Great Circle Sailing : shortest distance measured along the earth's surface between two places is called the Great Circle Distance. The departure and arrival positions are marked on a Gnomonic Chart and joined by a straight line. Waypoints are transferred from Gnomonic to Mercator chart and it appears as a Curved line on Mercator chart.
Mercator Sailing : Used to find the Rhumb Line course and distance between two positions. It uses the following formula -
Rhumb Line: Rhumb Line is a line drawn on a Mercator Chart which cuts all meridian at same angles.
Composite Sailing: Sometimes, it is not possible to execute a full great circle for a voyage. This could be due to presence of navigational dangers in between OR if the Master decides not to go beyond a certain latitude owing to weather conditions. In this case, a combination of rhumb line and great circle sailing. Together this type of sailing is called as Composite Sailing.Also read this What is the difference between AIS A and AIS B?
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