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Author Topic:   SONAR Image from EDMUND FITZGERALD
jimh posted 05-10-2006 12:52 AM ET (US)   Profile for jimh   Send Email to jimh  
The shipwreck of the EDMUND FITZGERALD is in about 530-feet of water. I have this fond notion of visiting the wreck site and getting a SONAR image from the bottom that would show the wreck. Based on my experience with my current SONAR, a 200-kHz LOWRANCE unit, I do not think it would be able to show me much--if it would even return a bottom echo at all.

What sort of SONAR would be needed to get a decent look at a shipwreck like this in 530-feet of water? I would be very interested to hear first-hand reports of SONAR units that would be capable of getting a good look at the wreck. What sort of detail would I be likely to see?

I know I won't get anything like this image. But I'd like to be able to see something on a SONAR display to indicate we were on the wreck site. Is this feasible?

Chuck Tribolet posted 05-10-2006 08:45 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
If your SONAR will reach deep enough, you will see the relief
of the hull off the bottom, just like you would see a rock.
I located the wreck of a liberty ship off SF no sweat. Once
I figured out which way it was oriented, I ran the length of
it and the SONAR showed a very low res profile of the ship
(it's upright), including the superstructure.

Dr. Robert Ballard said that the Titanic would have shown up
on a good trawler's SONAR.


bsmotril posted 05-10-2006 08:48 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
I have fished on boats with a dual frequency 50/200khz through hull transducer equipped Furono color CRT fishfinder that did very well. It was 600 watts RMS, 2000 watts peak. We were able to make out well heads and pipelines on the sea bottom in 200-600 feet of water. It was nothing like the detail of the images you posted, but more of just a profile with no real break or discrimination line between the seabed and the structure. A typical Well head is all metal and about the size of a large 8'-10' tall christmas tree. BillS
handn posted 05-10-2006 09:14 AM ET (US)     Profile for handn  Send Email to handn     
My Furuno is similar to Bill S' with a thru hull transducer.
It would show the lump of the Edmund Fitzgerald. It has a zoom which would enable me to zoom in on the bottom and see detail. Since the ship is iron and the bottom presumably mud, the ship would project a thicker, different color echo.
550 feet is not all that deep. Any dual frequency fish finder would pick up the ship. Budget single frequency units usually fade out about 400 feet or so.
More powerful dual frequency units show some detail down to 3000 feet.
Looking for the ship sounds like fun, take and post pictures.
bigjohn1 posted 05-11-2006 08:08 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
I agree with everything said so far. We had some real trick sonar equipment for mine hunting in the Navy that would show images like Jim's first post but that equipment had many different frequencies and LOADS of wattage power. Sticking to what's available to us boaters for a
"reasonable" price, my vote would be for a 200kHz unit capable of 1-2 kilowatts of power. It is common knowledge among hardcore off-shore guys that 200kHz is fairly worthless deeper than around 400ft (just as handn states). That said, it will continue to produce "good" returns for a few hundred more feet if you are able to pump up the power. It will not however give detail and clarity like the picture you show Jim. The image in your first post is without a doubt from a military-grade sidescan sonar unit.

If you had $2,700 to spend, I think the new top-of-the-line NAVMAN (8120 is it?) fishfinder/chartplotter would let you easily see that wreck with 200kHz. Again though, it will not be near as good as that high-power sidescan image.

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