Angling the glider downward, trading altitude for speed, allows the glider to fly fast enough to generate the lift needed to support its weight. A plane's lift, drag and glide ratio characteristics are governed solely by its construction, and are predetermined at takeoff. A heavier glider will sink faster that a light glider. The glide ratio is not affected by weight because while a heavier glider will sink faster, it will do so at a higher airspeed. In order to help them fly faster, some gliders have tanks that can hold up to 500 pounds of water.
Higher speeds are desirable for cross-country flying.
To prevent this, the water ballast can be jettisoned at any time through dump valves, allowing the pilots to reduce the weight of the plane to increase climb rates, or to reduce speed as they come in for a landing. The way you measure the performance of a glider is by its glide ratio. This ratio tells you how much horizontal distance a glider can travel compared to the altitude it has to drop. This means they can glide for 60 miles if they start at an altitude of one mile. If the glide ratio were the only factor involved, gliders would not be able to stay in the air nearly as long as they do.