Unlocking the Chart


Ft. Lauderdale entrance chart.

The nautical chart is for the mariner what the road map is for the driver. The traditional chart is made from paper and has a large format. Now, we also have electronic charts that work with our GPS units. Both electronic and paper charts provide information necessary to safe navigation.

In order to get the most out of the information on this page you'll find many of the buoys, beacons, and lights are thoroughly covered in Aids To Navigation.

Some of the information on charts is in written format but with many abbreviations. Other information is in symbol format such as the lighted aids to navigation in the chart at left. There is a wealth of information on a typical nautical chart. The depth of water, buoys, lights, dangerous areas, hazards, and quality of the bottom for anchoring to name just a few.

Below, we'll be taking a very close look at the chart on the left. We actually call this small one a chartlet. The full size version includes a larger area plus a whole lot of information, things like the chart datum, the projection method, tides and currents, and who made the chart.

In the US most of our charts come from the Federal Government office called NOAA. All the charts used on this website are reproductions of NOAA charts. Fortunately, these are legal to reproduce in the US.

Charts come in large scale and small scale sizes to provide the most relevant information for the task at hand. If I wanted to navigate (or pilot) my vessel into Port Everglades (the port for Ft. Lauderdale, FL) I would use the chart at left which is a large scale (think small area) chart. If we wanted to plan a trip to Key West this chart would not suffice. We would need a whole series of large scale charts or we could use one or two smaller scale charts. One big advantage of electronic charts is the ability to zoom in or out on any chart without having to go to another chart altogether. The disadvantage here is that you cannot look at both charts at once. Below is a small scale chart called 'Straits of Florida and Approaches'. It includes the southern half of Florida and all of the Keys. You can barely see Ft. lauderdale in the chart but it is just north of Miami.

Small scale chart of Florida

We'll be talking about Chart #1, you may order a hard copy from our Ship's Store. This is not a chart at all but a guide to NOAA charts. In it, is listed all the definitions of the various symbols and abbreviations used on charts. A highly useful guide. If you have the patience you can look up anything from the chart in Chart #1. You can download or look here: http://www.nauticalcharts.noaa.gov/mcd/chartno1.htm Some examples of what you'll find follow. Aids to navigation (buoys, markers, and lighthouses) and their associated lights are covered on a different page, Aids To Navigation.


Excerpt from Chart #1

The numbers on the far left are for reference purposes only and carry no meaning for what is being described.

Leading light (11) and Lighted range (11a) are essentially the same. The characteristics of the lights will be found next to them on the chart.

Sector light is just that, a light that shines through a certain sector typically warning of danger also true for the Directional light.



Excerpt from Chart #1

Wreck symbols found on charts. Remember dotted lines surrounding the symbol emphasize the danger to navigation.



Excerpt from Chart #1

Current symbols found on charts. Kn stands for the current's drift (speed) in knots while the set is indicated by the direction of the arrow.


Excerpt from Chart #1

Rocks that are above the water at least some of the time.




Excerpt from Chart #1

Dotted lines emphasize danger. These are some of the most important symbols on the chart indicating rocks and obstructions. Take extra precaution.



Now, let's delve into the heart of the above harbor chart of Ft. Lauderdale, FL (Port Everglades). We'll go through everything shown from top to bottom. Like most major ports this is a very well defined entrance.

Port Everglades seabuoy

This is the sea buoy for Port Everglades entrance channel. Please refer back to Aids To Navigation for a full explanation of buoys. It is a mid-channel buoy which we know because "RW" translates to red white vertically striped. We also know it is a lighted, floating buoy because of the solid magenta (purple) circle at the center. Just after the "RW" we see "PE", short for Port Everglades, that will be painted onto the buoy. It's set off with quotation marks because that is what the buoy actually says on it. It flashes "Mo (A)" at night which is morse code "A"; one short flash followed by a longer flash and repeats every few seconds. Since the light's color is not listed, by default we know its white. We also see "RACON (-)" which is a device that reflects back an incoming radar beam with a dash so it can be recognized better. Sea buoys are mid-channel buoys meaning they can be taken on either side as they have good water all around. The numbers 111 and 93 are depths of the water in feet. See below.

