The stage rigging basics have changed significantly since the old hemp systems of the “Golden Age of Sail” (1850-1900). For starters, riggers have far more choice of materials in hardware and soft goods today. Hemp, wood, leather, canvas, and metal have given way to thermoplastics and synthetic fibers.
Synthetic Stage Rigging Ropes
The advent of modern, high-strength synthetic ropes has added such advanced options as:
- High modulus polyethylene (HMPE) like Dyneema®
- Liquid crystal polymers (LCPs) like Vectran®
- Aramids like Technora®
Technology has even made it possible to manufacture polypropylene ropes that closely resemble authentic hemp braids—such as Classic-Tex and Spunflex by Robline®—but with all the advantages of high-strength inorganic fibers.
Modern Stage Rigging Hardware
Stage hardware has also grown stronger and lighter than ever before with the help of materials like:
- Self-lubricating stabilized acetal pulleys that combine low friction and high durability
- Nylatron® sheaves that handle fiber ropes and steel wire equally well
- Torlon® needle rollers in high capacity blocks such as the Ronstan® Series 60 Orbit Blocks™
However, cutting edge synthetic fiber ropes have become something of a double-edged sword for their counterparts in the latest stage rigging hardware. Pulley advances simply haven’t been able to keep pace with the astounding leaps in maximum load tolerance enjoyed by the newest synthetic ropes.
High Tensile Strength vs. Lower Breaking Loads
There are ropes out there now that outperform steel cable by a factor of 15:1, weight-for-weight. This is great news for the increasing weight of technology-laden drops and smart lighting fixtures. However, it may be challenging to find a pulley, or attachment point, strong enough to take full advantage of this incredible load tolerance. The maximum load of a pulley is usually lower than that of the rope that fits into its sheave(s).
One option is to rig a block and tackle that will reduce the individual load experienced by each pulley—as is commonly done to handle unbalanced loads in fly systems. For every factor of mechanical advantage in the system, there is a matching reduction in stress on the constituent sheaves. For example, consider this combination of rope/hardware for a 1,000 lb drop:
Purchase Line: 8mm Dyneema® SK-78
- This sort of Dyneema® line has a minimum breaking load (MBL) of over 6 tons
Block and Tackle: 2x Ronstan® Series 60 Orbit Blocks™ (Double-Blocks)
- Each double-block has an 8,820 lb maximum working load
- 4:1 mechanical advantage from the “twofold purchase” block and tackle (two double-blocks)
In this scenario, the mechanical advantage helps the stage rigging rope and hardware to work together. Each sheave must support only 250 lb of the 1,000 lb drop’s load. This means everything respects a 10:1 (or better) safety factor of operating load to breaking load.
- The rope’s breaking load is over 12,000 lb vs. the 1,000 lb drop (12:1 safety factor).
- Each pulley block’s breaking load is over 8,000 lb vs. the 500 lb each double-block must support (16:1 safety factor).
Maximum Load vs. Friction
Another consideration is how the stage rigging system will minimize friction while also maximizing load tolerance. Traditionally, a bushing block is ideal for high loads, since it distributes the load on a pulley across the maximum surface area. Ball-bearing blocks, on the other hand, are better for reducing friction—they minimize contact with the pulley hub. How can one set of stage rigging hardware do both?
We developed the Ronstan® Core Block™ series to handle both dynamic and static loads with an innovative two-stage bearing system. At low loads, ball bearings keep friction from interfering. As the load increases, they push aside, and a bushing takes the load from the central hub. This helps your stage rigging hardware adapt to any situational usage of the rope—for dynamic motion or maximum load.