1. Parallel Sailing
Parallel sailing means sailing along a parallel of latitude which also means maintaining a true course of east 090 or west 270.
The distance sailed would be the departure at that latitude.
Departure / D’long = Cos Lat
2. Plain Sailing
we can assume small areas of the earth surface are flat and can apply trigonometry without any error, But after 600 nm we cannot do this.
Departure / D’long = Cos (Mean LAT)
Tan (Co) = Dep /d’lat
For sake of convenience in
Rhumb line – Rhumb line is a line that cut all meridians at the same angle. All lines drawn are Rhumb line on a Mercator chart.
Characteristics of a Mercator Chart
- Equator appears as a straight line.
- All meridians appears as st. line parallel to one another.
- meridians cross equator at 90degree.
- Distance between consecutive meridians are constant.
- Polor regions do not appear.
- Parallel of latitude would appear as a stright lines Parallel to one another.
- Distance between parallel of lats increases as latitude increases.
- One minute of d’long is same size in all parts of the chart.