Navigation: How to Identify Hazards on a Chart

I mentioned in last week’s blog, How to Judge the Tide and Not Run Aground, that to become a competent boater there are three basic things you will need to learn in order to preserve the value of your boat by staying off the rocks: know the height of the tide, learn how to identify hazards on a chart, and learn how to plot your position on a chart so you know where you are in relation to the hazards.  This week I’ll focus on chart symbols you need to be able to identify as serious hazards.

A hazard such as a wreck can have multiple symbols to indicate the type of hazard

I’m assuming that as a boat owner or prospective boat owner you have some rudimentary knowledge of charts. However a quick review will help our discussion.

Official U.S. government charts published by NOAA have publication dates on them. Waterways may change, and artificial aids to navigation may be altered with little notice. Therefore, old or uncorrected charts should be avoided. A prudent mariner uses the most up-to-date chart available. Fortunately, charts are available online.  Note this site also supplies topographical maps and aerial photos of the same areas for comparison.

Most nautical charts show waterways from our round world on a flat surface by using a Mercator projection. Geradus Mercator came up with a standard way to maintain the angles and shapes of small objects, in 1569, while also being able to represent courses as straight lines.

green can bouy
Keep green marks to port when entering from seaward in the U.S.

Lights, buoys, day marks, and fog signals mark channels, but they also warn mariners of dangers such as rocks, wrecks, and obstructions.  In 1977, the International Association of Lighthouse Authorities (IALA) endorsed two maritime buoyage systems putting an end to the 30 odd systems existing at that time. The two main buoyage systems in the world are IALA System Region A and  Region B. The U.S., North and South America, Japan, and the Philippines are in Region B where red markers and buoys are on the right when returning from sea or going up a river (“red right returning”).and green buoys are on the left.  Europe and the rest of the world are under the IALA System known as Region A, and of course are reversed. Now that we’ve reviewed which side the colored marks should be passed in your area, we are ready to explore beyond them.

red bouy
Remember: Red, right, returning.

Charts use symbols, shading and colors to relate the position and nature of features useful to navigators, such as sea bed information and landmarks. Shading and colors distinguish between man-made features, dry land, sea bed that dries with the tide and seabed that is permanently underwater, and also can indicate water depth—pure white or the lack of color indicates deeper water.

Chart symbols used to describe obstructions and hazards such as rocks, reefs, or wrecks are the ones we want to be able to identify. Each type of hazard has multiple symbols denoting some attribute.  For instance, a wreck that is exposed has a different symbol from a fully submerged wreck or a submerged wreck that is not dangerous. NOAA’s chart 1, has a full list of all chart symbols used on U.S. charts, but the rocks, shipwrecks and obstructions subset are portrayed as follows;chart symbols

Now that you are able to identify depths from my previous blog, and know hazards and obstructions from this one, I’ll address how to fix your position on a paper chart so you can visualize where you are in relation to these hazards in a future post. Staying afloat, maintaining your vessel’s value, and the safety of those onboard are worth the effort.

Written by: Peter d'Anjou

A USCG licensed captain and former merchant mariner, Peter d'Anjou is now a freelance writer and editor. A one-time executive editor at Sailing World magazine, he writes about his passion for racing and boating. Having managed a large yacht repair facility in the NE U.S. his background in boat construction and repair translate to the practical side of boat ownership.