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Flotation as a function of ski flex, length and skier weight

I have a counterintuitive question. I've read on this forum that, given the same ski length and dimensions the stiffer a ski, the worse the flotation in powder (ie softer skis float better). Also, given the same ski, the shorter the ski the worse the flotation (ie longer skis float better). Additionally, given the exact same ski in the exact same length a lighter skier will flex a ski less than a heavier skier (ie lighter skiers generally should be on a softer ski).

Given the above reasoning, it seems to me that if a lighter and a heavier skier are on the exact same ski (relatively stiff flex) with the exact same length skiing powder, the lighter skier will experience worse flotation due to his or her inability to flex the ski. If you're still with me and your head doesn't hurt, is this reasoning correct? I ask because it's counterintuitive and doesn't seem to make sense. Any thoughts? Maybe a good one for Physicsman to tackle.
Let's assume same skier on 2 skis with same dimensions but different flex.

The softer skis only float better at speed since the softer tip has a chance to flex and come back to the surface when the skier is moving at certain speeds.

Let's assume same ski with 2 skiers of different weight.

The weight is critical here. If you are so light that the ski does not flex at all, you will sink when the tip goes under. If you are so heavy that the ski flexes too much you will sink just as easily because the weight of the skier is simply too much for the given speed of movement. Pick the right weight and you have the ideal float (for the given speed). Pick zero speed and the lighter the skier, the better the float .

There are too many variables so it is all relative. You reasoning may make sense in specific situations, but not as a general statement.
Width plays a role in floatation.
Quote:
 Originally posted by cololi:Width plays a role in floatation.
Really? Come on, seriously... :

I think a lot of it depends on the width of the ski in relation to the weight of the skier. For instance, I weigh 200 lbs, and float considerably more on my 190cm K2 AK Launchers (88mm waist) than my 198cm Atomic 10.EX's (86mm waist I think). There is actually more surface area on the 10.EX's, but because they are so stiff, they submarine much more. However, if someone on the same ski weighed 40lbs lighter, the width might be enough to float them to whatever point they desired. And then there's that -- how much do you actually want to float? In other words, what TomB said.
OK, to start off with, the following responses are my OPINION, and may not be factually accurate (that's the political way of saying they may be completely wrong)

Quote:
 Originally posted by Prosper:I have a counterintuitive question. I've read on this forum that, given the same ski length and dimensions the stiffer a ski, the worse the flotation in powder (ie softer skis float better).
True, in the same way that a flexible sheet of plastic will float better on water than a stiff sheet. When a wave comes along, the sheet deforms (flexes) up and over the wave and down the other side, while the stiff sheet either has to through the wave or else it will go up one side, and have less surface in contact with the water.

Quote:
 Originally posted by Prosper:Also, given the same ski, the shorter the ski the worse the flotation (ie longer skis float better).
True. Although it's not just about length, it's about surface area (which can be seen with a snowboard - not as long as skis, but a bigger surface area, so better floatation)

Quote:
 Originally posted by Prosper:Additionally, given the exact same ski in the exact same length a lighter skier will flex a ski less than a heavier skier
This is true, but is unrelated to floatation.
The idea of a soft ski flexing in the snow is similar to the sheet of plastic floating on the water. The floatation is increased by the ski flexing as a result of the snow, not as a result of the skier forcing it to flex.
If the force acting down is increased, there will be less floatation, so, a heavier skier on the same ski will not float as well as a lighter one.

At least, that's my take on it.

S
Quote:
 Originally posted by Prosper:I have a counterintuitive question. I've read on this forum that, given the same ski length and dimensions the stiffer a ski, the worse the flotation in powder (ie softer skis float better). Also, given the same ski, the shorter the ski the worse the flotation (ie longer skis float better). Additionally, given the exact same ski in the exact same length a lighter skier will flex a ski less than a heavier skier (ie lighter skiers generally should be on a softer ski). Given the above reasoning, it seems to me that if a lighter and a heavier skier are on the exact same ski (relatively stiff flex) with the exact same length skiing powder, the lighter skier will experience worse flotation due to his or her inability to flex the ski. If you're still with me and your head doesn't hurt, is this reasoning correct? I ask because it's counterintuitive and doesn't seem to make sense. Any thoughts? Maybe a good one for Physicsman to tackle.
Then, there are at least three separate factors that people always tend to lump together when they are comparing the "float" of different skis in powder:

1) The average depth of the flexed ski under the surface of the snow;

2) The depth to which the skier (or at least his boots) is immersed in the pow; and,

3) The tendency of the ski to nose dive and auger in to bottomless powder.

