(1) Short for log-book, in
which all necessary navigational information and ship’s progress is recorded.
Was originally a ‘log-board’, taking the form of two black-painted boards
hinged together to open like a book, on which the readings of the Log (2)
could be written in chalk.

Log (2) Short for log-chip (or log-ship), a fan-shaped wedge of wood,
weighted to float upright, which was streamed astern on a line of known length
so that the ship’s speed could be determined from the time taken for the line
to run out. About a hundred years ago the Patent log began to come into use,
streaming a spinner at the end of a plaited line which rotates the mechanism in
the recorder onboard, showing distance run which is far more valuable than
speed. Rarely used today.