Cranes are intended to be set-up on firm, level ground. The rules change when cranes are placed on a ship or barge. Cranes mounted on unstabilized, non-jacked ships can create a major problem.
As a barge mounted crane lifts a load, the barge will push down into the water creating list or trim, causing the crane to become unlevel. Special load charts are available that compensate for up to 5°. Additional ballasts or counterweight are required to level the barge so as not to exceed the 5° allowance.
While the heavy lift vessel, BBC Coral, was commissioning her cranes, something went wrong. The two cranes mounted on the deck were being load tested by lifting a ballast pontoon. The pontoon dropped, half on the deck and half on the dock, ripping one crane from its pedestal.
Learn more about the importance of proper load testing procedures in our Mobile Crane Inspector program.
It is always important to consider ground support around the entire working area, not just where the load will be lifted.
It is common to think that if the ground is firm enough under the outriggers toward the lift, then the crane will be supported. However, this 500 ton All-Terrain crane has several tons of counterweight being supported by the outriggers on the opposite side of the crane.
If the crane swings over an outrigger, thousands of pounds per square inch of pressure impacts the float and the ground beneath it. Generally, the times three rule for blocking is adequate, but the actual load pressure on the ground for a crane configured similarly must be calculated. Additionally, a compaction test should be conducted to determine ground support.
After obtaining this information, a proper size blocking can be chosen for lifting the load safely.
Read the entire story at Vertikal.net.