I'm still trying to finesse a aero engineer into helping me with this, coefficient of lift for a ski shovel yet to be determined.)
post #13 of 23
Quote:
Originally Posted by beyond View Post
(Yep, I know not everyone buys a fluid model, but I'm still trying to finesse a aero engineer into helping me with this, coefficient of lift for a ski shovel yet to be determined.)
I think it would be quite difficult (though perhaps good fun) to make a model with meaningful results. I've yet to see the "virgin freshie pow-pow" material definition in any CFD package. There is a bunch published about the mechanics of snow, but mostly for the purpose of avalanche research.

So what are you going to do? Snow is generally seen as a non-newtonian dilatant viscoplastic material in its bulk form. I don't know if off the shelf CFD (or if we are heading more toward solid than fluid, FEA) codes can really deal with that kind of material. I see from some googling that the problem of wind deposited snow has been successfully modeled, but that is a long ways from a ski moving through the bulk material.

Forgetting the snow for a moment, just getting a handle on how a ski responds to applied loads would be pretty difficult, and from my intuitive understanding of how different skis "float" pretty important as well.

Sounds like it would be a pretty cool project for a Masters or something.

I'm currently 195lbs. I ski a 110mm ski that is 193cm long. On some dense cheesy/creamy wind deposited snows I'm riding the surface in a comfortable centered position even at low <10mph speeds. In real blower, I don't feel completely "on the step" (if that is a reasonable analogy) unless I'm tailgunning it at 30+ mph. There are certain times when I definitely wish I had more ski under my foot, or some reverse camber, or whatever...mainly for stability and the ability to stomp turns rather than "float" per se.
post #14 of 23
"just enough (+5mm)' works best for me.
post #15 of 23
Quote:
Snow is generally seen as a non-newtonian dilatant viscoplastic material in its bulk form. -Garrett
:
One of the best lines I've seen in a while. I won't be a dilatante and start addressing that line.

As for floating, this year in vt we've had some pretty good snow in "bulk form". (In between the rain of course). Now I thought I was pretty well prepared on the widest ski underfoot I've ever owned. 71mm underfoot with big tips.(121 71 107mm) (yeah I know that's like a stick...)
Imagine my surprise when on a decent pitch slope I come to a screeching halt in dense snow up to my knees. One is no longer skiing at this point but confronting more simple "Newtonian" things like sinking to the center of the earth.

Now had someone been on the side of the trail selling fat skis like they do umbrellas in nyc when it rains, I would've beaten a little old lady with my pole to get something fat. Maybe 120 underfoot?
Yeah call me dense but then I finally got all the squawking about fat skis.
Of course in vt the snow seems to be in a simpler solid form, ie. "ice" where slalom skis work just great.

Maybe there's some sort of Heisenberg Uncertainty Principle of floating on skis?
post #16 of 23
Garret hit the nail on the head. Snow simply does not meet the important criteria of a fluid, and so the aerodynamic analogies are not valid. I really think ski float is more akin to the "dune buggy tire on sand" situation. I am sure someone has looked at that problem from an engineering standpoint, and it may provide a good starting point.
post #17 of 23
Quote:
Originally Posted by Tog View Post

Maybe there's some sort of Heisenberg Uncertainty Principle of floating on skis?
I think you've got it:

If you stop to measure your speed on a pow day, you don't know where you're at, and if you know where you're at on a pow day, you certainly won't spend time measuring your speed.
post #18 of 23
Quote:
Originally Posted by Tog View Post
Maybe there's some sort of Heisenberg Uncertainty Principle of floating on skis?
(Graffiti seen in a Stanford Physics Department bathroom stall: "Heisenberg might have been here.")
post #19 of 23
Aleph, good one. Perhaps we're getting some where..

doogie, was there any grafitti in there about Schrodinger's Cat?
I can't remember the story or even what Scrodinger did (energy states?) but somehow I think we should drag that cat into this.
post #20 of 23
Quote:
Originally Posted by Tog View Post
:

One of the best lines I've seen in a while. I won't be a dilatante and start addressing that line.

As for floating, this year in vt we've had some pretty good snow in "bulk form". (In between the rain of course). Now I thought I was pretty well prepared on the widest ski underfoot I've ever owned. 71mm underfoot with big tips.(121 71 107mm) (yeah I know that's like a stick...)
Imagine my surprise when on a decent pitch slope I come to a screeching halt in dense snow up to my knees. One is no longer skiing at this point but confronting more simple "Newtonian" things like sinking to the center of the earth.

Now had someone been on the side of the trail selling fat skis like they do umbrellas in nyc when it rains, I would've beaten a little old lady with my pole to get something fat. Maybe 120 underfoot?
Yeah call me dense but then I finally got all the squawking about fat skis.
Of course in vt the snow seems to be in a simpler solid form, ie. "ice" where slalom skis work just great.

Maybe there's some sort of Heisenberg Uncertainty Principle of floating on skis?
I've floated on east coast powder standing still on 70mm waisted skis.
post #21 of 23
Quote:
Originally Posted by skier219 View Post
I really think ski float is more akin to the "dune buggy tire on sand" situation. I am sure someone has looked at that problem from an engineering standpoint, and it may provide a good starting point.
Makes a bunch of sense to me. When I started googling in that direction, I found some papers discussing the "tire on snow" situation. So useful models are out there, and I think it would be fun to see if the mechanics of snow they model are general and accurate enough that you could increase the depth and throw a ski at it.
post #22 of 23
Quote:
Originally Posted by Ghost View Post
About 4 times as fast as Bushwacker if I'm on 68 mm SGs.
60 miles an hour in powder on Sg skis, you must have some incrediable skills to stay balanced on those.
post #23 of 23
It helps if you don't turn too sharp. The problem I had wasn't staying balanced (at least after the first few days); it was not getting bogged down when I wasn't on something moderately steep and going fast. Skinny SG skis, low slopes, and deep snow don't mix that well.
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