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Preparations

lowaspossibleinordertoobtainlongrangeanddependableinterpretation.Thenoise

thatcontributestothesignaltonoiseratioonhydroacousticinstrumentsmaybedivided

intothefollowingtypesofnoise:

•Selfnoise

•Ambientnoise

•Fishinggearnoise

•Electricalnoise

•Reverberation

Selfnoise

Therearemanysourcesofselfnoise.

•Machinery:Mainengine,Auxiliaryengines,Gears,Pumps,Blowers,Refrigerator

systems,etc.

•Electric:Electricmotors,Groundloops,etc

•Propellers:Propellerbladeproperties,Cavitation,Shaftvibrations,Staticdischarges

•Flownoise:Laminarow,Turbulentow,Cavitation,Bubbles,etc

•Rattlenoise:Looseparts

•Interferences:Otherhydroacousticsystemsonyourownvessel

Wewillheregointosomedetailsinordertoanalysethedifferentsourcesofselfnoise

onavesselandhowtheymayinuenceuponthenoiselevelofthehydroacoustic

instruments.

Machinerynoise

Themaincontributorisusuallythemainengineonboardthevessel.Thecontribution

fromauxiliarymachinerymay,however,beconsiderable,especiallyifsomeofitisin

poorshape.Themachinerynoisecanbetransmittedtothetransducerasa:

•Structure-bornenoisethroughtheshipstructureandthetransducermountings

•Water-bornenoisethroughthehullintothewatertothetransducer

Electricnoise

Modernvesselsarenormallyequippedwithalotofelectricinstrumentssuchas

hydroacousticsystems,radars,navigationsystems,andcommunicationequipment.Any

electricinstrumentsmayinsomecauseelectricalinterferenceandnoise.International

regulationsandcerticationsareusedtocontrolandreducethis,buteventheseare

limitediftheelectricalsystemsarepoorlyinstalledandmaintained.

Propellernoise

Thissourceisoftenthemainsourceofnoiseathighervesselspeeds.Variablepitch

propellersorfastmovingpropellersusuallymakemorenoisethanxedpropellersor

slowmovingpropellers.

381293/A

Simrad SU90 Installation Manual

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