Page 47: of Maritime Reporter Magazine (April 1998)

PROPULSION UPDATE

Low Noise Mechanical Drive Propulsion System Alternatives

For more than 80 years, mechanical drive propulsion sys- tems consisting of reduction gears and various prime movers have proven their reliability and perfor- mance onboard numerous commer- cial and navy ships. GE has more than 40 years of continuous experi- ence in the design, manufacture and performance/noise testing of

SSN, SSBN, CVN and DDG main propulsion reduction gears, and has reportedly accumulated the largest industrial database of

Naval propulsion system noise per- formance. This database was used extensively in the development of the DDG 51 main reduction gears (MRGs), and yielded a system with noise performance at least 18 dB below specification. Based on this extensive experience, GE believes that mechanical drive propulsion systems can deliver the low noise, high power density, operational flexibility, reliability and perfor- mance needed to satisfy 21th cen- tury Naval ship mission require- ments. Currently, GE has approxi- mately 240 MRGs in service on over 170 U.S. Navy surface ships and submarines. These MRGs com- bine high reliability with high availability (approx. 99 percent), high efficiency (greater than 98 percent), high power density (gen- erally less than 0.1 lb./ft.-lb. output torque), and very low maintenance designs. GE's low noise propulsion gearing satisfies the operational and noise requirements of these ships.

Propulsion System Noise

Sources

The first step in developing a low noise propulsion system is to identify and characterize the noise sources. In general, a propulsion system consists of one or more prime movers (gas turbines, steam turbines, electric motors, diesel engines), reduction gears, and iso- lation systems; a ship foundation; and various auxiliary systems.

The noise generated by the propul- sion system includes contributions from all of these components.

Table 1 (page 40) presents a list of the typical noise sources associ- ated with the principle propulsion system components and identifies general approaches to control these sources. Note that the mounting system (isolation system plus ship foundation) is a control mechanism for all propulsion system noise sources.

Design Approach And Features

Of Low Noise Gearing

The development of low noise propulsion gearing requires a total system approach. Once the noise sources are identified and charac- terized, the design of the reduction gear system progresses along three fronts:

Design and manufacture the gear casing and rotating elements to minimize the amplitude of the stimuli; j

Design the mounting system to isolate gfear-based vibration from the ship foundation; and

Estimate the overall noise per- formance to ensure that the reduc- m SAILOR

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