Barge crawl

From the installation of steel piling in Durban to the construction of new bridges in the US, crawler cranes are a popular choice for wor k that involves lifting from a barge. Of course this kind of wor k is not easy. The conditions are dynamic and so the potential for tilting of the barge has to be factored into the capacity calculations and the weather has to be monitored e ven more carefully than usual. Added to this the barges ha ve a limited ground bearing capacity and, unlike land-based lifts, ground preparation cannot help.

"You need a crane that isn' t going to punch a hole through the deck of that barge," remarks Dustin Soerens, marketing manager for lattice cranes at manufacturer Manitowoc. Earlier this year the fir ms released two new machines, the MLC300, which is par ticularly aimed at the barge market, and the MLC650.

Both have the firm's unique variable position counterweight (VPC) technology. "By moving the counterweight based on boom position, it better balances the crane out and gives better ground bearing pressure than a standard crane would," says Soerens. The machines are still undergoing testing and so are yet to be deployed on a barge, however they build on previous crawler models that have been popular in the sector. "There is a great deal of interest in putting both of these cranes, but mainly the MLC 300, into barge applications," says Soerens.

A company that is enjoying high demand for its crawler cranes on barges is Japanese manufacturer Kobelco, with its CKE G and CKS series which are cur rently being used on projects all o ver the world. "The really popular models for barge applications range from 80t through to 250t," says Mark Evans, sales manager for Kobelco Cranes Europe. "There is lots of wor k on construction of new docks, piling works and breakwaters," he says.

Because of the large amount of demand for crawlers in water based work, the firm includes the barge rating char ts and supplementary data in its brochures and provides an online application for calculating ground bearing pressure depending on the configuration and site requirements. "It might be wh y so many people use us," says Evans, explaining that the char ts give the inclination limits for front to back which is about 3 degrees. Right to left (or left to right) is 1.5 degrees. "Ob viously you can't put a fully loaded crane onto barges so we have to reduce the counterweights and take off carbody weights so they can't use all of the boom length that the y might have purchased with the crane."

On the CKE 800 for example, lifting with a 12.2m boom length at a 4m radius the crane has a rated capacity of 72.6t, but on a barge this drops to 50t for the same conditions albeit with a reduced counterweight configuration. To lift higher over a greater radius, the rated capacity on a barge for the crane at a 32m radius with a 36.6m boom length is 3t. This compares to 4.3t on land.

One firm that has recently been impressed with the performance of Kobelco's CKE 1800, CKE1100 and most recently the CKE 1350, is African contractor Steffanutti Stocks Marine. The firm has been using the cranes for the installation of 25t, 27m long combi-wall piles at the New Maiden Wharf project in Durban, South Africa as w ell as for suppor ting anchor piling.

"The cranes pitch the piles, load the piles into the guide frame, and also suppor t the free-hanging piling hammers during pile driving," explains Andrew Pirrie, contracts director, Steffanutti Stocks Marine. The contractor is also using a Kobelco CKE 1000 machine for a project at the Port of Mombassa for marine piling operations as well as for placing the precast jetty, pouring insitu concrete and installing the structural steel topsides shiploader unit.