Water Temperature and Drag Force

[Wish]

I've had fun reading this. I get it for the most part. Even changed my mind on a few thoughts/misconceptions I've had regarding water temp and the affect on a ski. So I'm going to take measures based on what I have read to ensure better performance this winter to better my chances as the season approaches.

 

Step 1. take my tape measure, calipers, wing angle gauges, log book and leave them in the bag as planned cause screwing with that kind of thing this time of year just takes away from skiing.

 

Step 2. develop better techniques regardless of water temps at easier line lengths.. ad nauseam.. to force correct muscle memory for when the line gets short in the spring.

 

Step 3. Continue to read this thread for amusement and scientific knowledge.

 

Thinkn this should serve me better then a .000something change.

[wilecoyote]

@AdamCord with all due respect, the only time the ski is operating as a displacement hull is when you are swimming behind it and pushing it back to the boat (which I tend to do a lot) In displacement mode, your ski can only support a maximum of about 5lbs.

[AdamCord]

@wilecoyote moving from displacement to planing is not an either/or situation, it's a transition that moves along a curve. We are never fully "displacement" because as you said, we'd sink. But we are on the curve which is why drag increases as you slow down...you are starting to sink. On the other end if we were purely planing the drag would increase as speed increases, which we don't really see until we hit pretty high speeds on a ski. The other thing to understand is that the ski is almost always sliding sideways to some extent, so different areas of the ski can be at different points in the transition. Clear as mud?

[DaveD]

@AdamCord The last time I had my ski transition to displacement, it was immediately followed by a painful displacement of body parts.

[DanE]

@Wish You live in Florida, cold water??

Hahaha!

@MISkier "Therefore, it is still difficult to get wide early, even if you were to be traveling faster"

If you ski faster cross course you have a good opportunity to get wide and early.

If you have increased slippage downcourse that would mean you are traveling slower.

So like the chicken and the egg, wich comes first? Are you getting more slippage because you are traveling slower or are you traveling slower because of more slippage?

[Wish]

Our problem is hot water vs warm-ish. Hahaaa!! And still not worth messing with much of anything this time of year other then my technique..

[wilecoyote]

@AdamCord, while I agree that there is a curve, and we are not completely planing, for practical purposes, we are. Since a water ski is only capable of as I said about 5lbs of lift as a displacement hull, my remaining (classified) mass must be lifted by planing, so while technically it is a combination, there is so little displacement going on, it can be ignored. I would argue that the reason that drag increases as we slow down is because in order to generate enough lift to keep the ski on the water, the angle of attack has to increase, which increases induced drag. On the other point, parasitic drag will increase as speed increases, but induced drag goes down as the angle of attack goes down. For a planing surface, the best L/D occurs IIRC just under 5 degrees, which we we rarely get close to on a slalom ski, so the bulk of the drag we feel is induced drag. I would say this is the the reason why it feels as though drag is decreasing while speed is increasing. It is because the faster we go, the further aft the centre of lift moves, which brings the tip down, which reduces induced drag.

[RazorRoss3]

@horton, can you have @mattp write up some code that blocks any IP address coming from the south from posting about cold water? These Florida boys who can't pronounce "dry suit" much less have a need to own one

 

 

***sarcasm/joke font***

[eleeski]

@AdamCord and @wilecoyote Waterskis are always fully planing in all phases in the course. There is always a clearly defined wake behind the ski. Water never envelops the tail.

 

I have worked on the top edge of the ski to manage the flow but the effect has been to generate skidding or prevent excessive roll over - never to immerse the ski.

 

I've added ridges and grooves to the ski to add drag in the turn. I do pull ups to make the drag of the ski trivial conpared with the geometric loads of generating speed and angle when I have the 300hp to work with.

 

Skis are designed and tuned for the water conditions associated with the important competitions. Nationals in August drives a ski that works well in 80f water. (A ski for Tahoe in the winter is a snow ski.) My nearly 100f water needs a thick ski with sharp edges. 40f water calls for a thinner ski with rounded bevels. I'm not sure fin settings can optimize that wide a temperature range. Adam is 100% right about ski design able to make any water feel right - even if I doubt his theories about why.

