How do skis react to cold water? or do they?

[6balls]

If I remember my statistics correctly, the .73 correlation coefficient would predict that for Scoke 73% of the variablity in his performance is explained by changes in water temp, leaving 27% of the performance variablity explained by "other" variables not included in the study.  

Might be interesting to include data from more skiers, and other variables (multiple regression) like whether water temperature has any effect on the chance that one's current girlfriend is a crazy, naked sleep-walking, former Hawaiian Tropic model. 

 

   

[rfa]

Interesting discussion! At first I assumed the original graph depicted “performance†in terms of “skier performance†(e.g. buoy count, or simply how the skier “felt†he skis in those different temperatures).  And while I am not able to quantify anything other than buoy count, I was not surprised by the shape of the graph, especially once Scoke added the “time at each temperature†info. I drew the same conclusion (qualitatively) that H2OSKI1326 did (quantitatively) with his much more elegant analyses.

But it seems that the question being asked was strictly about the ski and how it is impacted by water temperature. This is of course, very difficult to quantify, but likely a non-issue if we were to focus strictly on the ski itself…material property things like thermal expansion, elasticity, etc. are likely minute in the narrow temperature range we are interested in (that which one can get in the water to ski…). (Has anyone tested a ski’s flex at 50 F vs. 90F? I suspect very little difference but have not bothered to go look up carbon properties…)

However, there is a performance impact that Scoke and about everybody else has felt…it comes from the interaction between ski (no change) and water (primarily viscosity change as already shown, neglecting other non-temperature driven water properties for simplicity). This is the same impact everyone feels when driving the same set of tires on dry vs. wet vs.  iced pavement. The point is yes there are some tire (rubber) property changes between say 10F vs. 90F, but they are negligible compared to the interaction between tire and pavement surface conditions. “Performance†such as stopping distances or skidpad can be tested and/or calculated, but it is (for the same tire) primarily driven by pavement conditions, NOT tire (rubber) changes.

So, could we test or model a ski’s performance at different water temperatures?  Yes in terms of practical things like how deep does the ski ride, or more “academic†things like friction forces, etc. But these “performance’ attributes are due to the fact that one of the two things involved here (the water, not the ski) has changed with temperature. To translate this to actual skier performance, you need a test skier way better than me… one who could truly ski exactly the same way in 40F as in 90F water…the same way that to measure the tire vs. pavement performance you need a driver capable of driving exactly the same way in dry pavement as in ice.

Sorry for the long “blurbâ€â€¦full disclosure I also have graduate degree in Thermo/fluids, (30+ years ago), so unlike H2OSKI1326, I don’t remember anything anymore, but I have enjoyed this conversation (as I do most others in here!)

[scoke]

Part of the problem is perception versus academia world versus real world,  that should be the true question most of this discussion, what is real?

 

My point is, 8 skiers felt the nearly the exact same things with their Goode skis. Most of them skied in different water in other states, most body types were of varying sizes, albeit with high strength to body weight ratios, all are highly experience into 38-39-41 and they unanimous agreed to the same conclusion? That sure seems like a high percentage of complete data points in the real world.

 

With that said, yes water cooling and our physical make up is a part of what we perceive as performance drop but I still contend that the skis actually perform and differently in the real world to the changing water temp. Maybe a small percentage of the performance loss but enough to make it noticeable.

   

If you run statistical analysis on a common fin change, the conclusion would be in black and white with a resounding NO as an answer to the question: Would the skier riding a ski that has a large surface area make a minor adjustment to a small piece of equipment on it feel the change?

 

362.35 square inches of surface area of the ski with an attached fin:

 

Fin length, 6.852 changed to 6.847. That’s a change of 00.07% or 5 thousandths of an inch (0.005). Academia world would tell you that you shouldn’t be able to feel that and can’t feel that while experienced skiers in the real world will tell you otherwise. Am I right?

[baja]

I didn't stay at a Holiday Inn last night but my guess is that the impact of the fin on the performance of the ski has lots to do with it's function as a foil moving thru fluid and that very small changes at the proper end of a lever can have significant effects. Same as flight control surfaces of an airplane. So maybe academia would expect you to feel the difference. I know that cold balls never help my skiing. I hate slapping a buoy when it's cold.

[h2odawg79]

Agreed, Cold Balls can be a real Hinderence!

[GAJ0004]

My take on skiing in cold water. Since I ski in Pennsylvania from April-October I ski in a water temperature range from 46-82 degrees Fahrenheit. The colder water affected me more when I used to ski 36 MPH. I have been on only 4 slalom skis. 1986 O'Brien TRC, 1993 O'Brien Synergy Z, 2000 O'Brien Mapple Signature Model, and a 2008 D3 Nomad RCX. My older skis were more affected by the cold water. When the water is in the 40's it made 32 MPH feel like 36. The main thing I always noticed was it was harder to slow the ski down in the preturn. On my O'Brien Mapple I never changed the fin settings,  but I would change the wing angle as the water got colder. I would keep it at 5 degrees in warm water, and adjust it up to 7 degrees in cold water. My D3 I keep everything on the factory setting. The cold water is not as much of a factor at 34 as it is at 36. The three things I do, is shorten the time I pull across the wakes(just a tiny bit), and keep extra soft knees around the turn to avoid a blow out of your fin. Wearing a drysuit does negate some of the effects of cold water. The extra weight helps the ski ride a little deeper in the water.

 

[GAJ0004]

I also wear cold water gloves. I normally wear half finger gloves when the water is warm. The water does not change much, but I would guess that the temperature changes the ski itself..