It is important to keep a record of course and speed at intervals during each watch. For centuries seamen used a traverse board (see Chapter 5, Figure 5.8).
The upper half of a traverse board is a compass rose marked out in 32 points. Eight holes radiate out from the centre and are drilled along each point. In the centre are eight pegs, each on a length of string. Starting from the centre, each hole represents half an hour's sailing and the eight holes on each point made up one four-hour watch. Each half hour the Officer of the Watch (OOW) would place a peg in the hole corresponding to the course steered.
The four lines of holes along the bottom of the board record speed. These are divided into two blocks. The number of horizontal holes in each block should be at least one greater that the boat's maximum speed. At the end of the first half hour the log would be cast and, counting from left to right, a peg inserted on the top line in the hole corresponding to that speed. This would be repeated each half hour. Each block represented two hours and together they made up a four-hour watch. At the end of each watch the traverse board gave the navigator the information needed to work up a DR.
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