During June last year the first in a series of four 1,950 passenger-capacity cruise vessel, the Millennium, was delivered by Frances Chantiers de lAtlantique, St Nazaire to Celebrity Cruises, part of Royal Caribbean Cruises Ltd (RCCL).
The second in the series, to be named Infinity, will be delivered during the first quarter of this year, the remaining two by the first quarter next year (2002). The propulsion system for each vessel comprises two Kamewa (part of Rolls-Royce)/Alstom Mermaid pod drives with power supplied by a low emission gas turbine power plant.
Each of the pod propulsors is rated at 19.5 MW and swings a 5.75 m diameter fixed pitch propeller. The propeller acts as a tractor unit located in front of the pod. This ensures an optimum undisturbed water inflow to the propeller, thereby decreasing vibration and noise and also increasing propulsion efficiency.
The electric drive is provided by the latest synchroconverter drive technology supplied by Alstom, which gives the Mermaid system stepless control of propeller speed and hence propeller thrust to provide seamless ship propulsion.
The pod can be rotated through 360 degrees to provide the required thrust in any direction. This eliminates the requirement for stern tunnel thrusters and ensures that these latest generation vessels can maneuver into the smallest of ports without the need for tug assistance. A further benefit is the ability to reduce propeller pressure pulses and propeller-induced noise using the tractor pod concept. Pressure pulses can be the main source of propeller-induced vibrations by using the Mermaid thruster, passenger comfort is considerably enhanced.
However, the Mermaid, too, has had its teething problems. In January, Celebrity Cruises announced yesterday that it was placing the ship Millennium in dry dock for two weeks to repair what it described as an under-performing electric motor in one of the ships two propulsion units.
The drydocking necessitated the cancelation of two one-week Caribbean cruises.
Richard Sasso, president of Celebrity Cruises, said: Although the under-performing motor has no impact on our guests safety or comfort, it has reduced Millenniums maximum cruising speed of 24 knots, to 20.5 knots, and has the potential to affect arrival times in certain ports of call. We want to regain that power as soon as possible and the only way to accomplish this is to undertake this repair
Celebrity said it expected the repair costs to be covered under normal warranty provisions. It said it was reviewing the issue of lost revenue with the manufacturer.
Rolls-Royce and Alstom are currently looking to introduce a range of Mermaid drives starting at 500 kW up to a maximum of 25 MW. Outside of the cruise ship market, three rigs for Sedco Forex will each be driven by four 7 MW Mermaids and fitted with a very efficient DPS 900 dynamic positioning system.