Glass-bottom boat  A glass-bottom boat is a boat with one or more sections of glass, or other suitable transparent material, below the waterline allowing passengers to observe the underwater environment from within the boat. When a boat is a glass bottom, the view through is better than simply looking into the water from above, because one does not have to look through optically erratic surface disturbances. The effect is similar to that achieved by a diving mask, while the passengers are able to stay dry, out of the water. Glass bottom boats are used almost exclusively for giving tours, as they are usually designed to allow the maximum number of tourists to view out the glass bottom and are not really suitable for other uses. Glass bottom boats are in use in nearly every seaside tourist destination. However many of them are gradually being replaced by semi submarines, which offer a better view of the marine life. Glass bottom boats were first used near Santa Catalina Island off the coast of Southern California. They also became popular in Florida at several areas of natural springs that became tourist attractions, for example, Silver Springs, Wakulla Springs, Rainbow Springs, and Weeki Wachee Springs. The oldest glass bottom boat ('Princess Donna' 1934) from Silver Springs is still operating on Jug Creek in Bokeelia Florida. The most modern glass bottom boats have ultra-durable bottom window shaped as an optically regular spheroid which size is 2x3 m. These boats also have a hydrofoil. This is a contemporary product of Russian boatbuilding company - Paritetboat [1]. Typical tours in these boats include views of underwater flora and fauna, reefs, shipwrecks, and other underwater sights.