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Slalom skier speed during a cut


Sunapee

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Can't give you speed but think of it this way. Boats going 34 mph and the skier is excellerating at a very fast rate towards the boat to make the next buoy. Then take line length into consideration, Another factor

to add.

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Find one of those Shadow Box Live things. They stuck on your wakeboard to tell speed, jump height/time, etc.

I think they're out of business. But if you could find a used one and stick it on your ski it would tell you all you ever wanted to know.

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ahopkinsVTX

I have always wondered this for myself too. I have a few apps for snow ski tracking and Mtn biking that seem to track speed pretty good. I also have sealed water proof bags. Maybe I will figure out a way to attach my phone to myself this spring.

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Wonder if a wrist Garmin for running would capture it? I know mine will track max speed over a run. I will try that this season and see what it gets. Good question.

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There's some interesting info in this paper that I just skimmed through. Looks like in their testing, the maximum skier velocity was 141% of boat velocity. Tested what they referred to as 'intermediate' skiers.

http://www.soe.uoguelph.ca/webfiles/jruncima/Waterskiing%20top_files/Water%20Skiing%20Biomechanics-%20a%20study%20of%20intermediate%20skiers,%20non-publisher%20release.pdf

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There's some interesting info in this paper that I just skimmed through. Looks like in their testing, the maximum skier velocity was 141% of boat velocity. Tested what they referred to as 'intermediate' skiers.

http://www.soe.uoguelph.ca/webfiles/jruncima/Waterskiing%20top_files/Water%20Skiing%20Biomechanics-%20a%20study%20of%20intermediate%20skiers,%20non-publisher%20release.pdf

The guy in "figure 2" isn't exactly hauling a$$. I suspect shortline skiers can hit much greater speeds than 140% of boat velocity.

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There's some interesting info in this paper that I just skimmed through. Looks like in their testing, the maximum skier velocity was 141% of boat velocity. Tested what they referred to as 'intermediate' skiers.

http://www.soe.uoguelph.ca/webfiles/jruncima/Waterskiing%20top_files/Water%20Skiing%20Biomechanics-%20a%20study%20of%20intermediate%20skiers,%20non-publisher%20release.pdf

Greenman

Quote from the last paragraph!

" Aging skiers struggle with weight gain and simultaneous strength and endurance loss. For the intermediate skier, our study indicates that the Fastback ski offers performance advantages that may potentially improve their enjoyment of the sport and their overall dynamic performance "

Guess I'm buying a new FASTBACK Waterski this summer !.........lol.....

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Greenman

Quote from the last paragraph!

" Aging skiers struggle with weight gain and simultaneous strength and endurance loss. For the intermediate skier, our study indicates that the Fastback ski offers performance advantages that may potentially improve their enjoyment of the sport and their overall dynamic performance "

Guess I'm buying a new FASTBACK Waterski this summer !.........lol.....

That does it, Dare. I clearly have to trade in my Radar Vice on a FASTBACK!

Maybe a '69 Mustang...?

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So, I just thought I would briefly feign mathematical brilliance. Actually, it's more like Google querying that loosely assumes competence...

Remember that the article I referenced earlier had measured(?) the maximum skier speed at 141% of boat speed.

Just assume for a moment that one crosses the wake at 45 degrees to the direction of the boat. I figured it would be interesting to work out the relative length of the hypotenuse of a right angled triangle where the other two sides are of equal length and therefore the angle of the hypotenuse to the other two sides is 45 degrees. This site was useful http://www.calculatorpro.com/calculator/hypotenuse-calculator/ in showing that, rather interestingly, it is 141%.

Therefore, if you travel at 45 degrees to the boat direction you must travel 41% further than the boat in order to keep up with the boat, so you must be doing 141% of the boat speed at that point.

What I don't know is the most acute angle that an elite skier may cross the wake. I've YouTubed a few bits and pieces of aerial footage and the general appearance to me is that the wake crossing seems pretty close to 45 degrees. I know that is a very, very subjective assessment! Still, I'm sure it's not, say, 30 degrees.

Turns out that, surprisingly, I'm not Einstein so, if I've made some mistakes here, I won't be all that surprised!

Edited by GreenMan
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UPDATE! A bit more research found this handy on line calculator: http://easycalculation.com/trigonometry/triangle-angles.php

Adjust it to calculate Hypotenuse side and Opposite side.

Enter 1 into Adjacent side field. This represents boat direction and speed.

Enter a chosen angle into the Angle q field. This represents the angle of the skier's travel relative to the boat. 10 degrees is very casually and slowly crossing the wake. This returns a hypotenuse length of 1.01 which makes sense. Skier travelling at 1.01 time boat speed covering 1.01 times the distance the boat travels. Barely faster than the boat. Boat doing 36, skier doing 36.36.

