🔍 Key Concepts

• Mercator sailing relationship between difference in longitude, difference in latitude, and course: ( \tan C = \frac{\Delta \text{Long (in minutes)}}{\Delta \text{Meridional Parts}} ) or its equivalent form. • How to find difference in latitude from distance and course: ( DLat = D \times \cos(C) / 60 ) and decide if you are going north or south. • Using the meridional parts (MP) table for the starting and ending latitudes to get ( \Delta MP ), then using that to find ( \Delta Long ).

💭 Think About

• Is your course 241° T taking you toward the equator or toward a pole? Use that to decide whether your latitude increases or decreases. • Once you compute the new latitude from the distance and course, what are the meridional parts for the initial and final latitudes, and what is their difference? • Given a southwesterly course, should your longitude increase or decrease in the western hemisphere, and by roughly how much for a 2000+ mile run?

✅ Before You Answer

• Make sure you convert the distance to difference in latitude in degrees using ( DLat = D \times \cos(C) / 60 ). • Verify you are using the angle from the meridian (0–90°) in the Mercator formula, not the full 0–360° course when applying ( \tan C ). • After computing ( \Delta Long ), check the sign and hemisphere: starting at 123° W and moving on a southwesterly course, should the final longitude be greater or less than 123° W?