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Podded propulors have a number of advantages that have made them the propulsion system of choice in the latest generation of cruise ships. They are also, of course, finding growing acceptance in a number of other vessel types, with manufacturers now producing compact versions for smaller vessels. Not too surprisingly, like all innovative systems, podded drives have had their teething problems. These can be expensive, not least in terms of lost passenger revenues. Because cruise lines have to tell large numbers of passengers when cruises are rescheduled, pod problems have received a lot more attention than they might have had they been primarily applied for, say, tanker propulsion. Royal Caribbean International is monitoring the mechanical health of podded propulsion drives on its Voyager and Radiance-class ships with Stress Wave Analysis technology developed by Swantech, LLC, Fort Lauderdale, Fla. A podded drive’s sealed design makes it difficult to monitor for mechanical health. Pods can be costly to maintain, especially if unscheduled downtime is required for repair. Harri Kulovaara, Royal Caribbean’s Senior Vice President of Fleet Operations, says “Swantech’s Stress Wave Analysis technology is the technology that has proven capable of providing a real-time status of the operating health of podded drive systems. Swantech systems enable a ship’s engineers to easily monitor and evaluate a device’s condition, scheduling maintenance at the optimal point.” The technology is based upon ultrasonic sound waves, which are detected and measured in terms of energy content and then analyzed to identify and trend the incidence of damage in a machine. The software analysis tools also pinpoint the source of damage and provide early warning in terms of the progression of damage. This information is used to schedule maintenance before severe damage to the machine, or equipment failure occurs. According to Joseph E. Carpenter, Jr., President and CEO of Swantech, Stress Wave Analysis technology has demonstrated its superiority over other condition monitoring technologies available for podded drive system mechanical health monitoring. “SWAN technology is proving to be an extremely cost-effective prognostic maintenance system for podded design propulsion systems,” he says. SWAN technology also instantly assesses the severity of a problem. Sensors are placed at key points, based on structural paths to components of interest, such as bearings and shafts. The amount of stress wave energy detected by each sensor can be viewed real-time and is stored for historical trending.
Data from healthy drives establishes health-indicating color zones (green, yellow, and red) for tracking the operating history of a drive. Even minimally trained operators can quickly and reliably determine a drive’s health by looking at the stress wave energy relative to the color zone.
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