Hey Nice Work! That heavy thingy reminds me of before there was Garmin...a guy had to have a heavy little dealie to toss over the side to ascertain the depth...A lot of us just used a heavy sinker, or a small window sash weight, or something similar, not too heavy and easy to toss and retrieve...some were brass....
Before Garmin, You Had to have one!....No topo charts, or GPS or any idea of where you were half the time out on the water........After just a little use, a guy could 'feel' the composition of the bottom by bouncing it along... you knew if it was mud or gravel or rock or whatever...and the current strength even, so a guy knew where to drop anchor and fish at a nice gravelly drop off edge or submerged logpile or something....then a guy would take care to look at the shoreline and try to triangulate some features so you could get back on the Hotspot! It was not easy! ..
It had to be sort of smallish and easy to deploy over and over, yet get down fast...Thats where Samuel Langhorn Clemmons came up with his pen name...from tossing a 'depth finder' over the side constantly and hollering out the depth of two fathoms, or..."Mark Twain"...12' of safe water and easy running...Is there an eye on the top of it to tie a line?
Theres probably a lot of them old skool depth finders down there of various configuations...its all a guy had to know what the depth and composition was like...40yrs ago....every boat or fisherman had several....now EVERY single boat out there has a Garmin, except for mine! I still dont have one! I dont need it! I just shadow the other boats and fish where They are fishing!
Boats have WAY too much power nowadays, and they are sold to folks who have not an idea how dangerous a river system can be when speed is involved...250hp on a fishing boat would been unthinkable not that long ago...
Sheeit!...If you had a Johnson 16hp Sea Horse you were really something! I still run a 15hp four stroke on my big boat...its plenty fast enough...tracked it at 17mph on my cell phone one day! Starts on the first pull!