Gearboxes help put world's largest liner on course

Edited by the Engineeringtalk editorial team Apr 6, 2004

When the Queen Mary 2 completed her maiden voyage in January 2004 she manoeuvred smoothly and precisely into Fort Lauderdale Harbour in Florida courtesy of a new podded propulsor system.

When the Queen Mary 2 completed her maiden voyage in January 2004 she manoeuvred smoothly and precisely into Fort Lauderdale Harbour in Florida courtesy of a new podded propulsor system.

Central to this four pod system are two steering pods each employing four, three-stage Brevini PDL planetary gearboxes to provide rudder control via a slewing ring drive.

The Queen Mary 2 is the largest passenger ship in the world, at 150kt, a length of 345m and a width of 41m.

It is also the most expensive ship ever built at Eur 870 million euros (US $1.1 billion) and at a height of 72m it is taller than the Statue of Liberty in New York.

Some 3000 workers in the docks of Saint-Nazaire in France took two-and-a-half years to build the ship, welding together 52kt of steel, installing 2500km of electric cable and 500km of piping and laying 250,000m2 of carpet.

More than 250t of paint was used, 2000 bathtubs installed, 5000 stairways and 80,000 lamps.

Apart from sheer size and grandeur, what also sets the Queen Mary 2 apart is its Azimuth podded propulsor system developed jointly by Rolls Royce and Alstom Power Conversion.

Consisting of four pods hung from the stern of the vessel, the system revolutionises marine propulsion, removing conventional shaft drives and replacing them with electric motors, which directly drive the ship's propellers.

Over the last five to six years, podded propulsors have become more and more important.

Particularly on cruise liners, the units have proven to be of major importance as a means to reduce cavitation and vibration and hence have lead to a new standard for a high comfort class of cruise ships.

The podded propulsor system also offers additional benefits such as reduced fuel consumption and remarkably increased manoeuvrability.

On the Queen Mary 2 the latter is achieved by designating two of the four pods for steering: each pod containing a slewing ring gear driven by four Brevini PDL three-stage planetary gearboxes.

The Brevini gearboxes are ideal for this application as they are remarkably compact and lightweight, and require little installation space.

They are also able to deliver high reduction ratios in small packages, and to transmit several times the torque of similarly sized, conventional gear units.

The choice of Brevini gearboxes for the project dates back to before 2000, when Brevini worked with Rolls-Royce in Finland, providing gearboxes for naval engines.

The success of this project meant that, when the system for the Queen Mary 2 was discussed, Brevini could offer proven products and also the requisite experience and technical knowledge necessary to ensure that the crucial gear drive component of the steering pods was completed smoothly without delays.

Prior to their installation, the eight PDL Series gearboxes were subjected to a six week long bench test.

During this test Brevini's customer, Rolls Royce Sweden, was supplied, weekly, with data such as torque and input speed diagrams, number of cycles and hours run, and analysis of oil temperature.

At the culmination of this process the gearboxes were certified by Lloyd's Register.

The calculation methodology and dimensioning used by Brevini was verified by Lloyd's London office, and the assembled and tested gearboxes by Lloyd's Ravenna (Italy) office.

Also tested and certified for use on the Queen Mary 2 are gearboxes from Brevini's Standard series.

These are employed on the winches that lower the Queen Mary 2's lifeboats in the event of an emergency.

The Standard Series gearboxes offer all the space, weight saving and high torque to size benefits of the PDL Series.

Although exposed to the elements, high on the ship's super structure, they are designed to operate reliably, first time, should they ever be required.