You asked whether a lighter skier on the same skis will experience worse flotation due to their inability to flex their skis.

What will happen is that for your hypothetical lighter skier, #1 will be less, #2 will also be less, but #3 will be more. So, for some light people, the most noticible thing about a particular ski (in bottomless powder) may be its propensity for un-nerving tip-diving, so they will simply report that this ski "doesn't float well", even if most of the time, it was only a few inches under the surface because of their light weight.

Basically, the apparent paradox which you found only arose because of the vagueness (multiple-meanings) in the commonly used term "float".

I could go on for pages about what design parameters influences each of the above three observables, but I think the most important points for deep powder (ie, not in stratified or partially compacted conditions) are:

1) A flat ski tends to dive for exactly the same reason that a flattened hand held out of a car window at 60 mph tends to get pushed down if it is at all tipped downward. Ball up your hand (ie, let the ski flex a bit) and this effect goes away. If a stiff ski is always tip-up, it will give you lots of support in bottomless conditions, but make even a little fore-aft error in such conditions, and you will go over the handlebars.

2) The average depth of the flexed ski under the surface of the snow (#1, above) is determined pretty accurately by the total load bearing area. A simple and surprisingly accurate formulat to calculate this is just A = Length * average_width, where average_width = 0.25*tip_width + 0.5*mid_width + 0.25*tail_width.

3) The depth to which the skier feels immersed in powder (#2, above) is not the same as the average depth of immersion of the ski because in bottomless conditions on soft skis, due to the flex of the skis, your boots may be many inches below the average depth of your ski. With stiff skis (relative to the skier's weight), there will be almost no difference between #1 and #2, but with soft skis, the middle of the ski can easily be 6 inches further immersed than the tip (even if the ski is level), and this will contribute to an overall feeling of being more "in the powder" or "less float" for a soft ski of the same surface area as a stiff ski.

HTH,

Tom / PM

[ September 05, 2003, 09:35 AM: Message edited by: PhysicsMan ]
This is a great thread that I hope got viewed more than the reply count indicates.

I'm a huge fan of fat skis, but so many people are going about them the wrong way. You can take one look at Powder's forums or the Powder gear guide and see that everyone is about getting the stiffest, biggest fats they can find. Big Daddies, Explosiv's, SuperNobis, etc. If they aren't decambering for you, you're LOSING float. I've felt the see-saw phenomenon first hand on Volkl Explosiv's and Atomic 10.EX's. Why do the Volant Spatulas work so well? Because they're decambered for you already.

Despite all the heckles I got, I skied most of last year on Pocket Rockets. I skied the previous few years on G40, G41, G4, 10ex. I could have bought any pair of skis on the market, and I went with the PRs. Yeah, they're soft, but thats why they work so well for me. At 160 lbs, the 185 PR works about perfect. For pow - even at speed - the PR actually works better than the bomber Explosiv for my weight.

If you aren't tipping the scales, make sure you don't get more ski than you need. Its not a matter of working more (although you will!), but it will actually reduce the very performance you're trying to gain by buying those skis. Theres a reason why the new fats from Salomon (PR, Hot line), K2(Pistol, Kahuna), and Volkl(Gotama) are soft.

If you're buying an ultra stiff fat for crud and hardpack performance, its still a bad move. It'll be a medicore pow ski, and a sub-par crud/groomer/all-mtn ski. (The big mids like G4, REX, 724 Pro, K2 XP are better crud boards than stuff like the Explosiv - its all about sidecut).
Matter -

As you point out, crud performance is very important to advanced skiers. To me, almost any ski (including 210 cm skinny straight sticks) will do just fine in nice untracked powder in wide open country, but what really differentiates non-groomer skis is their crud performance, particularly when they are to be used in tight quarters. As you also mentioned, overall stiffness and sidecut are two of the most important design variables that influence crud performance. Swing weight, initial camber and flex distribution are other important design parameters. A detailed discussion of exactly how ski design influences crud performance could easily be the subject of its own thread, but here is my quick take on the subject.

My definition of a ski with good crud performance is one that minimizes the response of random external influences on the ski while preserving reasonable response to intentional input from the driver.

For example, a pair of 188 G4's in thick cut up slop may be as stable and smooth as a train on rails, but may require so much driver input that it is impossible for a lighter skier to get them to turn in the space available. I don't think anyone would say the g4's are an appropriate crud ski for this person.

