"This is like a small dream in the crane world," says Ingo Noeske, global production director for Manitowoc's crawler line. "You can lift the load and not take care of your counterweight." The VPC-MAX attachment also requires a derrick or fixed mast to support the counterweight behind the machine, all of which can be set up in about a day, Manitowoc estimates.
Essentially, the VPC allows users to increase lifting capacity with less counterweight than a conventional machine. The MLC300 is rated for a load moment of 14,410 ft-kips in standard mode and 29,790 ft-kips in VPC-MAX mode. Although the cranes cost about 10% to 15% more to buy and rent than a convention crane of the same size, according to ALL, the company expects the user to see savings in ground preparation costs, onsite travel and, in the case of VPC-MAX users, assembly and disassembly costs. The MLC650 is even beefier, with load moments of 28,114 ft-kips in standard mode and 65,473 ft-kips with the VPC-MAX.
The new system also takes heavy-lift crawler cranes to a new level of mobility. "An important point not usually acknowledged: It is impractical to move an unloaded crawler with a wagon attachment on a jobsite due to the extremely high ground-bearing pressure on the wheels of the counterweight wagon," Settlemier says. "These high ground-bearing pressures force the owner-contractor to spend money and precious time on the travel-path improvements that are only required for the heavy-lift crane." The cranes also use interchangeable parts, such as counterweight boxes and pinion drives.
For marine work, the VPC and VPC-MAX cranes can roll onto the barge with all the rigging onboard from the start. "The use of mast-derrick setups with suspended ballast in a barge application is typically not allowed by the manufacturer," ALL explains. "Therefore, the MLC300 can do work off of barges that mast-derrick and suspended-ballast crane setups cannot do."
Crane owners say early feedback has been positive, but it will take time for users to understand how the cranes can be applied. "We anticipated a learning curve with the machine, which is to be expected because of the radically different technology involved with the VPC," ALL says. "However, this learning curve has in no way affected the machine's ability to do everything being asked of it."
Settlemier adds, "We believe the advantages will be more apparent in the 650-ton and larger class of crawler," especially because the crane "will have a smaller footprint with higher capacities than anything ever built."
Risks associated with the cantilevered counterweights are expected to be similar to today's crawler cranes, as users are already required to manage the crane's tail- swing area around the lifting zone. "We believe the reduction in crawler ground-bearing point loading will offset any known or unknown risks from the moving counterweight," Settlemier says. Also, a series of visual and audible alerts let users know when the counterweights are on the move.
During our demonstration in Manitowoc, we watched as an MLC300 fitted with 177 ft of main boom and 295 ft of luffing jib began lifting its boom from a horizontal position on the ground. Filled with 20 boxes for a total weight of 234 tons, the counterweight tray began sliding backward; a flashing light and audio alarm alerted us to the motion. A few moments later, the counterweight shifted back to its original position as the operator began to set the boom back down.
The humble counterweight is no stranger to controversy. The International Trade Commission in April ruled that a crawler from China-based Sany Group violated Manitowoc's VPC patents. Manitowoc also has defended attachments such as the MAX-ER wheeled counterweight wagon and RINGER circular rail base. American Hoist & Derrick Co. is another pioneer credited with early designs for heavy-lift counterweight enhancers. In 1965, it invented the Sky Horse guy derrick and mobile wagon.
With three VPC models, Manitowoc sees room for more. "We think it's possible to add it to models," Kennedy says. "We generally think it will be appropriate for any crane above 300 tons."