So you've got the entire crust of the Earth, ripped up into continent-sized chunks and sent hydroplaning across the top of the water. The entire surface of the Earth is now
on top of the water, and the only open water is in the open spaces between those chunks.
Did all this happen before or after the ark made landfall?
Whether you know it, or not, a large part is still on water.
In subduction zones, millions of gallons of water are leaked in each day.