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ren0312

CODAG vs. COGAG vs. Diesel Ship

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Posted (edited)

What are the advantages and disadvantages of each setup, say if you want to build a 35 knot ocean liner that can cruise at 30 knots all day long, like the QE2 or SS France? Diesel engines are bigger than gas turbines but use less fuel, and take forever to accelerate to 30 knots, gas turbines are smaller but use a lot more fuel. Did the QE2 cost less to run at 30 knots cruising speed using her diesels compared to the QM2 at 26 knots cruising speed? Because if the price of crude oil stays near 30 dollars a barrel for the long term, that might open up some possibilities towards say, Cunard, building a new ocean liner again, since the QM2 is nearing 20 years old.

Edited by ren0312

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Posted (edited)

QE2 retired at 40, not because she was old, but because the SOLAS 2010 regulations would have required her to have a massive rearrangements of cabins (possibly among other things...)  Give it another 10 years before anyone at Cunard/Carnival start thinking about replacing QM2.  EM

Edited by Essiesmom

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CODAG????   COGAG???  Please provide a translation for those of us who are ignorant.

 

DON

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2 hours ago, donaldsc said:

CODAG????   COGAG???  Please provide a translation for those of us who are ignorant.

 

DON

CODAG is combined diesel and gas turbine propulsion. The Princess ships having the imitation jets (Diamond/Sapphhire/Coral/Island) and QM2 have this type of engine arrangement. Other ships also have 

 

COGAG - is multiple Gas Turbines per prop shaft.

 

With Diesel you also have multiple similar size engines and configurations with 2 different sizes of engine. 

 

Diesels are bigger and heavier than gas turbines and have a higher efficiency. When the QE 2 reverted from steam to motor, they installed 9 engines, unfortunately can't remember the size.

 

Regarding diesels taking forever to accelerate, this has not been my experience. On a large high speed ferry with 4- MTU V-20 engines, we went from 0 to 40+ knots very quickly, couple of minutes. The propeller also dictates the acceleration, especially if it is controllable pitch, as the hydraulics control the pitch change speed.

 

For other specifics, I'll let the Chief comment in greater detail.

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2 hours ago, donaldsc said:

CODAG????   COGAG???  Please provide a translation for those of us who are ignorant.

 

DON

 

CODAG = COmbined Diesel And Gas turbine

This is for ships like the Queen Mary 2 - both the main propulsion diesels [four big engines ] and the LM2500 gas turbines directly drive generators. This provides power to the ship's propellors [Rolls Royce 'Mermaid' pods] and all the 'hotel' loads [air conditioning, water makers, lights, elevators, galleys ....] via a husky electrical switchboard.

 

There are advantages to having multiple prime movers - during an eastbound crossing a few years back one of the diesels was offline for scheduled maintenance - but the only impact was burning the more expensive gas turbine fuel ['marine gas oil'] in one of the gas turbines instead of the cheaper fuel used by the big diesels .

 

There used to be some ships that had direct geared CODAG configurations - these were mechanically troublesome. The only one  I recall in US service was the Hamilton Class 'High Endurance' Coast Guard cutter.  

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Posted (edited)

Of cruise ships currently in service, Gas Turbines seem to have been chosen for a few reasons.

 

5 hours ago, TheOldBear said:

There are advantages to having multiple prime movers - during an eastbound crossing a few years back one of the diesels was offline for scheduled maintenance - but the only impact was burning the more expensive gas turbine fuel ['marine gas oil'] in one of the gas turbines instead of the cheaper fuel used by the big diesels .

Indeed, and having different types can be beneficial on a ship like the QM2.  Because power required increases exponentially with speed, a ship like the QM2 takes A LOT of generating capacity to squeak out the last couple knots.  QM2 doesn't need to hit her top speed very often, so lugging around a couple of extra heavy and space-consuming diesels for the occasional need isn't the best solution.  Thus, the designers put a couple of powerful but compact and lightweight gas turbines up on deck.  As you noted, QM2 can fire these up when a higher speed is needed, or when a diesel is down for some reason.

 

Turbines also tend to have better emissions profiles.  Celebrity's Millennium class, for instance, used turbines to meet emission standards in Alaska.  Of course, it seems that other technologies (scrubbers, LNG, etc.) have become more popular in recent years.

