CRANES ON BARGES
There are often times that an operation requires the placement and operation of a land-based crane on a floating vessel. These operations can be very effective in providing lifting services at sites where an adjacent body of water allows a crane to reach areas of the site that would otherwise be prohibitively expensive, or impossible, to reach from the land.
The very nature of land-based cranes is such that they rely on a solid and immoveable surface on which to rest during lifting operations. Large capacity cranes operate by carefully balancing counterweight and load in a balancing act, where the load path acts along the plane of the boom and counterweight arrangement. Deviation from this plane caused by side forces or tilting of the crane can impose large loads on the boom and outriggers for which the crane is not designed.
As a result of this, cranes operating on floating vessels often come with a de-rating of their capacity curves which reduce the allowable load that can be lifted in any given configuration when compared with a similar land-based operation.
During operations, to ensure the vessel deck remains as level as possible, both sea state and ballasting operations need to be carefully managed with the resulting load transfer to the crane and slewing of the lift choreographed with the on-board movement of ballast water.
The stability too of the system needs to be carefully checked taking cognisance of the fact that when lifted clear of any supports the effective centre of gravity (CoG) of the lift and its impact of vessel stability, translate to act through the boom tip and not the local cog of the load itself.
This myriad of considerations underlines the need to undertake lifting on floating plants carefully, being aware of all the risk and mitigations required to ensure that the operation is caried out safely and successfully.