In the very early days of sailing ships, the ship's records were written on thin shingles cut from logs. These shingles were hinged and opened like a book. The entire record was called the "log book." Later on, when paper was readily available and bound into books, the record maintained the name.
Today, almost any record can be called a log. The ship maintains several legal records in logs. The ship's Deck Log is the primary record of daily events. It is maintained on the Bridge while underway and on the Quarterdeck while inport. In both locations, entries are supervised by the Officer of the Deck. While underway, a Ship's Position Log traces the path of the ship across the ocean. The Engineering Log records happenings within the ship's engineering plant. The Bell Log (or Bell Book) records orders from the Bridge that command response from the ship's engines. Taken together, they can completely describe what and where events occurred. The miscellaneous logs that are kept on a ship are too numerous to mention, although many are directed for administrative and audit purposes.