 

FWIW, I have waterskied in a snowstorm and in lakes with ice on the edges. Too often (twice would be too often). So don't say I can't post. At least I have enough sense to avoid having most of my training in those conditions. This thread will peter out when things warm up.

 

Eric

[SkiJay]

Just because the ski rides higher in water that is more viscous, that doesn't automatically equate to there being less of the ski's edge in the water. Since nearly all of the drag acting on the ski is on the bottom, and the wing is even further below the bottom of the ski, and most of the momentum of the skier is way above the ski, consider how increasing low-slung drag will tend to pivot more ski into the water. The illustration below exaggerates the geometry of this concept:

 

I've studied a lot of cold water skiing, and despite the tendency for the ski to ride higher in cold water, I've not found any compelling photo or video evidence that this leads to less of the ski's length contacting the water. It just means the ski rides flatter through the water. This is consistent with the increased tip-sensitivity and higher drag-related workload skiers experience in cold water.

[AdamCord]

@wilecoyote I'm sorry if I wasn't clear initially. I'm not saying that the ski is ever acting as a displacement body, that only makes sense if it is submerged partially. What I am saying is that it is moving along the curve toward a displacement body as we slow....in other words we are starting to sink.

 

This is sometimes called the transition mode, and it's described simply like this:

 

What you are talking about with the increase Lift/Drag as speed drops, is exactly right! What you are referring to is the actual science behind how a hull lifts up onto plane. Initially a displacement body will create a bow wave as it pushes the water ahead if itself. This is the induced drag acting directly opposite to the direction of travel. As the speed increases, the angle of attack changes so that the resultant lift force (the combination of induced drag and vertical lift vectors) begins to point more upward.

 

This balancing act of Lift and Drag vectors is something that we are always manipulating as we ski, and the best skiers do a very good job of it. We'll get into a lot of the details of this in the soon-to-be published GUT articles.

[Than_Bogan]

Bam! Scienced!

 

Or should it be "You got scienced!"

[Horton]

I hate to interject among the science geeks but I have to.

 

I would suggest that what you feel on the water when it is cold is as much about you the skier being cold as the water being different. Your joints are stiff, you are wearing too much rubber so you are not a fluid and are likely on the back to the ski. The result is you ski ball to ball and it feels fast and crapy.

 

You can take big numbers, transmute them, and calculate their load bearing tangents but if you can focus on skiing more technical most of the issues fix themselves.

 

[DanE]

@Horton My joints are stiff all year round so not an issue

[eleeski]

@Horton Some winter days at my lake are sweltering hot air but icy water from yesterday's windstorm and clear cold nights. The water feel difference is real. The same thing happens in summer salt water. And the differences exist for trick skiing as well. I know that cold water feels fast and hard and adjust my style to compensate.

 

It is fun to geek out and try to explain the effect mathematically. @SkiJay and @AdamCord are making wrong assumptions or ski completely different from most of us but the back and forth is entertaining. If some good tuning tips come out of this, great! But in a few months we'll be back to the summer setup (where the added drag feel is real).

 

Eric

[Horton]

@eleeski

 

"@SkiJay and @AdamCord are making wrong assumptions or ski completely different from most of us"

 

I almost awarded the first ever Quad Panda but that is like a perfect 10 and I do not believe there is really such a thing as perfect score.

 

http://media.tumblr.com/fe497dd337d9af8479bb6398b9565d16/tumblr_inline_mg6n5ltl6X1rxe4lt.gif

http://media.tumblr.com/fe497dd337d9af8479bb6398b9565d16/tumblr_inline_mg6n5ltl6X1rxe4lt.gif

http://media.tumblr.com/fe497dd337d9af8479bb6398b9565d16/tumblr_inline_mg6n5ltl6X1rxe4lt.gif

 

[eleeski]

@scotchipman Tasters who evaluate whiskey or olive oil are able to make valuable and repeatable evaluations based on personal senses. Don't discount completely what we feel.

 

Regarding @AdamCord and @SkiJay "I can't believe they are pros. I'm so much better than them!" (GNAR points and Pandas!)

