An eighteenth century Dutch traverse board, used as a memory device by mariners in dead-reckoning navigation.

Dead-reckoning was used throughout the age of discovery. It relied on three calculations: the ship’s compass heading, the ship’s speed, and the time spent travelling for each direction and speed. If a navigator, beginning at a known position, kept track of these three things then he could calculate the distance travelled in a certain direction, and thereby know his current location.

The traverse board made it simple for mariners to keep track of this crucial information. The top part, a standard compass rose with 32 points, was used to mark the direction travelled. The bottom part was used to mark the speed of the ship. Wooden pegs were inserted into the holes at half hour intervals, thus keeping track of time. At the end of the watch, the information recorded on the traverse board would be noted in the ship’s log. This straightforward and easy to use device remained popular with mariners until the nineteenth century.

As with all nautical instruments, mortality rates for traverse boards are high and so few remain intact today. Examples can be found in the National Maritime Museum, Greenwich (three examples), The Mariners’ Museum and Park, Virginia, and Penobscot Marine Museum, Maine.