I was tying up after an afternoon trip punching into a stiff southwest breeze, and getting Irish G’bye ready for the next day, when a new dockmate began asking questions about navigating, and thus … this month’s column.
For those of you new to boating or those who unfamiliar with charts, what follows is a primer, a look at the basics of charts and charting no matter their format. The following info is common to both paper and electronic charts.
Please remember … this is a primer. It includes enough information to get you started … and enough to get you in trouble.
Do every boater — and yourself and family/friends — on the water a favor. Take a safe boating class. First, you’ll actually learn how to boat safely; second, you might meet people just like you; and third, I guarantee you’ll learn at least one thing that will save the day (and make you look like Captain Courageous) on that one time when you get in trouble.
What’s in a Name?
Charts are made by the Coast and Geodetic Survey (under the National Ocean Service). Originally called the Office of the Coast Survey, it was formed in 1807. It later became the US Coast Survey (1836) and then the US Coast and Geodetic Survey in 1878. In 1970 it became the National Ocean Survey under the then-new National Oceanic and Atmospheric Administration (NOAA), and in 1983 was renamed the National Ocean Service (NOS). In December ’82 the Office of Charting and Geodetic Services was created within the NOS and in 1991 the name was changed to Coast and Geodetic Survey, and it is now known as the Office of Coast Survey (OCS), under which the Marine Chart Division is responsible for … ta-dah … charts. The changes in business stationery alone show you how the government spends money!
What Is a Chart?
A navigation chart is a graphic representation of the US coastline and other navigable US waters covering some 3.4 million square miles of nautical territory and is a road map for mariners.
Charts change, on average, every two years but can change as often as every six months or as little as every 12 years. Significant navigational items, such as buoys, lights, day markers, range markers, etc., called ATONs (Aids to Navigation) can change weekly. These changes are logged by the US Coast Guard in Local Notice to Mariners or LNMs; an LNM’s date of issue is expressed as a fraction, so the eighth week of 2012, would be issue 8/12 (52/12 would be the last week in 2012).
Charts are numbered and usually retain that number. The box containing the chart number will also denote how recently the chart was produced. You’ll also find the scale of the map near this box (usually), expressed as a ratio; i.e., 1:24,000, etc. The larger the number after the colon, the less detailed the map. A chart showing Shinnecock Bay, Inlet and Canal would be about 1:48,000; i.e., one inch on the chart represents 48,193 inches in real life or about 2/3 of a nautical mile (or 3/4 of a regular mile) on the chart. Anyway — the bigger the number the more area covered, but the less detail shown. And in navigation, as in everything else, the devil’s in the details.
LNMs are issued by each of the Coast Guard’s nine districts. We in the Long Island area are in the 1st District, which is headquartered in Boston (the 5th is HQ’d in Portsmouth, VA; 7th — Miami; 8th — New Orleans and St. Louis; 9th — Cleveland; 11th — Alameda, CA; 13th — Seattle; 14th — Honolulu; and 17th — Juneau).
It behooves boaters too, if not correct charts based on LNMs (which you should be doing), at least know what changes are occurring in your boating area, because some of them (such as misplaced and/or destroyed buoys or extinguished lights, etc.) can be seriously dangerous if you’re unaware. ENCs are updated electronically, either by DVD/CD or via an Internet connection from the chart manufacturer. The NOS (www.nauticalcharts.noaa.gov/staff/chartspubs.html) produces both paper charts, ENCs, updates and more.
Reading Your Chart
There are zillion ways of using your chart to navigate, plan a trip, locate a marina, return to a favorite fishing hole (well, GPS certainly can help with that, but so can good navigation skills and a chart), but all of them require interpreting the chart’s symbols and other data.
Soundings. These are the numbers located all over the chart. They can be in feet or fathoms, or both, or even metric. You must know what measurement is being used especially since each unit of metric measurement (i.e., one meter) equals three (3) feet; and every unit in fathoms (i.e., one fathom) equals six feet. Quite a bit of a difference if you think fathoms are feet! The measurement unit being used on NOS charts is usually in a distinctive color. It’s also important to note that soundings are taken (Usually. And it’s specified) at MLLW — Mean Lower Low Water — which should mean that unless you are at the lowest time of the tide cycle (MLLW), there should be more water than indicated.
