Bridle

A bridle is used when the place a load needs to hang is not where the building provides a point. Two legs run down from two separate attachments and meet at an apex, from which the motor or the load hangs.

The instinct is that two legs each carry half the weight. They do only when the legs are vertical. As the legs open out, each one carries more, and the increase is not gentle. Measuring the angle from vertical: at forty-five degrees each leg carries about seven tenths of the whole load, so the two together are handling nearly half again as much as the load weighs. At sixty degrees each leg carries the entire load on its own. Past that it climbs without limit.

The second consequence is the one buildings object to. A splayed leg pulls sideways as well as down, and that horizontal force lands on a structural member that may have been designed only for vertical load. At sixty degrees the sideways pull on each point is more than eight tenths of the load.

So a bridle is calculated, drawn and checked rather than rigged by eye, and a wide bridle is the arrangement most likely to need engineering review. The practical rule is that a bridle buys position and pays for it in tension, and the shallower it can be kept, the less it costs.

Staging and rigging — owned inventory, our own crew, and a site survey before anything is specified.

• Dead hang A straight vertical suspension from a single point — the simplest and cheapest way to hang anything, and the reason rig positions are negotiable.
• Point load The force delivered into one attachment — the number a building is rated against, and the reason total rig weight is the wrong thing to quote a venue.
• Rigging plot The drawing that says what hangs where, how heavy each point is and how high it trims — submitted to the venue weeks ahead, not produced on the day.