Sling angle and force

Two legs do not split the load in half. They split it according to the angle —
and the arithmetic is unforgiving.

Why the force rises

With the slings vertical, each leg pulls straight up. As they splay outward,
each leg must also pull sideways to hold the load together. That sideways
component is free as far as the load is concerned, but not for the sling: it adds
to the weight the leg is already carrying.

The flatter the angle, the larger the addition. At very flat angles the force
in each leg becomes many times what the weight alone would suggest. This is not a
safety margin being eaten into — it is real tension in the sling.

Calculate it, do not estimate

The sling calculator works out the force in each
leg for the angle and number of legs you are actually using, and shows its
working. Use it in preference to rules of thumb.

See also the article Sling angles multiply load.

What the calculator does not do

It tells you the force. It does not tell you whether the sling
will take it — that is on the sling’s marking and in the documentation for that
specific sling, and the WLL differs between hitches. See
hitch types.

Practical consequences

• Longer slings give a steeper angle and lower force — where headroom allows
• More legs help only if the load actually shares between all of them
• On a rigid load with three or four legs, two of them may carry nearly everything
• A lifting beam removes the angle entirely — see the
  lifting gear reference