CODLOG Arrangement

[el_studentino]

I've been reading recently that a CODLOG arrangement is baseline design for the Royal Navy's Type 26 Frigate and wondered if someone could answer a query for me...

I know a little in terms of how the CODLOG operates with a gas turbine and a propulsion motor powered by a diesel engine. From my limited technical knowledge i know that one can only operate at a time but will the propulsion motor not be reversed and turn into a generator when the gas turbine is powering?

I'm guessing that the clutch stops the gas turbine fron being affected by the shaft turning but I can't get my head round how the propulsion motor doesn't cause crazy stuff to happen to the side that supplies it with power

Apologies if it is not clear, I'm just extremely nosey at times

 

[My2Cents]

CODLOG stands for CObined Diesel eLectric Or Gas turbine.

The acronym indicates that the diesel and gas turbine turn generators, and that the propulsion is supplied by an electric motor. Interesting that they go with the or rather than the and, so they are only running one generator system at a time. A CODLAG system would require a smaller gas turbine. Possibly this is to provide redundant supplies, or allows for more load growth by operating it as a CODLAG.

 

[Anixtu]

The acronym indicates that the diesel and gas turbine turn generators, and that the propulsion is supplied by an electric motor.

The GT drives mechanically through a gearbox, only the DGs drive electrically through electric motors.

 

[StobieWan]

Is the motor clutched out when the GT's are running ? And why CODLOG vs CODLAG? Is CODLAG mechanically much more complex or more expensive?

I'm just wondering as the French FREMMS are CODLAG and the Italian ones are CODLOG I believe - what would the driver be for making that decision?

 

[My2Cents]

The GT drives mechanically through a gearbox, only the DGs drive electrically through electric motors.

Can you provide a link for this? It seems an overly complicated and expensive way to do it, unless they are using separate propellers for GT and electric drives.

 

[EnigmaNZ]

The electric motor and GT input into the gearbox and either can be clutched in to drive the ship. GT for high speed, electric for cruise and slow speed antisubmarine search. No more complicated than CODOG as used on many frigates. I believe it was selected to provide very quiet propulsion when hunting submarines at slow speeds, probably getting its power from the smaller quieter auxilary diesels, or even something more exotic like a stirling engine.

 

[StobieWan]

Can you provide a link for this? It seems an overly complicated and expensive way to do it, unless they are using separate propellers for GT and electric drives.

Here y'go - half way down, quotes from various sources.

The Type 26 Global Combat Ship – Equipment | Think Defence

It's actually less complex than CODLAG as there's no need to balance the output of the two systems running simultaneously as far as I can tell so you can optimise each power input for a given speed range - and the diesel side of the Type 26 gives a quiet cruise at a higher speed than Type 23 does, wheras presumably the GT input can be optimised for higher speed running rather than across a wide range of conditions - but I'm guessing here.

 

[Anixtu]

I expect T26 propulsion layout to be similar to the CODLOG French FREMM (Italian FREMM is CODLAG): http://www.dcnsgroup.com/wp-content/uploads/2010/10/6157.pdf Note especially the diagram at the bottom of the last page. (Though the propellers are mislabelled as propulsion motors...)

Electric motors are not clutched to the shaft, nor are they connected through a gearbox, they drive the shaft directly as per T23. I don't know how they deal with the motor/generator issue when running on GT (I'm no electrical engineer), but there is another article that mentions that on the Italian CODLAG version the electric propulsion motors can deliberately function as generators when in GT-only mode.

 

[My2Cents]

Here y'go - half way down, quotes from various sources.

The Type 26 Global Combat Ship – Equipment | Think Defence

Sorry, but it is a dead link for me. However Anixtu’s link is probably similar, so I see how they are doing it.

I expect T26 propulsion layout to be similar to the CODLOG French FREMM (Italian FREMM is CODLAG): http://www.dcnsgroup.com/wp-content/uploads/2010/10/6157.pdf Note especially the diagram at the bottom of the last page. (Though the propellers are mislabelled as propulsion motors...)

Electric motors are not clutched to the shaft, nor are they connected through a gearbox, they drive the shaft directly as per T23. I don't know how they deal with the motor/generator issue when running on GT (I'm no electrical engineer), but there is another article that mentions that on the Italian CODLAG version the electric propulsion motors can deliberately function as generators when in GT-only mode.

Any induction motor can be used as a generator. The only problem is frequency control, so they would need to add some COTS power conditioning equipment, assuming the others aren’t also doing it as well.