A nautical chart is a map made for travel on water. It helps sailors, boaters, and harbor pilots understand depths, hazards, shorelines, navigation aids, and safe passages. Unlike a road map, it shows information below the water surface as well as landmarks above it.
Reading a nautical chart matters because a small mistake in depth, direction, or position can put a vessel in danger.
Key Facts
- Depth soundings show water depth, often in meters, feet, or fathoms depending on the chart.
- 1 fathom = 6 feet, so 4 fathoms = 24 feet.
- Latitude lines run east and west and measure distance north or south of the equator.
- Longitude lines run north and south and measure distance east or west of the prime meridian.
- A compass rose shows direction and helps convert a planned route into a bearing, such as 045 degrees.
- A safe route should avoid shallow water, rocks, wrecks, restricted areas, and traffic separation zones.
Vocabulary
- Nautical chart
- A nautical chart is a specialized map that shows water depths, shore features, hazards, and navigation aids for traveling on oceans, lakes, bays, and harbors.
- Sounding
- A sounding is a number on a nautical chart that tells the measured depth of the water at a specific location.
- Buoy
- A buoy is a floating marker that guides vessels, marks channels, or warns of hazards.
- Compass rose
- A compass rose is a circular diagram on a chart that shows directions and bearings in degrees.
- Bearing
- A bearing is the direction from one point to another, measured in degrees clockwise from north.
Common Mistakes to Avoid
- Ignoring the chart units, which is wrong because a depth of 5 meters, 5 feet, and 5 fathoms mean very different levels of safety.
- Assuming all blue areas are safe water, which is wrong because color shading only gives general depth information and must be checked with soundings and hazard symbols.
- Plotting a straight route through obstacles, which is wrong because boats must follow safe channels and avoid rocks, shoals, wrecks, and restricted areas.
- Using magnetic direction without checking the compass rose, which is wrong because charts may show true north, magnetic north, and local variation that affect the bearing to steer.
Practice Questions
- 1 A chart uses fathoms for depth. If a channel is marked 3.5 fathoms deep, how many feet deep is it?
- 2 A boat needs at least 2 meters of water beneath its keel for safe travel. If the boat draws 1.4 meters and the charted depth is 4.8 meters, how much clearance is below the keel?
- 3 A plotted route from a harbor to an island crosses an area marked with several rock symbols and shallow soundings. Explain how you would revise the route using the chart.