The Log

The ship’s log. What is it?  There are a few logs on a ship. A navigation log on the bridge would record the ship’s position, weather, sea temperature among other things.  In the engine room, temperatures, pressures and machinery status would be recorded.  A movement log would be kept on the bridge and in the engine room to record telegraph movements.  The captain would keep a log of the ship’s business as well as ocassionally recording the name of a malfeasant crewman.  A process known as being “logged”.

But that is not the concern of this belles-lettres.  The log of which I speak is the one which measures the vessels speed and/or distance travelled. Why I don’t hear you enquire is the speed measuring equipment call a log?  In days of yore, when ship’s were made of wood and men were made of iron, the ship’s speed could be determined by tossing a log into the water at the bow and measuring the time it took to reach the stern.  As the length of the ship is known the speed can thus be calculated.

Later the hand log, a flat, quarter-circle piece of wood. A lead weight on the circular side of the piece, or chip, caused it to float upright and to resist towing. It was tossed overboard attached to a line having knots in it at known distances. Specifically a distance of 47’3″ between knots and log glass of 28 seconds would measure the speed in knots. (for example). The term knot, meaning one nautical mile per hour, comes from the knots in the log line. Clever, but not too convenient.  

As technology advanced, various means of measuring speed or distance were developed.