 

Eric

 

PS cold water is fast. And the earth is round.

[BG1]

Chuck Norris can tell how fast or slow the water is just by tasting it.

[dchristman]

http://s2.quickmeme.com/img/ed/ed835527bfeacd63ea6338ab33c474b69744c6b8218d8f6d52437fc92139772b.jpg

 

[MISkier]

I'm waiting for the experiment that proves it one way or another in relation to an actual water ski (not a barge or a planing hull, either). I saw a lot of measuring equipment strapped to the Denali during development. Something must be able to measure this in a controlled experiment that closely approximates slalom skiing.

 

We had a lot of great math behind the space launches over the last 50+ years. We didn't decide to go to the moon without a few experiments to back up the calculations.

[liquid d]

The math has been proven...add .48 degree of wing angle and increase dft by .005....or maybe just bend your knees a little more in the preturn.

[Than_Bogan]

I realize you're trying to be funny, but nevertheless you've given me the opportunity to remind people that the burden of mathematical proof is extremely high, and we're no where near there. We may or may not even have the right basic set of theories in this thread.

 

I would view this thread's goals, in order, as: 1) off-season entertainment. 2) might learn something "interesting." 3) might learn something that we can actually use to improve our results (not necessarily in cold water!)

[Bruce_Butterfield]

$&@# it! I hate to agree with @Horton. Yes cold water is different, but the bigger effects are on the dry side of the ski.

[SkiJay]

FWIW, I totally agree that athletic adaptation holds the ultimate key to skiing well in cold water.

 

Travelling between Florida and Canada is how my whole obsessive-compulsive fin-tuning adventure began. But after years of empirical testing that was focused specifically on this issue, I'm now firmly in the camp that believes a good setup remains a good setup regardless of water temperature. A crappy setup will be even crappier in cold water (and I see more crappy setups than good ones), but a good cool-water setup will work well in any temp.

 

Can a good cool-water setup be improved for hot water? Sometimes a little, but WAAAAAY less than most people think, and there will likely be negative trade-offs. In other words, a novice ski-tuner who already has a great performing setup is quite likely to do more harm than good when tuning for temperature swings.

 

But just because athletic adaptation is paramount, that doesn't mean we don't need to talk about viscosity and ski behavior. Establishing a good setup to begin with is still a worthy endeavor. Even Nate Smith, the king of set-it-and-leave-it-alone, spent all last week tweaking setups on test skis for the upcoming season—see picture below.

 

Another reason to understand how temperature swings affect our skiing is to improve our athletic adaptation itself. Knowing what to expect when viscosity changes, can only improve the quality of our athletic adaptation.

 

The pursuit of understanding is not a waste of time.

 

[TravisNW]

As the water gets warmer the viscosity goes down, the result is the ski sits a little deeper it makes things seem slower but remember the molecules don't have as strong of an attraction providing less support as a seemingly solid surface at speed. This less supportive surface with warmer water makes the attitude of the ski more reactive therefore your movements on the ski may be more dramatic. More pressure on the back foot and the tip will rise more, more pressure on the front foot and the tip goes down more.

 

For fin setup I tend to run the fin a little longer and a little shallower in cold water the depth adjust allows the ski to slide in the denser water and the increased length helps the ski initiate the turn and drag some speed off. I keep dft, wing angle and binding placement the same.

 

I know that @AdamCord has the exact science down and so it seems many others do also but remember you can't substitute skill and determination.

[eleeski]

Science tells us the world is round. We know lines of latitude get tighter (smaller radius). So the world (and the course) gets more curved as we head toward the poles. That curve means we will be heading effectively downhill as we approach the buoy - making it harder to turn.

 

Careful how science and clever (but wrong - like above) explanations can seem reasonable.

 

Why do swimmers prefer a bit of salt in the pool? Salt adds viscosity so they should not be setting records in salty water - yet they do.

 

There is a real difference between warm and cold water. Knowing the exact scientific reason is not important, just adapt properly. If we react to a factor that is not relevant or even counterproductive, we might make the wrong adjustments.

 

Something far more important than viscosity could be in play. Or we don't understand how viscosity affects skiing. Be careful rationalizing viscosity's effects.

