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How can .001" or even .005" make a difference?

SlalomSteveSlalomSteve Posts: 84 Baller
edited November 2020 in Skis Fins Bindings
First a quick clear-cut question: when making fin adjustments to the thousandths, is it only ever in increments of .005" (so the final measurement ends up at .xx0" or .xx5"), or are there people ending up with measurements like .xx3"?

Then the real question: I am fairly new to course skiing, and have yet to learn much about fin adjustments, but I certainly plan to, as I really like the gear/tech side of things.
But I have to confess: I don't understand how moving a fin .001" or even .005" could make a difference in performance. An average human hair is about .003." So we're talking an adjustment of roughly the width of a single strand of hair… intuitively, it just doesn't make sense to me.

I am curious to hear people's subjective opinions, but most especially if there's any definitive "lab testing" that shows what difference, if any, can come from such a tiny adjustment. And maybe a scientific explanation to replace my unscientific intuition of how that's possible.



  • Than_BoganThan_Bogan Posts: 6,898 Mega Baller
    edited November 2020
    To my intuition, it makes no sense that even 5 hundreths would really matter, but all you have to do is try that with a standard fin, and you'll see it dramatically changes your ski -- may even render it almost unskiable.

    But does a thousandth really matter? That's less clear. I am pretty confident that 1/10,000th can't matter, because the expansion of 7" of aluminum under a few degrees temp change is on that order of magnitude.

    So somewhere between 1/20" and 1/10000" there is a cutoff of what actually matters. My personal experience suggests that if I get within 1/200" (i.e. 0.005") of a previous measurement the ski will feel basically the same. But a full hundredth off might not quite feel the same.

    Some princesses may be able to sense smaller peas, if you will.
    Nathaniel Bogan -- GUT Padawan
  • jjackkrashjjackkrash Posts: 864 Crazy Baller
    The numbers drive me nuts because I personally don't trust the accuracy of the measurements down to .001 even with the best calipers, at least not when I'm the guy taking the measurements.
  • HortonHorton Posts: 30,396 Administrator
    You are a musician right? When you tune a guitar how many degrees of a turn on the tuning peg between in and out of tune?

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  • Than_BoganThan_Bogan Posts: 6,898 Mega Baller
    @jjackkrash Sweating about a thousandth is almost surely a waste of time -- especially if you don't want to in the first place!

    Side note: The repeatability with a good caliper and a consistent methodology can get pretty close to 0.001". Accuracy is doubtful at that level, but you mostly want to compare against your own measurements with the same caliper and same methodology, so repeatability is more important than absolutely accuracy.
    Nathaniel Bogan -- GUT Padawan
  • jjackkrashjjackkrash Posts: 864 Crazy Baller
    edited November 2020
    At Than_Bogan I think I am getting fairly proficient at repeatability and I don't sweat a .001" variance, but like its point out in the Fin Whispering book the jaws on the caliper themselves cut into the fin if you are not extremely careful and its very difficult to get consistent measurements without some modest pressure on the calipers. Little variances like this add up in a hurry when we are talking about .001-.005.
  • DWDW Posts: 2,307 Mega Baller
    Any movement of the fin will 'change' the characteristics to some degree. I don't see the water ski fin adjusting community rounding the adjustments to the nearest half hundredth (.005") so when you finally clamp it tight and make record that measurement which will have moved slightly from where one intended it to be, that's whats recorded and rightly so. As noted numerous variables and 'white noise' in the system and out on the water have more impact than the smallest of fin changes, although depending on how sensitive the ski / skier is, .005" can probably be felt by a tuned in skier. Small movements can produce a significant change, water is 25x the density of air.

    Until you know the effect of a change, one test technique to try, if you know directionally where you want to go, make a relatively large change which could overshoot the optimum, give you a good feel for direction then dial back to fine tune the change. That way ensures you should feel the first change and give you some confidence it actually made a difference. And always mark the original location so you can come back to it. A series of small moves can easily dial your ski right out of the performance window so proceed with appropriate caution.

