213
1 INTRODUCTION
Thehydrofoil(HF)issuperhigh‐speedvesselsandis
animportantvesselinJapanthatconnectstheremote
islandswiththemainlandforshortertraveltimethan
that of ferry and is superior in seaworthiness.
However, in recent years the accidents of the
collision between HF and large cetaceans have
occurredandimmedia
tecorrespondencetoavoidthe
accident is required. Since the HF cruising sound
level at 100m from source had 126.3dB re 1μPa
(source level 146.3±2.6 dB re 1μPa‐m), the sound
level was assumed to be probably too low to make
cetaceansreacttothesound(Y
amadaetal.2012).
The Under Water Speaker (UWS) has been
installed ontheHF for avoiding the collisions with
large cetaceans. However, its effectiveness is still
uncertain.Thus,itisthemostimportantmeasureto
improveeffectivenessofthecurrentUWSintermsof
issue of collision avoidance. In thi
s study, for the
purposeofcollisionavoidanceoflargecetaceansand
HF,thefollowingthreestudiesweremadein order
todevelopthenewsoundofUWS.
1 WeadjustedtheUWSsoundtotheaudiblerange
ofcausalcetaceansonHFroute.
2 We developed the new sound by synthesizing
soundpot
entiallyhascetaceansrepellent.
3 We demonstrated acoustic properties of the new
soundproducedfromtheUWSofthecursingHF.
2 ADJUSTMENTOFTHEUWSSOUNDTOTHE
AUDIBLERANGEOFCAUSALCETACEANS
For development of the effective UWS sound, it is
most important to identify the sound frequency to
Development of the Effective Underwater Speaker
Sound Modulated by Audible Sound Frequency Range
of Large Cetaceans for Avoidance with Ship Collision
H.Yamada,N.Kobayashi,T.Nakashima&H.Kato
TokyoUniversityofMarineScienceandTechnology,Tokyo,Japan
ABSTRACT:The underwater speaker (UWS) has been installedon high speedvessels; hydrofoils (HF) with
low‐noise during their cruises, to avoid sudden collisions with large cetaceans, while its performance has
remaineduncertainbecause of the problem inqualityof theproduced sound.Thus, we developed a sound
source for the UWS by modula
ting the sound based on the audible range of major large cetaceans so as to
increaseitsutilities.Toinvestigatetheaudiblesoundfrequencyrangeofcetacean,wetriedtwoprocedures,(1)
indirect‐estimationfromrelationshipbetweencetaceansaudibilityandvocalizat
ion,and(2)indirect‐estimation
frommeasurementsonthecochlearbasalmembrane.Wealsosynthesizedthetwonewsoundsourceswhich
wecanpotentiallyexpectanavoidancewithlargecetaceans.Throughseveralfieldexperimentswithdeploythe
new sounds we reached a tentative conclusion that the new sound was effective in terms of inducing the
cetaceansʹ av
oidance reaction and would be also expected to be applied to other low‐noise vessels. (Patent
appliedfor,JP2014‐171411)
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 9
Number 2
June 2015
DOI:10.12716/1001.09.02.08
214
effectivelyrepelcetaceans.Therefore, it is necessary
to identify the audible frequency range of cetacean
species which is considered to cause the collision
withvessels.Currently,therearenodirectmeasures
ofaudiblerangeforanylargecetaceansbecausethey
cannot be investigated with conventional
audiometric techniques of psychoacoustical or
electrophysiological analysis. However, the audible
rangecanbeassessedindirectlybythefollowingtwo
procedures,(1)indirect‐estimationfromrelationship
between cetaceans audibility and vocalization, and
(2) indirect‐estimation from measurements on the
cochlear basal membrane. It can be assessed by
vocalization, as to correspond the dominant
frequenciesofthe
vocalization(e.g.calls)tothemost
sensitiveregionofreceptorsysteminvertebratetaxa
(Green and Marler 1979). Alternatively, a
comparativeanatomyapproachistheusefulwayto
estimate the audible range because anatomical
structureofinnerearcorrelatestofrequencyrangein
multiplemammalianspecies(Echteleretal.,1994).
