Suppose we have a ship that is deballasting in a closed drydock, in afloat condition. So, there is no ingress or escape of water from the drydock. Will the water level of the drydock change? (please back your answer with a justification)
No, as long as it is floating.
Adding x m3 of ballast water to a ship will increase its volume of displacement by x m3.
The water level is equally affected by:
A) The volume displaced by the ship
B) The volume of water in the dry dock
Since the ballast water is being moved from A → B, the level in the dock will not change.