Simrad TRANSDUCER - INSTALLATION GENERIC REV H Manuale di Installazione Pagina 25

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Installationplanning
Forthesamereason,itisveryimportantthatthehullareaaroundthetransducerfaceisas
smoothandlevelaspossible.Eventracesofsealingcompound,sharpedges,protruding
boltsorboltholeswithoutllingcompoundwillcreatenoise.
Avoidtheboundarywaterlayer
Mountthetransducerattheforwardpartofthehulltominimisetheeffectsfromthe
boundarywaterlayer.
Whenthevesselforcesitswaythroughthesea,thefrictionbetweenthehullandthe
watercreatesaboundarylayer.Thethicknessoftheboundarylayerdependsuponvessel
speedandtheroughnessofthehull.Objectsprotrudingfromthehull,anddentsinthe
hull,disturbtheowandincreasethethicknessoftheboundarylayer.
Theowinthisboundarylayermaybelaminarorturbulent.Alaminarowisanicely
ordered,parallelmovementofthewater.Aturbulentowhasadisorderlypattern,fullof
eddies.Theboundarylayerincreasesinthicknesswhentheowgoesfromlaminarto
turbulent.Thegurebelowillustratestheboundarylayerofavesselmovingthrough
thewater.
Figure4Boundarywaterlayer
ATurbulentow
BLaminarow
CAirbubblesinthewater
Furthermore,airbubblesintheseawaterarepresseddownbelowthehullandmixed
intotheboundarylayer.Theboundarylayeristhinunderneaththeforwardpartofthe
vessel,andincreasesinthicknessasitmovestowardsaft.Ifthesidesofthehullare
steep,someoftheairbubblesintheboundarylayermayescapetotheseasurfacealong
thevesselsides.Itisourexperiencethatawideandatbottom,witharisingangleless
thanaround13degrees,ispronetogivingairproblemsforthetransducer.Inanycasea
transducerlocationintheforwardpartofthehullispreferredinordertominimisethe
inuenceoftheboundarylayer.
331549/B
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