Enter 45 into Angle q and the old 1.41 is returned and further validates earlier comments. Boat speed of 36 mph means skier speed of 50.7 mph.

If you're good enough to achieve an angle of 55 degrees to the boat, you are doing 1.74 times boat speed. For a boat speed of 36 mph, the skier is doing ~62.6 mph.

I found all this rather interesting as I have often wondered about it myself. I hope I have it right!

No idea what angle I cross at but I'm fairly confident it will be somewhat shallower than Andy Mapple...

Regards, Stephen.

Edited by GreenMan
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The guy in "figure 2" isn't exactly hauling a$$. I suspect shortline skiers can hit much greater speeds than 140% of boat velocity.

He's definitely not setting a world class pace! They do mention that he achieved 124% of boat speed. That suggests a cut angle of about 36 degrees.

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It will be a rag top, right?

In our oases here in the WET COAST, thinking hard top. But I must say a rag would be nice for those sunny days.

Then again that would be the only time she'd be out. ?..Right!!

Just love the look of a HT.

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UPDATE! A bit more research found this handy on line calculator: http://easycalculation.com/trigonometry/triangle-angles.php

Adjust it to calculate Hypotenuse side and Opposite side.

Enter 1 into Adjacent side field. This represents boat direction and speed.

Enter a chosen angle into the Angle q field. This represents the angle of the skier's travel relative to the boat. 10 degrees is very casually and slowly crossing the wake. This returns a hypotenuse length of 1.01 which makes sense. Skier travelling at 1.01 time boat speed covering 1.01 times the distance the boat travels. Barely faster than the boat. Boat doing 36, skier doing 36.36.

Enter 45 into Angle q and the old 1.41 is returned and further validates earlier comments. Boat speed of 36 mph means skier speed of 50.7 mph.

If you're good enough to achieve an angle of 55 degrees to the boat, you are doing 1.74 times boat speed. For a boat speed of 36 mph, the skier is doing ~62.6 mph.

I found all this rather interesting as I have often wondered about it myself. I hope I have it right!

No idea what angle I cross at but I'm fairly confident it will be somewhat shallower than Andy Mapple...

Regards, Stephen.

Vettesetter's numbers sound about right to me. I think the issue with your calculations is that if I had to guess the max speed occurs after the wake crossing. So the calculations coming into the wakes are probably accurate, but after the wake the skier gains on the boat without really losing much lateral speed. So that 141-174% + some number I don't feel like calculating = 72+ mph

I don't really feel like trying to work out the math right now because after the wake the skier is no longer travelling linearly making the math messier.

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On second thought what I said still doesn't make much sense to me because most top level skiers edge change almost instantly after the wakes, and I can't imagine they'd be gaining speed after that...

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Hi 'hood. Thanks for the comments.

Obviously, the slowest point is at some point around the turn. After that, I imagine it's acceleration to about immediately after the wake crossing after which it's changing edge and then slowing down.

I'm confident the Pythagoras deal is pretty close - if you're at angle x to the wake the mathematics should be able to readily interpolate a pretty close velocity.

Trouble is actually knowing the angle! I'd like to see some direct overhead aerial footage of a top level skier. Could freeze the film and hold a protractor on the screen to measure it...

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I seem to recall a test that Waterski magazine or someone did a couple years back with Marcus Brown at various line lengths. He was consistently hitting 55 MPH or better.

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In our oases here in the WET COAST, thinking hard top. But I must say a rag would be nice for those sunny days.

Then again that would be the only time she'd be out. ?..Right!!

Just love the look of a HT.

Here in the wet coast (more like torrential down pour) the rag top is more important because of the lack of sunny days. When it's sunny the top must be down to experience that cruising on holiday in Hawaii feeling that we are missing so bad for 10 months when it's pouring all the time. Believe me (I've had convertibles for 25 years) when you get off of work and it's sunny you put down the top and it is like your cruising in heaven instead of stuck in traffic. To me it would be like owning our boats with hard tops. Plus every time you pulled up beside a rag top with the wind in their hair you would regret not getting it instead. Edited by Vettesetter Z06
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I seem to recall a test that Waterski magazine or someone did a couple years back with Marcus Brown at various line lengths. He was consistently hitting 55 MPH or better.

Seems to make sense. Equates to a maximum cut angle of ~49 degrees.

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I was pretty sure I'd heard the 70+ figure a few times in the past, now I'm kind of curious about the jumpers since they are accelerating all the way to the base of the ramp.

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