Ambient hydro-acoustic noise in the ocean

1
Ambient hydro-acoustic noise in the ocean
impact of merchant ships, and developments at IMO

• Martin Renilson, (martin.renilson_at_hct.ac.ae)
• Higher Colleges of Technology
• Russell Leaper,
• International Fund for Animal Welfare, and
• Oliver Boisseau,
• Marine Conservation Research International
• Date of document 30 August 2014

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Contents

• The problem of underwater noise pollution from
  shipping
• International recognition of the need to address
  the problem
• Action by IMO
• Key aspects of the shipping noise problem
• Practical technologies for reducing noise on
  merchant ships
• Research needs and recommendations
• Concluding remarks

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The problem of underwater noise pollution from
shipping

• Documented increase in ambient noise across
  oceans in recent decades of 20dB
• Affects all marine life with sensitive hearing
• many fish species, and
• marine mammals
• For many species, sound is most important sense
• Underwater noise pollution causes
• displacement
• stress
• masks sounds used for communication and finding
  food

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• The main frequencies from shipping noise overlap
  whales, dolphins, fish, seals and sea lions, but
  particularly the large baleen whales such as fin,
  blue, right and humpback (Figure taken from IMO
  MEPC 58/19)

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International recognition of the need to address
the problem

• First raised in the 1970s, but serious attention
  only in recent years
• The International Workshop on Shipping Noise and
  Marine Mammals in 2008 target of a reduction in
  shipping noise levels in 10-300Hz range
• 3dB in 10 years and
• 10dB in 30 years
• The European Union Indicator for Good Environment
  Status will include low frequency underwater noise

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Action by IMO

• In 2008 IMO MEPC added Noise from commercial
  shipping and its adverse impact on marine life
  as a high priority item
• The IMO correspondence group was tasked with
  developing non-mandatory guidelines
• ship-quieting technologies
• potential navigation and operational practices

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Key aspects of the shipping noise problem

• Little attention to underwater radiated noise in
  ship design and construction to date
• Noise output may vary substantially due to
  otherwise relatively minor changes
• ballast
• trim
• propeller damage
• speed
• controllable pitch settings

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Key aspects of the shipping noise problem

• Quieting relatively few of the loudest ships is a
  potential way to efficiently reduce the overall
  contribution of shipping noise to the global
  ocean noise budget
• noisiest 10 of vessels cause the majority of the
  noise pollution
• Mandatory Energy Efficiency Design Index (EEDI)
  introduced by IMO presents an opportunity to
  address noise reduction alongside increased
  efficiency

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Practical technologies for reducing noise on
merchant ships

• Propeller cavitation is main culprit for noisiest
  ships

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Practical technologies for reducing noise on
merchant ships

• Propeller cavitation is main culprit for noisiest
  ships
• Specialist warship propellers avoid cavitation,
  so are quieter, but reduce efficiency not
  acceptable for merchant ships
• Cavitation cannot be avoided altogether for
  merchant ships but can be reduced for the
  noisiest ones

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Practical technologies for reducing noise on
merchant ships

• Strategies for noisiest merchant ships
• Propeller design
• Wake flow into propeller
• Changes to operating procedure

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Practical technologies for reducing noise on
merchant ships

• Propeller design
• Strategies
• High skew propellers

High skew, high BAR
No skew
High skew
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Practical technologies for reducing noise on
merchant ships

• Propeller design
• Strategies
• High skew propellers
• Contracted loaded tip
• propeller

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Practical technologies for reducing noise on
merchant ships

• Propeller design
• Strategies
• High skew propellers
• Contracted loaded tip propeller
• Kappel propeller

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Practical technologies for reducing noise on
merchant ships

• Propeller design
• Strategies
• High skew propellers
• Contracted loaded tip propeller
• Kappel propeller
• Other specialist propeller types
• Redesign propeller for actual operating condition
  once known special care for CPP
• Propeller hub caps (various concepts)

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Practical technologies for reducing noise on
merchant ships

• Propeller Hub Caps

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Practical technologies for reducing noise on
merchant ships

• Wake flow into propeller

www.largestships.com
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Practical technologies for reducing noise on
merchant ships

• Wake flow into propeller
• Strategies
• Wake inflow devices

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Practical technologies for reducing noise on
merchant ships

• Wake flow into propeller
• Strategies
• Wake inflow devices
• Propeller/Rudder interaction

Rolls-Royce
www.Sva-potsam.de
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Practical technologies for reducing noise on
merchant ships

• Wake flow into propeller
• Strategies
• Wake inflow devices
• Propeller/Rudder interaction

• Improve design to hull form (only possible at
  design stage)
• Consider ballasting and trim for when operating
  in light condition

www.algemeiner.com
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Practical technologies for reducing noise on
merchant ships

• Changes to operating procedure
• Slow steaming may reduce noise output in dB
  roughly proportional to log of speed
• Strategies
• May be necessary to consider redesign of
  propeller for new operating speed
• Revise CPP control law for low speed

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Practical technologies for reducing noise on
merchant ships

• Some technical unknowns
• Effect of modified merchant ship propellers on
  hydro-acoustic noise
• Effect of propeller hub caps on hydro-acoustic
  noise
• Effect of wake flow improvement devices on
  hydro-acoustic noise
• Effect of vessel loading condition on
  hydro-acoustic noise
• ballast, trim
• propeller close to, or piercing water surface

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Research needs and recommendations

• Development of standard method for full scale
  noise measurements
• ISO has been developing a standard for measuring
  underwater noise from ships
• ANSI/ASA agreed a standard in 2009
• Identify noisiest vessels.

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Research needs and recommendations

• Full-scale at sea noise measurements across a
  range of operating conditions and types of
  vessels.
• Independent noise measurements are needed on
  propeller design concepts or devices developed to
  increase propulsive efficiency.

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Research needs and recommendations

• Increased design effort, including model testing
  and CFD analysis for new ships accompanied by
  noise measurements.
• For ships which spend time in ballast, testing
  and measurements should be extended to include
  optimisation of the propeller design and wake
  flow in that condition.

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Concluding remarks

• There is wide agreement that reducing shipping
  noise is necessary, feasible and may become a
  legal requirement in the future.
• We are cautiously optimistic that the noisiest
  ships can be quietened using existing technology,
  whilst improving their propulsive efficiency.
• The recent focus of attention on reducing
  underwater noise and the clearly identified
  research needs provide new opportunities in the
  field of propulsion systems and ship design.
• martin.renilson_at_hct.ac.ae