 

Edited by AL3XCruise

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21 hours ago, ren0312 said:

What are the advantages and disadvantages of each setup, say if you want to build a 35 knot ocean liner that can cruise at 30 knots all day long, like the QE2 or SS France? Diesel engines are bigger than gas turbines but use less fuel, and take forever to accelerate to 30 knots, gas turbines are smaller but use a lot more fuel. Did the QE2 cost less to run at 30 knots cruising speed using her diesels compared to the QM2 at 26 knots cruising speed? Because if the price of crude oil stays near 30 dollars a barrel for the long term, that might open up some possibilities towards say, Cunard, building a new ocean liner again, since the QM2 is nearing 20 years old.

Uh, the France was a steamship, hence the "SS".  Steamships are even less efficient than diesels or diesel electric, which is why they have been relegated to service where fuel efficiency doesn't matter, like nuclear power, and LNG tankers that burn the boil off cargo.  The acceleration of a ship has absolutely nothing to do with which type of power plant is has, but is determined by a couple of factors;  the mass of the ship that needs to accelerate, the waterplane area of the hull, the block coefficient of the hull, the power available to drive the ship, the torque limitations on the shafting and propeller, the diameter of the propeller, and the pitch of the propeller.

 

As noted above, the USCG had some CODOG power plants (note the second "O" in the acronym) which had diesel engines and gas turbines geared to the same propeller.  They were not only difficult to maintain, but it was found that the fuel requirement of the gas turbine was such that it was rarely used, and therefore the capital investment was not justified.

 

As discussed above, the QM2 has CODAG power plant, where both the diesel engines and gas turbines generate electricity which then drives electric motors in the podded propulsion units (they are not ABB, so not azipods).  Diesel electric propulsion has been found to be the most efficient power source for cruise ships, given their large hotel load requirements.  Multiple generators (several diesel generators, or diesel generators with gas turbines) allow for close tailoring of the generating capacity to power demand, in order to keep the prime movers (diesels or GT) in their most efficient operating range.

 

As noted, gas turbines have better emissions than diesels, but they are less fuel efficient than diesels, especially at lower loads, so they are better suited for applications where they can be utilized exclusively at maximum load.  While many of the cruise ships that have gas turbines installed, and they go beyond Princess and Cunard to RCI, Celebrity, and HAL, were supposed to use the gas turbines while in port in Alaska to reduce emissions, it was found that using them at the low load required by the hotel load on the large turbines installed was not fuel efficient, and those ships that strictly had gas turbines were refitted with diesels to take hotel load when in port.  The gas turbines do provide the benefit of being able to "throttle back" in Alaska (i.e. less propulsion power needed, so lower generating capacity needed) with no change in emissions (diesels have more emissions at lower loads) which is a benefit in environmentally sensitive areas like Alaska.

 

I would say that the QM2 style plant is about the most efficient for a ship that has a requirement for that amount of power (117Mw).  The gas turbines are only needed for the last few knots, so they are always used at full load, and their low weight and small size justifies their inclusion for "occasional" power usage.

 

As for building a new ship to replace the QM2, first off, regardless of what the price of oil is, the cruise lines realize there is a very limited demand for a ship that could do in excess of 24 knots, with it's attendant capital cost in power and propulsion equipment, and in operating cost for fuel.  Secondly, the QM2 engines meet the lowest of the IMO's emissions requirements (tier 1) since she was built before 2011, and any ship that would be built to replace her would need to meet the current tier 3 requirements, with the attendant cost of these improvements in emissions control.

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Posted (edited)
1 hour ago, chengkp75 said:

Uh, the France was a steamship, hence the "SS".  Steamships are even less efficient than diesels or diesel electric, which is why they have been relegated to service where fuel efficiency doesn't matter, like nuclear power, and LNG tankers that burn the boil off cargo.  The acceleration of a ship has absolutely nothing to do with which type of power plant is has, but is determined by a couple of factors;  the mass of the ship that needs to accelerate, the waterplane area of the hull, the block coefficient of the hull, the power available to drive the ship, the torque limitations on the shafting and propeller, the diameter of the propeller, and the pitch of the propeller.

 

As noted above, the USCG had some CODOG power plants (note the second "O" in the acronym) which had diesel engines and gas turbines geared to the same propeller.  They were not only difficult to maintain, but it was found that the fuel requirement of the gas turbine was such that it was rarely used, and therefore the capital investment was not justified.

