One of the most used items in rigging and possibly one of the most abused items has to be the ‘Screw pin Shackle’. They come in many different capacities and types, namely the Bow and D-type, the D-type is not so common in the entertainment industry due to it only being suitable for a straight in line pull, and as a bow shackle can do that it’s easier to keep just one type.
When using shackles for rigging the most important thing is to make sure the equipment is load rated and not a low grade commercial type that’s not suitable for lifting. It’s also important to know what the applied load will be, overloading any lifting equipment is forbidden in every country around the world that have any type of rigging or lifting regulations.
Bow shackles can be used in many orientations, but the most important thing is the direction of the force(s). The bow is designed to absorb a bridle force, where the pin side is to only be loaded perpendicular to that pin. When the bridle apex point is in the bow the shackle is loaded correctly. In the examples below the arrows marked in red are not acceptable.
When used in a straight pull, it’s important to ensure the forces are on the pin and the crown of the bow only, but it is also important to make the correct choice for the orientation. It’s important to understand that the Centre of Gravity (COG) in a shackle is always going to be closer to the pin due to the weight displacement of the shackle.
Therefore, it is wise to have the pin side facing down and the bow facing up, this will help prevent in a slack situation, the natural tendency for the shackle turning itself (the heavy part always wants to be downwards) ending up in a transverse load. This is a simple but effective and an example of good rigging practice.
Other good rigging practices when using shackles are:
- Avoid Folding, bunching or pinching of synthetic slings, which will reduce the Working Load Limit of the shackle and sling.
- Screw pin should be fully engaged but not tightened and should be moused.
- Applied load should be centred in the bow to prevent side loading.
- Multiple sling legs should not be applied to the pin.
- If side loaded, the Work Load Limit shall be reduced.
It’s important to note the maximum bridle angle should not exceed 120° (2 x 60°)
The first thing to make sure when using shackles is that they are designed and manufactured for lifting purposes. Most countries require a minimum amount of identification on the shackle. The picture shows the sort of information you should find on a shackle from a reputable manufacturer.
All lifting components safety can be affected as a result of use, abuse, wear and so need to be inspected at least once a year and should be examined prior to each use by a competent person and shackles are no exception.