probetacking

Probetacking is a navigation technique used on boats to estimate an accurate position at sea. It involves using a magnetic compass, a length of cord or twine, and a series of vertical marks known as stakes or tacks to chart a boat's course.

The technique relies on the principle that the angle between the boat's course, the magnetic compass, and the position of the sun or a landmark remains relatively constant, known as the "probetacking angle." By measuring the angle between these elements, a sailor can determine the direction of the boat's course and, consequently, its position at sea.

To use the pro betacking technique, a sailor typically sets up a series of stakes on the deck or on shore, with the twine or cord tied to the boat. The magnetic compass is then placed on the boat, and the angle between the compass needle and a landmark or the position of the sun is measured using a protractor or similar instrument.

With the probetacking angle known, the sailor can calculate the direction of the boat's course and, using a chart or map of the area, determine the boat's position at sea. While more complex than other navigation methods, probetacking can be an effective technique for estimating a boat's position, particularly when other methods are not available. However, it does require a relatively steady and level horizon, and can be affected by the presence of magnetic interference or other external factors.