 

As discussed above, the QM2 has CODAG power plant, where both the diesel engines and gas turbines generate electricity which then drives electric motors in the podded propulsion units (they are not ABB, so not azipods).  Diesel electric propulsion has been found to be the most efficient power source for cruise ships, given their large hotel load requirements.  Multiple generators (several diesel generators, or diesel generators with gas turbines) allow for close tailoring of the generating capacity to power demand, in order to keep the prime movers (diesels or GT) in their most efficient operating range.

 

As noted, gas turbines have better emissions than diesels, but they are less fuel efficient than diesels, especially at lower loads, so they are better suited for applications where they can be utilized exclusively at maximum load.  While many of the cruise ships that have gas turbines installed, and they go beyond Princess and Cunard to RCI, Celebrity, and HAL, were supposed to use the gas turbines while in port in Alaska to reduce emissions, it was found that using them at the low load required by the hotel load on the large turbines installed was not fuel efficient, and those ships that strictly had gas turbines were refitted with diesels to take hotel load when in port.  The gas turbines do provide the benefit of being able to "throttle back" in Alaska (i.e. less propulsion power needed, so lower generating capacity needed) with no change in emissions (diesels have more emissions at lower loads) which is a benefit in environmentally sensitive areas like Alaska.

 

I would say that the QM2 style plant is about the most efficient for a ship that has a requirement for that amount of power (117Mw).  The gas turbines are only needed for the last few knots, so they are always used at full load, and their low weight and small size justifies their inclusion for "occasional" power usage.

 

As for building a new ship to replace the QM2, first off, regardless of what the price of oil is, the cruise lines realize there is a very limited demand for a ship that could do in excess of 24 knots, with it's attendant capital cost in power and propulsion equipment, and in operating cost for fuel.  Secondly, the QM2 engines meet the lowest of the IMO's emissions requirements (tier 1) since she was built before 2011, and any ship that would be built to replace her would need to meet the current tier 3 requirements, with the attendant cost of these improvements in emissions control.

So why are a lot of US Navy ships like the Arleigh Burke, OHP, and Ticonderoga classes COGAG? They do not do 30 knots all day and more often cruise at a slower 15 knots or so, from what I know.

Edited by ren0312

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1 hour ago, ren0312 said:

So why are a lot of US Navy ships like the Arleigh Burke, OHP, and Ticonderoga classes COGAG? They do not do 30 knots all day and more often cruise at a slower 15 knots or so, from what I know.

 

The FFG-7 and DD963 and its derivatives [and I assume the DDG51 - but that is after my time] used two gas turbines [GE LM2500] per shaft, coupled to reduction gear to controllable pitch propellors. Since the turbines only provide propulsion, there is no 'CO' acronym.

 

The FGG's had four, one megawatt diesel generators for electrical loads, including a pair of 350 hp 'outboard motors' or APUs that could be extended from the hull just beneath the bridge. These did not work quite as intended, so I normally had the port one facing forward, and the starboard one facing right and just started and stopped as needed to position the bow for docking.

 

An interesting feature of the controllable pitch propellor is that by flipping the propellor's pitch from full ahead to full astern, you can bring the ship from flank speed to dead in the water within the length of the ship. Every new FFG7 skipper seemed to try that at least once 😉

 

I think the DDG 1000 [Zumwalt class] have an integrated electrical system, allowing for future directed energy weapons. This would be a good thing as the Navy decided to not buy any ammo for the so called 'advanced gun system'.

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1 hour ago, ren0312 said:

So why are a lot of US Navy ships like the Arleigh Burke, OHP, and Ticonderoga classes COGAG? They do not do 30 knots all day and more often cruise at a slower 15 knots or so, from what I know.

Because the Navy wants the small size and light weight of the turbines, and don't care how fuel efficient they are.

