The recently commissioned floating crane is used to hold the loads in place while they are integrated into the bridge and also to move independently with suspended bridge sections.

After a six month planning phase, Germany's Schottel GmbH and the Chinese design office SDARI were awarded the contract for the propulsion units of the first floating crane. The 8,365 ton catamaran has an overall breadth of 46m, with each hull being 14m wide and fitted with two type SRP 330 Schottel Rudderpropellers rotating in opposite directions and an electric motor driven bow thruster. Four Deutz diesel engines for the main propulsion units are each rated at 537kW, with the two middle engines fitted with a second PTO which can alternatively be used to power hydraulic pumps.

The priority of the operator was that the crane should be able to manoeuvre and position itself without tug assistance, resulting in a high degree of flexibility during the transportation and assembly of the bridge sections. Onsite, positioning is carried out using only the two outer Rudderpropellers, the transverse thrusters and, if required, anchor operation.

The inner Rudderpropellers are uncoupled and the second PTO from their diesels can be used to drive the hydraulic pumps for the crane winches and anchor operation.

Another operator requirement was for infinitely adjustable thrust regulation over the whole speed range. For this purpose, 'low duty' MCD clutches were installed between the diesels engines and the Rudderpropellers, making it possible to regulate power transmission even below the idle speed.

To simplify the handling of the four main propulsion units, the Rudderpropellers are steered in pairs using synchronous co-pilots. Depending on specific requirements, the Rudderpropellers in each hull can be operated either singly or together and it is also possible to manoeuvre the floating crane with a Masterpilot that controls all four Rudderpropellers and both thrusters.

The same operator has awarded Schottel a contract for four SRP 550s, each rated at 900kW, for installation in a second floating crane due to be commissioned mid-2005. This is to be used in the construction of a 30km bridge spanning the Bay of Hangzhou.

MJ Information No: 20221