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The most common design is one similar to a ship. The passenger cabin is relatively low, a few meters below sea level. The cabin is equipped with large windows into the water. The passengers can observe the marine environment that is passed during the voyage.
There are significant differences between a submarine and a semi-submarine from an engineering point of view. Submarines are human-occupied pressure vessels, while pressure concerns apply to a lesser extent to semi-submarines. As the pressure close to the water surface is relatively low, the viewing windows can be bigger. In some advanced designs the windows enclose the majority of the submersed hull, creating an experience comparable to scuba diving. Customers can leave the submerged cabin for the unsubmerged deck at any time.
Semi-submarines can be used for research, but they are most commonly used in the tourism industry. However, large tourism-orientated semi submarines should not be confused with narco-submarines which are smaller home-made semi-submarines used to smuggle drugs.
Semi-submarines do not have an international classified status. Their operating range from the native port might be limited by the local authorities.