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Posted (edited)

Coast Guard operates the 378 high endurance cutters still today altho they are in the process of being phased out ... they've been around for better than 50 years and have an OR plant. For cruising there are two diesels engines, one per shaft, 2 x 3500 shaft HP for a total of 7000. Each shaft also has a gas turbine providing 18,000 hp for a total of 36,000.  Operating on diesel alone speeds of 18 knots (two shaft) are reachable and endurance exceeds 30 days.  Running both turbine at flank speeds of 29 knots or a lil more are reached BUT fuel consumption raises such that the full load is consumed in 3 days .... 21 knots can be achieved running 1 turbine at flank and free wheel the other shaft.  This extends range.   One runs EITHER diesel, OR turbine ... but the cut over can be done 'on the fly' ... in a matter of just a couple of minutes.  <CO MUNRO 00 - 02>  The remaining 378 STILL have the combined plant. (USCGC DOUGLAS MUNRO WHEC-724, Kodiak Alaska is scheduled to be the last to be retired; 9 have been transferred / sold to other countries and continue to be operated by respective Navy/Coast Guard ...)

 

the 210 foot medium endurance cutters (RELIANCE) class were originally built with an AND combined plant. 2000 hp diesel and a small turbine, I believe 1500 hp, where on each shaft. The turbine could be 'added' to the shaft for extra speed. It was soon realized that the speed increase was small while fuel consumption went up dramatically. This small speed improvement coupled with the relatively small fuel capacity resulted in removal of the turbines fairly early on ..before all were built .... and the 'B class' 210 were redesigned to have 2500 hp diesel per shaft and no turbine assist. When the A class was overhauled in the 90's the main engines were replaced with the 2500 hp ones used in the B class.

 

The 378 cutters are being replaced by the 'National Security Cutter' which is an AND design: 

Propulsion:

Combined diesel and gas

2 × 7,400 kW (9,900 hp) MTU 20V 1163 diesels

1 × 22 MW (30,000 hp) LM2500 gas turbine engine

 

220px-CODAG-diagram.svg.png

 

8 of planned 11 have been delivered.

Edited by Capt_BJ

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Posted (edited)
4 hours ago, TheOldBear said:

 

The FFG-7 and DD963 and its derivatives [and I assume the DDG51 - but that is after my time] used two gas turbines [GE LM2500] per shaft, coupled to reduction gear to controllable pitch propellors. Since the turbines only provide propulsion, there is no 'CO' acronym.

 

The FGG's had four, one megawatt diesel generators for electrical loads, including a pair of 350 hp 'outboard motors' or APUs that could be extended from the hull just beneath the bridge. These did not work quite as intended, so I normally had the port one facing forward, and the starboard one facing right and just started and stopped as needed to position the bow for docking.

 

An interesting feature of the controllable pitch propellor is that by flipping the propellor's pitch from full ahead to full astern, you can bring the ship from flank speed to dead in the water within the length of the ship. Every new FFG7 skipper seemed to try that at least once 😉

 

I think the DDG 1000 [Zumwalt class] have an integrated electrical system, allowing for future directed energy weapons. This would be a good thing as the Navy decided to not buy any ammo for the so called 'advanced gun system'.

Interesting, since the newer frigates of European navies like the Saschen class and FREMM use CODAG and CODLAG instead of a pure turbine setup. Although unlike the US they do not have 30+ knot carriers to keep up with.

Edited by ren0312

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1 hour ago, Capt_BJ said:

Each shaft also has a gas turbine providing 18,000 hp for a total of 36,000.  Operating on diesel alone speeds of 18 knots (two shaft) are reachable and endurance exceeds 30 days.  Running both turbine at flank speeds of 29 knots or a lil more are reached BUT fuel consumption raises such that the full load is consumed in 3 days

Like I said about the government not caring about fuel efficiency 😀.

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Posted (edited)

a battle group drags an oiler (or the carrier serves as such) and underway refueling is every third day ... normal operations ....

 

normal UNREP speed is over 20 knots!

 

When deployed with a BG a WHEC was on birds nearly all the time just to keep up . . .

Edited by Capt_BJ

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Posted (edited)

Like I said about the government not caring about fuel efficiency 

 

well, I thought of it as the ship equivalent to a fighter jet's after burner.  Yes it sucks fuel like heck ... but it isn't for 'everyday use' NOR would you put it on a 727 or a Cessna .... 

 

OR

 

should we design a battle tank that gets 40 MPG?  Abrams gets less than 2 mpg (on a turbine btw)

 

OR if your ship was in need of assist and help was available from 2 ships (no helo)

ONE was a CG WMEC 210 which can hit 20 knots on a good day

OTHER was a CG 378 which can hit 30 ...

