Watercrafts, also known as marine vessels, are vehicles employed in water with a propulsive capability. The most common examples of marine vessels are ships, boats, hovercrafts, and submarines. The utility of a marine vessel can be categorized for its use in the maritime industry, and marine vessels are generally used for seafaring education or leisure activities, transportation of cargo or passengers, and for conducting combat. An effectively designed marine vessel balances internal capacity, speed, and seaworthiness. In the past marine vessels were powered by people with poles, paddles, or oars; this was followed by steam turbine until 1914 and diesel fuel at the turn of the 20th century. Today, technological developments are aiming to identify cheaper and less polluting sources of propulsion.