Lesson routeWhat a Chart Is For0/4 read
Lesson 1 of 4
What a Chart Is For
A chart is not just a map of water. It is a working safety document showing depth, drying areas, hazards, buoyage, coastline, lights, tidal information, and local notes.
For beginner navigation, the chart answers three practical questions: Where am I? What is around me? What do I need to avoid next?
- Use the chart before departure, not only when lost.
- Depths, drying heights, hazards, and notes matter for small craft.
- Chart symbols need checking against the chart's own key or publication.
- Keep your position awareness updated as the trip develops.
| Chart feature | What it tells you | Beginner check |
|---|---|---|
| Depth figures | Charted depth below chart datum | Compare with tide height and vessel draught |
| Drying areas | Areas that cover and uncover | Avoid unless the tide and route make it safe |
| Symbols | Rocks, wrecks, buoys, lights, cables, restrictions | Use the chart key or almanac to confirm meaning |
| Latitude/longitude | Position reference | Use consistent format when reading GPS or giving position |
Lesson 2 of 4
Position Awareness
Position awareness means knowing roughly where you are, where hazards are, and whether the boat is still on the intended route. It does not require a formal fix every minute.
Use multiple clues: depth, buoyage, bearings, transits, GPS, chart plotter, coastline shape, harbour features, and time since the last known position.
- Cross-check electronic position with what you can see.
- Do not wait until uncertainty becomes a problem.
- Use depth as a warning, not as the only navigation method.
- Record or remember the last position you trusted.
Lesson 3 of 4
Latitude, Longitude, and Formats
Latitude and longitude give a position reference. Beginners often make mistakes by mixing formats, missing a decimal place, or reading minutes as seconds.
When copying a GPS position, write the complete format, hemisphere, and datum where relevant. For emergency communication, slow down and read the position clearly.
- Latitude is north or south; longitude is east or west.
- Do not mix degrees-minutes with decimal degrees.
- Check leading zeros and decimal points.
- Read position slowly during a call for help.
Lesson 4 of 4
Depth and Draught
Charted depth is not the same as water under the keel. You need charted depth, tide height, vessel draught, and a safety margin.
A beginner should avoid marginal depths until the method is comfortable. It is easier to stay in safe water than to recover from an avoidable grounding.
- Draught is how much water the boat needs below the surface.
- Tide height adds water above chart datum.
- Allow a margin for waves, pressure effects, squat, and uncertainty.
- Do not treat a depth sounder as a complete navigation plan.