Traverse board
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The traverse board is a memory aid formerly used in dead reckoning navigation to easily record the speeds and directions sailed during a watch. Even an illiterate crewmember could use the traverse board.
The traverse board is a simple wooden board with peg-holes and attached pegs. It is divided into two parts.
The top part is for recording direction sailed. It has a representation of the compass rose with its 32 compass points, just as it would have been shown on the face of the ship's compass. Eight concentric rings are inscribed on the compass rose, each with one peg hole at each point of the compass. Eight pegs are attached to the center of the compass rose with strings.
The bottom part is for recording speed. It has 4 rows of holes. Each column represents a certain speed, measured in knots. Eight pegs are attached to this part of the board.
Each half-hour during the watch, a crewmember would insert a peg in the top portion of the board to represent the heading sailed during that half-hour, just as it is shown on the ship's compass. The innermost ring of peg-holes is used for the first half-hour, the second for the second half-hour, and so on until all 8 rings were use.
Each hour during the watch, a crewmember would insert a peg in the bottom portion of the board to represent the speed sailed during the hour. The speed would have been measured using a knot log. If the speed for the first hour of the watch were 10 1/2 knots, the crewmember would count over 10 holes in the first row and place one peg, then place another peg in the column marked "1/2". In the second hour of the watch, the crewmember would use the second row of pegs, and so on until all 4 rows were used.
At the end of the watch, the navigator would collect the information about the speeds and directions sailed during the watch, clear the pegs from the board, and use the information to figure the vessel's dead reckoning track. Meanwhile, the helm of the new watch would begin recording the new sailing headings and speeds on the traverse board.
[edit] External links
- The Pilgrims & Plymouth Colony:1620 -- Navigation: The Traverse Board by Duane A. Cline -- line drawing of traverse board
- The Åland Maritime Museum -- Traverse Board Photo of crude wooden traverse board with pegs
