You are approaching an island landfall two miles ahead. You've heard from other sailboat cruising sailors to keep clear of the razor sharp coral reefs on each side of the entrance. But do you know what these chart symbols would look like on a navigational chart? Boost you sailing navigation skills with these five infamous danger symbols you need to know for safe sailing

1. Know Your Shoal Colors

Scan your chart for blue or green coloring when you approach land. Chart makers make blues darker when the water gets shallower. Use this easy memory key "Then darker the blue, the more danger to you". But you will find many charts that show only one shade of blue.

Highlight the boundary of each shoal that shows depths less that 2 1/2 times your draft. For example, if your small cruising sailboat has 6 feet of draft, you should highlight any shoal water less than 15 feet. Raise this factor as you see fit (to 3 x or 4x draft).

Look for green tinting along the shoreline. This indicates areas that cover and uncover with the tide. In most cases, these shoals will be invisible at higher stages of the tide. Stay well clear of green tinted areas to avoid going aground.

2. Learn Bottom Abbreviations

Know the most common two to three letter abbreviations that tell you the type of sea bottom. These are:

M = mud
S = sand
Rk or Rky = rocks or rocky
Co = Coral
Cl = Clay

Notice that each abbreviation shows slanted letters. Chart makers use slanted lettering on objects that change with the wind, tide, or current. To learn more chart symbols and abbreviations, click this link for a FREE download from the Office of Coast Survey. ==> http://www.nauticalcharts.noaa.gov/mcd/chartno1.htm

3. Beware of Plus Signs

Rocks that are underwater at all stages of the tide look like a "plus" sign. You may see these clustered together or as a solitary symbol. Make sure you highlight them so that they stand out on your nautical chart in all light and weather conditions.

4. Stay Clear of Plus Signs with Dots

Chart makers add dots onto the four open corners of a plus sign if the rock becomes awash==or breaks the water surface==at the low water stage indicated by your chart. In heavy weather, breakers will form over rocks like this. Stay clear to stay safe!

5. Look for Asterisks that Uncover

At low water, some rocks or small islands==called islets==uncover so that part of them becomes visible. Rocks are shown as asterisks, and islets as small, squiggly, uneven circles. Look for an underlined height near the symbol. This shows how much of the rock or islet will be visible at the low water. Some islets show as smooth (not squiggly), uneven circles. These islets are visible at all stages of the tide.

These five chart navigation secrets will get you started on your way to learn the most important chart symbols and abbreviations for safe sailboat cruising. That way, you will gain the confidence you need to keep your sailing crew safe and sound==wherever in the world you choose to cruise.