Ambient hydro-acoustic noise in the
ocean – impact of merchant ships,
and developments at IMO
Martin Renilson, (martin.renilson@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
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
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
Practical technologies for
reducing noise on merchant ships
Strategies for noisiest merchant ships:
1. Propeller design
2. Wake flow into propeller
3. Changes to operating procedure
Practical technologies for
reducing noise on merchant ships
Propeller design
• Strategies:
• High skew propellers
High skew, high BAR
No skew
High skew
Practical technologies for
reducing noise on merchant ships
Propeller design
• Strategies:
• High skew propellers
•
Contracted & loaded tip
propeller
Practical technologies for
reducing noise on merchant ships
Propeller design
• Strategies:
• High skew propellers
•
•
Contracted & loaded tip propeller
Kappel propeller
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)
Practical technologies for
reducing noise on merchant ships
Propeller Hub Caps
Practical technologies for
reducing noise on merchant ships
Wake flow into propeller
www.largestships.com
Practical technologies for
reducing noise on merchant ships
Wake flow into propeller
• Strategies:
•
Wake inflow devices
Practical technologies for
reducing noise on merchant ships
Wake flow into propeller
• Strategies:
•
•
Wake inflow devices
Propeller/Rudder interaction
www.Sva-potsam.de
Rolls-Royce
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
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
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 hydroacoustic 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.
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.
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.
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@hct.ac.ae