The Road Signs. While you can’t pull over to the side of the road when you’re boat engine goes bad, there are road signs called lateral marks, and referred to more familiarly as buoys. There are, essentially, two colors: green and red. Green buoys are usually shaped like cans, so they’re called cans, and they always have odd numbers. Red buoys usually have a conical top and are called nun buoys and always have even numbers. Buoys shapes may be different than described, but the numbering holds true regardless.
That said, there are green/red buoys, white buoys, black buoys, white/red, white/yellow. Generally —with the exception of the green/red buoys — these mark someplace where you don’t want to go for one reason or another; though small white/red are often used to mark private channels entering a marina, small inlet, etc.
Some buoys have lights (red ones have red lights, green ones green); some have horns, some bells. Regardless, the descriptions are located adjacent to the chart symbol (the symbol for a buoy is sort of an elongated diamond mounted on a small circle). You’ll see a legend such as:
Fl R 2.5s
The first line indicates the number buoy — 32 (even number, so it’s a red buoy). The second line notes it has a flashing (Fl), red (R) light that flashes every 2.5 seconds (2.5s). The third line notes that the 32 buoy also has a bell on it.
There are a wide variety of sounds, names for flashing based on how the flashing is timed, plus other signal devices. If you’re going to boat at night — which I suggest you omit from your repertoire until you’ve mastered boating in the day time — you’ll need to know what a flashing light is telling you by the way it flashes.
There’s a lot more to the “signage” — properly called buoyage — you’ll need to know. How lining up range markers works (and what it means when they don’t line up!), what green and red buoys mean (they mark preferred channels depending on which color is located top or bottom; green top means the channel is to your starboard; red top means it’s to port), and … well, there’s a lot more to learn, but that’s what makes boating so interesting. So take a safe boating course, for Pete’s sake.
Latitude and Longitude
A chart (or any map) is divided up by intersecting lines called latitude and longitude. The best way to remember which is which is that longitude has the letter N in it, and thus north/south.
Longitude lines run across your chart stacked from the Equator to the north and south; latitudes run vertically on the chart from east to west. Latitude starts at the Equator as zero degrees latitude and continues to 90 degrees at the north or south Poles. Longitude starts at Greenwich, UK as zero degrees and runs to 180 degrees east or west from there. By the time it reaches us it’s in the 70s. By measuring where these lines intersect you can tell where you are on the planet. Around here, the numbers are ascending as you head west or north.
If you use electronic charts, manipulating a cursor to a spot on your chart will (or should) give you the GPS coordinates, which are longitude and latitude. Paper charts have the numbers of major intersections down to minutes, which is the second set of numbers in a plot (location). To narrow down where you are you need to go to at least a third set of numbers. I live at 072° 26’ 37” W and 40° 56’ 09” N (i.e., 40 degrees, 56 minutes, nine seconds, north). Find Capt. Gary!
FYI: Loran was a different plotting method similar to latitude and longitude, but was used mostly close to shore. Unlike GPS, which is relatively easy to jam, Loran was considerably more robust, which probably accounts for why it was discontinued!
The Compass Rose
All paper charts have a compass rose. This is an image of a compass printed on the chart showing the four cardinal directions: north (0 or 360 degrees), east (90 degrees), south (180 degrees) and west (270 degrees). It also marks off every 30 degrees and has tick marks for the numbers in between.
The inner circle is based on magnetic north (the direction a compass considers north). The outer circle on true north (the direction along the earth’s surface to the North Pole).
Things get a little trickier here. There will also be a note stating that the magnetic north direction changes by whatever amount of degrees indicated and will have a date which usually coincides with the years the chart was drawn. When you’re navigating sans electronics you need to know what this means (its called declination). Anyway, you need to add or subtract in the directions stated to find magnetic north.
Those of you using ECDs … never mind!
There’s soooo much more to learn about navigation, whether on paper or electronically, but I hope this whets your appetite for more. You’ll need some tools (dividers and parallel ruler) to start, but you’ll learn a lot along the way. And everything you learn makes you a smarter, better and safer boater.