Challenges of calculating the vortex point of the great circle in international seafarers training guidelines

The Great Circle is the shortest sea route between two points on the sphere. This route is the most economical route for navigation, regardless of the wave and wind. In ocean voyages above 600 miles, the Great Circle Route should be used, which is why the International Maritime Organization has proposed an approved method for seafarers to solve this problem. The method of calculating the Great Circle with the vertex point (the closest point of the path to the pole) which is solved by logarithmic tables has been proposed by the International Maritime Organization. This method has been discussed in all navigation books. In this article, the advantages and disadvantages of this method to solve the problem of the Great Circle are discussed.In this paper, it is shown that the vertex point can be located on either side of the departure point. Therefore, determining its correct position can confuse the calculator.One of the results of this research is that, a method has been proposed to determine the approximate position of the vertex point relative to the departure point, which ensures the accuracy of the obtained results. Using this method, a sailor can calculate the vortex point without any confusion while navigating and use it to solve the Great Circle problem.