Bracketing (nautical)

As bracketing (engl. Einklammern, straddle ) is in the nautical navigation refers to a method with which one the Versegelungs can avoid correction of measurements to constellations or landmarks.

By measuring at the astronomical location determination can be reduced with the sextant, the elevation angle to two constellations A and B, has the second measurement on the time of the first (influence of the now traveled distance ). If, on the other hand, the first star is observed again (ABA) and the base line is averaged with the first, the influence of the distance (i.e. the sail) is largely eliminated. This "clip" (Engl .: bracket ) works with sufficient accuracy to the time differences of 3 to 5 minutes (usually takes a measurement of a maximum of 1 to 2 minutes).

The procedure is similar if you take a bearing on two landmarks near the coast in order to determine the ship's position on the nautical chart by intersecting two straight lines ( terrestrial navigation ). The first landmark is sighted a second time and averaged, which results in the ship's location at the mean time of the 3 measurements.

In radio navigation , bracketing is a simple method for taking drift into account . When heading towards a VOR rotary radio beacon, its bearing changes continuously due to the cross wind. You then change the course about twice as much in the other direction until the bearing "stands". Then the aircraft or ship moves exactly towards the radio beacon, while its longitudinal axis deviates from it exactly by the drift angle.

literature

• Benjamin Dutton: Navigation and Nautical Astronomy , Chapter IX (Celestial Observations). 10th Edition, US Naval Institute, Maryland 1951
• Aviation Handbook, VOR navigation