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
• 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
– Propeller design/modification to
reduce cavitation
B
A
• Hull Design
– Flow noise reduction
– Hull/propeller optimization for uniform wake field
C
D
• On-Board Machinery
– Damping, vibration isolation mounts, & equipment
isolation
• Operational Modifications
– Speed & load variations; Maintenance
*In priority order
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
Multipath
Science and Engineering Solutions
underwater acoustics test and evaluation
Ship Quieting & Speed
 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
Cumulative noise of ship passage
Reduction based on speed
At 35% of
ship’s
operational
speed
From:
McKenna et al. 2013
11
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
Multipath
Science and Engineering Solutions
underwater acoustics test and evaluation
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
Pile Driving with a Sound Shield
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
Noise
Attenuation
Device
Pile
Less noisy
Water
Noisy
Sediment
Noise
Attenuation
Device
Water
Courtesy of:
Per Reinhall, Peter Dahl, Tim
Dardis
Sediment
Pile
Less Noisy
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
HYDRAULIC
HOSE LINES
(900 ft / unit)
8X POWER UNITS
& CONTROL
ROOM
Courtesy of: Bill Ziadie
Drilled Foundations
• Vertical drilling with
excavation machines
• Larger diameters possible compared
Herrenknecht/Hochtief
Solutions
to impact piling
• Continuous noise: broadband
rms SL 160 dB re 1 µPa (117 dB @ 750m),
over 40 dB under German limit:160 dB (SEL) / 184 dB
(peak) @ 750m
• Noise emission mainly below 200 Hz, drill head
10-40 Hz
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 (peak)
@ 750m --in many cases using noise
mitigation methods
10-20 dB reductions
Sound shield surrounding pile cannot
prevent noise radiation from sediment
Avoiding noise is better than reducing it.
Consider alternatives