Chart showing water depths

Water depths are indicated by these black numbers. When they are located close to an aid to navigation care must be taken to identify them properly. Water depths on charts can be measured in feet, fathoms, or meters. The units of measurement are usually stated in large format on the edges of charts. Sometimes you'll see a number for depth written 32 for example. Right away, you know this chart does not use feet as its unit of measurement. If the chart units are meters you know the depth here is 3.2 meters. If the chart units are fathoms you know the depth here is 3 fathoms plus 2 feet for a total of 20 feet.

Cable area on chart

Cables lying on the sea floor are marked on charts. A rather important consideration when anchoring. The chart will either say 'Cable Area' or there will be a squiggly line. The dashed line at left is showing a boundary of a restricted area just outside the port.



Entrance to channel

Red, right, returning as we now enter Port Everglades channel marked by two floating, lighted buoys. The channel numbers start with 1 & 2 then go up from there as we progress into the port. Let's go over the buoy on the left to see if we can decipher the "code". "R" stands for red so we know as we enter to leave it to starboard. Since all red buoys have even numbers we expect to see a "2" and indeed we do. "Fl" stands for flashing. Already knowing what "R" means we expect, at night, to have a floating buoy that flashes red every 2.5 seconds.

Chart showing rocky conditions

Condition of the bottom. What I'd like you to notice here is the "rky" in the lower right corner which stands for rocky. This is a condition of the bottom and very useful information in finding an anchorage. Some other common conditions of the bottom you'll see on charts are; S for sand, M for mud, Co for coral.




Chart showing blue and white waterWhat I'd like you to notice in this illustration is the area where there is blue shaded water on the chart. The tan area below is dry land. Color of water is used to indicate depth and possible danger. Deeper water is white and more shallow water is shaded blue. The exact depth where one takes over from the other depends on the scale of the chart. Here, if we look closely, we'll see a depth of 6 feet right at the edge of where the two colors meet. Underneath and obscured by the depth of 4 feet it looks like the word "shoal" appears. Shoal water is shallow water.

Chart showing entrance lights

Now we come to the next set of markers (also aids to navigation) as we proceed into the port. These look different than the first outer markers. They don't have magenta circles but magenta tear drop shapes. This tells us they are attached to solid earth rather than floating. Here, we assume they are on pilings in the water and, since they are magenta, we know they are lighted. Let's look at the one on the left and see if we can figure out what it says. We know that 10 is simply the depth of the water but just under the marker we can read "Fl R 4s" and under that is "5M "4"". We should know by now how to read the first letters as: Flashing red every 4 seconds. The second phrase translates as: The light is visible, in perfect conditions, for 5 miles (statute) and you will find a number 4 on the buoy.

Beacons. Do you notice the small square boxes on the left side of the above illustration? There are two and they are both labeled "W Bn". The "W" stands for white while the "Bn" stands for beacon. We can see from the chart they are probably warning us of the shoal water just ahead. Beacons are typically diamond shaped and white and usually are warnings of shallow water.

Chart showing tower

Towers. Look right in the center of this illustration and you'll see a black circle with a dot inside. You'll also see it is labeled "TR" which stands for tower. Now, we're inside the port and passing markers 6 and 7. Going in a bit further we see a small rectangular harbor on the right, it is labeled "CG" which stands for Coast Guard. There is a Coast Guard station in Port Everglades.



Chart showing a security zone

In the lower right corner you will see the words "Security Zone". This came into being after 9/11 as an enhancement to the security of the port. Often, cruise ships dock here and you'll notice a police boat patrolling the area.