Shakata et al. (2008) and Tsuji et al. (2013)
identified sperm whale (Physeter macrocephalus),
Bairdʹs beaked whale (Berardius bairdii), common
minke whale (Balaenoptera acutorostrata), Brydeʹs
whale (Balaenoptera edeni) and humpback whale
(Megapteranovaeangliae)aspossiblecausalspeciesof
thecollision on the sea
route ofthe HF in Japanese
water.Thevocalizationfrequency range were made
referencetopreviousresearchofspermwhaleinthe
southeastern coast of Chichijima, the Bonin
(Ogasawara) Islands of Japan and Bryde’s whale in
the waters of Kochi on the south western coast of
Japan(Yamada et al.
2012) and humpback whale in
theRyukyuregionofJapan(Maedaetal.2000).This
study estimates the audible range of sperm whale
beaked whale by describing the anatomy used the
Kawamotofilm‐sectioningmethod(Kawamoto2003)
oftheirinnerearsandapplyingthemodeldescribed
byKetten(2000)extendedYamada
etal.2012dataof
common minke whale and Bairdʹs beaked whale
(Table1).
However, since the maximum sensitivity of the
current UWS is 8kHz‐30kHz, sound pressure of
frequencies below 8kHz characteristic tends to
decrease. Therefore, considering the maximum
sensitivityofthespeakershardware,thefrequencyof
the
newUWSsoundwassetat5kHz,themaximum
dominantaudiblefrequencyofthespermwhaleand
the humpback whale that pose a particularly high
collisionrisk(Katoetal.2012),whichisadownward
shift by 1kHz from the currently used frequency
rangeof6‐18kHz.
As far as
the Brydeʹs whale is concerned, the
challenge lies in how to infer its audible frequency
range using the anatomical predictions since its
dominant audible frequency is significantly lower
thanthefrequencyofthenewUWSsound.However,
given that the audible range of the common minke
whale, which belongs
to the same family, is 0.12‐
15.93kHz, it is extrapolated that 5kHz might be fit
wellwithintheaudiblerangeoftheBryde’swhales.
3 SYNTHESIZINGOFNEWSOUNDSFORTHE
EFFECTIVEUWS
Usingorsynthesizingapotentialrepellingsoundfor
cetaceans would be effective for making large
cetaceansavoidancefrom
HF.Forexample,Watkins
(1986)reportedthat cetaceans often react tosudden
or loud sounds of vessel, such as from an engine
starting, a close approach, changes in direction,
putting engine in and out of gear, and propeller
cavitations during reverse or sharp turns. We
synthesizedthetwosoundsources
inordertoinstall
theUWS1)dieselengineshipnoiseoftheJapanese
whale research vessel 2) the clang sound produced
byhittingthemetalpolewithahammer,whichwe
canpotentiallyexpectanavoidancewithcetaceans.It
is described below in detail about the two sounds
thatwere
usedinthesynthesis.
1 Shipnoisewhaleresearchvessel:Weusedahigh‐
passfilterwith0.12kHzforcruisingnoiseatthe
time of the maximum speed (16.7kt, 200rpm) by
theJapanese whale research vessel Yushin Maru
No.2 (747t , 69.6m, Owned by Kyodo Senpaku
Co.,Ltd.)with2
cycleslow‐speeddieselengine.
2 Theclangsoundproducedbyhittingtheametal
pole: We recorded clanging sound by hitting a
metal pole in the water and adjusted the
frequencyandsoundinterval.Forfrequency,we
modulated2.00kHzasanoriginalsoundto5.00
kHz, 8.00 kHz, and
10.00 kHz, and then
alternatelyarranged3frequenciesoftheclanging
sound. This frequency was adjusted with the
maximum frequency of dominant audible
frequencybycausalcetaceansandthemaximum
speaker sensitivity. In addition, for the sound
interval, we also modulated 0.52 second of the
original sound to approximately 0.09
second in
accordance with the interval of whaling vessel’s
diesel knocking sound. The spectrograms and
frequencycharacteristicsofthesynthesizedsound
sourceareshowninfigure1and2.Thefrequency
characteristic was assessed by 1/3‐octave bands
analysis using Avisoft SASLab Pro (Avisoft
Bioacoustics, Germany.Ver.5.2.) because sound
levels in 1/3‐octave
bands are useful in
interpretingnoiseeffectsonanimals.
