Germany: RENK has been chosen to supply the CODELAG gear units sets for the new propulsion system on four new Class 125 frigates ordered by the German Federal Office of Defence Technology and Procurement (BWB).

The order for the vessels were placed in mid 2007 and was for the ARGE 125, to be built by an industrial consortium formed by Blohm and Voss Nordseewerke (BVN) and Lürssen Shipyard.

The F125 is not an upgrade or replacement of previous concepts. Rather, it is to be a ship designed to meet present and future mission profiles. The German Navy thus consistently complies with the diverse requirements placed on a ship in peace-stabilising missions and in fighting international threats such as terrorism and piracy.

The propulsion concept provides for the combination of a gas turbine with two electric motors. RENK has already previously delivered gear units for electromechanical CODELAG (combined diesel-electric and gas turbine) drives of similar performance.

The propulsion system planned for the F125 provides for a main gear unit on the port side and starboard side, respectively; both are interconnected by a cross-connect gear. Two electric motors and a gas turbine centrally located between the propeller shafts drive both propellers in different cruising conditions: slow and march movements with electric motors, high-speed movement with the gas turbine and both electric motors running at the same time (CODELAG).

The electric motors are positioned forward of the gear unit and drive the propeller shaft directly without a reduction gear stage via shiftable multi-disk clutches. The gas turbine is linked to the cross-connect gear via an overrunning clutch.

A ship of this size must be driven with a considerable amount of power. At 4,500kW per electric motor and 20,000kW at the gas turbine, a total of 29,000kW is produced in the CODELAG mode.

A special feature is the arrangement of the clutch between electric motors and main gear units. Two coaxial shiftable multi-disk clutches each supply power to the propellers depending on the required power flow in march or high-speed movement. A sophisticated control system – equally part of RENK’s scope of delivery – ensures smooth shifting between all operating states – which is a further proven characteristic of RENK’s gear unit systems.

The mechanical components of the gear units, such as gearings, bearings and housings, are manufactured by RENK with its proven technology. High-precision double-helical toothing with correction by grindings in the micrometer range, even with output gears of more than three metres in diameter, ensure a minimum of noise. Anti-friction bearings are designed to the latest state of the art in terms of durability and the housings are weight-saving welded constructions. Still, the complete gear unit set weighs in at 145 tonnes.

In the period between 2011 and 2014, RENK will deliver four systems to shipyards and the Navy that will perfectly fit into yet another pioneering propulsion concept of a new fleet unit.