cold water, less wing?

[skiron07]

after reading Paul Jager's article of fluid dynamics for years now I finally tried something counter intuitive hoping to at least try something instead of doing the same thing year after year-

our water has been cooling down rapidly and seems to be under 65 at the moment- last week the natural "fast water" syndrome became readily apparent and it seemed that no matter how hard I tried (pulling) I just couldn't keep up and get cross course like in warmer conditions. I reduced my wing from 8 to 7 degrees and voila, it almost felt like I was back in warm water again.  This is just the opposite of what I've done for the past 8 years and I'm so glad to have tried.

 Is this power of suggestion stuff or does this make sense in light of Paul's theory? 

 thanks-

[Chef23]

It doesn't make sense to me.  I know I added wing when it got cold and it seemed to work for me.

[Ali]

More wing, more ski in the water no?

cheers

Ali

[skiron07]

might be reading his theory a bit wrong but if "fast" water is really "slow" water and the sensation of fast is due to lack of course course speed, it suddenly occurred to me that reducing wing would conversely give me back a bit of speed...

turning the ski is certainly no issue

 

[Steven]

Paul's program doesn't make any sense at all when you first look at it, it goes against everything I thought I knew about ski set up (which isn't much) but I've had my best season ever! (in practice, tourneys sucked) I don't get the opportunity to ski behind ZO, so that's my excuse! LOL

[ktm300]

skiron    It is a simple question.  However, having asked it a lot, my guess is that not many people really know the answer.   I still don't.  Paul's viscosity theory is stated as a scientifically accepted principle. Is it?  If Paul is correct that the cold water is slower (more viscosity=more friction), then adding wing can't be the answer.  Of course the tail rides higher in the cold so that added wing would pull the tail back down but, it would also exacerbate the loss of speed.  I asked Paul if the extra friction of the cold was not offset by the ski riding higher.  He said no but, I'm not sure why.  A lot of things in this sport that fly as common knowledge aren't really known or proven.  One interesting thing (at least to me) is the notion of keeping speed up in the turn and being light on the line.  Did you see the strain gauge in the West Coast video?  Is 750 lbs light?  I rode in the boat with a guy who is a hell of a good skier and one smooth cat.  Strain gauge- 650 lbs.  Are people really keeping their speed up in the turn?   If so, how much?  At 41 off how much difference in the ski path can there be?  Anybody ever measure it?    I have another friend who is a really good 55k skier who says " go around the orange ones".  He honestly does no further analysis of anything.  Given that most of these physical property questions seem not to have an answer, maybe he is on to something.

[skiron07]

thanks ktm- appreciate the feedback and clearly understand the thought process

 I'm a master of overthinking anyhow and now love to try something counter intuitive since as an architect I go by intuition a lot

simply going around the orange ones has never (will never) be my outlook- very much enjoy the science of things and love to be a student of anything

took enough physics classes to know that the premise of Paul's article is dead on - it's just what you do with it can be very subjective...

"mistakes are portals of discovery" (JJ)

[Mark Cogan]

Skiron07

 

I think you’ve got it right.  As the water becomes cold or more viscous it creates more drag and your ski moves through it more slowly.  To combat this effect you can decrease wing angle which decreases drag. 

 

I think the confusion comes from defining cold water as “fast†which would infer you should add wing angle to slow down the ski.  But fast in this context refers to the sensation or perception of the skier feels.  Because you are moving slower through the water it is easier to get narrow in the course, there is less time for the pre-turn or turn and as a result things “feel†fast.

 

This analogy may not work for you, but when I’m skiing into the wind the combination of the wind speed and my speed give me the sensation that I’m traveling very fast when in fact the wind is actually slowing me down.

[skiron07]

cool- I've been trying to explain the difference between perception/sensation vs. actuality to a lot of people and just get shaking heads...too much "perception is reality" stuff

when I ski into the wind I feel like things slow down a bit but at some point it makes me narrow; conversely skiing with the wind makes me feel fast but I tend to pull too long

golf at 55

[tjm]

Think of it relative to how the ski naturally planes out.  If water temp was the only variable, then in very cold water the tail of the ski would not ride as deep, think of ice being the coldest water, the tail of the ski would ride on top and not sink at all.  This could be why a lot of out the fronts happen in colder water.

Adding more wing brings the tip of ski down and thus the tail of the ski up.  Reducing wing angle brings the tip of the ski up and lets the tail ride deeper.  

So more wing angle seems to only increase the effects of cold water, and less wing angle would seem to reverse the effects of cold water.

 

[skiron07]

agree as to your last statement -but- I had thought adding wing brings the tail down and tip up vs. decreasing wing lets the tail up/tip down?

I just know what I did works!

 

[Dirt]

I thought cold water was more dense and caused the ski to plane higher or ride higher in the water for the same boat speed. An airfoil creates more lift in cold dense air but drag is always a bi-product of lift. Is that what you guys are saying? Colder water creates more drag even though the ski rides higher?

