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Passenger Ship Technology

Passenger Ship Technology

STX France unveils energy-savings triumph of Symphony of the Seas

Mon 09 Apr 2018 by Rebecca Moore

STX France unveils energy-savings triumph of Symphony of the Seas
Symphony of the Seas undergoes last minute touch-ups before its delivery (Credit: Royal Caribbean)

STX France reveals the challenges and considerations behind building the largest cruise ship in the world

Symphony of the Seas has been delivered to owner Royal Caribbean International – not only is it the largest cruise ship in the world but also, alongside sister ship Harmony of the Seas, it is over 20% more energy efficient than the rest of the Oasis-class ships.

STX France vice president of projects and ship performance Stéphane Cordier told Passenger Ship Technology about the challenges of building the largest cruise ship in the world and about the techniques used to achieve such energy savings.

At 228,000 gt, it beats its predecessor Harmony of the Seas by just 1,000 gt to be crowned the largest cruise ship in the world.

Mr Cordier said “It is slightly larger than Harmony of the Seas because we added some staterooms towards the aft, meaning that 5 m have been added to the ship’s superstructure, compared to Harmony of the Seas.” Symphony of the Seas has 2,759 staterooms and capacity for 6,800 passengers.

The other main difference between the two ships is that the speed and power performance has been improved. Mr Cordier explained “At the reference speed sea trial of Harmony, we were a little bit surprised by the result because, although it was quite an improvement on the previous Oasis ships, we felt that we could have done even better.”

On closer examination, the STX team worked with ABB to optimise the pods running conditions and Symphony was able to surpass the performance of Harmony and achieve more speed at less power.

Another difference between Symphony of the Seas and Harmony of the Seas is the Solarium, which has been extended by including another deck level and adding a double-storey space between two of its restaurants.

Surpassing energy efficiency standards

Energy efficiency was a huge factor for the ship and Mr Cordier explained how the ship and its sister Harmony became more than 20% more energy efficient than the other Oasis-class ships. 

“The whole hull form was changed to improve resistance,” he said. Furthermore, the vessel has been fitted with an air lubrication system, which was first used in the cruise industry on Quantum of the Seas. It generates a stream of air bubbles that are driven beneath the hull, creating a layer of air that allows the ship to glide more easily through the water, thus improving energy efficiency and improving fuel consumption by 7-8%. The air layer also reduces excitation from the propellers, which cuts noise and vibration levels in the aft part of the ship.

Another important element for energy efficiency is that a steam turbine is used to recover waste heat from the engines and convert it into energy to power aspects of the hotel load, such as laundry. The 2 MW unit was provided by Japanese company Shinko, but STX France created the whole steam turbine package, which included STX France’s patented heat recovery system, which generates heat from the diesel engine’s cooling system. This system not only reduces the need of oil fire boilers, it also uses the excess heat to provide significant free electrical power output through the steam-powered turbine.

Mr Cordier explained that the ship’s size was beneficial when it came to installing a steam turbine. “It was possible because of the scale of the ship – on a smaller ship it is difficult to justify due to the cost of investment which is less favourable, but on this ship it makes sense and is quite unique.”

Symphony, like sister ship Harmony, has been fitted with a ducktail at the aft of the ship offering a lower resistance through water and reducing the energy required to reach the same speed.

Symphony of the Seas has also had scrubbers inserted to meet the new emission regulations for SOx. Mr Cordier said “That is not a small item because there is a lot equipment to be fitted in the casing; a large volume is involved and this puts constraints on the upper decks, with the various machines associated with it. For example, the power of the pumps for seawater circulation is above 1 MW, so that is a big system in the machinery space.”

Two Wärtsilä  hybrid scrubber systems are installed within the funnel casings. The Wärtsilä system has the flexibility to operate in both open and closed loop mode, using seawater to remove SOx from exhaust gases.

The engine configuration consists of three engines in each of the two enginerooms. Wärtsilä supplied the 12- and 16-cylinder 46F series engines. Mr Cordier commented “This is a high number of engines for today, it offers a lot of flexibility and in case one goes down, the ship can maintain normal ship operation.”