Table1.Summaryofaudiblerangeofcausalcetaceans.
__________________________________________________________________________________________________
SpeciesDominantaudiblerangebyAudiblerangeby
vocalization(kHz)Anatomicalpredictions(kHz)
__________________________________________________________________________________________________
OdontocetiSpermwhale1.87‐4.78(Yamadaetal.2011)0.29‐47.75
(toothedwhales) Bairdʹsbeakedwhale0.27‐33.09(Yamadaetal.2011)
MysticetiCommonminkewhale0.12‐15.93(Yamadaetal.2011)
(baleenwhales) Baird’sbeakedwhale 0.13‐0.37(Yamadaetal.2011)
HumpbackWhale0.03‐4.80(Maedaetal.2000)
__________________________________________________________________________________________________
215
mV
00
500
-500
1 2 3 4
Time (s)
5
10
Frequency (kHz)
Figure1. Envelope curves (above) and
spectrograms(below) of the new UWS sound source.
Spectrograms were made with a 1024‐point FFT, 75.0%
overlap,andHammingwindow.
0.8
5.0
6.3
8.0
10.1
-25
-20
-15
-10
-5
0
0.05 0.5 5
Normalized 1/3 OB level (dB)
Frequency(kHz)
Figure2. The 1/3 octave‐band spectrum measured of the
newUWSsoundsource.Filter:ANSIS1.11‐2004standard.
Thecharacteristicofthenewsoundsourcewould
be using a potential repelling sound for cetaceans
andsynthesizingaudiblefrequencyfor whales with
collisionrisk(Patentappliedfor,JP2014‐171411).
4 THEEFFECTIVERANGEOFTHENEW
UNDERWATERSPEAKERSOUND
It is necessary to evaluate whether such frequency
characteristicandsound
pressurecanevokeresponse
bycetaceanswhenweplaybackthenewUWSsound
throughHFspeakersduringthecruise.Thereforewe
recordedthenewsoundplaybackedfromHFduring
its cruise at service speed (38‐39kn) from a small
vessel at a distance of 150‐163m. Recordings were
made using
a Aqua Sound modelAQH‐020
(frequencyresponse20Hzto20kHz)omnidirectional
hydrophonehassensitivityofapproximately‐193dB
re1V/μPawith10mcable.Itwasconnectedviapre‐
amplifiers, on a Sony PCM‐D50 digital recorder
(16bit 44.1 kHz). The estimated source levels of
underwaternoise(at1m)ofthe
HFwere calibrated
byTransmissionLossandAbsorptionLoss(Francois
&Garrison1982).
Asaresult,thefrequencycharacteristicindicated
apeakfrequencyat5.0kHz,6.3kHz,8.0kHz,andthe
sound below 8kHz as the maximum speaker
sensitivitywasalsoreproduced(Fig.3).
0.6
5.0
6.3
8.0
130
135
140
145
150
155
160
0.05 0.5 5
1/3octavebandlevels(dBre1μPaat1m)
Frequency(kHz)
Hydrofoil(1)
Hydrofoil(2)
Figure3. The 1/3 octave‐band spectrum measured of the
playbacks new UWS sound source from the two types
operationalHF.
The frequency range overlapped with audible
rangeofcetaceanshasbeenexpandedsincealower
frequency as 5kHz was added to the present UWS
frequencyrange(6,10,14,18kHz).
For the evaluation of response‐evoking distance
(theeffectiverange),wehavesuccessivelyrecordeda
sound pressure change of the new UWS sound
sourcereproducedfromJFasclosingtoarecording
point. The reference for the effective range sound
pressure was set as being higher than the lowest
sound pressure 102dB re 1μPa (Frankel et al.1995)
witharesponseoftheHumpbackwhaleandalsoset
apointwithaconstant
102dBastheeffectiverange.
Furthermore, the effective range was calculated by
trigonometricfunctionwithdistance/timeatthetime
of the closest approach, vessel speed, and time
coefficientat102dB.
