The world's largest passenger vessel, the Queen Mary 2, utilizes an online condition monitoring system, including remote monitoring via satellite, to keep all systems go. Instead of the usual large diesel engine driving a shaft and propeller, the QM2's propulsion system is four pods suspended below the ship's hull. Two are fixed and two can rotate 360 degrees. The ship actually doesn't have a rudder or stern thrusters and, instead, steering and maneuvering is achieved by swiveling the two rotating pods.
To detect and give an early warning of any mechanical problems in the four propulsion pods, the condition-monitoring system is vitally important. The system used on the QM2 is a MasCon48 developed by SKF Condition Monitoring Center in Luleå, Sweden.
Each pod contains an electric motor with a small shaft that projects from the pod to provide the propeller mounting. Four diesel engines and two gas turbines drive the generators that provide 118 MW of electrical power, or enough to power a city of 300,000.
The pod monitoring system is designed to measure vibration, temperature, speed and other parameters. It relays any anomalies to maintenance personnel onboard, together with advice for correcting existing or impending conditions. At the same time, the data is relayed via satellite to the SKF Condition Monitoring Centre and the Rolls-Royce Control Centre in Kristinehamn, Sweden.
According to Per-Erik Larsson, manager of product development and technical support at the SKF Condition Monitoring Center, the biggest technical achievement in the pod monitoring system proved to be an enveloping technique used to accurately detect and interpret very weak signals in the noisy environment. The enveloping technique is a mathematical method implemented in sophisticated algorithms that find and amplify weak impulses in noisy signals.
“One of the biggest technical challenges was to run the system on a cruising ship and yet be able to view and control the measurements from land-based locations,” Larsson says.
The satellite transmissions serve two purposes: as a record of the condition of each of the four propulsion pods and for troubleshooting by on-shore propulsion pod specialists in case of trouble.