🔍 Key Concepts

• Mercator sailing: use meridional parts to find difference of longitude from course and distance • Relationship between departure, DLo, and mean latitude in Mercator sailing • Convert true course and distance into difference of latitude and difference of longitude

💭 Think About

• From the given course and distance, what is your approximate track direction (southwest, northwest, etc.) and should longitude increase East or West? • How do you find difference of latitude from course and distance, and then use mean latitude and meridional parts to get difference of longitude in Mercator sailing? • After you compute the difference of longitude, how do you correctly apply its sign to the starting longitude to get the final longitude?

✅ Before You Answer

• Confirm whether the vessel is going toward or away from the equator so you can tell if latitude should increase or decrease • Check that your difference of longitude is reasonable for a 3599‑mile run at that latitude (not more than 180°) • Before choosing, verify that the resulting longitude is on the correct side of Greenwich (E or W) based on the course quadrant