Theeffectiverange(X
2
)=(a
2
) × (b
2
)
a：ClosestdistancetotheHF
b：vessel speed×(Closest time‐time coefficient at
102dB)
Asaresult,we found thatitwasreproducedby
response‐evoking sound pressure of cetaceans from
the average distance 389.8m (max 459.4m/min
294.2m).
Table2.TheeffectiverangeofthenewUWSsound.
_______________________________________________
# (A)Time (B)Closest(B)‐(A)Closest The
coefficient timetothe (s) distance effective
at102dB(s) HF(s)tothe range(m)
HF(m)
_______________________________________________
1 01’38” 01’58” 20 150 459.4
2 15’32” 15’44” 12 150 294.2
3 01’55” 02’13” 18 163 415.7
_______________________________________________
216
10 20 30 40 50 60
5
10
15
Frequency (kHz)
01:38
01:58
0
2
4
6
8
10
12
14
16
90
100
110
120
130
140
00:59 01:09 01:19 01:29 01:39 01:49 01:59
Frequency(kHz)
Receivedlevel(dBre1μPa)
Recordingtime(min:sec)
Receivedlevel
Peakfrequency
102dB
Figure4. A sound pressure change(a red line) and peak frequency(outlined circles) of the new UWS sound source
reproducedfromHFasclosingtoarecordingpoint(below).Spectrogramsweremadewitha1024‐pointFFT,0%overlap,
andHammingwindow(above).
Thisdistancewaslongerthanapproximatelyover
140mwhichwouldbea distance toanobstacleas a
condition where water landing/emergency‐stop ship
maneuveringshouldinstantlybetakenbyautomatic
control when a HF finds any obstacles at 46 knots
(Yagi 1991). In addition, when Kagami (2011)
conducted questionnaire survey
for HF officers, she
found that a collision could be avoided if an
emergencywaterlandingismadewithadistanceof
100m or longer; therefore, it can be said that ship
officers will have enough distance to avoid such
collisionifitisreproducedwiththeeffectiverangeof
cetaceans from the minimum distance of 294m. On
the other hand, it was discussed whether how
cetaceans responded to the new sound source and
howitevokedarepellantbehaviortowardcetaceans,
but such issue was examined by Nakashima et al.
(2015)submittedtothesamevolumeastheseparate
dedicatedpaper.
5 CONCLUSIONS
ThestudymadeanimprovementfortheUWSsound
source in terms of collision‐avoidance between HF
andcetaceans.Theimprovement was carried out on
the basis of aural characteristic of cetaceans and the
frequency adjustment with 5kHz, 8.00kHz, and
10.00kH.Furthermore,2soundsweresynthesizedas
a potential repelling sound for cetaceans. When the
newsound source created in the study was actually
playbacked from HF during the cruising, it was
reproduced by response‐evoking sound pressure of
cetaceans from the average distance of 390m;
therefore, we concluded this distance could be
enoughdistancetoavoid
acollisionbyHFofficers.A
developmentofthenewUWSsoundsourceaimedat
a collision‐avoidance with cetaceans while adjusting
dominant audio frequency of cetaceans for a risk of
collision and using a potential repelling sound for
cetaceans. In fact, it was examined by Nakashima et
al. (2015)
how the new UWS sound source would
evokearesponsebycetaceans.ThenewUWSsound
would be also expected to be applied to other low‐
noisevesselslikeayacht.
ACKNOWLEDGMENT
We would like to special thank for supporting for
investigation Sado Kisen Co., Ltd. and Kyodo
Senpaku Co., Ltd.,.
Key specimens provided by the
InstituteofCetaceanResearch.Wewishtothankthe
help given by Dr.Okanoya of Tokyo University and
Dr.Kawamoto of Tsurumi University in analyzing.
Thanks to Laboratory of Maine Biology, Tokyo
UniversityofMarineScienceTechnology,particularly
gratefulfortheassistancegivenbyKimikaTsujiand
KazuyaKitayama.ThisworksupportedbyKawasaki
HeavyIndustriesCo.,LtdandKHIJPSCo.,Ltd.
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