 

only ONE will respond .....

 

PICK . . .

 

would you care about their fuel burn numbers????

 

*******************

when I was a CG Cutter CO, fuel burn WAS a factor in our evaluations. But not simple miles versus gallons (tons) .... when you were 'tasked', fuel conservation went out the window.  The question became 'do you have a way to get there with the fuel you have and how fast is that?' .... SOMETIMES the orders came in SPECIFICALLY saying to use turbines ... they saw urgency and eliminated any question from MY mind.

 

In other words, when you call 911, do you want the police to worry about their MPG during the response?

Edited by Capt_BJ

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1 hour ago, Capt_BJ said:

In other words, when you call 911, do you want the police to worry about their MPG during the response?

And that is why I said only government vessels will continue to use gas turbines, they don't have to show a profit.

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On 5/25/2020 at 8:28 AM, ren0312 said:

So why are a lot of US Navy ships like the Arleigh Burke, OHP, and Ticonderoga classes COGAG? They do not do 30 knots all day and more often cruise at a slower 15 knots or so, from what I know.

The Tico's, Spruance class DD's (the Tico's were built on Spruance hulls) and Kidd class (modified Spruance class built for Iran) all had/have 4 LM2500 turbines for propulsion. They also had 3 GTG (gas turbine generators) for electrical power. I don't recall any diesel generator. If we lost the load and went dark.....we better hope we had some good GS's and enough compressed air to start the generator that was is in emergency stand by.     And for the record....I never dropped the load while switching from shore to ship power or in the reverse.  Knew a few guys, including the MPA (main propulsion assistant) who got the "Prince of Darkness" pin..but thankfully I never "won" it. 😁

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On 5/25/2020 at 6:52 AM, chengkp75 said:

.As for building a new ship to replace the QM2, first off, regardless of what the price of oil is, the cruise lines realize there is a very limited demand for a ship that could do in excess of 24 knots, with it's attendant capital cost in power and propulsion equipment, and in operating cost for fuel.

But it sure was fun sailing at 31+ knots on the QE2! 

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On 5/26/2020 at 2:24 PM, retafcruiser said:

But it sure was fun sailing at 31+ knots on the QE2! 

 

Remember seeing the QE2 in the builder's yard before launch, certainly an impressive looking ship. Also have many great memories cruising at 30+ kts on SS Oriana.

 

Unfortunately, the QE2 experienced boiler issues, from the late 70's until conversion, as on Oriana and Canberra, we routinely passed her. Once she was re-engined in the mid 80's, with more HP, she was even faster than as built.

 

While 30+ kts on the old liners was impressive, going 45 kts on a large High Speed Craft ferry was even more impressive. Sitting in the Bridge, the action happens real quick.

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7 hours ago, Heidi13 said:

While 30+ kts on the old liners was impressive, going 45 kts on a large High Speed Craft ferry was even more impressive. Sitting in the Bridge, the action happens real quick.

I had the pleasure of riding one of the old hydrofoil ferries between the Hawaiian Islands back in the 70's, that were 45 knot vessels.  Quite a ride.

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5 hours ago, chengkp75 said:

I had the pleasure of riding one of the old hydrofoil ferries between the Hawaiian Islands back in the 70's, that were 45 knot vessels.  Quite a ride.

 

In the late 90's, we built 3 large HSC (240 cars & 1,200 pax) but unfortunately they didn't work out well in our waters. With 4 MTU V-20's (8,000 HP each) with 10 turbos per engine, rather than the lighter and more powerful GT's, we couldn't make the design speed of 37 kts fully loaded. Just before going operational, we took the shipyard workers out for a cruise and put it through the paces. With only fuel and water, we achieved mid 40's at full power.

 

They handled incredibly well and you actually felt the acceleration pushing you back into the seat when opening the throttles. Because of the huge GM, high speed turns didn't list more than a few degrees. At full speed, pushing all jets hard over  brought the stern zipping around at a heck of a rate.

 

However in wind, with shallow draft and considerable sail area, it handled like a beach ball on water. 

 

Rather sad, the day they took the new toys away from us. The Chief Engineer and I lived fairly close, so we car-pooled daily and on boarding the HSC, we both went to the Bridge, as ECR was on the Bridge. Back on the conventional ship, I headed to the Bridge and he went down to the E/R - sad day.

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