Chart showing bascule bridge

Several things to talk about here. Notice the two dotted lines just above the security zone. This represents the Intracoastal Waterway; a major channel of water running from New Jersey to Texas. Looking at the upper left corner you'll see two thin strips of land trying to cross the Intracoastal but not quite joining. This is a bridge. Bridges and sailboats don't always mix so let's see if we can figure what's going on here. If we read just below the bridge we will see its description. These are two Bascule Bridges and under that we see the clearances of 125 ft horizontally and just 55 feet vertically. Any larger sailboat will not be able to pass! Except, it is a bascule bridge rather than a fixed bridge so that tells us it opens. Bascule meaning the bridge swings up and down using counterweights, what we normal people call a draw bridge. One more thing (actually two) before we leave this illustration. Notice what the chart says underneath the clearance numbers: "OVHD CAB" then "SUBM AT CHANNEL"; you might be able to guess this one: Overhead cable(s) submerged at channel.

Chart showing lighted range.

Do you recall lighted ranges in an illustration from Chart #1 above? Well, that's what we have here if you look at the lower center of the chart at left. You can see the dotted line between two lights that extends out straight through the center of the channel. Now, take a look at the heights of the lights. The one further away from the channel should be higher than the one closer to the channel so it will show up on top of it. This is indeed the case as we read the RWG light is 135 feet high while the F G light is 85 feet. We know that RWG must be the light's colors but what of the F in the second light? F stands for fixed, it's on all the time. We can use these lights to guide us directly down the center of the channel, if we keep the further one right on top of the closer one, or use them as a reference. Just like driving on the road we should stay on the starboard side of any channel. Even in Europe, where they often drive on the left, we stay on the starboard side of channels.

Chart datum. This is the point or plane from which water depths are measured. In an area with a large tidal range it can make quite a difference whether the depth is measured from high or low tide. The same can be said of inland lakes that go through seasonal changes in their height of water. So, just where is the depth of water measured from? It is usually measured from the average of the low waters or mean low water abbreviated MLW. Most of the time the water depth will be greater than what is stated on the chart. Every chart will tell you exactly where the water depths are measured from.

Heights above water. Just as with the chart datum above there is a reference point for measuring heights above the water. Usually heights are measured from the average of the high waters. This provides a margin of safety when going under a fixed bridge as most of the time the actual height of the bridge will be greater than what is stated on the chart.

Chart showing traffic lanes.

Traffic Lanes. At the entrance to many major ports and harbors you will find traffic lanes on the chart. These lanes are for large ships. This is a very good thing because now you will know where the big ships are when the fog rolls in as it often does off the coast of New England. Smaller recreational boats should avoid the traffic lanes. If you want to cross one you can but do so quickly and at a right angle to traffic. The separation zone in the middle acts just like the median on an Interstate highway.


Chart showing a compass rose

Compass rose. These show magnetic (inner circle) and true (outer circle) readings. These are covered in True & Magnetic.










Other publications of interest to mariners:

Local Notice to Mariners, published by each Coast Guard district, is used to update the chart after purchase. You can subscribe to this government publication for free or read updates on the Internet. Either way, when the chart changes for any reason you'll be notified.

The Coast Pilot is a series of books that describe, in detail, anchorages, harbors, and inlets.

Tide tables are essential in areas of high tidal range and strong tidal currents. There are many sources for this important information; some are free while others may be included with much other information as in a cruising guide.

The Light List is another US Coast Guard publication. This one covers all lighthouses and lighted buoys giving all their characteristics.

Cruising Guides provide an important source of valuable information and are published privately. A typical cruising guide will include descriptions of harbors along with the relevant chart and many now are updated with several GPS coordinated. Also included may be draw bridge schedules and how to contact the operator. Shopping, marinas, dive and snorkel spots are also covered. It's hard to get by without at least one cruising guide for the area you are sailing in.

For those who would like to explore this subject more, Nigel Calder has written an excellent book on chart reading which you may order from our Ship's Store.

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If you are ready to find out for yourself what it's like to sail a 35-50' boat, receive meaningful sailing lessons, and get a taste of the sea then check out an excellent resource: Blue Water Sailing School. All sailing lessons lead to ASA certification and are taught by experienced instructors who are licensed by the U.S. Coast Guard (Captain's license).