An integral part of the dead reckoning system, chip log is supposed to the first navigational tool for measuring a ship's speed.
Anyone who is aware of the ancient navigational technique of dead reckoning will also be aware of the first navigational tool - chip log. Chip log is a small wooden tool that was used in the ancient time for measuring the speed of the ship.
Before the chip log was invented, a ship’s speed was measured by dropping a small wooden plank in water just ahead of the ship’s forward. The amount of time taken by the ship to move away from the wooden board was then noted and on that basis an approximate speed was found out. It is to note that this speed was just an approximate speed, but then, so was the whole system of dead reckoning.
As mentioned earlier, chip log is navigational tool made of a wooden board attached to a log line. Holes are made at uniform spacing on the board and have one end of the log lines tied to them. The log line is then wound around a reel for making the chip log easier for use.
The shape of the wooden board is usually that of a one-fourth circle and there are holes made at each of the three edges. Just to ensure that the wooden log properly floats in water, the lower side of the board is made of lead. Moreover, to prevent snapping of lines, they are made of strong and durable materials.
Using the Chip log
When the speed of the vessel was to be measured, the sailor would throw the chip log into the sea towards the stern of the ship. The log line was then released in such a way that the wooded plank stay at the same place in water. The log line was allowed to run out of the reel for a specific amount of time and then stopped. Markings were made on the log line which represented the distance traveled by the ship. A sand glass was also used to measure the time taken by the ship to move away from the chip log. According to the length of the log line released over the stern and the markings on the line, the speed of the ship was calculated.
The main disadvantage of using a chip log was that it neglected various factors such as the sea condition, speed and direction of currents, stretching of the log line and inaccuracy of measured time. Moreover, two men were required to use the log, one to hold the reel and other to throw the wooden piece.
Apart from the traditional chip logs, various mechanical chip logs were also invented and used in the later years which worked more on the basis of physical properties and thus provided accuracy. Today, chip logs have been substituted by the ultra modern GPS systems.