If you are boating for the first time, you must know how to read a nautical chart. The good news is that you won’t have any trouble navigating if you have a basic map understanding. The most significant difference between a map and a nautical chart is that the latter is more detailed and outlines the dangers of boating on a certain route.
If sailing on one of the Great Lakes, we suggest you use a chart. It will tell you about any obstructions that will be clearly visible and hidden under the water. The chart will help you pinpoint things like water depths, land contours, and more. You will be easily able to spot green buoys and red buoys.
Following are a few basics that will help you decipher a nautical chart:
You have a choice between a large-scale and a small-scale chart. The scale on the chart is symbolized as a fraction. Here’s an example to help you understand this:
- 1:30,000 = 1 inch (on chart) = 30,000 inches (real life)
- 1 inch = 0.4 nautical miles
- 1 nautical mile = 2.5 inches
Though this is the basic scale calculation, do look at the units mentioned on the chart to ensure you are calculating right.
- A small-scale chart covers a small area but offers great detail. It is usually a harbor chart with a scale of 1:20,000
- A large-scale chart covers a large area but offers less detail. It is usually a coastal chart or general chart with a scale of 1:80,000 or more than 1:1,000,000
Understanding the Basics
Contour Lines
The first thing you will see on a nautical chart is blobby, irregular lines forming different shapes. The lines will be in light and dark shades of blue. These contour lines show the underwater landscape and are represented in fathoms
1 fathom = 6 ft.
As the fathoms will change, so will the water depth. Again, check the chart’s scale to make sure you are making the right calculations.
Depth
Water depth on a nautical chart is depicted by a number. For example, if a number is written on a certain line, it indicates the water depth in that area. Depths are also called sounding, which is denoted in feet or fathoms. These are old measurements and have been updated for the new charts.
When it comes to soundings, they show the lowest tide. The number represents the average depth calculated over 19 years. So, it’s possible that the number might not be accurate. A dramatic change in the tides might lower your calculations.
Chart Symbols
Rocks
Any round symbols with dots show rocks. A rock symbol with a plus sign shows a rock submerged in water. If it has an asterisk, it’s at low tide.
Islets
A blob with a number inside or outside shows how high the islet is above water.
Breakers
A beehive-like sign represents danger. It shows a swell that has doubled in size after hitting a sea bed.
Coral Reefs
A coral reef looks like an amoeba with plus signs in it. This symbol shows places where you can scuba dive but are not safe for sailing.
Obstructions
An obstruction is not a rock or reed. This round symbol with two numbers shows tree stumps, poles, and even submerged cars.
We have shared what the basic symbols on a nautical chart mean. Bookmark this post and revisit it to familiarize yourself with these symbols. Next time you head out for a sail, take a nautical chart with you to memorize the signs.
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