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  1. #1
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    Default Basket hitch rigging question.

    Iíve got a rigging question that I canít get a definitive answer on.

    Iíve got a unique situation to where I need to take a chain and make it into a continuous loop, with one end looped around the machine and the other end looped around a shackle that is attached to our lifting equipment.

    The problem arises in what capacity we are talking about. I always assumed that putting a chain in a continuous loop doubled the capacity over the single leg WLL. My rigging supplier says it will be 1.4 times the single WLL. Another engineer says that it will not increase capacity at all because both ends arenít terminated on a hook (as in a true basket hitch)

    Iíve looked through all my reference material and searched the web but I canít seem to find any definitive info on this type of hitch. Iím just throwing it out here to see if anybody could provide some helpful info.

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    Using a chain in a continuous loop with the two sides of the loop parallel and vertical doubles the capacity, like two parts of rope on tackle blocks.

    However if the chain goes around a load of significant width but hangs from a single hook, so that the parts of the chain above the load going over the hook make an angle greater than zero degrees, the stress in the whole loop increases, as it does in the legs of a conventional basket hitch. To calculate this, multiply the load by the secant of half the angle between the legs, and divide by two. EG, if your load is 1,000 lb, and the legs of your hitch make a 90 deg angle, .1000 x sec 45 deg or 1.41= 1410 lb, half of this is the load in one leg or 705 lb.

    NB your load is likely to fall out of the loop sideways, and even if it does not, failure at any point in your continuous chain drops the load.

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    Here is a crude drawing of what I'm talking about. Most of the info I've found says that is rigging hitch is no stronger than if the chain is just singled out. In other words, I'm talking about 5/8 grade 100 chain, the WLL of the chain is 22,600 LB, most of the info I've found says that even in the loop configuration, the WLL is still 22,600 LB.

    Now if the rigging has two ends and both ends terminate at the hook, as in a choker with two looped ends placed over the hook, that will double the capacity. Something about the chain being able to move through the hook reduces the capacity.

    I'm just having trouble rapping my head around the fact that if you double a piece of rigging in a true basket hitch, you double the capacity, but if it's a "double basket" on both ends, it does not. I'm just trying to figure out the why, so I can apply it to other rigging practices. We get into all kinds of non-conventional rigging, due to limited space and odd pieces to try and rig, and sometimes the published info doesn't cover it. It helps to know the principles involved so when you get into some unconventional rigging hitches, you don't get yourself into trouble.
    Attached Thumbnails Attached Thumbnails loop-rigging.jpg  

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    Since the ends are bent over on themselves I think that reduces the load capacity similar to a wide spread angle. If they terminate in a hook or shackle the load is parallel to the chain and hooks/shackle are rated with weird angles allowed?
    Bill

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    Let me take a stab at this. In your sketch, you think you have two chains between the hook and load. But in reality, you only have ONE chain that passes over the hook, and the link on the hook has to support the entire load, so the rating of that one link governs the whole set-up. As an aside, the same situation exists where the chain contacts the load.

    Dennis

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    Quote Originally Posted by Modelman View Post
    Let me take a stab at this. In your sketch, you think you have two chains between the hook and load. But in reality, you only have ONE chain that passes over the hook, and the link on the hook has to support the entire load, so the rating of that one link governs the whole set-up. As an aside, the same situation exists where the chain contacts the load.

    Dennis
    That is basically how it was explained to me by my rigging supplier.

    The problem I have is apparently the same situation doesn't exist where the chain contacts the load. Look at this pic I found on the web (the single basket type), they list the WLL as 39,100 LB for 5/8 chain, as apposed to a WLL of 22,600 LB for a single leg chain. What you are looking at is doubled WLL with deductions made due to sling angle. I'm just trying to figure the reason the extra capacity applies to one end but not the other. I think it has something to do with you are ok basketing one end but not both on the same setup.
    Attached Thumbnails Attached Thumbnails basket_chain_slings.jpg  

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    First, I AM NOT a rigging expert, so please do not take my advise without consulting A professional. ( I wish more here would be upfront about their qualifications before expounding)

    Just hypothetically speaking, based on my limited understanding;

    A basket configuration where a sling passes under a load is assumed to be ( should be) loaded over a number of links or a large enough radius that the load is transferred substantially by friction and or mechanical engagement (in the case of chain). This is the case on a sheve too, even though the pivot is low friction, the engagement of the rope or chain to the OD of the sheave is “frictional” or mechanical. This is why basket configuration is rated higher than single.

