I could tell you about my submersible 6" . but I will leave for another day. although my 4" went under and filled with water, then the river went down and left me pondering why my motor wouldn’t start and was full of water. another carry out to the repair shop.
Suffered drowned dredges twice back in the 1980s - one did the submarine act in deep water and on my own had trouble getting the engine to the surface.
I ran outa suction one day so stood up to investigate , only to find my dredge gone, how can that be I was just holding on to the nozzle a minute ago, so under I went here she was sitting on the bottom overloaded to hell, takes ages to get a dredge out on snorkel from the bottom.