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RENK on the International Exhibition SMM 2006, September 26-29, 2006, Hall A3 – Booth No. 100
Marine Propulsion Systems:
RENK is World Wide Leader in Combined Plants

Mechanic Systems have been known for marine propulsion for decades. Prime movers like diesel engines, gas turbines or, in former times, steam turbines are mechanically linked to the propeller, using a reduction gear in most cases.

Combined Mechanic Systems using different prime movers for different power requirements have been introduced especially for modern military application, like frigate propulsion systems. There are CODOG-Systems (COmbined Diesel Or Gas turbine), CODAG-Systems (COmbined Diesel And Gas turbine) and COGAG-Systems (COmbined Gas turbine And Gas turbine).

Electric Propulsion Motors show advantages with respect to noise behavior. The propeller is operated by an electric motor, directly or via a reduction gear. The electric power is provided by a separate generator, driven by a diesel engine or a gas turbine. Such generator sets can be flexibly located in the hull and isolated to prevent structure borne noise from being transmitted to the hull.

Parallel Hybrid Systems combine most benefits of electric and mechanic propulsion. With a CODLAG-System (COmbined Diesel eLectric And Gas turbine) a gas turbine and an electric motor are used for propulsion thruogh a combining gear.

With Series Hybrid Systems main propulsion is done by an electric motor where the power is provided from different sources.


CODOG (COmbined Diesel Or Gas turbine)

In the 80ies and 90ies, RENK delivered more than 60 CODOG gears amongst others for major NATO-fleets, e.g. Germany, Turkey, Greece, and Portugal, see figure 2. All class F122 and F123 Frigates of the German Navy are equipped with such propulsion systems. With two independent plants -port and starboard- diesel engines and gas turbines are operated alternatively according to the required propulsion power. Automatic overrunning clutches provide trouble free change over between the operating modes, a multi disk clutch allows to engage the diesel engine to the standing still propeller.


CODAG (COmbined Diesel And Gas turbine)

Based on the concept of the CODOG plants, CODAG allows to use of all prime movers simultaneously. The first modern CODAG plant was delivered by RENK for the German frigate class F124, see figure 3. The diesel engine speed for operation with and without gas turbine is adjusted by a multi stage input gear. A cross connect gear, which connects the main reduction gears, transmits the power of the gas turbine in equal shares to the propellers. Moreover, both propellers can be operated by one diesel engine only. A similar configuration is found on the new “National Security Cutters” of the US Coast Guard, because the Americans were convinced by this “proven in service” concept.

With the 4 corvettes of the South African Navy, the gas turbine drives a central booster over a separate “locked train” two-stage reduction gear. The diesel engine gears are linked by a cross connect gear and feature three reduction ratios. Hereby, they can perfectly be adjusted to the referring operating conditions.


COGAG (COmbined Gas turbine And Gas turbine)

COGAG combines two gas turbines for individual or common propulsion of one water jet of propeller. For the propulsion system of the Skjold class vessels of the Royal Norwegian Navy, a system with the world wide highest power density is applied, see figure 4. The power of two high speed Pratt&Whitney gas turbines (16,000 and 20,000 rpm) is transmitted via SSS overrunning clutches to the common output on one water jet. Envelope and minimum weight of only
3.6 tons per gear unit are relevant factors for the actual configuration.

For big aircraft carriers, COGAG plants are used as well. As a most recent example, RENK will deliver two 80 ton ship sets for 2 gas turbines LM2500 on each propeller to the Indian Navy.


CODLAG-Systems (COmbined Diesel eLectric And Gas turbine)

Figure 5 shows the conceptual CODLAG propulsion plant for the German class F125 frigate. Comprising a cross connect and two main reduction gears, it has been derived from CODAG applications. For loitering and cruise operation, the electric motors have sufficient power for propulsion and feature lowest noise emission. For higher speed requirements, the gas turbine takes over, providing the favorable efficiency of the mechanical drive. For sprint speed, all prime movers can operate simultaneously. To this end, the electric motors are engaged by a new designed clutch system.

Also for the French-Italian „FREMM“ project a similar solution has been proposed.


Extraordinary Features of the RENK Gear Technology

All described gear arrangements show features of RENK technology which are essential for reliable and low noise operation. Double helical gears which have been developed to perfection by RENK over many years with respect to low noise, are used with all applications. To further reduce noise radiation, elastic mounts may be provided. SSS overrunning clutches or multi disk clutches out of RENK’s own production are operated and guarded by modern programmable control systems, which also have been developed by RENK. Finally, RENK gear systems are adjusted to specific ship yard requirements to perfectly fit the complete propulsion concept.



Figure 1:
Schematic Overview of Different Marine Propulsion Systems




Figure 2:
CODOG Propulsion Plant



Figure 3:
CODAG Propulsion Plant for F124



Figure 4:
COGOG Propulsion Plant for Skjold Class



Figure 5:
CODLAG Propulsion Plant for F125