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Force on tow rope

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  • Force on tow rope

    Surely in the course of designing and testing ski pylons and wakeboard towers someone has measured the force a skier or wakeboarder exerts on a tow rope. Anybody here ever seen data on this? I'm mostly just curious, but just in case I decide to build a tower in the future I'd like to have an idea of what I need to allow for (plus a generous safety margin of course). It's tempting to borrow a load cell from work but I'm not too sure I want to be responsible for replacing it if something happens.
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  • #2
    Re: Force on tow rope

    my suggestion is find someone who has a professioal tower or ski bar on thier boat and put a force guage on it. then have them pull a skier/wakeboarder and read what the pull force is for each type of pasenger then make yours so that it will exceed this amount by at least 1-200lbs. However I can tell you those guages are not cheap about 500-900 depending on size.

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    • #3
      Re: Force on tow rope

      I was just out with a former professional water skiier a few weeks ago. He told me that adult male slalom skiiers will exert roughly 800 # of pressure on the two rope.
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      • #4
        Re: Force on tow rope

        It sounds like you're an engineer. Or you're coming at it from that mindset.

        I've looked for info like this online over the years and haven't seen anything too specific. Usually this discussion arises from a comparison between the forces on a pylon/tower pulling a tube (the object being towed is hard-fastened to the boat) and a rider of some sort (where grip strength is the limiting factor).

        I have read (but can't locate the quoted info nor the original data) that 15-20 yrs ago, someone had measured static line load for some pro-level slalom skiers. I remember a momentary load figure of 600 lb for female skier Camille Duvall. Those sort of figures would obviously represent some extremes. I'd say somewhere around 200-300 lb is pretty common for an aggressive skier wearing high-traction gloves, etc.

        Here is an article I just found talking about handle recoil accidents with various projections based on line loads. Maybe that is of interest to you. http://www.triodyne.com/20090127152024.pdf

        The leverage a tall tower or pylon has on the boat is another factor. Depending on the rider that can be pretty much straight behind the boat. For aggressive skiing the load comes at a point that is much wider or higher on the boat.

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        • #5
          Re: Force on tow rope

          I was just out with a former professional water skiier a few weeks ago. He told me that adult male slalom skiiers will exert roughly 800 # of pressure on the two rope.
          If true that's pretty impressive. That would be (assuming he's gripping the tow handle with both hands at that instant) 400 pounds of force per hand. No wonder all the kids have switched to wakeboards.


          It sounds like you're an engineer.
          Yes. I'm mostly just curious, but might just get ambitious enough to calculate the loads my ski pylon is putting on the boat.

          I remember a momentary load figure of 600 lb for female skier Camille Duvall
          Well, that's in line with 800 pounds of force for a professional male skier.
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          “Anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.'”

          ― Isaac Asimov

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          • #6
            Re: Force on tow rope

            A couple quotes I found. I don't know their sources for their data:

            "Skier speeds in excess of 80 KPH are attained in slalom courses with towrope loading in excess of 2000 N." (Conversion: 2000 newtons = 449.617886 pounds force)
            came from here:
            http://www.robertsski.com/webpgws/safety.htm

            "Polypropylene ropes for water skiing have a breaking strength of 800 pounds"
            came from here:
            http://www.ehow.com/how_2191105_pick-tow-rope.html


            I guess if I were designing something like this, I'd want the rope to break LONG before anything else did...like the pylon, or the boat for example. So make sure whatever you build can withstand forces notably greater than the ropes themselves...

            IMO, engineer it to withstand a minimum of 1,000 pounds. Preferably more.

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            • #7
              Re: Force on tow rope

              And towable ropes are rated at 2,000-4,000 pounds for tubing, so I guess this is why it is not recommended to pull tubes from pylons and towers.
              Mike

              '96 ProCraft 200 Combo w/ Mercury 200HP XRi

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              • #8
                Re: Force on tow rope

                Originally posted by metriccrescentwrench View Post
                If true that's pretty impressive. That would be (assuming he's gripping the tow handle with both hands at that instant) 400 pounds of force per hand. No wonder all the kids have switched to wakeboards.




                Yes. I'm mostly just curious, but might just get ambitious enough to calculate the loads my ski pylon is putting on the boat.



                Well, that's in line with 800 pounds of force for a professional male skier.
                Many years ago Dave Benzel had a gadget at his ski school that recorded the rope tension and angle using a load cell and what passed for a laptop back then. I weighed about 165 lbs then and running mid to shortline (28-32 off) in the slalom course my peak force was around 650-700 lbs but that was for a fairly short time (< 1/2 sec). The average force was much lower. If I got a little slack and banged on the rope (bad form!) the peak was higher and very short lived. In those days the ropes had a breaking strength of 1000-1200 lbs and even new ones broke regularly, now we use a rope that's almost twice as strong and breaks are much more rare.

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                • #9
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                  Re: Force on tow rope

                  Originally posted by craze1cars View Post
                  I guess if I were designing something like this, I'd want the rope to break LONG before anything else did...like the pylon, or the boat for example. So make sure whatever you build can withstand forces notably greater than the ropes themselves...
                  You beat me to it, testing the rope is easy and will give you some good data (probably already available), however, the forces on the rope are nearly all tension, the pylon will be facing shear and tension.

                  Have you thought of taking some measurements of an aftermarket pylon and building yours based on that?

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