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Backstaff Instruments

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The Traverse Board
The Traverse Board was used to record course and speed over a four hour watch. This example was made from oak. The points of the compass rose and the fleur d'lis were hand carved.
This instrument was used from the 16th through the early 18th centuries.

The Traverse Board was used to record the course and speed of the vessel for an entire four hour watch. The speed was measured by the chip log, and the course was obtained from the compass.

Each 4 hour watch was broken up into 8, 30 minute segments. At the start of a new watch, the log was hove. The measured speed was indicated in knots and eigths of a knot by placing pegs in the first two rows of holes at the bottom of the traverse board. The first row denoted knots; the second eigths of a knot. There are eight sets of two rows of holes at the bottom of the Traverse Board: one set per 30 minute "glass" of the watch.

The heading was obtained from the compass and a peg was placed in the appropriate hole in the inner ring of the compass rose at the top. There are eight concentric rings of holes: one ring for each 30 minute "glass" of the watch.

Once the four hour watch was up, the traverse board was taken below to the chart. The courses and speeds recorded thereupon were used as the basis of the Dead Reckoning plot. In Cabot's time, you were done, with the exception of a latitude reading taken with, say the cross staff. In Napoleonic times, sextant or quadrant readings were taken and your latitude reckoned (if you could see the sun or North Star). The Chronometer gave you your longitude. But all was checked against the DR plot.