The ABCs of reading charts

Fall 2008

Navigation

This is an article from WaveLength Magazine, available in print in North America and globally on the web.

To download a pdf copy of the magazine click here: > DOWNLOAD

By Adam Bolonsky

Learning to read charts is one of those simple yet oddly engrossing skills anyone can pick up in an hour or so. Written, maintained and printed or distributed via a variety online and print sources by the U.S. Hydrographic Service and the National Ocean Service, charts are a wonderful trip planning resource.
Reading them as is much art as skill. With a little practice, you can use a chart to create richly-detailed trip plans that extend to being able anticipate where shorelines will be landable, where waves are likely to be powerful and tidal currents swift, and where to take cover in a storm.
Here, then, is a brief guide to some of the more useful chart symbols: those that mark major lights and landmarks, boat or shipping channels, and what kinds of coastline, from sand to cliffs to boulders, you can expect to come across anywhere you paddle.
The information is for NOAA charts. For Canadian charts use Chart 1, Symbols Abbreviations Terms. The principles are generally the same.
The information below is from NOAA Chart No. 1. The information in bold type and brackets corresponds to the section heading on the NOAA download page, if you wish to download just that portion.

NOAA Chart No. 1 detail. It's the end of an era. NOAA no longer prints Chart No. 1 in book form. It’s now available only online as a pdf file. Download it at http://nauticalcharts.noaa.gov/mcd/chart1/chart1hr.htm.

Nature of the shoreline symbols, page 14 (natural features section). Note the extent to which charts represent the kinds of shore (and thus the types of landing challenges and camping challenges we can expect) anywhere along the coastline of North America. The symbols above also are useful for helping you figure out where you are. If you see dunes, hills or a boulder-strewn shoreline on the nearshore horizon, look for that shoreline on your chart to figure out where you are – or where you are not!

Shoreline contour detail, page 15 (natural features). Charts also give the contour and spot heights of the shore. Using these symbols and phrases, your chart will describe prominent visible shoreline features like ridges, mountaintops, cliffs, etc., and the spot height of visible stands of trees or forest. They’re doubly useful to such advanced navigation skills as such triangulation, creating ranges to compensate for tidal set and drift, and drawing LOPs (lines of position) if you keep a log to mark your location over time.

Light symbol detail, page 61 (lights). Of particular interest to ocean kayakers are major and minor lights, whether onshore or off, all marked with the lavender exclamation point above. Lavender exclamation point symbols for a major light are always followed by a code that spell out the light’s color (white unless otherwise remarked), how often the light flashes, in what kind of pattern, and the light’s height and range. The simple alphanumeric codes are easy to decipher, as you’ll see in the next example:

Light period, elevation, range, page 64 (lights section). These codes that follow the lavender exclamation point are for major lights only. They describe the light’s period (how often the light flashes) its height above mean high water level in either feet or meters, and finally the light’s range, or from how far away it is visible at night.

Light color codes, page 63 (lights). A major light code will also include the light’s color. The code isn’t tricky. W means white, R equals red, and so on. Fortunately, most lighthouses throw a white light, which makes them easy to distinguish from other flashing navigation lights in the area. Other than white, green and red are the most common light colors you’ll see at night. Both colors may be visible at the same time at night, when two buoys close to each other mark a channel. Other times you’ll see red or green only, oftentimes at the edge of a channel or to mark the preferred route around a headland or other hazard.

Flash light types descriptors, page 62 (lights). Lights are also distinguished, and coded, according to their flash pattern. To get a grip on those various flash patterns, scan the table columns above from left to right. The two left-most columns give the coded abbreviation for the flash patterns to look for. The third, middle column gives the light’s description with a variety of technical terms. Finally the right-hand column shows, graphically, what those different flashes actually look like at night. Being able to distinguish one type of light from another is especially helpful at night.

A complete lighthouse code, page 64 (lights). Putting all those elements together is not all that difficult; indeed, here’s what a full coded lighthouse description looks like. First note the distinctive lavender exclamation point, then the code:
FL (3) WRG 15S 21FT 11M
In the example above, the light in question flashes white, red or green three times every 15 seconds (FL (3) WRG 15s). The light is 21 feet tall (21 FT) and is visible at a range of eleven miles (11M), not including its looming. To figure out the period and pattern of a light you see on the horizon, a simple count will do. Count the number of flashes, then count one one-thousand, two one-thousand to time it. Instantly you are much more aware of where you are than you were a moment ago.

Bells and Buoys detail, page 75 (Buoys, Beacons section). Here are the symbols and words used to describe bells, gongs and whistles buoys you’ll come across both inshore and off. Each type is wave activated: as they move up and down in swell or waves their bellows or clangors create a distinct, some would say reassuring sound. The symbols in the two lowest rows shown above (the starboard and port buoys R “2” and “1”) are used to mark, respectively, the numbered red nuns and green cans you’ll see on water. If a nun or can makes a sound or is lit, its code will say so. (The pictured black can doesn’t exist anymore.) Red nuns and green cans mark the channels we as kayakers should stay out of, should cross in tight, easy-to-detect groups, or cross in limited visibility after making a traffic control security call. Keep in mind the mnemonic for boat channels: red right return, which means that boats returning to harbor will leave red nuns to the right (starboard), green cans to port (left). Remember too that wave-activated bells, gongs and whistles, mark either hazards or channels. Their clangs and hoots can be reassuring to hear at night and in fog.

Depth contour line detail: Depths are also of great interest to sea kayakers, especially if a shallows abuts great depths and the wind or sea are up. If the sea or wind are up, shallows adjacent to depths will be lively with swell, breaking waves and whitewater, surge or overspill. Depending on your skills and interests, those kinds of conditions will be either fun or nightmarish.