Kongsberg Simrad EK80 - Mount the Transducer at Forward Part of Hull to Minimize the Effects from the Flow Boundary Water Layer

50
394149/D
Mountthetransduceratforwardpartofhulltominimizethe
effectsfromtheowboundarywaterlayer
Theupperwaterlayersoftheseacontainamyriadofsmallairbubblescreatedbythe
breakingwaves.Whenthehullmovesthroughwateritwillcauseadisturbance,andthis
willgeneratefriction.Thefrictionzoneiscalledtheowboundarylayer.
Theowinthisboundarylayermaybelaminarorturbulent.
•Thelaminarowisanicelyordered,parallelmovementofthewater.
•Theturbulentowisadisorderlyowpattern,fullofeddies.
ATurbulentow
BLaminarow
CAirbubbles
Airbubblesabsorbandreectthesoundenergy,andtheymayinworstcasesblockthe
soundtransmissionaltogether.
Theboundarylayerincreasesinthicknesswhenitbecomesturbulent.Theboundary
layeristhinintheforwardpartofthevesselhull,andincreasesasitmovesaft.The
thicknessdependsonshipsspeedandontheroughnessofthehull.Allobjectssticking
outfromthehull,ordentsinthehull,willdisturbtheowandwillincreasethethickness
oftheboundarylayer.Whentheowspeedishigh,theturbulencecanbeviolentenough
todestroytheintegrityofthewater.Smallvoidsorcavitiesinthewaterwilloccurand
thisiscalledcavitation.
Itisourexperiencethatawideandatbottom,witharisinganglelessthanaround13
degrees,ispronetogivingairproblemsforthetransducer.Inanycaseatransducer
locationintheforwardpartofthehullispreferredinordertominimisetheinuenceof
theboundarylayer.
Relatedtopics
Wheretoinstallthetransducer,page48
Preparations,page43
SimradEK80InstallationManual