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Re: [PSUBS-MAILIST] SONAR

Adam,
 
The finder I use in my sub came with a diagram describing the shape of the sonar "cone" projecting below the boat.  When I see a fish image displayed, what I'm seeing is the return bouncing off something situated somewhere in that cone.  Without checking the manual (and remember, I bought it 12 years ago) I think my transducer projects a 20 degree cone.  Basically, unless I'm getting a false return, it's only telling me there's something down there in that general area below the boat, but it's close enough to work with in most practical circumstances not requiring extreme precision. 
 
I use mine as a "sonar altimeter" to give me a readout of the distance between my keel and the bottom; and it also provides some visual representation of what's below me.  Not high tech, perhaps; but much better than nothing at all.  In use, it's been very helpful, especially since my sub's design does not enable me to look straight down visually.  I'm presently rebuilding the control panel, and the fishfinder is staying aboard.
 
VBR,
 
Pat
 
 
----- Original Message -----
From: Adam
To: personal_submersibles@psubs.org
Sent: Friday, August 10, 2001 5:41 PM
Subject: [PSUBS-MAILIST] SONAR

Okay,
 
I have a question about "civilian" SONAR.  I have seen fish finders in action but I never really understood what I was looking at.  I saw a little picture of a boat and then the water under us.  And a couple fish :)     I'm wasn't really intrested in the fish but the technology when I saw this at the tender age of...???  um??? like 12? I think?
 
Anyway my question is.... when OI saw it it a apeared as a 2d section...  a plane straight down from the boat....  Now this image may have deviated a little from what I actually saw in my memory, but if that is what I saw then that doesn't seem very useful for our purposes.
 
Basiclly, what i'm asking is: Can someone explain to me how fish finders work.  Not the fundamental PING and Return time with the calculation involving time, distance, and the speed of sound in water, but in what type of plane does the ping get read. 
 
In otherwords, it ping in 3D, but is it read in 3D and if so, how is that displayed using a 2D display.....  I hope I have explained my queston sufficiently.
 
Adam