Chantiers de l’Atlantique vice president of projects and ship performance Stéphane Cordier discusses how his yard achieved such impressive energy efficiency gains on the cruise ship Celebrity Edge
Celebrity Edge was delivered to its owner Celebrity Cruises by French shipyard Chantiers de l’Atlantique in October this year. It is an impressive vessel in many ways, notably in terms of its environmental credentials and its demonstrated energy efficiency, achieved in part by an innovative hull shape.
The result of eight years of work by Chantiers de l’Atlantique (formerly STX France), the design of the hull formed part of the initial proposal to Celebrity Cruises and is unique in that it incorporates a bulbous bow within a straight, vertical shape.
The shipyard’s vice president of projects and ship performance Stéphane Cordier said: “We wanted to develop a hull form to reduce the resistance of the ship in sea state, but that did not compromise on calm water resistance.”
This was eventually achieved using a state-of-the-art bulbous bow for calm water, combined with what Mr Cordier explained is the “finer angle achieved with a vertical bow, that means less resistance in waves and less excitation in terms of comfort. The overall result, as demonstrated in the recent sea trials in heavy weather, is remarkable and the response of the ship gives an impression of great seaworthiness.”
The propulsion system includes two 16 MW pods from ABB, in contrast to Celebrity Cruises’ previous smaller Solstice-class ships, where ABB pods of 20 MW have been installed. Mr Cordier explained that this illustrates the reduced power requirements for the ship, leading to fuel savings. The ship also has an air lubrication system installed to save energy.
Propulsion consists of four main diesel engines and a smaller generator, all provided by Wärtsilä. The engines are fitted with scrubbers and selective catalytic reduction (SCR) systems to meet emissions requirements.
Mr Cordier said: “The four diesel engines allow the ship to operate in all circumstances and a fifth smaller one allows the ship to meet the required performance with one main engine down.”
Chantiers de l’Atlantique developed and implemented an engine schedule that features uneven load-sharing between the engines; typically, the number of diesel engines on board to meet propulsion power load and hotel are all run at the same load. But on Celebrity Edge, as Mr Cordier explained, “all but one engine will be running at optimum load in terms of fuel consumption, with one adjusted to match the load requirement. This makes energy consumption more efficient.”
“Instead of using incinerators to dispose of waste, a hydrothermal oxidation solution was used; the waste is put under high pressure and temperature, which disintegrates the material to form water and dust”
The ship also exceeds standard practices in terms of getting rid of waste. Instead of using incinerators, which are a source of gas emissions, the shipyard looked at alternate solutions to eliminate the need to burn refuse. A solution involving hydrothermal oxidation was used, where the waste is put under high pressure and temperature, which disintegrates the material to form water and dust. Placed in the machinery space, the solution consists of two pressure vessels that have to be loaded, in contrast to a continuous process.
This is the prototype installation on a ship and part of an R&D effort co-funded by the EU through the Leanship project.
Mr Cordier said: “This is a higher investment than using incinerators and reduces pollution to a minimum, as incinerator emissions are not counted in the IMO emissions criteria.”
Heat recovery systems are also being extensively used to recover energy from the diesel. “At the end of the process the water is not that hot, but even this is used to heat the swimming pools,” said Mr Cordier.
Mr Cordier emphasised that energy efficiency control was also being applied to variable-speed chillers and fans.
The success achieved by Chantiers de l’Atlantique in reducing energy consumption in part stems from a method developed in its ECORIZON programme, which uses an analytical model of all the ship's energy-consuming systems. This allows the company to simulate the impact of the energy-saving features and make investment decisions based on validated expected returns. On the Edge project, a specific energy gain target, based on a comparison with the previous class of ships, had to be met. The shipyard achieved this, resulting in 20% less fuel per passenger being used compared to the previous Solstice-class vessels.
Magic Carpet concept
Aside from energy efficiency, the design and construction of the ship’s multi-purpose venues are notably innovative in the way they have addressed areas such as noise, vibration and HVAC.
The ship’s Magic Carpet is the world’s first cantilevered platform, reaching heights of 13 storeys above sea level. The Magic Carpet concept came out of a discussion between Celebrity Cruises and Chantiers de l’Atlantique in the shipyard pre-bid phase. Celebrity Cruises insisted that one of the main characteristics of the ship be the access platform to tenders. “They wanted a ship that could go to places other ships of that size cannot call, due to minimum harbour facilities,” Mr Cordier said.
The tender platform needed to handle two tenders at a time, requiring the integration of a very large platform to accommodate two tenders at the waterline; however, this was not without its challenges: “Usually the platform is recessed into the hull, but the size of the platform is so large (30 m by 6 m), that it could not be integrated into the hull at that level,” said Mr Cordier.
And this is where the idea of the Magic Carpet began – to make it more than just a tender platform. “We had the idea of storing it higher and then potentially using it in different higher positions, using it as an outside venue complementing decks overlooking the water as well as a tender platform,” said Mr Cordier.
As such, the platform has four working positions: water level and decks 5, 14 and 15. The platform is moved by a hydraulic system on two main tracks that run vertically to the top of the ship. “We had to make qualifications and risk assessments for all aspects of safety, noise and vibration,” explained Mr Cordier. These risk assessments included examining loads at water level due to the slamming of waves and boat impacts. “We needed stiffness and strength all the way up because it needs to withstand motions and wind loads in storms.”
And in terms of comfort, Mr Cordier said the sea trials have shown that the vibration levels and wind comfort “are remarkable”.
Three other Edge-class vessels will follow Celebrity Edge, with a potential fifth vessel also possible.
Stéphane Cordier, Chantiers de l’Atlantique
- Currently vice president at Chantiers de l'Atlantique; also head of ship performance
- Previously head of naval and specialised projects at Chantiers de l'Atlantique
- Other positions have included chief naval architect at DGA and technical director at the Bassin d’essais des carènes.
- Mr Cordier’s education includes a DSc in fluid mechanics at the George Washington University and an MSc in naval architecture (hydrodynamics) at Massachusetts Institute of Technology