Short Deep or Long Shallow

HortonHorton Posts: 24,486 Administrator

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santangeloChunkydandjulesjimbrakechris55bf`
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Comments

  • ScottScottScottScott Posts: 418 Crazy Baller
    Who's in charge of blowing the leaves off that nice new prostar?
    Hortonkeithh2oskier
  • HortonHorton Posts: 24,486 Administrator
    @ScottScott believe it or not I intentionally left those leaves on the cover and the swim step as decorations for this video. They will be gone tomorrow. Now back on topic please

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  • gregygregy Posts: 2,398 Mega Baller
    There is also a forward movement, not all side slide. Not sure how that effect things.
  • Bruce_ButterfieldBruce_Butterfield Posts: 1,147 Mega Baller
    @horton, wow, you are actually learning something:)
    If it was easy, they would call it wakeboarding.
    Horton
  • Ed_JohnsonEd_Johnson Posts: 1,688
    This is precisely the reason I used differential depth on my NRG of .020 to improve the offside turn. Really made it smoother with a little bit of smear to help set angle.

    Loving the Reflex Supershell with R Style Rear !!!
    WishHorton
  • gregygregy Posts: 2,398 Mega Baller
    From a physics standpoint. If fin area and DFT stay the same then the force exerted on the fin by the water should remain approximately constant. Then what changes is the center of force on the fin. If you have a deeper short setting then the center of force will be moved back (further back from the fulcrum) so it should increase torque in a plane perpendicular to the water surface pulling the ski downward in the rear. But also there will be a increase in the torque resisting the rotation of the ski around the buoy for the same reason.
  • HortonHorton Posts: 24,486 Administrator
    edited December 2017
    @Gregy

    In terms of "center of pressure" I do think you are correct. The center of pressure has to move as we swap length for depth.

    I have zero science to back this up but I think that the interaction between the pressure on the bottom of the ski and the pressure on the face of the fin has an impact on how much downward pressure there is. A deeper the fin is the less the bottom of the ski interferes with it. If my theory is not right, I assume there is some other phenomena to the same effect.

    I do not think exchanging length for depth has the exactly same impact as changing DFT but I do agree that they might be related. ... Interesting.

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  • gregygregy Posts: 2,398 Mega Baller
    There's definitely a lot going on. Any ME students out there need a fluid dynamics project? This would be interesting. Mount on ski on some mechanism you can rotate to simulate a slalom turn. There's probably simulation software out that you could use to predict it.
  • AdamCordAdamCord Posts: 535 Open or 55K Rated Skier
    @Horton good video. My favorite example of this is Mapple, especially when he competed. He always ran short/deep settings. It's not a coincidence that he also had the best offside turn in the business. But his onside turn suffered as a result, and he was known for slam dunking that side, because that was what he had to do to get the tail to wash enough. When I skied with him he never even tried long/shallow settings, because he hated how it felt on offside.
  • skibugskibug Posts: 1,911
    I hate offside tail blow outs if/when I am late and have to push on the ski. That is why I always wide up short/deep.
    Bob Grizzi
    DragoBarry
  • Ed_JohnsonEd_Johnson Posts: 1,688
    edited December 2017
    @AdamChord ... Could you please go into the benefits of differential fin depth and how it can improve the onside turn. After all, I believe this was your idea with the original washer trick, and developing that into the Denali.

    Also what do you consider an ideal range to strive for. One washer took away .020 for me and I noticed immediate improvement. THX


    Loving the Reflex Supershell with R Style Rear !!!
  • fu_manfu_man Posts: 333 Solid Baller
    He said doo-doo.
  • AdamCordAdamCord Posts: 535 Open or 55K Rated Skier
    @Ed_Johnson I could probably write a novel on this so I will keep it to the elevator pitch version:

    The shallower fin will start to wash (smear?) the tail earlier and more easily. As @Horton stated in his video, pretty much everybody is more on the tail into and through their onside turn. The downside of this is that we are not engaging the tip of the ski as much, which would use the bevels and concave to slow the ski down and "steer" the ski back toward center. Because there is less of this effect on onside, we need the tail to have less resistance to rotation.

    If you are falling over on your onside or getting "dumped", where you finish with too much angle and not enough speed (too much load), it's not because the ski turned too much, it's because it turned too little. Basically the ski kept going straight when your body was moving to the inside of the turn, and you fell over. The ski then is forced to rotate all at once at the finish of the turn, hockey stop style. If the tail had started washing earlier and more easily, you would have had a more progressive turn and you'd end up with a tighter line, in a balanced position, and without dropping into a hole.

    In a perfect world we would run a fin that is shallower, longer, and further forward for onside, and back, deeper, and shorter for offside. If only someone could come up with and patent something that does this... ;)

    As far as how much "offset" to put in with a washers? As much as you can.
  • Ed_JohnsonEd_Johnson Posts: 1,688
    @AdamCord ... Thank you for the response and shedding light on this. When I tried a thin washer, it reduced the differential .010 and I felt no difference. With a standard washer it was .020 and I felt a smoother, earlier entry off the apex. I thought I had read somewhere the limit was .030. Guess I will just have to try it and find out...Thanks again for the insight.
    Loving the Reflex Supershell with R Style Rear !!!
  • JASJAS Posts: 166 Baller
    What would be downside of a fin that was adjustable from 90 degree axis
  • santangelosantangelo Posts: 157 Solid Baller
    @JAS nothing, but can't be used in AWSA tournament skiing per rule 8.03 C. Fins must be fixed.
  • HortonHorton Posts: 24,486 Administrator
    @santangelo I think you misunderstand what @jas said.

