Simrad SU90 - Self Noise

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.
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