Installation manual
SimradES120-7C
noiseatcertainfrequencies.Donotplaceanechosounder
transducerinthevicinityofsuchobjects,andespeciallynot
closebehindthem.Forthesamereason,itisveryimportant
thatthehullareaaroundthetransducerfaceisassmoothand
levelaspossible.Eventracesofsealingcompound,sharpedges,
protrudingboltsorboltholeswithoutllingcompoundwill
createnoise.
Mountthetransducerattheforwardpartofthe
hulltominimisetheeffectsfromtheboundary
waterlayer
Whenthevesselforcesitswaythroughthesea,thefriction
betweenthehullandthewatercreatesaboundarylayer.The
thicknessoftheboundarylayerdependsuponvesselspeedand
theroughnessofthehull.Objectsprotrudingfromthehull,and
dentsinthehull,disturbtheowandincreasethethicknessof
theboundarylayer.Theowinthisboundarylayermaybe
laminarorturbulent.Alaminarowisanicelyordered,parallel
movementofthewater.Aturbulentowhasadisorderlypattern,
fullofeddies.Theboundarylayerincreasesinthicknesswhenthe
owgoesfromlaminartoturbulent.Thegurebelowillustrates
theboundarylayerofavesselmovingthroughthewater.
Figure1Boundarywaterlayer
ATurbulentow
BLaminarow
CAirbubblesinthewater
Furthermore,airbubblesintheseawaterarepresseddownbelow
thehullandmixedintotheboundarylayer.Theboundarylayer
isthinunderneaththeforwardpartofthevessel,andincreasesin
thicknessasitmovestowardsaft.Ifthesidesofthehullaresteep,
someoftheairbubblesintheboundarylayermayescapetothe
seasurfacealongthevesselsides.Itisourexperiencethatawide
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