Underwater Noise Mitigation for Shipping and Pile Driving Lindy Weilgart, Ph.D.

Ocean Noise Background noise levels doubled every decade for last 6 decades in some areas, mainly from shipping (Andrew et al. 2003; McDonald et al. 2006)

Solution: Ship Quieting propeller cavitation The largest source of noise from large ships is propeller cavitation Cavitation noise is wasted energy  Reduction has possible ancillary benefits of reducing fuel consumption, air emissions, and maintenance costs Navies and fisheries research vessels have long used ship-quieting techniques  Techniques must be adapted for commercial applications

Recent Observations: Small Improvements are Possible & Can be Significant Reducing noise by 6 dB from the loudest 16% of all vessels  60% reduction in ensonified area Merchant ships currently differ by 40 dB between quietest and noisiest vessels  room for improvement Reduction of cavitation levels by 6-10 dB is currently feasible  greater reductions require further research Modeling basin studies/optimization for large commercial ships likely <2% of total vessel cost  insignificant relative to anticipated fuel savings

Ship Quieting  Most improvements can be done at the design stage for new ships vs. retrofitting old ones  Noise has never been a consideration for designing merchant ships  Only the large ships use model basins in their design phase  Only 5% of new ships use prop cavitation model testing during design  To reduce cavitation, need as uniform a flow into the prop as possible, i.e. uniform wake field  Prop needs to be designed for actual operating conditions, not full power

Highly skewed prop reduces noise and vibration Propeller Boss Cap Fins attached to prop hub reduce cavitation Grothues spoilers: curved fins on hull ahead of prop, straighten flow into prop improving efficiency

Ship Quieting & Efficiency  The noisiest merchant ships probably not operating at optimal efficiency  More efficient prop and improved wake flow improving efficiency will also like decrease noise  An increase in efficiency of 5-10% yields an annual savings of $500,000 to $ 2 million From: IFAW 2009, Leaper and Renilson 2012

IMO Recommendations Focus Areas for Quieting*: Propulsion Propulsion – Propeller design/modification to reduce cavitation Hull Design – Flow noise reduction – Hull/propeller optimization for uniform wake field On-Board Machinery – Damping, vibration isolation mounts, & equipment isolation Operational Modifications – Speed & load variations; Maintenance * * In priority order

Multipath Science and Engineering Solutions underwater acoustics test and evaluation Noise Control Maintenance Establish a routine inspection and maintenance program to identify and correct conditions that increase ship noise  Propeller inspection and cleaning –Marine fouling of props causes: –- cavitation onset at reduced speeds –- substantially increases cavitation noise and damage at all speeds –- reduces prop efficiency  Machinery condition –Normal degradation of pumps and other rotating machinery often produce increased vibration and noise levels Courtesy of: Chris Barber, Multipath Science and Engineering Solutions

 Noise reduction efforts should focus on ships with tones, older ships, and reducing vessel speed  Cavitation Inception Speed around 10 kts for most merchant ships  For vast majority of ships, decrease in speed = decrease in noise (exception: variable or controlled pitch props (CPP) with fixed shafts)  Vessel speed reduction should consider cumulative noise, trade-off between SL reduction and time spent in a region Ship Quieting & Speed

11 Cumulative noise of ship passage Reduction based on speed From: McKenna et al At 35% of ship’s operational speed

Multipath Science and Engineering Solutions underwater acoustics test and evaluation Real Time Noise Monitoring Shipboard Noise and Vibration Monitoring system can provide real-time feedback to ship operators on ship noise levels Cost-effective monitoring systems can be incorporated into new design ships or back-fitted to existing ships –Shipboard vibration sensors at noise critical locations: hull above propellers for cavitation noise directly on main machinery noise sources Use vibration sensors together with a one-time ship radiated noise test to get real-time ship noise estimates –Provides both operational guidance and tracking of degradations indicating maintenance may be required Courtesy of: Chris Barber, Multipath Science and Engineering Solutions

Ship Quieting: Needs & Future  IMO Energy Efficiency Design Index (EEDI) and Ship Energy Efficiency Management Plan (SEEMP) should be done in concert with noise reduction  Noise measurements may point to energy efficiency Issues  Model tank testing needs to incorporate noise as matter of routine  Requirement to measure each ship’s noise output  Compare model tank tests with real at-sea measurements of ships in typical operating conditions  Minimize time spent in locations where noise propagates into deep sound channel, i.e. go offshore

Ship Quieting: Needs & Future  IMO guidelines now have checklist for ship designers to have considered noise  Compliance through port authorities, ship classification and green certification programs, regs, economic incentives  Menu of quieting options for future consideration and action  Funds for modelling basin research

Courtesy of: Per Reinhall, Peter Dahl, Tim Dardis

Courtesy of: Georg Nehls

Dewatered Cofferdams Baltic Sea 15 m depth Decrease 23 dB (SEL); 19 dB (peak) Courtesy of: Sven Koschinski & Karin Lüdemann

Large Diameter Active Bubbling Curtain Mentrup 2012 (©Trianel GmbH/Lang) J. Rustemeier et al. / ISD 2010 Courtesy of: Sven Koschinski & Karin Lüdemann

Sound Transmission Through Substrate Pile Noise Attenuation Device Water Sediment Less Noisy Less noisy Pile Noise Attenuation Device Water Sediment Noisy Courtesy of: Per Reinhall, Peter Dahl, Tim Dardis

APE’s (American Piledriving Equipment, Inc.) Multiple Linked Hydraulic Vibratory Hammer System (MLHVH) PILE TYPE: STEEL DIAMETER: 44 FOOT (13.5M) PILE THICKNESS:.5” (14MM) PILE LENGTH: 112 foot (34 meters) PILE WEIGHT:200 US Tons (181 metric tons) Courtesy of: Bill Ziadie

HAMMER 8X POWER UNITS & CONTROL ROOM HYDRAULIC HOSE LINES (900 ft / unit) Courtesy of: Bill Ziadie

Drilled Foundations Vertical drilling with excavation machines Larger diameters possible compared to impact piling Continuous noise: broadband rms SL 160 dB re 1 µPa ( m), over 40 dB under German limit:160 dB (SEL) / 184 dB 750m Noise emission mainly below 200 Hz, drill head Hz Herrenknecht/Hochtief Solutions Courtesy of: Sven Koschinski & Karin Lüdemann

Conclusions for Pile Driving Quieting  It is possible to meet the German legal requirements--160 dB (SEL), 184 dB 750m --in many cases using noise mitigation methods  dB reductions  Sound shield surrounding pile cannot prevent noise radiation from sediment  Avoiding noise is better than reducing it. Consider alternatives