Accordding to the International rules anything that floats is termed a vessel not a ship. A ship is a vessel that is fully square rigged on three or more masts, people tend to call large vessels as ships through ignorance, a boat often refers to small vessels often used as an auxiliary to a larger vessel or similar small boats, lifeboats are termed as such as they were originally designed similar to a ships lifeboat boat but were somewhat improved upon. So large vessel's are referred to Motor Vessels, Steam Vessels, Paddle Steamers and etc.
