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This product is intend for trained and competent persons and should only be considered as a guide only. TSA takes no responsibility for any information a person uses from this documentation.
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Guide to Theatre Fly Systems
Single Purchase
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the stage. The cradle, which carries a variable number of metal counterweights, moves up and down vertical tracks alongside an o
vertical travel (movement).
The top of the cradle is permanently suspended by several wire rope loft wire lines. The loft wire lines run from the top of the cradle up to the head block, across the stage to evenly spaced loft blocks, then down, terminating at the batten, a load-bearing
pipe that spans much of the width of the stage.
If the loft blocks are mounted to the grid deck, at the loft block wells, the system is called a grid-mount, or upright counterweight rigging system. If the loft blocks are mounted to roof beams (loft block beams), the system is called an under-hung counterweight rigging system. Under-hung systems have the advantages of maintaining a clear grid deck surface for spot rigging and facilitating crew movement across the grid.
The cradle's vertical position is controlled by means of a rope known as the operating line, hand line, or purchase line. The operating line forms a loop by running from the bottom of the cradle down to and around the return sheave/block, through the rope lock, up and over the head block and back down (alongside the loft wire lines), where it terminates at the top of the cradle. The head and return sheave/blocks are located above and below the full extent of the cradle's travel (movement), respectively, thereby enabling an operator to pull the operating line up or down to move the cradle. When the cradle is raised via the operating line, the loft wire lines slacken, which causes the batten to lower under its own weight (and the weight of its load, if any). Conversely, when the cradle is lowered, the loft wire lines increase in tension, which in turn causes the batten to rise.
The combined weight of the cradle and its counterweights initially matches that of the batten so that when the batten is not being raised or lowered, it will tend to remain motionless at any arbitrary elevation above the stage. As more weight is added to the batten (in the form of curtains, scenery, lighting equipment, and rigging hardware), the system is rebalanced by adding more counterweights to the cradle. When the system is properly balanced, an unassisted operator (theatrical language), completely above the proscenium and out of view of the house, sometimes to heights in excess of 21m.
Double Purchase
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Double purchase counterweight systems are sometimes used where the vertical travel of the counterweight cradle would be inadequate due to limited fly space or stage-level wing space. In systems of this type, the operating and loft wire lines are double-purchased so that the batten will travel twice the distance of the cradle. In other words, for every meter of cradle travel, the batten travels two meters. This often results in the cradles remaining well above the stage deck, leaving the otherwise occupied wing space usable for cast and crew.!!!In a conventional counterweight system the operating and loft wire lines terminate at the top of the cradle after passing over the head block. In a double-purchase system, however, after passing over the head block the operating and loft wire lines pass through another block, which is mounted to the top of the cradle, before rising back up and terminating below the head block. In addition, the opposite end of a double-purchase operating line terminates at the fly gallery, off-stage wall, or stage deck, instead of the underside of the cradle, after passing through a block mounted at the underside of the cradle. The additional blocks result in the cradle moving at half the rate of the lift and operating lines.!!!In order to compensate for the reduced cradle travel, the loaded cradles must weigh twice as much as the batten load, resulting in cradles that are twice as tall. The additional mass on the cradle increases inertia, and the additional blocks increase friction, resulting in linesets that are more difficult to operate. In addition, double-purchase linesets are more expensive to install and maintain. For those reasons, double-purchase line sets are generally avoided, or limited to a few sets within a counterweight system, unless space issues preclude the use of a single-purchase system. The use of a cradle pit is an alternative approach to dealing with limited space for cradle travel.
Operation
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Below are the basic operation guide lines to a single purchase counter weight system:
Approach line set and grip both the front line and the back line together with one hand
slowly release cradle
pause to check that the line is balanced and that you have full control over system
slow the cradlemovement of the line
once you have to a complete stop with the line and you are happy with its position, then lock o� the line with the rope brake
Things to remember
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dangerous and should only be operated by competent persons
Deads' you must ensure that while inserting them through the rope strands you do not
You must never go over the systems W.L.L for operations
Annually to ensure it meets the necessary Australian Standards
No well maintained system should be noisy, squeaks and knocks are signs of wear and tear, possible defect and could arise to larger problems if left unattended
When ever moving a line during a bump in or out always clearly notify all persons on the stage and the grid when a line is moving
Loading Weights
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When loading weights into the cradle to equalise the line, you should ensure the below steps are followed:
You are aware of the weight of the item(s) that have be put onto the batten
You have locked o� the line and put on an additional hand lock
placed in or out of the cradle
Keep the area underneath and around the cradle and lineset set clear of all persons
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Haul / Over Haulthe bar and the weight in the Cradle is not equal.
Loading - Is when the weight loader is adding or removing weight to the cradle
Rope Cease / Rope Hand Lock sliding through the main cradle when the line is unbalanced
Unbalanced Line direction without assistance.
- Is the action of lowering a batten to the stage
- Is the action of raising a batten to the grid
- Is the action of transferring a batten from on lineset to another
Deads
Remember! If you are ever unsure or have any
We are always on hand at TSA to give free advice and answer any questions you may have no matter how big
or small they may seem.
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Call Us on (07) 5574 5327
References http://en.wikipedia.org/wiki/Fly_system#Counterweight_rigging_system
This product is intend for trained and competent persons and should only be considered as a guide only. TSA takes no responsibility for any information a person uses from this documentation.
Please consulate a professional on the best product for your use
www.theatresafe.com.au [email protected]
www.facebook.com/theatresafeaustralia
