A logbook (a ship’s logs or simply log) is a record of important events in the management, operation, and navigation of a ship. It is essential to traditional navigation, and must be filled in at least daily.
The term originally referred to a book for recording readings from the chip log, used to determine the distance a ship travelled within a certain amount of time. The readings of the log have been recorded in equal times to give the distance travelled with respect to a given start position. Today’s ship’s log has grown to contain many other types of information, and is a record of operational data relating to a ship or submarine, such as weather conditions, times of routine events and significant incidents, crew complement or what ports were docked at and when.
Most national shipping authorities and admiralties specify that logbooks are kept to provide a record of events, and to help crews navigate should radio, radar or the GPS fail. Examination of the detail in a ship’s log is often an important part of the investigative process for official maritime inquiries, in much the same way as a “black box” is used on airplanes. Logbook entries are sometimes of great importance in legal cases involving maritime commercial disputes.
Not everyone is aware of this but alterations or corrections in an official logbook must be initialled by the authorised keeper of the logbook and the original data entries which have been cancelled or corrected must remain legible so in other words, use one line to high light the error so the words on the underneath can be read. It is also very important to use a black ink pen rather than a pencil for the log as pencil entries could be changed at a later date and would not stand up in a court of law due this a technicality.
*Some of the above is taken from Wiki online