During the ancient time, there was no particular method for navigating at sea. Few of the earliest methods included celestial navigation and dead reckoning. The celestial navigational method was the most ancient and extensively used method for navigation, whereas dead reckoning was considered the most reliable ancient method, which also introduced the system of log keeping.
Transverse board is one such type of navigational equipment that was used on ships in the ancient times. Mainly used in dead reckoning method, transverse board is actually a normal wooden board which was used to record various parameters of the ship that were measured during navigating at sea.
As said earlier, transverse board was a simple wooden board with holes and small wooden nails. The board was divided into two parts – top and bottom part. The top part was meant for recording the direction sailed by the ship and had thirty-two compass points made on a compass rose (Similar to the one found on a conventional magnetic compass). A total of 8 concentric rings were there is the compass rose and each one of them had a hole made at each point.
The bottom part of the board was for recording the speed traveled. There were in total of 4 rows of holes. Each of the columns formed represented a specific speed in knots. The lower part had a total of eight slots per row made for the wooden nails.
Using a Transverse Board
In a dead reckoning system, the sailor at every half an hour of his watch inserts a wooden nail into the hole which marks that the ship has already passed that point. The first half an hour of the watch is represented by the first circle, which is nearest to the center. Thus as each watch is of 4 hours, at the end of each watch, all the eight circles would be nailed at different points.
In the bottom part, each column would represent the speed traveled for a particular watch. At the end of first half an hour, the sailor will insert the wooden pin in the column representing the speed of the ship in knots. For e.g. if the ship was traveling at 5 knots, the sailor on duty will count 5 from left to right and mark in the pin at the 5th column of the first row. Thus each row represents every half an hour of the watch whereas the columns represents speed traveled in knots. The speed would be measured using the pit log method.
At the end of each watch, all the details would be transferred to a rough paper or slate and the master would then use the information to fill in the log book. At the beginning of next watch, all the wooden pins will be removed and method would be repeated