log

(1) A record of a ship's speed, its progress, and any shipboard events of navigational importance, or the book in which the record is kept.

(2) A knotted length of line with a piece of wood at the end which is thrown into the water to determine a ship's speed based on how many "knots" run out in a set period of time. The line is usually on spool that can be reeled out and back in.