GPS INSTRUCTION

Basic Concepts in Coastal and Inland Navigation

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By far the most popular electronic navigation system is the Global Positioning System, or GPS. The low cost and superb performance of a handheld GPS receiver make it a near-essential tool to have on a boat. GPS uses multiple satellites as artificial stars to provide precise position fixes. To be effective, a GPS receiver must have a clear view of the sky above the boat and be able to simultaneously receive signals from four or more satellites.

The resultant three- dimensional fix provides precise north-south and east-west coordinates (typically expressed as a latitude and longitude), a nominal altitude (meaningless to the boater, though not to a pilot or mountain climber), and a precise time. GPS references your fix to a horizontal datum; you must be sure the datum selected corresponds to that used on your nautical chart.

By means of its built-in navigation computer, a GPS receiver can provide other useful information in addition to your position. By comparing your current position with one from a few seconds earlier, the GPS receiver can determine your boat’s direction and speed. And by comparing your position with the coordinates of a selected waypoint, the GPS receiver can provide the bearing and distance to that waypoint, plot a course to it, provide a continuous in dictation of how close you are to that course line, and calculate a time of arrival from your present speed. Some GPS receivers are hardwired to the boat’s power supply. If yours is not, be sure to stow extra batteries or a cigarette lighter—type adapter aboard. As with any electronic device, a GPS receiver is quire reliable but not infallible. If you use it as your primary position sensor, it’s a good idea to carry a backup GPS just in case. If all else fails, you will need to get out your plotting tools and limber up your chart-and-compass piloting skills. And remember, a GPS position is just an abstraction until you plot it on a chart.

Your GPS receiver has no inherent knowledge of the shorelines, ledges, or other hazards arrayed around your boat (unless you’ve programmed a few avoidance waypoints into its memory, as will be described. There’s just no substitute for a chart’s-eye view of your surroundings.

Piloting.
Being near shore, you generally can use landmarks and navigation aids in piloting. Offshore navigators do not have that support structure, but they are seldom exposed to the potential underwater hazards that the coastal or inland boater will encounter. Even in relatively familiar waters near shore, the recreational boater is faced with a challenging environment that requires solid skills and a good understanding of piloting in order to boat safely.
Piloting helps to answer some basic questions, such as, “Where am I?” and “How do I get where I want to go?” Unlike mariners in past ages, today’s boaters are armed with valuable tools like GPS that answer the first question with great ease and precision. In order to answer the second question, you need to use charts to plot your current position and the intended path to your destination. Often, the straight-line path from here to there is not available, either because land blocks the way, or because underwater hazards preclude a safe passage.

This course will explain the basic principles of navigation, including lines of motion (your course), lines of position (bearings), and fixes. It covers not only use of the GPS but also traditional methods that you also need to know.

This course will present you with two levels of techniques you can use to navigate safely. First, you will learn the time-tested of piloting. These typically involve the use of various instruments and tools. Second under the category of “Seaman’s Eye.” you be presented with some quick tips and techniques that will teach you how to estimate your boat’s position without formal instruments or tools.

Seaman’s Eye.
As an extension of the more formal process of piloting, you need to develop a sense of your environment. This helps to cross-check your navigation and alerts to conditions that may warrant some further action. “Seaman’s Eye” is a set of skills developed over time by experienced mariners.

This course will highlight a number of these skills to help you. It is essential that you not rely upon them for your navigation, but use them as supplements to the more detailed process of piloting.

Using Basic Piloting Skills to get the most from your GPS.
Charts are your road maps for the water, but they lack clearly defined highways. You will need to plot your paths on the water using information that you get from the charts.

Your chart is an accurately scaled depiction of the land and water area it covers. The chart scale, printed on the chart, represents a ratio (e.g., 1:n). For example, a 1:40.000 scale indicates that one unit of measure on the paper chart is equal to 40,000 of the same units in the real world. Thus one inch on the chart covers the same distance as 40,000 inches (0.6 nautical miles) on the Earth. A chart with a small value of n is called a large scale chat because one divided by a smaller n is a larger number. Generally a large scale chart covers a smaller area, but in greater detail. Each chart provides a distance scale, usually in nautical miles and statute miles and sometimes in kilometers. In addition, you can use the latitude scale on a coastal chart for measuring distance in nautical miles. This will be explained below. Mariners typically use nautical miles for distance. Each nautical mile (nm) is exactly equal to one minute of latitude and is approximately 6076 feet. For comparison, a statute mile (often used on lakes and rivers) is exactly 5280 feet.

Instead of roads, you will draw course lines. Each of these course lines will have a direction and a distance.
You will need to measure course direction in order to steer your boat. You will want to know the distance in order to estimate travel time.
Your position is indicated by a set of coordinates. