securely, since a skilled slalom skier can put a considerable amount of tension on the ski rope and the pylon. Safety measures As water skiing is a potentially dangerous sport, safety is important. There should be a wide skiing space and the water should be at least deep. The towboat should stay at least from docks, swim areas, and the shore, and other boats should steer clear of skiers by at least 100 feet. Without proper space and visibility skiing can be extremely dangerous. Skiers should wear a life jacket regardless of swimming ability. Specially-designed life jackets or ski vests allow movement needed for the sport while still providing floation for a downed or injured skier. The most common water ski injuries involve the lower legs, such as the knee, because a fall at high speed can create irregular angles of collision between the skier's body and the water surface. Another common cause of injury is colliding with objects on or near the water, like docks. The tow boat must contain at least two people: a driver and an observer. In most locales, the observer will need to be at least 12 years of age. The driver maintains a steady course, free of obstacles to the skier. The observer continually observes the skier, relays the condition of the skier to the boat driver, and if necessary, raises the "skier down" warning flag, as required, when a skier is in the water, returning to the boat, or in some localities, the entire time the skier is out of the boat. The skier and observer should agree on a set of standard hand-signals for easy communication: stop, speed up, turn, I'm OK, skier in the water, etc. History Water skiing was invented in 1922 when Ralph Samuelson used a pair of boards as skis and a clothesline as a towrope on Lake Pepin in Lake City, Minnesota. Samuelson experimented with different positions on the skis for several days until 2 July 1922. Samuelson discovered that leaning backwards in the water with ski tips up and poking out of the water at the tip was the optimal method. His brother Ben towed him and they reached a speed of . Samuelson spent 15 years performing shows and teaching water skiing to people in the United States. Samuelson went through several iterations of equipment in his quest to ski on water. His first equipment