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Thread: Towing Safety (Please Read)

  1. #21
    4 Star General rmgill's Avatar
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    The crossing doesn't weaken the chain. Tighter angles increases the force depending on what the vectors of that force are.

    TAke a rope, spread it across a wide angle, pull down in the middle. the forces pulling inwards are FAR higher than the force pulling down. It's a sort of leverage. Rock/Mountainclimbing rigging manuals warn against this as a method.

    Now, crossing chains up between sides of a vehicle CAN be just fine. It just depends on which way the force vectors are when the load tries to keep moving after the truck has stopped.
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    3 Star General kendelrio's Avatar
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    Default Safety towing

    The crossing doesn't weaken the chain. Tighter angles increases the force depending on what the vectors of that force are.
    Sorry, but that is incorrect.

    As a rigging supervisor and certified rigging inspector, I feel I have the knowledge to at least point ya'll in the right direction.

    While "Catching the bar" is a good reason, that is not the purpose of the chains. The purpose of the chains is to ensure the towed vehicle does not break loose from the towing vehicle. If your tow bar should break/become disconnected for any reason, without chains, the towed vehicle is now a rolling missle. The chains provide some degree of control over said vehicle until it can be safely stopped.

    Now the rigging part.

    The highest rated lifting angle on rigging (whether it be wire sling, nylon strap or chain) is 90 degrees. Lowering the angle lowers your capacity. If your tow bar should break, you will have "shock load" on your chains. This is a directional pull much greater than the weight being lifted (or towed). If rigging is in a less than optimal configuration, your rigging will fail. Take for instace heavy lift crane operations. Often times you will see a "spreader bar" in use. This is used to reduce the angle of the rigging above the load in order to ensure angles as close to 90 as possible.

    Crossing your chains reduces the capacity of your chains. It's simple physics (if there is such a thing).

    Here is a quote from "Hoisting and Rigging safety":

    Number of Legs and Angle with the Horizontal – The smaller the angle between the sling legs and the horizontal, the greater the stress on the individual sling legs. This increased stress effectively decreases the weight that can be safely lifted with any given sling size. Large (heavy) loads can be safely moved by keeping this angle as large as possible and, when necessary, distributing the weight of the load among more sling legs.


    I can send you the actual numbers (angle of rigging=loss of capacity) if any of you like. Feel free to PM me.
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    I was taught the main reason for Cross Chains is to keep the Lost Vehicle,** whether it's a Trl, or a Towed vehicle with Tow bar, or Wrecker,} in behind the Tow vehicle. Cross Chains will pull towed vehicle into Center of other vehicle and prevent it fomm Straying to the sides. It is also the Law to have 2 individual Safety chains, and Chain binders Must be tied off with Wire when traveling across State lines. The size of a Safety chains was never mentioned. I have seen Safety chains on towed from Kids Swing Set used as Safety chains!!?? This is a good topic to spread around. Good luck all, Phil

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    3 Star General kendelrio's Avatar
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    Quote Originally Posted by beaubeau
    I was taught the main reason for Cross Chains is to keep the Lost Vehicle,** whether it's a Trl, or a Towed vehicle with Tow bar, or Wrecker,} in behind the Tow vehicle. Cross Chains will pull towed vehicle into Center of other vehicle and prevent it fomm Straying to the sides.
    I can see the logic in that.......
    I guess the main difference is the end use of the chains. Are they being used to secure (or lift) or used as a control device? If securing a load I would go with the method I mentioned. I would still use straight chains for pulling though, because if your tow bar breaks, you are in a world of trouble anyhow and I would want maximum rating on my rigging.

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    4 Star General davidkroberts's Avatar
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    Tennessee DOT regs require the chains to be crossed but they also think floating the gears is unsafe so who knows. Ive done it both ways and never had a problem.
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    4 Star General rmgill's Avatar
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    Default Re: Safety towing

    Quote Originally Posted by kendelrio
    The crossing doesn't weaken the chain. Tighter angles increases the force depending on what the vectors of that force are.
    Sorry, but that is incorrect.
    I was being specific on the physics. With a good attachment point and good chains, the same load suspended perpendicularly will exert MORE force on two chains strung between the load to the side (ie a very tight angle between the support point and the load vector).

    Practically, the load you can support with the chains is reduced, but so are the attachment points on the support point. I was just trying to be specific over the difference of wrapping a chain or a rope over a corner or a rope with a knot because the knot itself or sharp redirect weakens the chain or rope itself.

    I do agree however that a big vector angle IS going to have a larger pull.
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    4 Star General MilitaryRestoration's Avatar
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    Default RE: Re: Safety towing

    beaubeau - well put...thats how i have always been taught and trained... crossing keeps load to center regardless if you lose on the other should not ever pull it off what it is sitting on...
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    Moderator, wonderful human being & practicing Deuce Doctor. Steel Soldiers Vendor clinto's Avatar
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    Quote Originally Posted by M1075 View Post
    Thanks for the tips. Here is a picture of how I do it. Any suggestions for improvement appreciated.
    How long is that chain? From hoop to hoop?

    Thanks

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    4 Star General Jones's Avatar
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    All good advice.
    But I'm still waiting for the attachment to open... after 5 minutes I'm still just seeing the clock icon.
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    4 Star General Keith_J's Avatar
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    Crossed chains in pairs provide resistance to lateral loads in addition to the primary. And always under the tow bar. Towing without is asking for trouble as the bar always breaks at the pintle eye. Then it wants to function as a pole vaulter's pole, usually taking out the frame rails. Seen it, back in the 1980s, chains were hardly used. Remember, regulations in the military are usually written in blood.

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