The Insider Article – D/d Ratio Explained
By Ashley Thacker
Passing a sling- synthetic or other- around a load can provide support by creating a cradle, but you must make sure that it is surely attached. Therefore you must understand D/d ratio.
I get asked a lot of questions about D/d ratio. I think it worries people because it looks like a complicated mathematical equation and reminds us of those brain fades at school. (If only education better applied things like algebra and trigonometry to engineering and real-life scenarios, but that is an article for another day.) However, D/d ratio isn’t really complicated.
First, let’s look at when this equation is applied. In the absence of suitable lifting points, the main options are to attach slings by passing them through or around the load. Passing through a suitable aperture has the advantage of making the load captive but you need to be careful that the material around the aperture is strong enough to take the whole load. Other aspects of the load to consider are whether it is flexible, in on e piece or needs holding together, is vulnerable to local damage, or must be manipulated in the air. It is worth stressing the need to consider at the planning stage the position and security of ….
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