[chris carter]

in another life i was a fighter pilot and engineer, so lots of time studing aerodynamics and practiciing it.....so the viscosity theory is correct in my view. but on the wing it is not quite that straigtforward:

 when you add lift you also add drag on any air foil and since water is many times more viscous than air, a small adjustment is mulitplied. a fin wing is similar to the elevator on an airplane and it intuitively adds downward "lift" to the tail of the ski, raising the nose, which is opposite to what the ski industry says.

actually with a small amount of wing angle it does bring the tail of the ski down, and raise the nose of the ski, until you add more wing angle and then the drag of the wing overcomes the lift of the wing and it creates the opposite affect. i dont know where that wing angle may be and it likely changes from ski to ski or when the water temp changes, but for discussion sake, if the wing angle starts to be positive, or hold the tail down at say 5 deg it may actually lift the nose of the ski at that shallow setting, but........when we increase it say an arbritary 10 deg , drag is likely more than the lift it provides and the wing  will "put more tip" or ski in the water because of the torque affect. the distance from the center of drag of the wing to the center of lift of the ski, (maybe about 2 inches times the amount of drag force) less the wing lift will be the net force on the ski  .......so as we discussed, somewhere between 5 deg and 10 deg the opposite affect occurs from a wing because the net forces of lift and drag changes, thus the confusion in the ski industry and what people feel, not knowing the different affects a wing can have on a ski....also the size of the wing can obviously change the whole equation, as in the difference of a mini wing, or one of the big ones that is used on Goode skis, as well as, the amount of drag just the mounting hardware provides. ski speed will also change this drag/lift relationship, as the Reynolds numbers will change quite a bit from 32 mph to 36 mph. You could actually have a wing at the same angle lifting the nose of the ski at 32 and lowering it at 36 if the angle was just at the "breaking point"

Bottom line: I think in most cases 4 to 5 deg of wing actually raises the tip of the ski, and 7 and greater lowers the tip of the ski affectively adding "tip".

 

sorry to ramble, but hope it makes sense.

[chris carter]

just another note on wing angle:

when a ski goes through the wakes, the attitude of the ski is slightly raised, so ideally, if the wing angle closely matches that angle, then the drag through the wakes will be minimal, or just the mounting and surfaces, ....when the ski is the the preturn/turn phase, the attutude of the ski lowers or is more parallel to the water and the wing has more affect to assist in turning the ski and that drag/lift relationship has precedence on the turn and lift characteristics of the ski. ski design would be optimized keeping these angles in mind. ...with of course many many more variables.

the amount of speed here is important, too much speed and your radius of turn is increased, and too slow and the boat runs away. add in the skier to all of this and we are back to an art and not just science.

[aguylikeshark]

good discussion. the basic is that is that anything that impacts or contacts the water will see a greater force applied to it. from there it gets more complex because of the variables we manipulate on a slalom ski to shape turns - from ski sizing, flex, boots, fin shape, fin dft, length, depth, fin surface area and finally wing angle itself.

Now 60 deg here and the water is heavy, i changed out all of the above - based on the simple principle, skiing great too for the conditions. wing resting at about 5 deg. any more my arms are falling off.

 if you are lucky or unlucky to be skiing in a shallow ditch then the effects of temp and water changes may be no big deal.

[Steven]

And why would skiing in a shallow ditch be less sensitive to water temp?

[ktm300]

One thing that Paul says that makes sense and that I feel when I ski is that in cold, the course feels shorter.   That being the case, a shorter ski for smaller radius turns would help.  Moving the fin and boots forward together as he suggests accomplishes just that.

[Steven]

Last week our water took a 10 degree drop, so I moved the boots and fin forward twice. After the second move, my ski was back to feeling like it did in the 80 deg water. Viscosity definately changes the way the ski rides and performs.

[aguylikeshark]

shallow, contaminated or polluted lakes - any lake with a lot of stuff in it that lowers viscosity (not minerals or acidic), and not much new input flow will see less of a fluctuation.

A living natural lake, deep will start to bloom in the summer, hold for Sept, but as the leaves & rain falls (more fresh input), start to purify over the fall and winter. So there is a double whammy going on  - esp for northern lakes.

[Jim Neely]

Steven,

What's the relationship between distance you moved your boots and distance you moved your fin?

[eleeski]

Cold water may be more dense and viscous but there is another factor. The surface tension is much higher in cold water. Note how a drop of water in the pan spreads out as the pan heats up. This effect may allow the ski to drop deeper into the water in warm water. More ski in the water = more drag and a slower feel. The conventional wisdom might not be all wrong.

When it gets really cold (55F in January - brrr) my water feels hard. It is difficult to roll the ski on edge. The ski bounces at the wakes more. The ski gets twitchy and very responsive. Perhaps the surface tension of the cold water is the major "feel" effect for me.

Hmmm, maybe dumping a few gallons of dish soap in the lake might soften that hard winter feel. This little gem is just to keep Horton entertained.

Eric

[Steven]

Jim,

I went from: Boots 29 5/8 to 29 3/4, DFT .721 to .728.

Now I'm at 29 7/8 Boots and .746 DFT