Where "C"wroteon Nov 25, 2022 "I'm no sonar engineer, but I'm still baffled why a sonar system in passive mode would consume upwards of 75Kw - active is different for sure - those are BIG numbers."
I'm also no sound engineer, but I would say:
A passive sonar uses a lot of power to amplify very weak sounds and for massive processing of signal tasks to make sense of sounds, esoecially identifying the precise source. See what Aaron describes in 2below.
SSKs and SSNs (all attack subs) are more famous users of spherical active and passive sonar uses for ASW and anti-ship work.
However attack subs also use very weak, discrete beam, active/passive navigation/movement sonar pulses to image the seafloor, seamounts and other obstructions that the sub would otherwise risk banging into. Again these are very weak pulses undetectable by enemy sonars/seafloor hydrophones but are received on a constant basis by the sub's active/passive bow sonar.
1.On what happens when this imaging system doesn't work or isn't efficiently used see my November 2021 reporting on the Seawolf class sub USS Connecticut's major accident hitting a seamount:
1A - here https://gentleseas.blogspot.com/2021/11/us-sub-did-hit-seabed-projecting.html
1B - especially the diagram here https://gentleseas.blogspot.com/2021/11/uss-connecticuts-sonar-navigation-wasnt.html
2 Aaron, a former USN Los Angeles class SSN and Ohio class SSBN Sonarman, does discuss how sonars/sonarmen work in detail here and on his "Sub Brief" Youtube website https://www.youtube.com/c/subbrief
Aaron's (aka Jive Turkey's) description is interesting:
2A - 2min45secs into "The Ping"https://youtu.be/24uLeEKma5g It sounds like Aaron was using a great deal of energy for his Active (anti-sub or surface ship) "Ping".
2B- 20min into "USS Connecticut South China Sea Collision"https://youtu.be/5VKQPBhu0z0 eg. avoid collision "tools...that they will not make public" which Pete suspects is navigation sonar mode.
2C - 1min30sec into "USS Connecticut Damage Update..."https://youtu.be/vB-eSTpvKgs shows what I think is the half spherical active sonar which, amongst other things, can send weak navigation pulses, picked up by the larger spherical passive sonar. (photo above)
So much for us all to learn on the edges of guesswork.