1. Ambient hydro-acoustic noise in the ocean – impact of merchant ships, and developments at IMO
Martin Renilson,
Higher Colleges of Technology
Russell Leaper,
International Fund for Animal Welfare, and
Oliver Boisseau,
Marine Conservation Research International
Date of document – 30 August 2014

2. 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

3. 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

4. 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)

5. 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 Hz range:
3dB in 10 years; and
10dB in 30 years
The European Union Indicator for Good Environment Status will include low frequency underwater noise

6. 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

7. 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

8. 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

9. Practical technologies for reducing noise on merchant ships
Propeller cavitation is main culprit for noisiest ships

10. 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

11. Practical technologies for reducing noise on merchant ships
Strategies for noisiest merchant ships:
Propeller design
Wake flow into propeller
Changes to operating procedure

12. Practical technologies for reducing noise on merchant ships
Propeller design
Strategies:
High skew propellers
High skew, high BAR
No skew
High skew

13. Practical technologies for reducing noise on merchant ships
Propeller design
Strategies:
High skew propellers
Contracted & loaded tip
propeller

14. Practical technologies for reducing noise on merchant ships
Propeller design
Strategies:
High skew propellers
Contracted & loaded tip propeller
Kappel propeller

15. 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)

16. Practical technologies for reducing noise on merchant ships
Propeller Hub Caps

17. Practical technologies for reducing noise on merchant ships
Wake flow into propeller

18. Practical technologies for reducing noise on merchant ships
Wake flow into propeller
Strategies:
Wake inflow devices

19. Practical technologies for reducing noise on merchant ships
Wake flow into propeller
Strategies:
Wake inflow devices
Propeller/Rudder interaction
Rolls-Royce

20. 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

21. 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

22. 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

23. 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.

24. 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.

25. 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.

26. 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.