Mercator Sailing

Rhumb-line (constant-course) distance and true bearing between two positions using Mercator meridional parts.

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This calculator requires JavaScript to compute its result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

\tan C = \frac{\text{DLo}}{\text{DMP}}, \quad D = \text{DLat} \cdot \sec C

Symbol	Meaning	Unit
$DLo$	Difference in longitude	min of arc
$DMP$	Difference in meridional parts
$DLat$	Difference in latitude	min of arc
$C$	Rhumb-line course	° true
$D$	Rhumb-line distance	nm

Source: Bowditch Ch.4; Norie's Nautical Tables

Rhumb-line (constant-course) distance and true bearing between two positions using Mercator meridional parts.