How are ballast tanks generally emptied quickly?

Ballast tanks are primarily emptied quickly using pumps. In marine engineering, pumps are designed to efficiently remove the water or fluid in the ballast tanks to achieve rapid changes in a vessel's buoyancy and stability. This is particularly important for maintaining optimal performance and maneuverability during various operational conditions.

Using water, nitrogen, or gravity are not common practices for quickly emptying ballast tanks. While nitrogen can be used for certain purposes, such as inerting or pressurization, it does not serve the function of expelling water from the tanks. Gravity can assist in the draining process but is often not a rapid or reliable method, especially in situations that require immediate adjustment of ballast. Pumps, on the other hand, provide controlled and efficient means to handle the water, ensuring that changes in weight and stability occur as needed.