OTOH, one can go to the opposite extreme and if you put a 200 lb, muscular, experienced big mountain skier on a pair of noodles of the same dimensions, and they will be always decambered excessively. They will always be wanting to make turns of undesirably short radius in uniform (untracked) soft snow. Even worse, in irregular soft snow, the degree of decambering will vary dramatically from moment to moment, and lead to turns of varying radius (if turning) and a bumpy ride when going straight. The ride may be so unstable and unsettling that even a good skier will be forced to throttle back. This is situation with at least some of the people that prefer the g4's and other stiff sticks in crud. OTOH, I have to agree with you that the rest of the people on g4's are only on them for the sake of appearance, not function.

Obviously, there is an optimal ski design between these two extremes, and that optimum will depend on the skier's weight, speed, technical ability and agressiveness, as well as the space available for turns and the type of snow underfoot.

As you also point out, the Spatula is a very interesting design in that the decamber is already built in. Unfortunately, the designers gave the ski a soft flex, so the (de)camber will still vary with weight, G-forces, terrain undulations, etc. I think this was a huge big mistake. Since a degree of camber adequate to making soft snow turns was already built in, I think they should have made the flex quite stiff so that this built in camber would only be slightly perturbed by these external variables. It then would have been even a better crud ski. IMHO, they also made a major error in the sidecut, but that's a subject which deserves its own discussion.

Tom / PM
Having never skied the Spatulas I'm hesitant to call any part of their design a flaw. However..

I think the reverse sidecut is a total mistake too. I'm betting most of what people are liking about the Spats is due to the reverse camber and not the sidecut. I think lots of sidecut on a pure pow ski isn't necessary, but going reverse is paying too much attention to water skiing.

I've only water skied once before, but I think the reverse sidecut on water skis is due to the way water skiers lean back and rail off the tails of the skis. Its similar to how a whitewater kayak surfs on a wave. Kayaks don't have sidecut (well one Corran Addison design called the Fury did, but it wasn't successful), and they carve on waves by using the rail on the middle and tail of the kayak being the only part of the boat functioning with the wave.

Skiers use more of the entire length of the ski rather than just leaning back and using the tails. Also on a practical point, reverse sidecut destroys any versatility the ski could have. Something like the Gotama, with a huge footprint, soft flex and low cut can be far more versatile, with probably near equal performance in pow.

I know I'd never buy a pair of Spatulas, but I'd really like to try them to see how close my thinking is.
Matter - I agree with absolutely everything you said in your last msg, incl. your comment that you would like to try them yourself to see if they fit your mental model of them.

Personally, I would like to have seen compound curves on both the camber and sidecut of the Spatula. In other words, I would like the middle third of the ski to be shaped like a conventional stiff fattie with normal sidecut and camber, but have the front and rear thirds (approx) start to upcurve early but subtly (giving a form of fixed reverse camber in just these areas - just like the Spatula) to give added resistance to tip diving, fore-aft stability, extra float, etc. in deep snow.

Instead of continuing the normal sidecut outside of the middle third of the ski, the front and rear third sections should probably be designed with a bit of reverse sidecut to reduce the overall swing weight of the ski.

With a design like this, on groomers, the center of the ski is the only part that is in contact with the snow, and it acts like a conventional (but short) fat ski, and can track/carve instead of always pivoting on a tiny contact length like the current Spatula does. This would add considerable stability and overall performance on groomers. In deep snow, this conventional middle section only constitutes 30 or 40% of the total load bearing area of the ski, and the overall feel of the ski becomes more Spatula-like.

Thoughts?

Tom / PM
mattet and PM

Have either of you skied the spatula?
Neither of us have 1st hand experience on the Spatulas. Both of us tried to make this as clear as possible.

In the first line of his post of September 10, 2003 09:51 AM, Matter said, "...Having never skied the Spatulas I'm hesitant...".

In the first line of my post of September 10, 2003 10:38 AM, I said, "...I agree with absolutely everything you said in your last msg, incl. your comment that you would like to try them yourself to see if they fit your mental model of them." (ie, I would also like to try them to see if they fit *my* mental model).

Given the above, why did you ask whether we have skied on them? I know you handle them in the shop and ski them. My comments on the limitations of the Spatula are based on reading numerous first-hand reviews of it, including yours, Spatula Review. My hypothesizing about how alternate designs might improve its groomer performance without seriously diminishing its soft snow performance is really based on quite elementary ski engineering principles. Do you think the proposed modifications wouldn't be successful for some reason, or do you disagree with something else that one of us said?

Tom / PM

[ September 12, 2003, 09:48 PM: Message edited by: PhysicsMan ]
I was just reading quickly, before coffee, and was wondering.
I didn't have time to read the whole post, but I will in a day or two.
just wondering if you have skied them, not that your ideas are wrong or right, just a harmless, early morning question