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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The way I read it, it has to do with “knowing where you’re going”. Yes, a great-circle would be shortest en you could go ‘fixed steer’, but what if you can’t be sure your steering is properly fixated? Fixating the rudder on a ship will not prevent it from drifting and turning (as opposed to rubber tires on concrete). Thus, you would prefer a method where you can constantly check and correct your course in a simple way. Doing this by keeping the same direction on a compass, gives you the ‘rhumb line’ as your traveled path.
disclaimer: I have no knowledge of the subject, just interpreting the text you provided.
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