# Chart Reading

### Nautical charts are maps of the sea and its coastlines. The charts include information on water depths and hazards as well as locations of navigational aids such as buoys, lighthouses, and landmarks.

### Charts, with the help of other tools, can be used to find a ship’s location or its heading (the direction it’s pointing). They can also be used to plot a ship’s course. The chart tools on display here have similar functions, but all work in slightly different ways.

*Helpful Defintions:*

The **compass rose** shows the directions on a map or chart. The star is true north and the arrow is magnetic north. The numbers represent the horizontal angles of any given direction.

A **nautical mile** corresponds to one minute of latitude. It equals 1.151 regular miles.

**Latitudes** and l**ongitudes** are imaginary circles around the globe that allow us to locate points on the globe. They are measured in angles. Latitudes, also called **parallels**, are horizontal lines that indicate north-south positions. The equator is at 0° and the north pole is at 90° North. Longitudes are vertical lines that indicate east-west positions. Half of a longitudinal circle is called a **meridian**. The designated 0° meridian, called the prime meridian, runs through Greenwich, England.

The many tiny numbers on a nautical chart are** soundings**. They show the depth of the water at a given point. Soundings can be measured in feet, meters, or fathoms (6 feet = 1 fathom).

#### Parallel Plotter (Weems & Plath #060)

The plotter is laid on a chart with its edge is lined up along a course. The wheeled base then allows the tool to be rolled to the chart’s compass rose where the direction of the course can be checked.

#### Parallel Ruler (Weems & Plath #140)

The ruler is laid on a chart with its edge is lined up along a course. Each edge is then moved alternately across the chart until the ruler reaches the compass rose where course direction can be determined. Designed so that when the edges move apart, they stay parallel to each other, the angle of the ruler is maintained as it moves.

#### Triangle Protractor (Weems & Plath #102)

The protractor is laid on a chart with the long edge lined up along a course. Using a second protractor to maintain the angle, the first is slid until the focal point (where the lines meet at the top center) touches a meridian on the chart. The direction of the meridian line is measured using the numbers on the short edges of the protractor.

#### Course Plotter (West Marine)

The plotter is laid on a chart with the long edge or any of the parallel lines lined up along a course. The edge is slid along the course until the point at the bottom center reaches a meridian. The direction of the meridian line is measured on the central protractor.

#### Divider

Measures the distance between two points on a chart. Each tip is placed at a point on the chart. The spread of the tips is then matched to the chart’s latitude scale. One minute of latitude is equal to one nautical mile.