RIGGING SYSTEMS: operation and safety rules

Fly or rigging system: allows safe support and quick change scenery and lighting used in proscenium theatre.

Part of Carpentry, involves own set of skills so is almost a separate department. The flys are run by the flymen, and under the control of the Head Flyman.

Systems come in several forms.

Earliest form: Rope/"hemp" system.

Borrowed from sailing ship industry, majority of terminology including the term "rigging" comes from sailing ships.


Rope system

Pinrail
--Rope systems were borrowed from square rigged sailing ships, a wooden rail with holes for belaying pins provides tie-off points for the ropes.
Pin rails are usually double tiered.
The upper bar is used to tie off ropes when the battens are at high trim (flown out for storage). The lower bar used to tie off scenery at low trim (playing height).

Pin rail may be located at floor level or on a catwalk above floor; called the flyrail.

Today the main fly system is rarely a rope system; but rope systems are often included as an auxiliary system.
Rope systems are often used for temporary or custom rigging, as rope systems are easier to adapt than counterweight or winch systems.
Well equipped theatres often have a flyrail on both stage left and right.

Scene loft or fly space: the large open area located above stage; curtains and flown scenery are stored here when "flown out".

Gridiron, or Grid for short, on which are located the pulleys for the fly system.
Pulleys are also called Blocks, a naval term for pulleys on a ship, or Sheaves.
Blocks may sit directly on the grid with pulley (wheel) up, called Overhung, or be fastened above grid to the ceiling, pulley hanging down, called Underhung.

Often main loft blocks located on or above pairs of heavy support beams with a gap between, called loft block wells.
A floor made of channel irons or bar grating (subway grating) fills the area between.
The Grid can supporting lightweight temporary rigs, called spot lines.

Grid may be made of bar (subway) grating or similar lightweight metal grate; old theatres the grid and beams were of wood.

In some theatres built on the cheap the grid dispensed with, and the rigging is underhung from the ceiling beams.
Lack of a Grid makes maintenance difficult and temporary rigging almost impossible.

Head blocks: located above the rigging rail, is a set of loft blocks where the multiple lines rising from the rail spread out over the grid to individual loft blocks.
Head blocks usually multiple-wheel blocks, i.e. a single block with several grooves or pulleys, or may be a set of individual pulleys used in association. Last scheme occasionally found in older hemp houses, but is rarely used today.

Headblock well: massive I-beams designed to resist both vertical and horizontal loads.
Pull on the headblock well consists of ALL the weight on the fly system both down to the rail and across the grid sideways to the loft blocks.
If not accounted for, sideways pull can bend headblock well open, causing headblocks to collapse down the well.

Traditional material for rope systems was manila hemp rope, usually 1/2" or larger.
Replaced by polyester double-braid rope; stronger, stretches less, reacts less to humidity, rot proof, no slivers.

Weight of scenery, curtains, lighting on battens can be tremendous; needs counterweight.
  
On rope system, counterweight is supplied using sand bags, which are secured to the purchase lines with a "clew", either a cast iron clew or wire rope loop called a "sunday".

Sandbags come in standard increments, e.g. 10, 25, 50, and 100 lb. when filled with dry sand.
The weight of the sandbags must be slightly less than the load on the batten but must be nearly weight of load so the flyman can control easily and safely.

At trim, the load is held in place by tying the lines to pinrail.
Sunday is placed just below the headblock when batten is in.
Note: a batten can never fly out higher than the distance between the clew and the pinrail when the batten is in.

Counterweight systems:


Counterweight system

A metal frame, called an arbor, is raised and lowered by means of an "endless" purchase line passing over headblock and under a floating block beneath rail.
The Purchase line passes through rope lock mounted on rail, which grips the line when the lock is closed.
A set of wire ropes (usually 1/4" aircraft cable) is attached to top of the arbor. These are the loft lines. The loft lines are attached to a "pipe" or "batten" on the other end to carry the load. A batten is usually made of 1 1/2" i.d. black iron pipe (i.e. gas pipe), or may be in the form of a ladder truss of structural steel tubing separated by steel straps.
The purchase line moves the arbor, and the arbor moves batten and it's attached load. When the line beneath arbor is pulled down (usually the rear line), it pulls the arbor down, raising the batten.
When the other (usually front) line is pulled, it raises arbor, lowering the batten.

The arbor is kept in line of travel either by "shoes" engaging a T-track, or by guide wires. The first is called a T-track system and the latter a Wire guide system.

Metal counterweights are placed on bars of the arbor to balance load.
This weight ideally should exactly balance load on the batten so that the endless purchase line can pull the arbor both up and down.

Pipe weight: part of load representing weight of the empty batten; pipe weight should be left on the arbor when the load and its counterweight is removed.

Trim chains: chain lengths attached to the batten end of lift lines in a counterweight set. Pipe battens at trimmed to level by adjusting these chains.

Counterweights are usually iron or steel, cast or flame cut from heavy plate.

Counterweights are often referred to as "bricks" or as "pigs" (short for pig irons).
Weights come in semi-standard sizes, e.g. 10, 20, 30, and 50 lbs.
Cast weights usually made to an actual weight. Cut weights may be uneven size, such as 26 or 38 lb., since they are often made to an even dimension rather than an even weight from a standard thickness of plate.

