Cocked hat.
When three or more bearings are taken from a moving ship, the resulting position lines will not as a rule meet in a point, but form a triangle. This triangle is known as a cocked hat. The name “cocked hat” probably refers to the type of hat worn by officers in the days of sail. The hats were slightly triangular in shape. Remember that a position line indicates a line on which the ship lies at a particular time. If the ship is moving, the intersection of two or lines obtained at different times will not show the correct position at either of the two times. To find the correct position, all the position lines except the last must be transferred by amounts equal to the course and speed of the ship for the differences in time between the observations and the last. Usually the speed of the vessel and the time interval between the taking of the bearings is such that the triangle is very small and hardly noticeable.
The causes of a cocked hat could be one of the following:
- Error in identifying the object.
- Error in plotting the lines of bearing.
- Inaccuracy of observation due to limitations of the compass.
- Compass error unknown or incorrectly applied.
- Excessive time interval between observations.
- Inaccuracy of the survey of the chart.
Mostly the cocked hat is caused by errors 5, 2, 1 and 4.
Example of a cocked hat.