Installation manual

SimradES70
1Theupperwaterlayersoftheseacontainamyriadofsmallairbubblescreatedbythe
breakingwaves.Inheavyseastheupper5to10metresmaybelledwithair,and
thehighestconcentrationswillbenearthesurface.Airbubblesabsorbandreectthe
soundenergy,andtheymayinworstcasesblockthesoundtransmissionaltogether.
2Anotherreasontogodeepisthecavitationinfrontofhighpowertransducers.
Cavitationistheformationofsmallbubblesinthewaterduetotheresultinglocal
pressurebecomingnegativeduringpartsoftheacousticpressurecycles.The
cavitationthresholdincreaseswiththehydrostaticpressure.
3Thetransducermustneverbeliftedfreeofthewatersurface.Transmittinginto
openairmaydamagethetransducerbeyondrepair.Mountingthetransducerata
deeppositiononthehullpreventsthis.
4Ifthetransducerisliftedupfromthewaterduringheavyseas,itmaybedamaged
whenthehullstrikesbackattheseasurface.Thisisespeciallyimportantforlow
frequencytransducerswithlargefaces.
Mountthetransducermidwaybetweenthebowandthesterntoavoidheaveeffects
Heaveistheupanddownmovementofthevessel.Itdisturbstheechotracesinthe
echogram,sothataatbottomisdisplayedasawave.Atransducerlocationinthe
middleofthevesselminimisestheinuenceofvesselrollandpitch.
Mountthetransducerawayfromprotrudingobjectsonthehull
Objectsprotrudingfromthehull,suchaszincanodes,sonartransducersoreventhe
vessel’skeel,generateturbulenceandownoise.Holesandpipeoutletsarealso
importantnoisesources.Theymayactasresonantcavitiesamplifyingtheownoise
atcertainfrequencies.Donotplaceanechosoundertransducerinthevicinityofsuch
objects,andespeciallynotclosebehindthem.Forthesamereason,itisveryimportant
thatthehullareaaroundthetransducerfaceisassmoothandlevelaspossible.Even
tracesofsealingcompound,sharpedges,protrudingboltsorboltholeswithoutlling
compoundwillcreatenoise.
Mountthetransducerattheforwardpartofthehulltominimisetheeffectsfrom
theboundarywaterlayer
Whenthevesselforcesitswaythroughthesea,thefrictionbetweenthehullandthe
watercreatesaboundarylayer.Thethicknessoftheboundarylayerdependsuponvessel
speedandtheroughnessofthehull.Objectsprotrudingfromthehull,anddentsinthe
hull,disturbtheowandincreasethethicknessoftheboundarylayer.Theowinthis
boundarylayermaybelaminarorturbulent.Alaminarowisanicelyordered,parallel
movementofthewater.Aturbulentowhasadisorderlypattern,fullofeddies.The
boundarylayerincreasesinthicknesswhentheowgoesfromlaminartoturbulent.The
gurebelowillustratestheboundarylayerofavesselmovingthroughthewater.
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