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Marine & Floating Plant Newsletter Machinery Alignment Expertise The alignment of machinery is al- ways a critical step to a successful problem free instal- lation. This is espe- cially true aboard ship as the entire platform flexes in a seaway. Dredges present unique alignment issues. No other type of vessel loads and unloads its cargo 7-10 times per day experiencing re- peated hull bending such as hopper dredges. Pipeline dredges are constructed on barge type platforms with extremely robust ladders which impart significant forces on the hull resulting in deflections that must be an- ticipated in the machinery alignment procedure. The alignment procedure is critical as is the flexible cou- pling selection. Shipyards tend not to have the most modern specialized alignment equipment such as lasers, strain gages, and analysis software to achieve the nec- essary precision. Recent ship- yard contracts have had great success with alignment ex- perts from Aiman Alignment Services and Diehl Engineer- ing, websites below. Just being within coupling tolerances is often not good enough. The magnitude of deflections on either side of perfect alignment are often unknown, so the closer to perfect, the better. Aim small, miss small... www.aimanalignment.com www.diehlengineering.com Vinton Bossert 215-656-6850 Vinton.c.bossert@usace.army.mil Motor to Gear Box Alignment Noise & Vibration USCG Navigation & Vessel Inspection Circular (NVIC) No.12-82 “Recommendations On Control of Excessive Noise” contains the Coast Guard’s recommended guide- lines to the U.S. maritime industry for addressing con- ditions of high noise. The effect of noise on hear- ing is a function of the actual noise level, its component frequencies, and the duration of exposure. The Coast Guard has concluded that the most meaningful method of evaluating excessive noise in the maritime industry is by measuring the cumulative noise exposure during the complete 24-hour day. In addition to consideration of the normal work time noise exposure, the 24-hour expo- sure measurement considers the time after exposure to high noise to evaluate whether sufficient quiet time is pro- vided to allow for recovery from temporary threshold shift (an elevation in the lowest level of sound detectable to the ear). The term used to express this measurement is the "24- hour effective exposure level," or Leff(24). NVIC 12-82 pro- vides examples how to calcu- late Leff(24). Each crewmem- ber's Leff(24) should be con- strained to a maximum of 82 dB(A). The maximum Leff(24) can be achieved by any combi- nation of engineering controls, administrative controls or hear- ing protective devices. Examples of engineering con- trols include acoustic insulation on boundaries, isolating ma- chinery vibration from its foun- dation, enclosures around high noise producers, etc. Administrative controls include restricting person- nel’s time in proximity to high noise or limit the time that high noise producing machinery is allowed to run. The difficulty in design is predicting the actual noise level after construction. Many shipyards have sub- contracted with Noise Con- trol Engineering, Inc. in Billerica, MA. They spe- cialize in shipboard gener- ated noise and vibration and the treatment of the same. www.noise-control.com Page 2PDF Image | USACE MARINE DESIGN CENTER Newsletter
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