A Thing, a Thing, a Marvelous Sling – Part 2
In the previous installment of our sling series, we covered the basket hitch. We shared how the rated capacity is double what is listed on the sling tag when utilized in a true basket setting. Progressing into the choker hitch, however, rated capacity is adversely affected rather than seeing an increase in lifting strength.
A properly formed choker hitch, utilizing appropriate rigging hardware or thimble eye slings when using wire rope, will see working load reduced by 25 percent in most cases. In other words, a 10,000-pound sling, for instance, would be de-rated by 25 percent, or 2,500 pounds and can now be used to safely hoist no more than 7,500 pounds when a choker is formed. Heavier loads can reduce capacity even further due to excessive pinching and bending of the sling body, possibly down to 50 percent of rated capacity.
With the inherent reduction in mind, what applications would warrant willingly de-rating a sling if other options are available? Simply put, for lifts that require a greater level of grip and control of the item being hoisted, say a large bundle of loose pipe.
Typically used from a single pick point, Choker hitches allow the rigger to hoist items that need to be held together for safe movement. One an evenly distributed item, the choke points would be set 25 percent of the length of the item from the end on both sides. For instance, to hoist a 25’ bundle of pipe. The choke points would be inset 6’3” from each end.
A nesting choke, where both sling legs pass under the load from the same direction, allows the rigger greater control of the load. This configuration, or its double wrap variation, would be used for bundling pipe and hoisting into place or flipping flat plates from horizontal to vertical for final positioning. It also allows only one rigger to control the choke points until the load comes under tension, so it can hold itself in place. This type of choker is more likely to employ the use of connecting hardware (thimbles, hooks or shackles).
Another variation is the leveling choke, used for hoisting an object square, typically seen more with ironworkers working on high-rise steel structures. To form this hitch, the sling is passed through the eye on the other end, which causes increased strain on the sling itself, but also allows for better body-positioning safety while removing the slings. This, however, also requires two workers to control the choke points until the load comes under tension.
The most important thing to remember with any style of choker hitch is that you should never, under any circumstances, force the choke by hitting it further down the sling than where it would naturally set when the load is lifted. Forcing the choke not only causes increased damage to the sling body, but it also reduces the capacity of the sling at a rate that can’t be accurately calculated and, therefore, creates a risky pick that can fail unexpectedly.
If the object being lifted requires more grip than can be achieved with a standard choke, a double wrap will achieve the desired level of grip without causing more damage to the sling body but will reduce the sling length considerably. If you choose to use a double choker, adjust the sling length to ensure sling angle never falls below 45-degrees.
It would also be wise to take precautions to protect both the sling and the object being hoisted from damage while choking a load. In a single choke, the sling must be protected from sharp edges and pinch points that can cut through the sling. When using a double wrap, check that the sling is not crossed over itself and is free from obstructions to avoid pinching the sling and causing irreparable damage to the sling body that can cause failure.
In addition, it is recommended to employ a shackle when creating a choker hitch for multiple reasons. Use of a shackle helps to preserve sling angle better than sling-on-sling applications and also serves to prolong the life of the sling by reducing some of the stress to the sling body caused by friction when the sling comes under load. When using a shackle, it should be installed with the non-running end attached to the shackle pin while the running end should run through the bow of the shackle. Installing the shackled with the pin along the running end risks loosening the shackle pin when the load is lifted and can cause catastrophic failure if used improperly.
For more information on slings, hitch types and different uses, visit our Web site at rentlgh.com to chat with one of our trained representatives, call us toll-free at 800-878-7305 or consult with your local LGH rental representative, found here.