He added that the ship was designed to be “very redundant”, which is why it has six engines, due to the number of people on board. It is also why it has

three pods; there is a problem with one of them the ship can continue its programme. “It means that the ship is very reliable in terms of scheduling,” Mr Cordier said. He added that the use of pods was the preferred solution for minimising fuel consumption. “Their main advantage is that they do not have shaft lines and rudders, which reduces the resistance of the ship. They have a good efficiency in themselves.”

Weight challenge

While both Symphony and Harmony are bigger than the other Oasis-class vessels with more systems on board, its weight is very close to theirs, which was achieved through a weight saving programme. Originally 1,000 tonnes was added to the ship due to the increase in systems and size of ship, but STX France was able to cancel out this added weight.

“We looked at everything, from the structure to the choice of materials and to many minor things; each trade had targets to meet. It was challenging as it was a very short timeframe, and we had to work on many different aspects to achieve this gain,” Mr Cordier said.

He singled out insulation technology as an example. “One big item [in terms of weight] was the insulation technology. We kept this weight down by only including what was necessary and choosing the lightest materials.”

The ship is the first to be granted SILENT-E class from DNV GL for its low level of underwater noise. This acknowledges the fact that the ship has a silent mode of operation where the underwater noise generated is below a published criteria to avoid disturbing marine life. Accordingly, this notation will enable Symphony of the Seas to sail in waters which are restricted to low noise vessels which have a minimum impact on the environment.

Mr Cordier said that this technical performance, which is the result of STX France’s Ecorizon research and development programme, opens the way to the attribution of the SILENT-E notations to future deliveries and vessels already in operation.

Synthetic flooring specialist Bolidt has launched a world-first glow-in-the-dark decking material that harvests and stores solar energy during the day to provide luminosity by night, which has been used on both Symphony and Harmony. It is called

Bolideck Glow and offers energy efficiency savings by reducing lighting requirements. When used outside, it can also harvest energy, storing solar energy generated by day that can be converted into exterior lighting at night. It could also bring safety benefits, Bolidt points out, by illuminating escape routes and signage, as the luminous material ensures decking areas remain highly visible in the dark.

In both cases, the product was installed in a 350 m2 area at the top of the 10-deck Ultimate Abyss slide (outside), which will be used in the dark as well as in daylight.

Wärtsilä has supplied its NACOS Platinum navigation and dynamic positioning system for the bridge, featuring highly advanced integrated navigation technology. Wärtsilä Funa International has supplied electronic and automation solutions including onboard CCTV, a house light dimming system for all public venues, a dimming system for suites and an LED wall for the theatre.

STX France will start work on the next Oasis-class ship this year, and there are options for two more vessels.


Stéphane Cordier, STX France

Stéphane Cordier has been vice president at STX France for three and a half years. Previous to this, he was head of naval and specialised projects at the shipyard. He is also head of ship performance, with responsibility for newbuild performance in terms of weights and stability, hydrodynamics, noise and vibration. Previous positions include chief naval architect at DGA and technical director at the Bassin d’essais des carènes. His education includes a DSc in fluid mechanics at the George Washington University and an MSc in naval architecture (hydrodynamics) at Massachusetts Institute of Technology.


Symphony of the Seas

Registered tonnage: 228,000 gt

Length: 362 m 

Beam: 66 m

Height: 70 m

Cabins: 2,759 passenger cabins

Passenger capacity: 6,800

Crew: 2,000

Decks: 18


Major suppliers





propulsion Azipods 

Autronica Fire and Security

fire protection systems 

Dorint Door International

door equipment




life rafts


bathroom/toilet fittings 

Henry Vacuums

vacuum cleaners 

Indel B

stateroom accessories (safe, minibar etc)





MTU Friedrichshafen

emergency generator

Premaberg Manufacturing

filtration systems

Puzzle Break

games room

Rain Bird Corp

plant care system

Robos Cruise Furniture

deck furniture




fire safety doors 


onboard display screens


main generator steam turbine

Schneider Electric

electrical plugs, charging sockets, light switches 

Spark Cooperative

Ultimate Abyss Slide (design)

Wave Loch

Flowrider water attractions

Wärtsilä Finland

onboard generators, navigation, dynamic positioning, scrubbers, CCTV systems

Vetrotech Saint-Gobain


Viking Life-saving Equipment

passenger evacuation chutes

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