The Traverse Board

The origin of the Traverse Board is unknown to us today, but we do know that it's use has has been documented since the mid-1500s, and it is likely it was developed as early as the 1500s.

A normal "Watch" period aboard a ship, the crew's work periods, were four hours long. They were typically broken up into half-hour segments because it was more convenient to use a half-hour sandglass. At the end of each half-hour, a bell was rung to remind you that it was time to record how fast you were going during the past half-hour as well as the direction you were steering. This information was obtained from the Traverse Board.

The Traverse Board has a diagram of a compass on it with all 32 points listed. The points are the directions the ship could be sailing. On each of these points there are eight holes drilled, from the center to the outside edge. You therefore have eight concentric circles covering all of the points of a compass. Each circle represents one half-hour segment of an eight-hour watch. In the center of the compass diagram there are eight pieces of line with a peg attached to each. After each half-hour, the ship's boy would place one of the pegs in a hole representing the direction the ship had been sailing for the last half hour. He would do that for each half hour of the watch and thereby create a record at half-hour intervals of all the courses steered during the watch.

At the bottom of the Traverse Board, there is a second "table." There are four rows of holes on the left side and four rows on the right. Each row represents a half-hour of the watch and allows a sailor to record the ship's speed. Each row corresponds to the concentric circles found around the compass. The first concentric circle on the compass is marked for the direction traveled at the end of the first half hour. The speed for that first half hour is marked on the first row in the lower table, the drilled holes in the row representing the ship's speed in knots. The third hole would be three knots, the fifth hole, five knots, etc. There are eight pieces of rope with pegs attached at the bottom of the Traverse Board to keep track of the speed during each half-hour.

Christopher Columbus

At the end of the watch the navigator can tell the direction and speed at each half hour interval by looking at his "computer," the Traverse Board. He then uses the board to come up with a composite, or single course and distance traveled for the four-hour watch period. It was easy to convert speed to distance for each half hour: four knots for half an hour is two nautical miles.

Of course, if the wind doesn't change at all during the four hours, neither the course nor the speed might change, but winds usually do change and thatís why there was the need to keep track of them.


Click on the Piece of Eight to return to the Main Page