Nautical charts are an important tool to support safe navigation at sea. Several projections have been studied to develop charts for various maritime applications. Among them, the only Mercator projection satisfies the requirements of a nautical chart. However, the disadvantage of Mercator projection is the distortion that increases gradually to both poles. Therefore, Gnomonic charts are used to replace Mercator charts for navigation in some areas. However, the Gnomonic chart does not satisfy the basic requirements of a nautical chart, not built by an equiangular projection and the rhumb line is the curve on the chart. For building the nautical charts, the article will study the theoretical and practical basis of using Gnomonic projection instead of Mercator projection in determining the limit that the distortion of the Mercator projection affects the safe navigation, the conditions which the distortion of a Gnomonic projection has an influence on the safety of navigation in the allowable limits and finally determining the conditions and providing a method of navigation when using the Gnomonic chart instead of the Mercator chart.