Combined diesel–electric and gas (CODLAG) is a modification of the combined diesel and gas propulsion 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. A variant, called the combined diesel–electric or gas (CODLOG) system, contains the same basic elements but will not allow simultaneous use of the alternative drive sources.

System

A CODLAG system employs

electric motor An electric motor is a machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a electromagnetic coil, wire winding to gene ...

s which are connected to the

propeller shaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power, torque, and rotation, usually used to connect o ...

s (usually 2). The motors are powered by

diesel generator A diesel generator (DG) (also known as a diesel genset) is the combination of a diesel engine with an electric generator (often an alternator) to generate electrical energy. This is a specific case of an engine generator. A diesel compress ...

s. For higher speeds, a

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 ...

powers the shafts via a cross-connecting

gearbox A transmission (also called a gearbox) is a mechanical device invented by Louis Renault (who founded Renault) which uses a gear set—two or more gears working together—to change the speed, direction of rotation, or torque multiplication/r ...

; for cruise speed, the drive train of the turbine is disengaged with

clutch A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...

es. This arrangement combines the diesel engines used for propulsion and for electric power generation, greatly reducing service cost, since it reduces the number of different diesel engines and electric motors, requiring considerably less maintenance. Also, electric motors work efficiently over a wide speed range, and can be connected directly to the propeller shaft so that simpler gearboxes can be used to combine the mechanical output of turbine and diesel–electric systems. Another advantage of the diesel–electric transmission is that without the need of a mechanical connection, the diesel generators can be decoupled acoustically from the hull of the ship, making it less noisy. This has been used extensively by military

submarine A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or infor ...

s but surface naval vessels like

anti-submarine An anti-submarine weapon (ASW) is any one of a number of devices that are intended to act against a submarine and its crew, to destroy (sink) the vessel or reduce its capability as a weapon of war. In its simplest sense, an anti-submarine weapon ...

vessels will benefit as well.

Integrated electric propulsion (IEP)

A system which uses both diesel engines and gas turbines to generate electricity for electric motors, where there is no mechanical transmission from either to the propellers, is not classified as CODLAG, but as

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) or integrated full electric propulsion (IFEP). Such an arrangement is in use on passenger ships like RMS ''Queen Mary 2'', with a pool of diesel generators for the base load and turbo generators for peak power, and on warships such as the

Royal Navy The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...

Type 45 destroyer The Type 45 destroyer, also known as the D or ''Daring'' class, is a class of six guided-missile destroyers built for the United Kingdom's Royal Navy in the early 21st century. The class is primarily designed for anti-aircraft and anti-missile ...

and the (DDG-1000/DD(X)).

List of CODLAG ships

Type 23 frigate The Type 23 frigate or Duke class is a class of frigates built for the United Kingdom's Royal Navy. The ships are named after British Dukes, thus leading to the class being commonly known as the Duke class. The first Type 23, , was commission ...

(

) *

FREMM multipurpose frigate The European multi-purpose frigate or FREMM (; ) is a Franco-Italian family of warships designed by Naval Group and Fincantieri. This surface combatant is known in France as the ''Aquitaine'' class (17 units planned, of which 9 were later cance ...

(Italian Navy version) * Defence and intervention frigate (

French Navy The French Navy (, , ), informally (, ), is the Navy, maritime arm of the French Armed Forces and one of the four military service branches of History of France, France. It is among the largest and most powerful List of navies, naval forces i ...

) * F125 class frigate (

German Navy The German Navy (, ) is part of the unified (Federal Defense), the German Armed Forces. The German Navy was originally known as the ''Bundesmarine'' (Federal Navy) from 1956 to 1995, when ''Deutsche Marine'' (German Navy) became the official ...

) * ''Pohjanmaa''-class corvette (

Finnish Navy The Finnish Navy ( , ) is one of the branches of the Finnish Defence Forces. The navy employs 2,300 people and about 4,300 conscripts are trained each year. Finnish Navy vessels are given the ship prefix "FNS", short for "Finnish Navy ship", but ...

) * ''Constellation''-class frigate (

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

) * GTS ''Finnjet'' (Finnish

cruiseferry A cruiseferry is a ship that combines the features of a cruise ship and a Ro-Pax ferry. Many passengers travel with the ships for the cruise experience, staying only a few hours at the destination port or not leaving the ship at all, while ot ...

)

List of CODLOG ships

Polar-class icebreaker Polar-class icebreakers , are heavy icebreakers operated by the United States Coast Guard (USCG). These cutters, specifically designed for icebreaking, have reinforced hulls, special icebreaking bows, and a system that allows rapid shifting of ...

(United States Coast Guard) * ''Daegu''-class frigate (ROKN) * ''Chungnam''-class frigate (ROKN) *

(French Navy version) *

Type 26 frigate The Type 26 frigate, also known as City-class frigate, is a ship class, class of frigates and destroyers being built for the United Kingdom's Royal Navy, with variants also being built for the Australian and Canadian navies. The programme, know ...

(Royal Navy, under construction) * ''Hunter''-class frigate (Royal Australian Navy, under construction) * River-class destroyer (Royal Canadian Navy, planned) * ''Wasp''-class amphibious assault ship (USN) * ''America''-class amphibious assault ship (USN) * F110-class frigate (Spanish Navy)

List of IEP ships

* RMS ''Queen Mary 2'' * Wave class tanker (Royal Fleet Auxiliary) * USNS ''Lewis and Clark'' (T-AKE-1) (US Sealift Command) * ''Albion'' class landing platform dock (Royal Navy) *

(Royal Navy) * ''Queen Elizabeth''-class aircraft carrier (Royal Navy) * (US Navy) *

Mistral-class amphibious assault ship The ''Mistral'' class is a class of five landing helicopter docks built by France. Also known as helicopter carriers, and referred to as "projection and command ships" ( or BPC) and "porte-hélicoptères amphibie" (PHA) since 2019, a ''Mistra ...

(French Navy)

References