According to wiki: “The Mercator projection was designed for use in marine navigation because of its unique property of representing any course of constant bearing as a straight segment. Such a course, known as a rhumb (or, mathematically, a loxodrome) is preferred in marine navigation because ships can sail in a constant compass direction, reducing the difficult, error-prone course corrections that otherwise would be needed frequently when sailing a different course.”
But also according to wiki: “A rhumb line can be contrasted with a great circle, which is the path of shortest distance between two points on the surface of a sphere. On a great circle, the bearing to the destination point does not remain constant. If one were to drive a car along a great circle one would hold the steering wheel fixed, but to follow a rhumb line one would have to turn the wheel, turning it more sharply as the poles are approached. In other words, a great circle is locally “straight” with zero geodesic curvature, whereas a rhumb line has non-zero geodesic curvature.”
Isn’t this contradictory? Maybe I’m not getting what constant bearing means. But why would sailors prefer to continue turning in a direction, as opposed to going constantly straight for the duration of the trip? Doesn’t it make more sense to do the latter
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All these explanations about constant compass heading are correct, but miss an important point.
To sail a great circle, you have To adjust your heading as you move. Your required heading is a function of where you are.
Before the era of accurate clocks (roughly 1800) ships at sea rarely had an accurate idea of their longitude. This makes it difficult to know the correct heading adjustment.
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