Complex sentence: The barge is no longer capable of submerging 100 percent; like other drydocks, it takes on enough water to allow entry of a vessel, then pumps out ballast until the interior of the dock is above water.
Split into simpler sentences: The barge is no longer capable of submerging 100 percent. Like other drydocks, it takes on enough water to allow entry of a vessel, then pumps out ballast until the interior of the dock is above water.