Just to give you an idea of how optimistic 50 tons an hour is;
An average size dump truck will hold 13 tons of material, so it will take almost 4 dump trucks to hold 50 tons of material.....now watch the video on Orca's post #2363 and see how much material is being pulled into the venturi of that dredge and then visualize how long it will take to fill 4 dump trucks.....a lot longer than an hour, I think.
Now, I do have to say, Im not familiar with the size of the material being moved or the depth and speed of the water they will be working in, but it will definitely have to be primo conditions to get 50 tons an hour.