Chesapeake Bay - Fish Finders for Archaeology

Greetings Enthusiasts!
Update on the Chesapeake bay expedition. We’ve been playing with fish finders, which have come very far indeed, for use in wreck surveys and pre-dive planning.

Siege of Yorktown, HMS Betsy. In 1988, an excavation erected and then collapsed a cofferdam over the wreck. We want to check it out and learn more about the +50 unidentified wrecks that still lay buried in the York River! The first image is from National Geographic, June 1988, the circular sonar is from a recent survey from JRS Explorations. The bottom 2 images are from our Garmin echomap 44cv.

Have many of you used fish finders in this way? If so, can you help with image analysis?



Yes, we have used both Garmins and Humminbirds to conduct side scan sonar surveys. We used to use DrDepth to post process the raw data. I’ll hunt around and get back to you on other packages.

@jim-n I’m not too familiar with Down Scan/Vu imagery. I think it’s like a 15 degree beam below the boat? If you can get the regular SideVu imagery, I can interpret that.

Not sure if this comparison will help:

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So any plans to stick a Garmin SideVu on a BlueRov? :grinning:

Check “Deepvision” on Facebook

Hi Kevin,
The down chirp screen is what I can get, no side scan at this time. One question I have is that it looks like i get returns below the surface, but is that more the return within the area circumscribed by the 15 degree beam? In the image you sent, it looks to me that the down scan is a 3D scan. Is that true?

I’m rather against facebook, but I will look into it, thanks!


Interesting, however, a quick scan returns that Dr. Depth is out of date and no longer available. Is this correct?

For reference, this is what a downscan from a Lowrance unit looks like. That’s pretty clear to interpret.

I just don’t understand the image that continues after the first return on the Garmin unit. I think the beam is narrower on Lowrance than Garmin and that what we are seeing on the Garmin is a wider beam that just joins like 7.5 degrees to either side into one acoustic image. That’s probably why you see shadows of the logs and tires in the same Downvu image in my previous post. I don’t think it is a 3D image but more of a combined one.

Dr. Depth has been unavailable for years. The designer sold his software to Lowrance and it became what is now Insight Genesis (it was one of the two). A suitable replacement is You can only use Lowrance and Humminbird sonar data because Garmin keeps their file format closed and proprietary so there isn’t anything you can do with their data besides taking screenshots. A bit frustrating if you wanted to make sonar mosaics.

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Humminbird bought Dr Depth.
They now sell it under the name “Autochart Pro”
For that little money it is really useful for charting with single beam or sidescan.

Very interesting, thank you! I am slightly regretting getting the Garmin now learning that they are so closed with the data…but only slightly. I was planning on investing in a higher end unit in the near future after I learned a little about them. Looks like hummingbird will be the vendor



I have not tried since I use old Dr Depth to my Lowrance stuff.
But I guess You can hook up Garmin as well to Humminbirds labled “Autochart”
If You are sending NMEA position, depth and XTF files I think that will work.

If your using a any of the commercial gear such as Lowrance, Hummingbird or Garmin. There is a program called Sonar TRX that will allow for post processing of the recorded data. I have done some testing with it and a Lowrance HDS 7 and had fairly good luck.

You can also check out “Reefmaster” I use it for 3d mapping of the seabed. You can add on modules for side scan mosaic and calculate masses etc.