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I found a sunken boat
(feddit.uk)
It's really long and quite wide but no sign of a mast. No idea what the history of this thing is.
It's not that old. Granted I only had one class in marine archaeology but I see treenails poking out here and there and I don't see a large keel. So I'm gonna guess built 19th or early 20th century and its a barge of some sort. Flat bottomed for river or lake work.