🔍 Key Concepts

• Mid-latitude sailing uses plane sailing for latitude and middle-latitude for longitude corrections • Relationship between difference of longitude, departure, and mid-latitude: Dep = ΔLong × cos(Mid Lat) • Right triangle on a Mercator chart: ΔLatitude, Departure, and Distance/course angle

💭 Think About

• First, decide the general direction: from 14°10'N, 61°00'W to 10°00'N, 53°23'W, are you going NE, SE, NW, or SW? That will tell you if the course should be more than or less than 090°T. • Compute the difference in latitude and the difference in longitude in minutes. How big are they relative to each other? That will suggest if the track is closer to east–west or north–south. • After you compute the course angle from the ΔLat and Dep triangle, convert that angle correctly to a true course (from north, clockwise 0–360°).

✅ Before You Answer

• Be sure you use the mid-latitude (average of the two latitudes) when finding the departure from ΔLong. • Keep your units straight: convert degrees and minutes to minutes of arc consistently before using trig or ratios. • After finding distance, check that your answer’s distance is consistent with your triangle: Distance should be larger than both ΔLat and Dep but not unrealistically large.