SCHOTTEL Debuts Underwater Mountable Thruster

SCHOTTEL has expanded its portfolio with the successful tests of the 5.5 MW SRP 800 U rudderpropeller, which can be installed afloat for vessels that cannot be docked easily due to their size or area of operation. Besides application in larger offshore vessels or rigs, the new and powerful SCHOTTEL thruster is suited for cable laying vessels, offshore construction vessels and crane ships.

“As a result of customer requests, SCHOTTEL decided to further develop the robust, well-proven rudderpropeller technology in the power range up to 5.5 MW,” said Roland Schwandt, SCHOTTEL Sales Director Tug & Offshore Energy.

SCHOTTEL  said calculations for increasing the power went hand in hand with developments for greater installation flexibility and higher safety factors that exceed the strict requirements of the classification society. This includes, for example, the full load gear test for checking the gearing of the bevel gear set that has now been carried out in the German test facilities successfully. 

The full load gear test was preceded by model tests at Potsdam Shipbuilding Research Establishment (SVA Potsdam), Germany and CFD simulations. The thruster sets superlative standards in real dimensions. Tests were carried out with a rated torque of 80,000 Nm at the power input of the underwater gearbox. This corresponds to continuous heavy-duty operation on the open sea using a propeller with a diameter of 4,100 mm. Two large hydraulic motors with working pressures of up to 300 bar provided the drive and braking power. 

The results of the evaluation show that the position and extent of the contact pattern exactly match the simulation, the manufacturer said. In the contact pattern, it can be proven that even with the high operating loads and the resulting displacements of the teeth, the torque is always transmitted ideally from tooth to tooth. 

With a view to safety, SCHOTTEL said customers benefit not only from the rolling-contact bearings, but also from the double-checked seals with a longer service life than required by the classification society. The certified LEACON propeller shaft seal was successfully tested. The endurance test under real operating conditions simulated water pressure and temperature fluctuations, for example. The key design feature of the system is an intermediate chamber between the propeller gearbox and the water. Multiple special seals on the propeller shaft and the connecting shaft separate lubricants from the seawater. 

According to SCHOTTEL, the SRP 800 U has been optimized with a focus on maximum market coverage in terms of fit variability. The design of the interface to the vessel corresponds to that of models commonly available on the market and is thus ideal both for new installation and as a replacement unit. Using a three-way roller bearing as the slewing ring, it was possible to reduce the required installation space and increase the compactness of the drive. Furthermore, the number and size of the protective caps was minimized for underwater installation. 

Two stem variants open up a broad application spectrum. In addition to the standard version with a 90° gearbox, SCHOTTEL also offers a variant with a propeller shaft inclined by 8 degrees. This reduces detrimental effects on the thrust of adjacent drives and interaction with the hull. In terms of flow characteristics, the azimuthing SRP 800 U thus adapts itself optimally to its area of operation, be it as a main propulsion unit in a drill ship or construction vessel, or as a positioning aid in a semi-submersible rig. The optimal flow contour was the result of CFD calculations as well as cavitation and maneuvering trials at the SVA Potsdam, Germany. Freedom from cavitation has been demonstrated at speeds of up to 16 kn.

Following testing, the SRP 800 U is now available for newbuildings or as a replacement unit in a wide range of applications.