Charts give details of depth, land and sea marks, harbours and hazards.
The seas are much more difficult to navigate and chart than the land because obstacles remain hidden below the water. This is why having accurate charts, careful planning and keeping a constant lookout are very important to being safe at sea.
Knowing how to read charts is very important. You can't always rely on technology to find your way.
Charts have contours that show the shape of the sea bed. Different makes of chart use different colours. The Admiralty charts use colours in this way (depending on the scale of the chart):
| Yellow | Land |
|---|---|
| Green | Areas that cover and uncover according to the tides |
| Blue | Shallow water |
| White | Deep water |
Charts are covered with numbers. In the blue and white areas these are charted depths and they show the depth of the water in metres. All these depths are measured from the lowest tide likely to occur.
The compass on a chart is called a compass rose, this is used for navigation. It's divided into degrees, like a circle. So north is 0°, east is 90°, south is 180° and west is 270°.
The compass rose on a chart shows you the difference between magnetic north and true north for the area shown on the chart. The difference between magnetic and true north varies slightly all over the world. However, if you don't allow for this variation when you plot your course you could end up miles out of your way!
Port can
Starboard cone
West cardinal
East cardinal
South cardinal
North cardinal
North cardinal
light buoy
Wreck
Church spire
See if you can find these symbols in the chart above.
