the air to expand in the tanks and accelerate ascent rate until excess escapes through the bottom valves and maximum buoyancy occurs. A submarine may have several types of ballast tank: main ballast tanks for diving and surfacing, and trimming tanks for adjusting the submarine's attitude (its 'trim') both on the surface and when underwater, and depth control tanks for fine adjustments of buoyancy. Floating structures Ballast tanks are also integral to the stability and operation of deepwater offshore oil platforms and floating wind turbines. The ballast increases "hydrostatic stability by moving the center of mass as low as possible, placing it beneath the centre of buoyancy." Ballast may also be adjusted to convert a platform from a deep draught reduced waterplane area mode optimised for minimum motion in a seaway to a lower drag towing mode. A floating dry dock is ballasted to sink the supporting deck below the depth of the vessel to be docked, and after the vessel has been moved over this surface and secured in place, the ballast is discharged to lift the docking platform and the docked vessel above the water. To make this possible, most of the structure under the supporting deck is divided into ballast tanks. A floating boat lift is a smaller version working on the same principle, which may be dedicated as the storage facility for a specific vessel. Dry dock and lock caisson gates are floated into position over the sill, then the ballast tanks are flooded to hold the gate in place and make a seal while the dock or lock is drained. Wakeboard boats Most wakeboard-specific inboard-engine boats have multiple integrated ballast tanks that are filled with water by ballast pumps controlled from the helm with rocker switches. Typically the configuration is based on a three tank system with a tank in the center of the boat and two more in the rear of the boat on either side of the engine compartment. Just like larger ships when adding water ballast to smaller wakeboard boats the hull has a lower center of gravity, and increases the draft of the boat. Most wakeboard boat factory ballast systems can be upgraded with larger capacities by adding soft structured ballast bags. Increasing the displacement by ballasting causes the boat to make larger waves at any given speed, at the cost of greater power requirements and propeller loading to reach that