    As for a lab test, a water tank would be useful to collect data to spend the winter months pouring over and 'bench skiing' over the results:-) CFD would be another 'lab test' although the modelling is really complicated.
  • RGilmoreRGilmore Posts: 97 Baller
    I had an engineering professor in college tell me that, if you have a 1" steel cable strung between two buildings under a 1,000 pounds-force tension, and a fly lands on the cable, it will bow (deflect). We may not have instruments precise enough to measure the bow, but it will be there.

    Under that logic, a fin change of 0.001" will change how it skis... but it's doubtful you'll notice the difference. Therefore, I think anything within 2 or 3 thousandths of your target number will be good enough. And to put the whole discussion into perspective, legendary slalom skier Chuck Forrest, who has put up scores in -41', has been said to routinely set his fin "by eye".
  • skibugskibug Posts: 2,109
    @RGilmore one might argue that he was leaving something on the table by not adjusting precisely and may have run 41 with that added advantage.
    Bob Grizzi
  • 6balls6balls Posts: 5,621 Mega Baller
    Read "Fin Whispering"...great basics.

    I was late to meaningful adjustments--grew up a hack who skied hard, then found some immediate success in the course. My adjustments were only as complex as the little card KD sent with the ski--it was like "want that thing to turn hard--move it forward and the front down---yeah and put the bindings forward while you're at it!" Measurements were basically the hash marks the factory put on the bindings. I tried to run skis forgiving of a lot of movement cuz I skied like a bull.

    Once it was set up like a shovel (not suggesting that as advice), I always found I had a lot more to work on technically above the ski than below it. Slight changes in arm pressure, knee bend, chest open or closed--finding what works...was a lot more meaningful than fin and wing for me even as a guy who was running 35 off 36 mph on occasion.

    After that when I got to 34 mph I got smart: I let @razorskier1 set up his skis with micro-tuning/coaching/consultation...then either stole his settings or his ski--worked great! All technique, baby!

    Only once I was running 38 did I really start to understand and tweak on my own--because running it consistently presented a challenge where the margins really mattered.

    So...long story, but agree with @horton set to stock and work technique until YOU are so consistent technically that you will not only feel but understand the adjustments by how it skis. Also agree with @Bruce_Butterfield re: boat/driver/wind/water/engine being large factors in how a skier feels/performs on their ski.
    Dave Ross--die cancer die
  • jjackkrashjjackkrash Posts: 864 Crazy Baller
    "Set it to stock" is a bit question begging because it presumes you know how to measure it accurately and are measuring it the same way using the same reference points that the factory lists as "stock."
  • liquid dliquid d Posts: 1,320 Mega Baller
    totally agree with @Bruce_Butterfield for the majority of the time....once you are at the top of your game, looking for minute changes in the effect at shortest line, .002 or .oo3 will make a difference.
  • JASJAS Posts: 309 Crazy Baller
    edited November 2020
    I suggest a blind test. It would be interesting to see who could identify a change, at what amount of movement, and in what direction. My prediction is that there would be surprisingly results that could change how we think of fin adjustments.
  • A_BA_B Posts: 4,300 Mega Baller
    I believe when Jeff Rodgers set the World Record on his Goode, the stock setting for depth was 2.449, and before his round he was heard by Schnitz or someone talking about a scant "half or one or one" depth adjustment, so thinking it was 0.0005 or 0.001.

    There are skis that you could almost throw the fin in backwards and run a pass and there are others that are very sensitive to minute fin adjustments or binding moves. The old Goode skis were 2.449, .690, 6.872 jaws with the correct Mitustoyo caliper, I don't recall the tips adjustment but it was north of 6.900. I found the 9100 and the 9500 pretty sensitive to very minor changes. Whenever I started skiing lousy, I would go back to reference stock and reset my skiing.

  • kurtis500kurtis500 Posts: 94 ★★★Triple Panda Award Recipient ★★★
    edited November 2020
    What about just switching out the fin material? Put in titanium or something and use the same shape...or narrow the thickness
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