Navigation and Seamanship

3.2.2. Chip log or Ship log

The chip log or ship log was a crude speedometer invented in 16^th century to determine a vessels speed. It was considered important first navigational tool for dead reckoning. Before the chip log was invented, a ship’s speed was measured by dropping a small wooden piece in water just ahead of the ship’s forward. The time taken by the ship to move away from the wooden piece was then noted with the help of sandglass and on that basis an approximate speed was calculated. This log was known as Dutchman's Log. The log had been used by mariners for a long time. Then this wooden piece was tied with a rope and used. The line was knotted and used for measuring the speed of a vessel. Over time, the log was standardized in construction.

The ship log was made with a quadrant (quarter circle) shaped wooden board attached to a log line. Log line was knotted at regular intervals and attached to the board with a bridle of three lines connected to the holes made at uniform spacing on the board . Just to ensure that the wooden log properly floats in water, the lower side of the board was made of lead or piece of lead at the centre of the circular side. The log line was wound on a free turning reel.

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