    I think what he is asking is "Why does a fin have to be 90 degrees from the top of the ski?" Interesting. If anyone tests this please take video.

    Seriously, I think Schnitz played with this. I think he told me once that he was working more adjustment parameters. Rudder right or left and tilt right or left is what I think he was testing.

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    santangelo
  • JASJAS Posts: 166 Baller
    My thought was that if a ski was adjusted from 90 degrees relative to the top, there could be some sort of asymmetric resistance to tail slide as discussed in hortons video. Would it be a useful difference, I don’t know.
  • skibugskibug Posts: 1,911
    widen the fin slot and shim all the way down one side if the fin under the block, test it out and tell us how it works.
    Bob Grizzi
  • adamhcaldwelladamhcaldwell Posts: 381 Open or 55K Rated Skier
    edited December 2017
    @Ed_Johnson
    As far as fin surface area offset is concerned, I just start to feel the synergy at about 30/1000s offset/differential.

    Once I have more speed&rotation through the onside turn, I typically start getting faster/earlier/wider into the toeside. This is good, but only if I can keep it from overshooting the targeted apex.

    Next step is usually to bump the fin longer/back/deeper (by a few thou. each) to get the speed into apex of the toe-side back under control.

    BUT...in order to not loose the on-side magic....each time I add had to tweak the fin deeper/back/longer to dial in the toeside, I would also have to put in more offset to sustain what magic was going on with the HS. If there was a combination move of deeper and back for the off-side, I would make the differential significantly more to correct & re balance it.

    I maxed out at 95/1000s of offset last summer. Had slowly ratcheted the settings up starting from 35/1000offset. It all adds up to more and more space before each buoy with far less effort!

    My lifetime practice PB this summer at 41 was run with depths of 2.520 (offside) and 2.425 (on-side).
  • Ed_JohnsonEd_Johnson Posts: 1,688
    @adamhcaldwell ... Thanks so much for that info. In my wildest dreams I never would have thought of that much offset. This really, really, helps a lot. I had thought 30 was probably the limit and you were starting at 35. Looks like I'll be buying more washers.
    Thanks again !!!

    Loving the Reflex Supershell with R Style Rear !!!
  • AdamCordAdamCord Posts: 535 Open or 55K Rated Skier
    @Ed_Johnson @adamhcaldwell the reason I said to max out the offset is because on a normal fin block using washers you can’t really get much more than .040” offset.

    The Denali fin block has the mounting screws spread further apart and it has an offset jacking screw that lets you get a lot more.
  • Ed_JohnsonEd_Johnson Posts: 1,688
    @AdamCord ... Thanks Adam, that Fin Block was a BRILLIANT move !!!

    Loving the Reflex Supershell with R Style Rear !!!
    AdamCord
  • HortonHorton Posts: 24,486 Administrator
    edited December 2017
    Hey guys I'd like to put this thread back on topic. Denali maybe growing and innovating but the vast majority of the readership here do not have a differential set screw in their fin block (yet).

    If somebody wants to start a new thread about the Denali differential setting go for it. On the other hand I have seen the 2018 Denali stuff and offset is much much less emphasized.

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    Bruce_Butterfield
  • Bruce_ButterfieldBruce_Butterfield Posts: 1,147 Mega Baller
    @horton understanding the interaction of balance points, fin depth on each side and how each skier controls the ski is very much on topic to your original post. Having different fin depths on either side - via a washer, unique fin block, or hacksaw - is definitely part of the short/deep vs long/shallow understanding.
    If it was easy, they would call it wakeboarding.
    WishScottScottEd_Johnson
  • HortonHorton Posts: 24,486 Administrator
    @Bruce_Butterfield understood but 99.43% of the readers live in a world without different depths on each side of the fin.

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  • Bruce_ButterfieldBruce_Butterfield Posts: 1,147 Mega Baller
    @Horton yes but if a baller is trying to understand/ experiment with short/deep vs long/shallow, asymmetric depth is definitely a factor and can easily make improvements in either configuration.

    If a baller has a set of calipers and an Allen wrench, they are certainly capable of putting a washer under the block.
    If it was easy, they would call it wakeboarding.
    Ed_Johnson
  • customskicustomski Posts: 56 Baller
    That video made a lot of sense to me, I was having too many hair on fire offside turns and went what i thought was "safer" with some more depth as well as slightly longer and less dft. Have had 6-7 sets since then and feeling and skiing better.
    Thanks for your explanation @Horton
  • Ed_JohnsonEd_Johnson Posts: 1,688
    I can totally testify what the Adam's are saying about differential depth adjustment. Takes less than 5 minutes to do it, costs about .15 cents, and the results are amazing. Adding one standard and one thin washer resulted in a depth change of .030, and completely solved my overturning issues with the D3 NRG. I cannot thank both of them enough for this advice.

    Loving the Reflex Supershell with R Style Rear !!!
    adamhcaldwell
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