History of Navigation: Keeping a Logbook

Log Entry for the Ship Brunswick

On naval and merchant ships, navigators must keep a logbook, even when a computer keeps track of position. Electronics fail, and a logbook is a record of more than course and distance; it is a place for recording weather and other ship’s business. Traditionally, the mate kept the log on a merchant ship.

Recording time is the first step in keeping a log, with an entry every hour or every other hour, on the hour. [Ship’s time] is different from civil or land time, because the day begins at noon rather than at midnight. Each log entry has the vessel’s course, either as true or magnetic course. Speed is entered, sometimes followed by the distance traveled since the last logbook entry. Wind speed and direction follows along with weather notes. On a sailing vessel, there could be notes on the managing of sails. At the end of each day’s entries, the ship’s position is recorded with a note that says how it was determined, by dead reckoning only or by celestial navigation. Dead reckoning positions are needed even if a celestial observation is not made as it is needed to solve future celestial positions.  A noon sight taken then can determine the vessel’s latitude and together with a chronometer, longitude.  Today, an electronic position would be noted. 

The logbook is a legal document serving as record of the captain’s actions in case of a collision, grounding or other accident.