MILLENNIUM is the first large cruise ship to use a new propulsion's system: Electric motors feed by Alternators actionated by combinated gaz turbine and steam turbine.
Although some technic isn't the most fascinating and usefull in this forum, I thought few succinct explanations about this system could interest few ones since it will be more and more used in the next buildings and this subject was fewtimes approached here. This is an innovative technical feature and, besides marketing, economy of scale, new activities available, etc..., technic represents an element of the product cruise.
Here,s a picture of one of the two turbines onboard the ship (source: Chantiers de l'Atlantique).

The principal advantages of this system are:
- lower costs of exploitation (lower and easier maintenance)
- reduction of nocive emissions (partially because gaz oil instead of fuel; -80% oxide of azote and -90% oxide of sulphur).
- gain of volume and weight considerable (especially combinated with Azipods; about 900 tons and 50 pax cabins + 20 crew's cabins have been added).
- lower noise and vibrations level, so better comfort and lower probability of failure for several equipments).

Here's a brief working of the system:
Electric power, for propulsion and other needs of the board, is produced by combinated cycle (COGES type): gaz turbines and steam turbines. The two main alternators (25 MW, 3,600 tr/min) are driven by two gaz turbines type LM2500+ built by General Electric. They are stemed from large aircraft ones. Each gaz turbine is equipped with a recuperative boiler (recuperation of the heat issuing of the combustion of gaz in the turbine) which produces the necessary steam to drive a steam turbine (one for the 2 gaz turbines) used to drive 9MW alternator.
The thermic output is then 43% instead of 39% with gaz turbine only.
The previous version of this gaz turbine model, the General Electri LM2500 is available for a long time onboard US Navy ships and other Navys(the LM2500+ has a higher power of 25%). They are very reliable turbines, only one serious breakdown for 48,800 hours functioning according statistics.
For Celebrity, these 48,800 hours would represent 10 years of commercial exploitation of the MILLENNIUM.
More, in case of failure, a gaz turbine could be able to be replaced in 8 hours only. (a spare one is stored onboard).
To obtain the same final power, lot of heavier and bigger Diesel Engines would be necessary, with higher maintenance costs and higher noise and vibrations.
Here, it's interesting to ntice, Gaz turbines are (at this time) only interesting in high speed vessels (like warships or quite fast passenger ships - max speed of 25kts and service speed of 24 kts for MILLENNIUM). This is due to higher price of gazoil instead of fuel for diesel engines and better output of diesels in lower speed too.
Gaz turbine systems, since they use gazoil, has the advantage to avoid pre-heating systems necessary for fuel in classic installation (which must be at 130°C before going within diesels), so a risk of fire.
A quantity 1000 less important of lubrication's oil is necessary too, (so its treatment and elimination of residues too).
Four "small" classic Diesel/alternators are available too for alternative/spare electric power production and sometimes for very low speed/mooring periods.
You can see the location of one of the gaz turbine onboard MILLENNIUM shown by the red arrow I added on the following picture.
(source: Chantiers de l'Atlantique).

Besides the 3 other MILLENNIUM class ships ordered in Chantiers de l'Atlantique, 6 "VANTAGE" class ships, (stemed from MILLENNIUM ones) using similar gaz turbine system are planned at Meyer Werft for RCI/Celebrity group.
That is quite a turn in the search of "always lower costs for companies and lower prices for customers" cruise product.
And as this system presents several other advantages such ecology or comfort...

Bye.

RCCL is the only line to have gone for a
COGAS system (COmbined Gas And Steam) for electric generation. Several other lines have now gone for a COGAD system (CObined Gas And Diesel). Several Carnival Corp ships and even P&O have specified a single gas engine on some of their newbuilds.

So far, I think only the FINNJET (ferry) relies only on gas turbines (COGAG). Interestingly P&O have gone for gas turbines but has yet to specify podded electric drives where the advantages have been now clearly demonstrated.

On past cruises on the Princess line, there were some days when the wind was blowing right that the fumes were so bad that I was unable to lounge on certains parts of the deck. If I understand the COGAS engine correctly, this fumes problem should be eliminated.
Flo

First, thank you to some peoples for their thanks.
Thank you too to other ones for having reacted in this topic.
By reading these replies, I think I should add few precisions about gas turbine systems to put few comments into perspective, and the MILLENNIUM in all of that. I'll try to keep a as succinct description as my post above and not add invading details.

