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

Ambient hydro-acoustic noise in the ocean – impact of merchant ships,

and developments at IMOMartin Renilson, ([email protected])

Higher Colleges of TechnologyRussell Leaper, International Fund for Animal Welfare, andOliver Boisseau, Marine Conservation Research International

Date of document – 30 August 2014

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

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

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)

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

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

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

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

Practical technologies for reducing noise on merchant ships

Propeller cavitation is main culprit for noisiest 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


Strategies for noisiest merchant ships:1. Propeller design2. Wake flow into propeller 3. Changes to operating procedure


Propeller design• Strategies:• High skew propellers

No skewHigh skew

High skew, high BAR


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


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


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)


Propeller Hub Caps


Wake flow into propeller

www.largestships.com


Wake flow into propeller • Strategies:• Wake inflow devices


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

Rolls-Roycewww.Sva-potsam.de


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


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


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

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.


• 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.


• 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.

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.

[email protected]

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