    That is one reason for a minimum bend radius (the other is bending/fatigue)

    When a sling or other lifting medium is passed over a shackle or hook. It is a “point load” and no load is considered to be transferred frictionally, in fact it INCREASES tthe stress on it by introducing bending load.

    This is why we put thimbles in wire rope eyes, to reduce the bend angle.( and for wear resistance)

    In the case of chain, we use cradle hooks or clutces on highly stressed chain to reduce point loading, but it still is a point load.

    If you were to use two properly matched cradle hooks or shortening hooks/clutches in a shackle, you could cobble up a shortening sling, but better to buy a rated assembly.

    Crosby makes a fantastic adjustable leg sling with an integrated shortening hook/master link. Google Crosby Eliminator.

    Make sense? Safe rigging, cheers!

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    The d/d ratio ( the minimum radius rigging can go around and still retain its max WLL) is 6:1. In other words, 5/8 chain would have to go around a minimum of 3.75” to retain its max strength. The crane hook is bigger around than that so I don’t think bend radius is a factor.

    I’m not trying to be argumentative, just trying to be safe and understand more. It’s easy enough to follow some rigging manufacturer’s printed advise but you need to know the forces applied so when you get into slight deviations you don’t get yourself in trouble.

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    I would agree that it does not increase the WLL at all, unless the both ends of the chain were attached to separate hooks on the lifting device, that would make a true basket that would double the WLL, what you are doing puts all stress on one link basically. The engineer might be right that in reality it does add a little bit, but I would play it safe and figure on same as single vertical leg.

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    I am entirely free of paper qualifications, but have been doing engineeering and design work for most of forty years. But I appeal to no experience nor authority, only reason.

    The OP's sketch shows two parts of line carrying the load. Where the chain turns around the hooks, you have equal pull in both directions, no different than when pull is in one direction against an anchor., and just like the parts of line in a block-and-tackle. I believe the WLL on a chain assumes that it may be secured with a grab-hook, which places a concentrated bending load on one side of one link, far more severe than looping over any slip or sling hook. This uncertainty can be eliminated if you join the ends with an appropriately-rated repair link or shackle.

    So IMO the only reason to de-rate the shown hitch below twice the WLL of a single chain would be to increase the safety-factor, because a failure at any point of the continuous chain drops the load. If the load were held by two chains each independently attached at both ends, and if the safety factor were at least two, there is a good chance that one chain could fail and the other still catch the load.

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    Quote Originally Posted by m16ty View Post
    The d/d ratio ( the minimum radius rigging can go around and still retain its max WLL) is 6:1. In other words, 5/8 chain would have to go around a minimum of 3.75Ē to retain its max strength. The crane hook is bigger around than that so I donít think bend radius is a factor.

    that 6:1 minimum radius is to avoid bending damage. when you say the hook is "bigger than that", what matters is the minimum radius of the tightest bend the chain makes going around the hook, that is very important, NOT how wide it is top to bottom, obviously. some VERY large hooks have relatively tight radii on the shoulders of the gullet.

    what the minimum radius is to be considered a basket configuration may (must?) be different. that is perhaps the distinction causing some confusion here? you did say in the first post that it was a shackle "underhook", in the quoted post, sounds like that changed. directly on a bigass hook.

    regardless, the optimum way to transfer a load from a chain to a hook is with properly rated connecting link(special purpose omega shackle, or hammerlock, "double E",) and a master link.

    IF you had a chain looped directly over a hook that was large in comparison, say a 3/8 chain on a 100T hook, it might be a large enough radius to be in "basket" territory, but since it is hardened steel on hardened steel, I think it would be prudent to derate.

    in fact, seems there are many loads that should be derated also, given those criteria? the point here is the guidelines are just that.

    generally, stick to a master link on the lifting hook, and use some common sense and caution on the load end.

    cheers, + safe rigging!

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    upon review, I am wrong on the frictional transfer requirement, of corse.

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    A derate to 1.4 instead of 2.0 sounds high at first glance, but some derate seems likely off of a straight pull.

    Cyanidekid has a good point about the hook being >3.75" being necessary but not sufficient, due to sharper radii at the edges of the hook. If instead you were running a 4" shackle, for example, that has a constant radius.

    If we were to take a theoretically perfect chain/rope/webbing, a basket would have double the rating of a straight pull. This would be true regardless of whether or not the basket legs were continuous or terminated individually. Unfortunately, reality isn't theoretical, so you'd expect some de-rate when the chain has to go around a corner; the smaller the radius, the more you de-rate it.

