A man who built his own submarine has sold it to a sea farm owner in Wuhan, central China's Hubei Province to help him harvest sea cucumbers. Zhang has named the submarine Twilight and has tested it underwater more than ten times to ensure it is safe. According to Zhang the local safety and quality department have also approved his invention, which can work continuously for ten hours at a depth of 100 metres. The submarine is equipped with fishing and safety devices and life support systems.