Counterweight systems come in two main flavors: Single purchase and Double purchase.

The Single purchase simpler, more common.
The arbor/purchase line travels between floor and ceiling; arbor travels one foot for every foot the batten travels, must put the same amount of weight on the arbor as the load weighs.

Everything, travel and weight is in 1:1 relationship.

The main drawback: one entire wall must be dedicated to the system; full floor to ceiling travel of batten requires full floor to ceiling travel of the arbor. The system doesn't work well from a fly rail, as pipe is at mid-travel when arbor is at rail.

Double purchase system: similar to reversed double pull block and tackle.

In Block & tackle, rope doubles back through a floating pulley: 2 feet of rope is pulled for every 1 foot of rise of load, but your need only pull half as hard. The load is twice the weight of the pull, and moves only half as far.

A double purchase system is similar, except that the load is on pull side, and arbor on the load side.
The Arbor moves only one foot for every two feet of batten travel; can therefore be run from a flyrail located halfway to the ceiling, and still allow the pipe to come in to the floor.

The major drawbacks: double purchase needs twice as much counterweight on arbor as there is on the batten (2 x the weight, 1/2 the travel).

Loaders typically must handle larger weights.
A single purchase "single" brick typically weights 20-25 lbs.; for double purchase a "single" brick weighs 40-50 lb., and a "half" brick weighs 20 lbs., the same as a single purchase "full" brick.

Double purchase systems cost more, are more complicated to use and maintain, and must have twice as much weight on hand for a full compliment (weighs are naturally sold by the pound, or ton).
Also, flymen can't double as deck hands because they are on a catwalk overhead.

Another place double purchase can be useful is where the side walls are lower than overhead grid, as with a grid located partway up a gable.
A single purchase would not allow full travel floor to grid, but double purchase with "muled" headblocks and loading rail halfway to the ceiling would allow full travel of the batten.

Proper procedure for loading battens should ALWAYS be followed when remotely possible.

To unload, reverse the procedure:

Motorized winches:

Primary advantages: can be run remote control by single operator. Using a control console, the operator can select and run several line sets at once.
Some forms of winches can handle far heavier loads than could be operated manually.

Drawbacks: more expensive per lineset than other systems.
More complex than other systems and so need more frequent maintenance.
Lack "feel", operator is disconnected from the piece being run and has no direct sense of when trouble is happening. On a counterweight or rope system, you can FEEL when lineset fouls or hits something. First indication on winch may be when something breaks.

BUT, for very large loads (electrics bridges and moveable ceilings) winches can be superior.

Winch systems come in several forms.

Chain motor rig:
A form of almost-synchronous winch system commonly used for show rigging.

Consist of industrial chain hoists, typically one or two-ton models, rigged to run inverted, used in sets to lift trusses or other loads.
Most chain motors are designed to be hung from ceiling, and the chain is lowered for the load.
Theatrical chain motors modified to be attached to load, and the chain hook is attached to ceiling.

Really the same motor with contactor inverted. These motors are fairly consistent in speed over their entire load range, and are single speed only. They are NOT identical, but they can work because:
a) they are set up and taken down regularly so that the accumulated errors don't add up.
b) they can be run both individually and together, so that single motors can be adjusted to line up with the others.

Disadvantages; get out of synch quickly, noisy, and slow.

BUT, allow you to fly heavy loads (in multiples of a ton) with a system that can be quickly set up anywhere the overhead can support the load and accommodate the chain attachment points, including outdoors with a ground supported roof trussing.

Large single motor and shaft which raises all the lift lines on a batten or truss.

Used for most motorized lighting bridges, a form of truss work specifically intended for supporting permanent electrics and sometimes including a catwalk for focusing. It is also used to lift the large lineal loads.
System is big, heavy, noisy, and slow, and runs at one speed only, BUT it allows the safe movement and support of heavy loads without the need for counter weighting.

Synchronous winch system:
One winch for each line on batten, all controlled by the same control signal.
Each motor MUST be exactly identical in speed to the others in the system; otherwise motors get out of synch fairly quickly, and the pipe will come in crooked.
Systems are usually single speed, as it is difficult to create a motor with variable speed AND uniform lift capability. Running a motor at slow speed also lowers effective power, so the motor will stall under load.
Biggest drawbacks: expense of all those motors and the ease with which they get out of synch; even a small variance accumulates over several runs.

The most common use: multi-use auditoriums where ceiling can be re-configured for different acoustics. These work because the loads are predictable and the motors are carefully tuned.

Spotlines:

Special purpose temporary rigging sets, usually with one lift line holding a single object, such as a chandelier. A loft block is placed in position and a line dropped where needed.
Often rigged as cable picks (pickups to carry bundle of electric cables offstage).
May be rigged for line sets in out of ordinary positions, as for battens run diagonally across the stage.
Spotlines are typically rigged using rope system rigging, but can be set up with chain motors, winches or counterweight arbors.


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Copyright © 2002, 2010 Mick Alderson