 

Eric

[wilecoyote]

I have to agree (somewhat) with @eleeski. However, I think knowing the exact reason is important, otherwise you end up chasing ghosts. For anyone in the audiophile world, you can see this in spades. Things like skin effect and transmission line theory abound in marketing of components, but no one ever backs up these known calculable effects with the math because the effect turns out so small you can't possibly hear it. (yet people claim they can, until testing becomes double blind, then they can't) On the cold vs warm water side, until you do the math, it's all just conjecture.

 

I'm a beginner, (pb 4 @ 52kph) and until I started getting into 52, I couldn't tell the difference between B1 and C2 (I'm still not sure I can) so there's absolutely no way I can feel a difference between cold and warm water, but I accept that the short liners can.

 

Still, viscosity changes seem a bit far fetched to me as any explanation. Assuming that there is a real difference between cold and warm water, I would suggest that the flex characteristics of the ski and bindings (and perhaps even rope stretch) probably make a bigger difference than viscosity. When you start going down the viscosity road, you are opening up a new can of worms with regard to salinity, hardness, weed pollen, and on and on.

[Than_Bogan]

Salinity, hardness, and maybe even pollen all matter. They don't matter a LOT, but we're operating right at the edge of our capability all the time, so these effects are greatly multiplied.

[eleeski]

Depth is another huge factor we are totally ignoring. Might be more of a factor than temperature. Changes the feel in substantial ways.

 

Kinesthetic awareness is a trait of many competent athletes. We really can feel subtle differences. One reason that I disagree with the gurus (to the advancement of my Panda count) is my tournament proven response to temperature changes. I reduce my trick speed in cold water. I raise it in deep water. Small amounts - but I love ZO because it does make solid .1 or .2 mph changes that I can feel.

 

Note that someone (in a similar thread) flex tested the skis and was unable to measure a difference in the skis at different temperatures. He didn't test them covered with pollen though.

 

There are many variables that affect the feel of the water (including the ski which could cause an inverse intuitive response).

 

Eric

[TravisNW]

Eric I was just explaining the influence of water depth to someone earlier today your absolutely right there are so many factors. I believe Broadside Harbor is rather deep 30+? Also rumor has it lake two is deeper on one end than the other, true?

 

I believe there is an optimum body position, The further from this a person deviates The more variables are present and the more factors such as these matter. If a person has very consistent timing and reflexes, has optimum body position, leverage and balance than these factors don't really effect the end result.

 

Certain elements matter to make it further and further down the line these we may consider as skills. Technique is possibly just refinements of these skills. You can't substitute time on the water, and atheletes need to understand how to be mentally prepared. This stuff is great to turn gears and develop products or new theories but it can definitely effect performances negatively when handled improperly. Just have fun.

 

 

 

[Horton]

@eleeski Correct me if I am wrong - just feelings - no science

 

If you take a ski that works well in 90 degree water and without any changes you ride in it in 50 or 60 degree water you will feel the following

 

1. Fast at the ball & trouble slowing down

2. Feels like the boat is a freight train

3. Late and round turns at the ball

4. Increased feeling that you are scrambling through the whole pass

 

True?

[DanE]

@Horton True if it was 45 degree water, at 60 degrees those symptoms start to go away.

[Texas6]

great point @DanE - Some of my best skiing is done every during that interim period between 60-80 degree water, after its warmed up a bit, but before it hits the 90's. Never have quite figured out why that it.

[eleeski]

@Horton I do agree with all your points. As @DanE noted, at 60F I can adapt. Same thing happens when skiing into a current (higher boat speed) or in salt water.

 

When it gets colder, there is one more factor that hurts my skiing the most - I can't roll the ski on edge or press more edge into the water. When it gets really hot ( @thager yes my water does sometimes get over 100F) , I have trouble with rolling the ski over too much and sinking the tip.

 

Eric

[Horton]

@eleeski all of those "feelings" are caused at least partly (if not mostly) by the fact that you are making less speed before the wakes so the boat is pulling you into the ball. If the water was lower drag and you were making more speed the result would be that you were wide and had more time at the ball.

