A nautical chart is a sailor's map of the sea – and learning to read one is both practical and surprisingly enjoyable. Unlike a road map, a chart is packed with information about what lies beneath the surface: depths, hazards, buoys and the safe routes between them. Even in the age of chartplotters and phone apps, understanding the chart underneath is what keeps you safe. Here's a beginner's guide to how to read a nautical chart.
What a nautical chart shows
- Depths (soundings) – numbers scattered across the water show the depth, usually in metres, at chart datum (roughly the lowest tide).
- Depth contours – lines joining equal depths, so you can see how the seabed shelves.
- Hazards – rocks, wrecks and shoals, each with its own symbol.
- Buoys and beacons – marks that show safe channels and dangers, colour-coded by a system called IALA.
- The coastline, harbours and landmarks – plus lights, whose characteristics are written beside them.
Latitude, longitude and the nautical mile
Position on a chart is given in latitude and longitude. The vertical scale up the sides shows latitude – and here's the elegant part: one minute of latitude equals exactly one nautical mile. That's why sailors measure distance with the dividers against the side of the chart, and why speed is measured in knots (nautical miles per hour). Never use the top or bottom scale for distance – only the sides.
Paper and electronic charts
Most boats now navigate with an electronic chartplotter or a tablet app, which shows your GPS position live on the chart – wonderfully convenient. But screens fail, so understanding the paper chart (and carrying one) remains essential seamanship. The symbols are the same on both; learn them once and you can read any chart, digital or paper.
Plotting a course
The basics of chartwork are simple: mark where you are, mark where you want to go, draw a line between them, and check that line for hazards and adequate depth. Then measure the bearing (direction) and the distance. From there you can estimate how long the passage will take and whether you need to allow for wind or current. It's a satisfying skill that turns a chart from a picture into a plan.
Chartwork clicks fastest with a chart in hand and a coastline ahead. Learn it on a skipper training week.
Do beginners need to navigate?
Not on a shared trip – the skipper navigates, but is usually delighted to show you the chart and let you follow the passage. It's one of the most rewarding parts of sailing to learn. More basics are in our sailing wiki.
Frequently asked questions
What do the numbers on a nautical chart mean?
They are soundings – the water depth, usually in metres, at chart datum (about the lowest tide). Depth contours join points of equal depth.
How do you measure distance on a chart?
Using the latitude scale up the sides: one minute of latitude equals one nautical mile. Never measure distance on the top or bottom (longitude) scale.
Do I still need paper charts with GPS?
Yes – electronics can fail, so a paper chart and the skill to read it remain essential backup and good seamanship.
Conclusion
A nautical chart reveals the hidden world beneath your keel – depths, hazards and safe routes – and reading one is a skill every sailor treasures. Ready to plot your first passage? Learn hands-on with a skipper training week.
