Combining Gears for Naval Propulsion
German gear specialist Renk produces complex main reduction gears for navies, among a vast range of propulsion gear units, drive elements and transmissions. The company, which is a member of the MAN group, explained that products like the Renk COmbined Diesel And Gas (CODAG) turbine propulsion gears have been utilized in several new vessels in the past years, such as the Sachsen class frigates of the German Navy or the U.S. Coast Guard National Security Cutters.
The company recently reached a milestone in the field of Renk gearing applications with its performance during factory acceptance trials of the CODAG combining gear set for the Turkish Navy program, MILGEM, one of two Turkish national warship programs. During the one-week trial used to check functionality of mechanical and hydraulic components up to full speed, the 130 tonne gear set provided its full capability in all operational modes.
The CODAG propulsion gear con-figuration consists of two propeller shaft lines, each connected to main reduction gears, and the power supply via a cross-connecting gear from one 20 MW gas turbine. Two additional diesel engines are arranged inboard for loiter or cruise speed, and sprint speed is achieved together with the gas turbine in CODAG mode. All three subgearboxes are positioned on hard elastic foundations designed by Renk.
The traditional combining gear set, the variant COmbined Diesel Or Gas (CODOG) turbine is installed in about 40 naval surface combatants in several different navies. It was recently ordered by Doosan Heavy Industries, which is the prime contractor for the Korean Navy, to build the new FFX frigate. Renk explained that it will provide the design authority and deliver major core components for the two locked train gears for the frigate’s separate propulsion shaft lines.
A third combining gear set by Renk is the COmbined Diesel-ELectric And Gas (CODELAG) turbine. This set is used in navy vessels over 5000 tonnes, where current designs often use speedcontrolled electric motors in place of diesel engines when cruising, while a gas turbine supplies additional power to two controllable pitch propellers for high speeds. CODELAG combines the three propelling machines to simultaneously generate power for the vessel top speed.
Renk reported that the first propulsion of this kind was developed by the Italian shipyard Fincantieri for the first two frigates for the Italian Navy within FREMM, a French-Italian bilateral project. The first trials at Fincantieri were successful and eight further frigates will follow, with Renk designing the gear arrangement and supplying the gear components. Renk said that CODELAG derives from the CODAG version. Its gear unit consists of a cross-connect gear that transmits the power of a 32 MW gas turbine to the two propeller shafts.
Each of the two main gear units is connected in the second stage to the propeller shafts and mechanically linked with the cross-connecting gear, formclosed ing a gear system that weighs 140 tons and is 12 m wide. A new Renk propeller clutch, type APC, is arranged between the main gearing outputs and each shaft line, and transmits half the gas turbine power. The electric motors arranged directly on the shaft lines supply their power individually with disconnected APC clutch for cruising speed, or in connection with the gas turbine with formclosed APC clutches for CODELAG top speed. Based on its experience with sophisticated gearing solutions aboard vessels in service with over 35 navies, Renk continues to build on this knowledge base to ensure a continued tradition as a supplier of products to a wide range of naval programs.