To ascertain the ship's speed by the common log four articles are necessary - a log-ship or log-chip, log-reel, log-line and log-glass.
The log-line is secured to this span and consists of two parts.
Sometimes a 30-second glass is used instead of a 28-second one, and the intervals between the knots on the log-line are then made 50 ft.
For speeds over six knots a 14-second glass is employed, and the speed indicated by the log-line is doubled.
The log-line, after being well soaked, stretched and marked with knots, is wound uniformly on the log-reel, to which its inner end is securely fastened.