    If your supplier has a source for the 1.4 number, I'd be interested to see it. Unfortunately, many of the de-rating factors in rigging are not well documented.

    I've never used chains for anything other than straight pulls,

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    Quote Originally Posted by m16ty View Post
    The problem I have is apparently the same situation doesn't exist where the chain contacts the load. Look at this pic I found on the web (the single basket type), they list the WLL as 39,100 LB for 5/8 chain, as apposed to a WLL of 22,600 LB for a single leg chain. What you are looking at is doubled WLL with deductions made due to sling angle. I'm just trying to figure the reason the extra capacity applies to one end but not the other. I think it has something to do with you are ok basketing one end but not both on the same setup.
    I'm having a hard time figuring that one out as well. I can't think of a physics/engineering reason why a 180 degree wrap around a 4" diameter steel rod would be any different if the rod is at the top or the bottom of the sling.

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    Thanks to everybody the provided insight to this problem.

    I ended up ordering a set of chains, attached to a lifting ring on one end, and then able to hook back into the ring with the loose end. With both ends of the chain loop terminating at the lifting ring, they are allowing me twice the the WLL over a single chain. 5/8 grade 100 chain, 40,000 lb with chain in a basket, 40,000 lb lifting ring.

    This setup will be tested and tagged at 40,000 lb WLL. The outfit I get my rigging from has the capability to make their own synthetic slings, make up chain rigging, make wire rope chokers, and test and certify anything they put together.

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    Quote Originally Posted by m16ty View Post
    Here is a crude drawing of what I'm talking about. Most of the info I've found says that is rigging hitch is no stronger than if the chain is just singled out. In other words, I'm talking about 5/8 grade 100 chain, the WLL of the chain is 22,600 LB, most of the info I've found says that even in the loop configuration, the WLL is still 22,600 LB.

    Now if the rigging has two ends and both ends terminate at the hook, as in a choker with two looped ends placed over the hook, that will double the capacity. Something about the chain being able to move through the hook reduces the capacity.

    I'm just having trouble rapping my head around the fact that if you double a piece of rigging in a true basket hitch, you double the capacity, but if it's a "double basket" on both ends, it does not. I'm just trying to figure out the why, so I can apply it to other rigging practices. We get into all kinds of non-conventional rigging, due to limited space and odd pieces to try and rig, and sometimes the published info doesn't cover it. It helps to know the principles involved so when you get into some unconventional rigging hitches, you don't get yourself into trouble.
    I wonder why anyone would select chain for the job in your illustration.
    Endless poly slings have come a long way in the last 20 or so years and prior to that I would have chosen Triflex wire rope over chain every time for the rig in your drawing.

    Regards,
    John

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    Quote Originally Posted by jmead View Post
    I wonder why anyone would select chain for the job in your illustration.
    Endless poly slings have come a long way in the last 20 or so years and prior to that I would have chosen Triflex wire rope over chain every time for the rig in your drawing.

    Regards,
    John
    There are a couple of reasons we selected chain for this application. The biggest is adjustability. Slings are a given length, and in the tight spots we get into, you need the ability to adjust the rigging to fit the need. Another reason is abrasion resistance. We were uprighting a 140,000 lb tile press, the rigging was wrapped around two trunion mount rigging points. We have used synthetic slings in this application before, and the trunions chew up the slings when they spin on the trunions.

    We completed this job and the tri-lifter we were using to upright the press was literally touching the ceiling when the press was finally standing. Rigging a few inches longer or shorter and we wouldn't have been able to complete the lift. Now I guess you could have piles of synthetic or wire rope slings in several inch increments to have any combination of what you need, or you can have one set of adjustable chain slings.

    Synthetic slings are great, we use them every day, but in some applications they just don't work.

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    Awfull lot of people like to use nylon slings.....
    EMD GT46C-ACe Locomotive Dropped on Delivery - YouTube

    Some places you just shouldn't.....

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    Synthetic slings do have their place. When you get into the bigger capacities, they are a lot easier to handle and cheaper than anything else. Steel rigging 100k+ capacity is almost impossible to attach by hand, it's just too heavy and unwieldy. Synthetic slings in that capacity starts getting heavy also but it's not anything a couple of guys can't handle.

    The main thing you have to watch out for is abrasion. Even being extra careful and padding all abrasion or cutting points, you'll eventually ruin them.

    Synthetic slings also have quite a bit of stretch to them that can cause problems in tight headroom situations. On the continuous round slings, the inside yarns don't stretch much at all, but the outer protective sheath stretches a bunch before the inside yarns ever get tight.


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