Today, crane manufacturers and crane service providers alike need to continue to look for innovative systems to enhance heavy lift capabilities whilst reducing manufacturing and operating costs.
One such system – which I have patented (US patent no. 6,651,961) – involves the use of multiple load blocks. This system provides enhanced lifting capabilities in either lift weight, hook travel height or a combination of the two whilst using smaller components and enhancing utilization of those components for greater returns on capital invested.
Depending on the specific application and needs of the lifting task, one or more of the following systems can be utilised:
1. Two reeved systems in series – one for heavy lift and one for lighter lifts with faster duties: This entails the provision of two reeved systems in series, the top system reeved for heavy lifts and the lower one reeved for light lifts. For most lifts on the project, the lower system can be used for fast hoisting and lowering cycle times with less frictional losses and wear and tear on wire rope and sheaves and bearings than if the full heavy lift reeving were used. For heavy lifts, the top system would be extended so that the hook block and middle block set are within reach of the ground. Steel link plates would then be attached between the hook block and the middle block set, effectively taking the light reeved system out of the load path. The upper, heavy lift reeved system would then be available to do the heavy lift. Following the lift, the link plates could be disconnected again, and light lift duties resumed. These changes would be effected without the need to lower the boom and change the reeving of the block, a time consuming and often disruptive activity to a site.
2. Two reeved systems in series – both with the same reeving: A similar opportunity exists to utilize smaller winch drums and related equipment for both systems in series. This provides the same overall lifting capacity and hook travel distance as a conventional reeving arrangement that would need substantially larger winch drums to provide the quantity of rope required.
The potential benefits that can accrue to crane service providers are therefore:
∑ Multiple uses of an asset will provide an enhanced capability to generate revenue. The more applications with which a service provider can utilize a piece of equipment, the greater the return on that asset.
∑ Smaller individual component sizes can reduce mobilization and transportation costs. Large capacity winch drums, for example, can be heavy and over sized resulting in high shipping and transportation costs.
∑ In some field applications, cranes may only be required to provide moderate lifting capabilities for most if not all of the time the machine is on site. In those instances it can be beneficial to have smaller rotating equipment, and utilize a much higher proportion of the hoist cable on the drums. The other winch drum(s) and reeving components may then be utilized on another project, providing greater returns for the capital invested in that equipment.
∑ Manufacturers may wish to consider the lease of a second set of winch drums and reeving components to existing clients to augment crane’s capabilities in this way. Crane service providers would then only have to pay for the enhanced capability.
Augmentation of existing assets to provide greater lifting capability is nothing new. Two winch drums used for one reeved system with hoist lines running in parallel have been around for many years. However, the use of two or more reeved systems in series may provide lower mobilization cost benefits, greater utilization of existing assets within a fleet of equipment resulting in a greater return on capital employed and will provide an economic solution for some heavy lift or high lift height applications.