 

It is totally counter intuitive but feeling slow at the ball means you had more speed before the wakes. Feeling fast at the ball means you had less speed before the wakes.

[eleeski]

Agree on the "totally counter intuitive" part.

 

Why does my trick skiing improve when I slow in response to cold water? I've got to get behind the boat with a scale to measure rope force.

 

Eric

[Than_Bogan]

Sidenote: 60F water is not cold. (Well, not in this context. It's true I would freeze my ass off in it without my trusty Camaro.) Where I notice fundamental ski behavior changes is usually in October, as the water dips into the 40s. At that point, I still have great equipment to throw at the problem, and in fact I've run -38 in a drysuit more than once. But at some point the water itself becomes a disadvantage, and relatively more so for certain skis.

[Horton]

@eleeski this conversation is about slalom skis.

 

On your trick ski my guess is faster boat speed makes the water feel firmer and that is a similar feeling you get with colder water.

[eleeski]

The title says nothing about slalom skiing exclusively. Water behaves the same regardless of the type of ski interacting with it. Give me another Panda because I'm going to talk a bit more tricks.

 

Trick speed selection is a balance of edge catching vs slipping out. Too slow and you catch edges from the ski riding too deep. Too fast and you slip out from the ski getting pushed too flat. It's easy and obvious to feel the differences. I'm pretty sure that there's less load on the rope at the higher speeds.

 

Cold water feels faster so I adjust my speed slower (even at Havasu with 110f air and ice water from the bottom of Hoover dam). Consistent adjustments with working results.

 

Back to slalom, I agree that the water feels firmer. I can't get enough ski in the water to get the drag I need to slow down enough to make a tight turn. I could care less if there's a bit more (or less) drag in my (always perfectly stacked) pull behind the boat. My cold water adjustment is a long pretty preturn to deal with the ski's extra glide.

 

Those who have seen me slalom know that I never make consistent speeds at the wake (regardless of water temperature). It's a wild ride into the buoy. So I've come into the buoy too slow and too fast in every water condition. I can't blame a minor change in pull position drag for what I feel. So all @Horton 's points need another explanation.

 

Like cold water has less drag?

 

@Than_Bogan We rarely ski at temps below 60f at my lake. On the other hand, lobsters cook in my summer water. The relative temperature swings will be what we feel. If something different happens near freezing and I am understanding this completely wrong then in RosannaDanna's words "nevermind".

 

Eric

[Horton]

@eleeski Ooo now I understand. Your slalom is wildly inconsistent so my explanation is wrong.

 

For those who do not know Eric and I, we are friends. I love Eric like the extra crazy uncle I never had. He knows a lot about trick skiing and thinks he knows a lot about slalom skiing. He means well and I can not bring myself to ban him.

 

Seriously Eric I love you man. You are always welcome to come ski at my house. I hope you come see me this year.

[eleeski]

@Horton The water's too cold right now. I always enjoy the times I get to ski with you (and all my friends that I argue with). Looking forward to skiing with you and turning your daughter into a trick skier.

 

Eric

[eleeski]

@Horton Don't you ski without a wing? That might make you a statistical outlier whose feel is not representative of most skiers.

 

Also you are at an unusually high performance level which may not be representative of most skiers. Limiting factors for you may be completely different from others.

 

Plus you ski too far south. Neither of us should be commenting? At least Panda fishing is entertaining.

 

Eric

[Adam Caldwell]

This is getting painful.

[Horton]

@eleeski i have skied with a wing for the last 5 or so years.

 

You ski on homemade skis.That might make you a statistical outlier whose feel is not representative of most skiers.

[eleeski]

Touche!

[Horton]

Not "touche". You throw softballs & i hit homers.

[rodecon]

Just spitballing here but, I would think one of the things we feel when skiing in cold water is the difference in the ski itself being cold and reacting/ flexing differently than when it is warm? I would think it would be stiffer/ faster feeling when cold?

[eleeski]

@rodecon Someone in this or a similar thread flex tested warm vs cold skis. The flex didn't change measurably with temperature. So the ski flex isn't a likely source for what feels different.

 

@Horton you hit on Homer?

 

Eric