UNDERWATER RADIATEDNOISEInmartec 2016Hans Petter Knudsen

ANY MOTORIZED VESSEL RADIATENOISE, MORE OR LESS, IN ALL DIRECTIONS

For many years, a lot of effort has been put in to reduce underwater radiated noise from research vessels.

WHAT ARE THE BENEFITS OF REDUCED NOISE?

Echo sounder performance

That is to run as fast as possible with acceptable noise level

(a good echo sounder is less worth with a noisy vessel). This has always been an issue.

Fish avoidance behaviour

Collect fisheries acoustics data under undisturbedconditions. Fish target strength and directivity is essential

Personal comfort level and work environment

Extended lifetime of machinery

10 100 1000 10000 100000

noise

leve

l

Frequency (Hz)

Line-components Continuous spectrum

10 100 1000 10000 100000

F requenc y (Hz )

nois

e le

vell

Composite spectrum

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F requenc y (Hz )

nois

e le

vel

BASIC TYPES OF NOISE

Examples of line frequencies:Blade rate = number of blades x rpm / 60 (~10Hz)Cylinder firing rate (~ 32 Hz)AC current frequency (50 -60 Hz)Reduction gear and ”singing” propeller (~ 800 -1000 Hz)Slot frequency (~ 1400 Hz)

BL = SPL + 10 log W

8090

100110120

130140

150160

10 100 1000 10000 100000

Band level

Spectrum level

Band limits1/3 octave bands

W = bandwidth in Hz

The levels areaveraged in

each 1/3 octaveband (BL)

Spectrum level(SPL) is obtainedby dividing the BL

by thebandwidth in

each 1/3 octaveband.

dB re. 1µPa (1 Hzband)

SPECTRUM LEVEL AND BAND LEVEL

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Frequency10

11,212,514,116

17,820

22,425

28,231,535,540

44,750

56,263

70,880

89,1100

70

80

90

100

110

120

130

140

150

0,01 0,1 1 10 100

dB re

1 µ

Pa

(1H

z ba

nd) @

1m

Frequency (kHz)

ICES 209

Corystes

THE BACKGROUND FOR ICES CRR 209RECOMMENDED BY ICES FISHERIES ACOUSTICS

SCIENCE AND TECHNOLOGY WORKING GROUP (FAST WG).

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TONAL COMPONENTS (LINE FREQUENCIES) IS PARTIALLYMASKED BY AVERAGING IN 1/3 OCTAVE BANDS, BUTTHEY ARE STILL PRESENT !

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AVOIDANCE REACTION THRESHOLD OF COD

SHIPPING, MODERATEWIND SPEED 11 – 16 KNOTS, SEA STATE 3

ECHO SOUNDERS

HERRING

ICES CRR 209 ASSUMES AVOIDANCE REACTION THRESHOLD OF COD IS 30 dB ABOVE THE HEARING THRESHOLD

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ICES 209 LEVELS AT 20 m

THE PROPOSAL WAS ADAPTED TO THE AVOIDANCE REACTION THRESHOLD OF COD AT 20 M DISTANCE.

10

20 m

11 knots

VISUALIZATION OF THE REQUIREMENT ICES 209 SETS

Undisturbed cod ?

SUMMARY (FROM ICES CRR 209)

Status in 1995

Many vessels built or used for fisheries research do not have a noise specification.

Fisheries research vessels are being built with high underwater radiatednoise levels

Controllable pitch propellers are incompatible with the noise requirements for research vessels

Diesel-electric propulsion has the best capability for low noise levels and has other advantages

Status in 2016

This is not true in 2016

This is not true in 2016

There has been a development in propeller technology since 1995

This is still true in 2016, but the price is also still high

«System's may be DC/DC, AC/DC or AC/AC. The first two options can provide smooth control from very low creeping speed up to full power and the same may be achieved with AC/AC systems following the introduction of the cycloconverter principle, although this has yet to be proved. No data appear to be available for the radiated noise levels of vessels using this form of propulsion»

CONCLUSIONS FROM ICES CRR 209:

The new RV Dr. Fridtjof Nansen, scheduled for deliveryNovember 2016 has AC propulsion motors.

FISH AVOIDANCE OF RESEARCH VESSELS AND THE EFFICACY OFNOISE-REDUCED VESSELS: A REVIEW

Alex De Robertis and Nils Olav Handegard (2012)

“Given the investment in noise reduced research vessels, there have been surprisingly few studies testing if noise reduction of vessels in fact reduces fish avoidance reactions. The sparse literature on this topic shows no clear evidence that this has been achieved.”

SILENT VESSELS ARE NOT QUIET

From: ”Silent research vessels are not quiet” JASA Express LettersEgil Ona, Olav Rune Godø, Nils Olav Handegard, Vidar Hjellvik,

Ruben Patel and Geir Pedersen.Institute om Marine Research, Bergen

Conventional propulsion system Noise reduced vessel

RV Johan Hjort

RV G.O. Sars

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SILENT SHIPS DO NOT ALWAYS ENCOUNTER MORE FISH (REVISITED):COMPARISON OF ACOUSTIC BACKSCATTER FROM WALLEYE POLLOCKRECORDED BY A NOISE-REDUCED AND A CONVENTIONAL RESEARCH VESSELIN THE EASTERN BERING SEA

Alex De Robertis* and Christopher D. Wilson (2011)

MF @ 50 m

A noise reduced vessel comparet to a rather noisy vessel

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UNDERWATER RADIATED NOISE, MEASUREMENT (NOISE RANGING) AND VERIFICATION METHODS

Several standards for noise measurement procedures exist:

• NATO STANAG 1136, 1995• DNV GL Silent class notation, 2010• ANSI/ASA S12.64 – 2009 (Part 1)• ISO PAS 17208 – 2012 (slightly modified version of ANSI/ASA S12.64)• Bureau Veritas, Underwater Radiated Noise (URN), Rule Note NR 614 (use

mathematical tools to remove background noise)

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PUBLICATIONS WITH LEVELS REQUIREMENTS

Two publications specify max levels:

• ICES Cooperative Research Report 209, ”Underwater Noise of Research VesselsReview and Recommendations”,1995.

• DNV GL Silent class notation, 2010. (part of ”Rules for classification of ships, newbuildings”. This notation specifies maximum levels of URN for a selection of vesseltypes:

• SILENT – A – Vessel using hydro-acoustic equipment• SILENT – S – Vessel engaged in seismic research activities• SILENT – F – Vessel performing fishery activities• SILENT – R – Vessel engaged in research or other critical operation• SILENT – E – Any vessel wanting to demonstrate a controlled environmental noise

emission.

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DNV GL COMFORT CLASS

AQUO (Achieve Quieter Oceans by shipping noise footprint reduction)This is a collaborative research project supported by the European Commission an one WP is to develop a measurement standard, also useful in shallow waters.http://www.aquo.eu/

RULES AND PROJECTS AIMING FOR REDUCTION OF URN

Eurofleets2: Guidelines and recommendations for ship design on noise and vibration reduction 03 December 2014, version 1.3

CONCLUSIONS AND RECOMMENDATIONS

• The grade of noise and vibration reduction is dependent on thepurpose of the vessel. In any case it is beneficial to have low noise.

• The upper limit for acoustic profile should be defined from what is achieveable within reasonable effort.

• A competent noise consultant should be contracted by the shipyard.• Noise ranging is recommended before acceptance and takeover of the

vessel.• Some marine life avoidance behaviour is poorly understood.