Great Circle Sailings
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Great Circle Sailings book
A Great Circle is a circle on the surface of the Earth which equally bisects the planet into two hemispheres, with the plane of the Great Circle passing through the centre of the Earth. The Equator is a Great Circle satisfying the definition, as are all meridians of Longitude. For short distances, there is not a terrific saving to be made by using a Great Circle track, but for oceanic voyages the Great Circles will arc up to the Northerly or Southerly Latitudes. The further North or South that the paths of these tracks follow, the greater the savings. The fundamental difference between a Great Circle and rhumb line course is that unlike a rhumb line track, the Great Circle course changes constantly and on a Mercator chart, the course line when plotted from Waypoint to Waypoint along the passage, follows a curved path with the course changing constantly.