Centre of gravity and balance

A load always hangs with its centre of gravity directly below the hook. The
only question is whether it gets there before or after it has swung.

What happens when the hook is off

If the hook sits to one side of the centre of gravity, the load rotates as it
lifts until the centre of gravity is beneath the hook. On a badly off-centre lift
that arrives as a snatch — and anything in the way of that movement gets hit.

It is also when the slings become unequally loaded: one leg may carry nearly
everything while the other hangs slack.

Finding the centre of gravity

• If the load is symmetrical and homogeneous it is usually near the middle
• Motors, switchboards, pumps and machinery carry their mass at one end
• Partly filled containers move their centre of gravity as they travel
• A designated lifting point is often placed by the maker for balance — use it

The centre of gravity calculator helps with the
geometry when the load is made of parts whose weights you know. The article
Centre of gravity carries the reasoning.

A high centre of gravity

A load whose centre of gravity sits above its attachment points is unstable: it
wants to turn over. It is not a question of whether it tips but when. Such loads
are attached below the centre of gravity, or secured so they cannot rotate.

The trial lift

Lift a few centimetres and stop. Does it hang level? Are the legs equally taut?
Has anything shifted? At that height the answer is still survivable. See
trial lift and landing.