Rhumb Line
The Rhumb Line: A conventional line on the Earth’s surface that intersects all geographic meridians at the same angle. It has the shape of a spiral that approaches the poles without going through them.
A ship moving between two points on the Earth, navigating in same course, will describe this spiral.
If the angle of intersection is 90° or 270°, it is parallel to the equator.
And, if the angle of intersection is 0° or 180°, it coincides with the meridian.
On the Mercator projection charts, the line appears as a right line, allowing you to trace the ship’s course and make quick and easy work on the chart.
This line intersects all the meridians at the same angle, equal to the ship’s course, approaching from the Equator to the pole, without ever touching it.
It’s not the shortest distance between of two points on the globe.
The shortest distance between two points on the Earth is the large circle arc passing through those points, called the Great Circle.
However, on short and medium distances, navigation is done only on the rhumb line, due to the great advantage of keeping the same course and in solving the navigation problems.
Rhumb-Line Course: The direction of the rhumb line from the departure point to the arrival point.
Rhumb-Line Distance: The distance from point to point along a rhumb line.
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