Simrad EK80 - Avoid Protruding Objects; Stay Far Away from the Propellers

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2Anotherreasontogodeepiscavitation.
Cavitationistheformationofsmallbubblesinthewaterclosetothetransducerface
duetotheresultinglocalpressurebecomingnegativeduringpartsoftheacoustic
pressurecycles.Thecavitationthresholdincreaseswiththehydrostaticpressure.
3Thetransducermustneverbeliftedfreeofthewatersurface.
Transmittingintoopenairmaydamagetheitbeyondrepair.Mountingthetransducer
atadeeppositiononthehullwillinmostcasespreventthis.
4Ifthetransducerisliftedupfromthewaterduringheavyseas,itmaybedamagedwhen
thehullstrikesbackattheseasurface.
Thisisespeciallyimportantforlowfrequencytransducerswithlargefaces.
Avoidprotrudingobjects
Objectsprotrudingfromthehullwillgenerateturbulenceandownoise.Thiswillreduce
theEK80performance.
Suchobjectsmaybezincanodes,sonartransducersoreventhevessel'skeel.Holesand
pipeoutletsarealsoimportantnoisesources,aswellasroughsurfacescausedbybad
welding.Alltheseprotrudingobjectsmayactasresonantcavitiesamplifyingtheow
noiseatcertainfrequencies.
Donotplaceatransducerinthevicinityofsuchobjects,andespeciallynotclosebehind
them.Forthesamereason,itisveryimportantthatthehullareaaroundthetransducerface
isassmoothandlevelaspossible.
Eventracesofsealingcompound,sharpedges,protrudingboltsorboltholeswithoutlling
compoundwillcreatenoise.
Stayfarawayfromthepropellers
Thepropulsionpropellersisthedominantnoisesourceonmostvessels.Thenoiseis
transmittedthroughtheseawater,andmayoftenreducetheperformanceofyourEK80
system.
Forthisreason,thetransducermustbeplacedfarawayfromthepropellers,whichmeans
ontheforepartofthehull.Positionsoutsidethedirectlineofsightfromthepropellers
arefavourable.
Onsmallvesselswithshortdistancesitisadvisedtomountthetransduceronthatside
ofthekeelwherethepropellerbladesmoveupwards,becausethepropellercavitationis
strongestontheotherside.Thecavitationstartsmosteasilywhenthewaterowsinthe
samedirectionasthepropellerblade,andthatistosomedegreethecaseatthatsideofthe
keelwherethepropellerbladesmovedownwards.
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