Something went terribly wrong while three cranes were moving the bow section of a ship in a Mississippi shipyard. One crane overturned and several workers injured.
Cranes are designed to smoothly lift and move loads within their capacity with the boom tip directly over the center of gravity of the crane’s load. When multiple cranes are working together, they share the load, but neither have the load positioned over the center of gravity.
As you can imagine, things become more complicated when three cranes are working in tandem, because the movement of a load has to be perfectly choreographed. In this case, the only safe maneuvers made would be to hoist, lower and travel. Hoisting and lowering shouldn’t be a problem as long as each crane’s share of the load is within its capacity. However, traveling induces dynamic forces on the cranes because they don’t travel in perfect synchronization. Like all equipment, cranes travel at random speeds no matter how careful the operators are to synchronize their speed. Being off by a small amount causes what could best be described as a pushing and shoving match between the cranes.
Industry accepted lift planning models for multiple crane lifts would require that no crane be loaded beyond 75% of capacity. This 25% safety margin is used to compensate for the dynamic forces.
Attend our Mobile Crane Operator training to learn safe operating practices.
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