Combined diesel and gas (CODAG) is a type of

propulsion Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived from ...

system for

ship A ship is a large watercraft, vessel that travels the world's oceans and other Waterway, navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally disti ...

s that need a maximum speed that is considerably faster than their cruise speed, particularly

warship A warship or combatant ship is a naval ship that is used for naval warfare. Usually they belong to the navy branch of the armed forces of a nation, though they have also been operated by individuals, cooperatives and corporations. As well as b ...

s like modern

frigate A frigate () is a type of warship. In different eras, the roles and capabilities of ships classified as frigates have varied. The name frigate in the 17th to early 18th centuries was given to any full-rigged ship built for speed and maneuvera ...

s or

corvette A corvette is a small warship. It is traditionally the smallest class of vessel considered to be a proper (or " rated") warship. The warship class above the corvette is that of the frigate, while the class below was historically that of the sloo ...

s. Pioneered by

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

with the , a CODAG system consists of

diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...

s for cruising and

gas turbine A gas turbine or gas turbine engine is a type of Internal combustion engine#Continuous combustion, continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas gene ...

s that can be switched on for high-speed transits. In most cases the difference of power output from diesel engines alone to diesel and turbine power combined is too large for controllable-pitch propellers to limit the rotations so that the diesels cannot continue to operate without changing the gear ratios of their

transmission Transmission or transmit may refer to: Science and technology * Power transmission ** Electric power transmission ** Transmission (mechanical device), technology that allows controlled application of power *** Automatic transmission *** Manual tra ...

s. Because of that, special multi-speed gearboxes are needed. This contrasts to combined diesel or gas (CODOG) systems, which couple the diesels with a simple, fixed ratio gearbox to the shaft, but disengage the diesel engines when the turbine is powered up. For an example the new CODAG-propelled s of the

Royal Norwegian Navy The Royal Norwegian Navy () is the branch of the Norwegian Armed Forces responsible for navy, naval operations of Norway, including those of the Norwegian Coast Guard. , the Royal Norwegian Navy consists of approximately 3,700 personnel (9,450 i ...

, the gear ratio for the diesel engine is changed from about 1:7.7 (engine:propeller) for diesel-only to 1:5.3 when in diesel-and-turbine mode. Some ships even have three different gear ratios for the diesel engines — one each for single-diesel and double-diesel cruises, and the third when the gas turbine is engaged. Such a propulsion system has a smaller footprint than a diesel-only power plant with the same maximal power output, since smaller engines can be used and the gas turbine and gearbox don't need that much additional space. Still, it retains the high

fuel efficiency Fuel efficiency (or fuel economy) is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical energy, chemical potential energy contained in a carrier (fuel) into kinetic energy or Mechanical work, w ...

of diesel engines when cruising, allowing greater range and lower fuel costs than with gas turbines alone. On the other hand, a more complex, heavy and troublesome gearing is needed. Typical cruising speed of CODAG warships on diesel-power is and typical maximal speed with switched on turbine is .

Turbines and diesels on separate shafts

Sometimes the engine arrangement of diesel engine and gas turbine with each system using its own shafts and propellers is also called CODAG. Such installations avoid the use of a complicated switching gearbox, but have some disadvantages compared to real CODAG systems: * Since more propellers have to be used, they have to be smaller and thus less efficient. * The propellers of the idling systems cause drag.

CODAG WARP

CODAG Water jet And Refined Propeller (WARP), a system developed by

Blohm+Voss Blohm is a surname. Notable people with the surname include: *Hans Blohm C.M. (born 1927), photographer and author *Hermann Blohm (1848–1930), German businessman and co-founder of German company Blohm+Voss *Irma Blohm (1909–1997), German politi ...

as option for their

MEKO The MEKO family of warships was developed by the German company Blohm+Voss. MEKO is a registered trademark. The portmanteau stands for "''Mehrzweck-Kombination''" (English: multi-purpose-combination). It is a concept in modern naval shipbuilding ...

line of ships, also falls in this category, but avoids the above-mentioned problems. CODAG WARP uses two diesel engines to drive two propellers in a

combined diesel and diesel Combined diesel and diesel (CODAD) is a propulsion system for ships using two diesel engines to power a single propeller shaft. System A gearbox and clutches enable either of the engines or both of them together to drive the shaft. Two advant ...

(CODAD) arrangement, ''i.e.'', both shafts can also be powered by any single engine, and a centerline water jet powered by a gas turbine. The idling water jet does not cause drag, and since its nozzle can be placed further aft and higher it does not affect the size of the propellers.

CODAG-electric

Another way to combine the two types of engines is to connect them to generators and drive the propellers electrically as in a diesel-electric. See Combined diesel–electric and gas (CODLAG) and

Integrated Electric Propulsion Integrated electric propulsion (IEP), full electric propulsion (FEP) or integrated full electric propulsion (IFEP) is an arrangement of marine propulsion systems such that gas turbines or diesel generators or both generate three-phase electricity ...

(IEP). This also permits propeller pods, with the propulsion motors being located inside the pods.

Land vehicles

The Swedish

Stridsvagn 103 The Stridsvagn 103 (Strv 103), also known as the Alternative S and S-tank, is a Sweden, Swedish Cold War, Cold War-era main battle tank, designed and manufactured in Sweden. "Strv" is the Swedish military abbreviation of ''stridsvagn'', Swedish f ...

utilizes a diesel engine for slow cruising and aiming, and a gas turbine for additional power..

References

External links