September 2004

Floating cranes with SCHOTTEL Rudderpropellers for bridge construction in the Shanghai area

There is a continuous need for new transport routes in the Shanghai area to link the booming economic metropolis to the surrounding regions and improve the infrastructure. One such construction project is the 27-kilometre-long Dong Hai Bridge , which will soon connect Lu Chao Harbour with Shanghai . Prefabricated bridge sections must be transported from on land to the steadily advancing local construction site where they are assembled. This is where the floating cranes come in: they are used to hold the loads in place while they are integrated into the bridge, and also manoeuvre independently with suspended bridge sections and can cover short distances.

After a six-month planning phase, SCHOTTEL and the Chinese design office SDARI were awarded the contract for the propulsion units of the first floating crane. This crane, a catamaran with an overall length of 84 m, overall breadth of 46 m (breadth of each hull 14 m), displacement of 8365 t and load-bearing capacity of 2500 t, has two Rudderpropellers of type SRP 330 in nozzle, rotating in opposite directions, and an electric motor-driven bow thruster installed in each hull. The four Deutz diesel engines for the main propulsion units each have a power rating of 537 kW and, in the case of the two middle engines, are fitted with a second power take-off which can alternatively be used to power hydraulic pumps.

One priority of the construction company that owns the floating crane was that it should be able to manoeuvre and position itself without the need for tug assistance. This results in a high degree of flexibility during the transportation and assembly of the bridge sections. At the construction site itself, positioning is carried out using only the two outer Rudderpropellers, the transverse thrusters, and, if required, anchor operation. In other words, the inner Rudderpropellers are uncoupled and the second power take-off of the diesel engines can be used to drive the hydraulic pumps for the crane winches and anchor operation.

Another requirement of the owner was infinitely adjustable thrust regulation over the whole speed range. For this purpose, “low-duty” MCD clutches were installed between the diesel engines and the Rudderpropellers. This makes it possible to regulate power transmission even below the idle speed.

To simplify handling of the four main propulsion units, the Rudderpropellers are steered in pairs using synchronous Copilots. Depending on the specific requirements, the Rudderpropellers in each hull can be operated either singly or together. It is also possible to manoeuvre the floating crane by means of a Masterpilot that controls all six units.

The vessel was commissioned at the end of August 2004. The same customer also awarded us a contract for four SRP 550s, each with a power rating of 900 kW, for installation in a second floating crane due to be commissioned mid-2005. This is to be used in the construction of a 30-kilometre-long bridge spanning the Bay of Hangzhou .