A COGAS (or COSAG) system uses gas turbines (conbustion of the gasoil using the same basic principle than combustion of the kerosen for aircrafts) and geared steam turbines ( using a steam produced by a classical boiler system using gasoil or fuel). Each sort of turbines (gas or steam) work separately and they drive shaft(s) through a gears. Alternator(s) are usually mated to the shaft(s) or gear(s) to produce the necessary electric power for the board (but not for the propulsion). COSAG systems were only used on British military ships "TRIBAL", "COUNTRY" class and BRISTOL entering in service between 1961 and 1973.
A COGAD (or CODAG) system, as Terry said, uses classical diesel engines instead of steam turbines in the example above (COGAS) and diesel engines or gas turbines can work separately too (and sometimes drive separated shafts too). Diesel engines are used at low speed or at mooring and gas turbines for high speeds. CODAG systems were used for the first time for large vessels by Soviets (and they were the pionners for gas turbine systems application in large vessels) from 1961 for their "PETYA", "POTI", and other class laters. The first US Navy ship to use this system was the "RELIANCE" class (Coast Guard) launched on 03-25-1963.
A COGAG system is a combination of several gas turbine only. The first large vessels to use it was the Soviet "KASHIN" class in 1964.
Derivated combinations of different powers gas turbines (COGOG) or with Diesel engines (COGOD or CODOG) are available too.
The first large passenger vessel with COGAG system was, as Terry said, the car-ferry FINNJET of May 1977 which can link the 660 nautical miles between Finland and Germany in 22h30min at the average speed of 30.5 kts. (24,065GRT, 212.8m X 25.4m; 2 Pratt & Whitney gas turbines of 75,000 HP, stemed from DC10 aircraft)
By the way, she's no longer a COGAG ship since the 1981's refit because, due to economical recession in Europe, two 15,500 HP Wartsila Diesel engines were added (areas on the main car deck were sacrified) to reach 18-20 kts and do the same trip in 38 hours during off-peak saison.

From the explanation above and the ones in my previous post, we can see MILLENNIUM doesn't use a classical COSAG system for two reasons.
First, she does not have primary boiler(s)/steam turbine(s) system but only primary gas turbine system and THEN, the heat issued of the combustion of gasoil in the two gas turbines is recuperated to heat a boiler which produce steam for a third smaller steam turbine. This steam turbine is only here to improve the output (43% instead of 39%) of the whole system. This is in fact a sort of COGAG system which is improved and not a COSAG one.
Secondly, compared to a traditional COSAG system, turbines don't drive shafts (through gears) and then propellers directly but alternators to feed the two electric Mairmaid pods.

In my post above, I just wanted to present gas turbines system in general as one with a future (since its advantages are reconized and nearly used by several major cruise companies) and discribe the one of MILLENIUM in particular since she is the pioneer with that system, even if other gas turbine solutions (CODAG for example) will be used by other companies.
It is possible, especially at the begining, few large cruise ships using these system may have few problems.
However they will be logically resolved and only the several advantages of these system will remain.
By the way, at this time, we still don't know if the problems MILLENNIUM had yesterday are directly issued from the gas turbine system (it may be a sub-contractor too) and if yes, the 40-year long use onboard warships in many navies worldwide show us this is not the principle of this system the cause.

GE Powers World’s First Cruise Ship to Use COGES

GE Powers World’s First Cruise Ship to Use COGES

7/7/2000
In a world first, the Millennium, a Celebrity Cruises ship,
started its 14-day maiden voyage July 1 powered by two GE LM2500+
aeroderivative gas turbines. The Millennium uses a combined gas turbine
and steam turbine integrated electric drive system (COGES)
configuration, which reduces environmental impact while creating
additional cabin space and a smoother ride.
“Celebrity Cruises is
incredibly enthusiastic about moving into the new millennium with
a state-of-the-art cruise ship that blends the beauty and grandeur
of turn-of-the-century luxury liners with breathtaking amenities
and breakthrough technological advances,” said James Lomonosoff,
senior vice president of marketing for Celebrity Cruises.
“The COGES ship, using GE’s most advanced aeroderivative gas turbine
technology, will dramatically reduce exhaust emissions, as well as noise and vibration.”

Robert Nardelli, CEO and president of GE Power Systems, said
the COGES configuration allows for a more efficient use of resources.
Energy otherwise lost in the exhaust from the gas turbines is
captured to produce steam from boilers for the steam turbines.
The gas turbine-based system powers electric motors that move the
ship through the water, he said.

The COGES configuration also provides for all on-board power
requirements including ventilation systems, cabin lighting and
entertainment systems. The high power density of the compact
GE aeroderativative LM2500+ gas turbines enables the power
plant to be installed in much less space than a diesel
electric system. This arrangement frees up space for up to 50
additional passenger cabins on each ship, plus additional spaces
for crew member cabins and public areas, Nardelli said.

S&S Energy Products, a GE Power Systems business unit and a
GE Marine Engines Marine Systems supplier based in Houston,
handled the engineering, gas turbine packaging and system
integration for the ship’s system.
Three additional
Millennium-class cruise ships being built for Celebrity
Cruises as well as four Vantage-class ships being built for
sister company, Royal Caribbean International, plan
to use LM2500+ gas turbine-generator sets for main propulsion and on-board power.

The first start-up of the gas turbines on the Millennium ship
took place in January, and sea trials completed in April.
A naming ceremony was held for the ship June 26 in South Hampton,
United Kingdom. Chantiers de l'Atlantique in St. Nazaire, France,
built the 91,000-ton Millennium ship. It measures 964.6 feet
long and 105.6 feet wide and has a cruising speed of 24 knots.
With 11 guest decks, the ship can carry 1,950 guests and 999 crew members.

Edited by April C. Murelio
editor@poweronline.com