Chart Navigation & Plotting · Mid-Latitude Sailing
In mid-latitude sailing, departure is converted to difference of longitude using:
- AdLong = departure multiplied by the cosine of mid-latitude
- BdLong = departure divided by the cosine of mid-latitude✓ Correct
- CdLong = departure multiplied by the sine of mid-latitude
- DdLong = departure multiplied by the tangent of the course
Explanation
Since departure = dLong × cos(lat), solving for dLong gives dLong = departure ÷ cos(mid-latitude). The mean (mid) latitude approximates the converging meridians over the run.
Authority: Bowditch (Pub. No. 9), mid-latitude sailing
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