How to Read Nautical Charts

In this day and age of GPS powered everything, nautical charts seem so... antiquated. But there are still some things charts can tell you that a GPS cannot. 

For example, this: 



This busted prop came to us a few weeks ago, perhaps a victim of an old rock pile out by Trout River. This particular pile is marked with "danger shoal" signs, but it may be unclear to those who don't know the area (or don't know what this means) how much area this signs refer to. So, even in waters you are familiar with, but especially in waters you are unfamiliar with, it's important to be able to read nautical charts.

As you likely know, there are a variety of charts out there to choose from. Depending on the location you will are navigating, different charts will be necessary because they are produced in different scales. Sailing charts are used for open ocean navigation. General charts are used for coastal navigation in sight of land. Coastal charts zoom in on one particular portion of a larger area and are used for navigating bays, harbors or inland waterways. Harbor charts are used in harbors, anchorages and small waterways.

First, you must know your latitude and longitude. They're easy to remember if you take a close look at each word. Latitude refers to the lines that go around the globe horizontally, while longitude lines circle the earth lengthwise.

The next most important function of a nautical chart is to show the depth and bottom characteristics (being able to read this would have helped the poor boater with the prop above!) through numbers, color codes and underwater contour lines. The numbers indicate soundings and show the depth in that area at low tide. Soundings in white indicate deep water (you'll notice your channels, therefore, are generally white). Shallower water is indicated by blue on the chart and should be approached with caution using a depth finder.

Fathom curves are the wavy lines, and they provide a profile of the bottom of your body of water.

Every chart will have a different distance scale, so it's important to take note of yours when using a particular chart. These scales are typically printed at the top and the bottom of your chart. 

There are other items of use and interest printed on nautical charts as well. Power lines, bridges, buoys and more are all marked. Take note of these markings as well. It's good to be aware of them, especially at night, and they will help you locate your current location on a chart.

This is just a brief overview of nautical charts. What other tips do you have for someone learning how to read a chart? What is your favorite chart to have on board for the Jacksonville area?