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PROPULSION UPDATE tion gear vibration requirements will be met. The design phase of low noise gearing focus- es on the five areas noted below. In all cases, the basic design objective is to minimize vibra- tion stimuli. • Rotating Elements - maximize balance, roundness, concentricity; • Gear Casing - ensure rotating element support and parallelism; • Bearings - optimize stability; • Couplings - optimize arrangement and shafting system dynamics; and • Mesh Design - maximize uniformity of load transfer. The benefits of these low noise gearing design features are realized through manufac- The new generation. Reliability. Efficiency. Assured quality. Combining these features, we provide profitability and total economy for offshore support operations. Our optimized supply vessel concept helps you to achieve the essential. Efficient operations. Everywhere. * •IW Aquamaster AZIMUTH THRUSTERS KAMEWA FINLAND LTD., P.O. Box 220, FIN-26101 Rauma, Finland Phone: +358 2 83791, Fax: +358 2 8378 4804. K A M E WAoroup EXCELLENCE IN PROPULSION www.kamewagroup.com ^ Part of the Propulsion Technology Division of Vickers PLC Circle 254 on Reader Service Card 40 Marine Sewage Treatment From The Market Leader The Model 15MX Process Module treats blackwater waste for a complement of 500 people (one of 12 standard sizes available) OMNIPURE™ MSD SYSTEMS The Marine Sewage System of Choice Around the World ^^KSSZ * Compact & Lightweight OMNIPURE'S space saving, fully automatic units treat sewage from 6 to 500 persons allowing discharge in full USCG/IMO compli- ance. > Retrofit Solutions OMNIPURE'S process modules are designed to be retrofitted utilizing existing shipboard tanks and are con- figurable to meet existing space and piping require- ments. ' User Friendly Installation of an OMNIPURE system is sim- ple due to factory pre-wiring. Daily maintenance is mini- mized with no chemicals or biological additives. Sludge removal is also eliminated. ' Large Complements Multiple units may be con- figured to run in parallel for even larger passenger/crew complements. Custom sys- tems are also available for space sensitive retrofits. Exceltec International Corporation (Formerly ELTECH International Corporation) 1110 Industrial Boulevard Sugar Land, Texas 77478 Telephone: (281) 240-6770 Fax: (281) 240-6762 Circle 338 on Reader Service Card turing processes which are highly accurate, consistent and controllable. Mounting System Design and Performance The ultimate objective of the mounting sys- tem design is to minimize the overboard radi- ated noise attributable to the reduction gear- ing. This is achieved by isolating the reduction gear from the ship foundation. Consider three typical mounting system configurations - hard mounted, metallic isolation and elastomeric isolation. Each of these configurations is shown schematically in Table 2, along with some of their performance comparisons. The mounting system selection must consid- er the following: Ship mission requirements; Performance comparison trade-offs; and level of isolation needed to satisfy the system noise performance (determined from noise performance evalua- tions). System noise performance evaluations should be conducted throughout the reduction gear design phase to ensure that noise perfor- mance requirements are satisfied. (Continued on page 54) Table 1 Table 1 Typical Propulsion System Noise Sources and Control Approaches Prime Movers Reduction Gears System Resonance Sources Rotationals & Harmonics • Blade Passing, Fluid Stream Crank-Effort Pulsations Electrical Tones, Power Converter, Pole/Slot Passing Sources • Shaft Rotationals & Harmonics • Mesh Tones • Undulation Tones Sources • Casing & Support Structures • Shafting System • Isolation System Control • Dynamic Balance • Rotor / Stator / Casing Design • Couplings / Bearings • Isolation System - Ship Foundation Control - Dynamic Balance Roundness & Concentricity • Couplings / Bearings • Mesh Design Manufacturing Accuracy • Isolation System • Ship Foundation Control Resonance Frequency Tuning • Stimulus Frequency Avoidance Component & System Damping • Isolation System • Ship Foundation Table 2 Table 2 Mounting System Comparisons Hard-Mounted Compound Metallic Single Stagtomeric System Complexity Low Complexity • Gear Casing Bolted Directly to Ship Foundation • No Shock Snubbers //////// Moderate Complexity Several Isolators Required Shock Required Snubbers Noise Performance - Foundation Vibration Higher Complexity Numerous Mounts Required Shock Snubbers Required Periodic Mount Replacement Higher Overall Vibration No Gear-to- Foundation Isolation • Non-Tunable Design for Given Ship Foundation Lower Overall Vibration • Tunable Design — Can Optimize to Foundation and Ship Mission Significant Attenuation Above Isolator Resonances (Limited by High Frequency Modes) Lowest Overall Vibration • Non-Tunable Design - Standard Application Mounting Frequency Significant Attenuation Above Mounting Frequency (Limited by High Frequency Wave Modes) Maritime Reporter/Engineering News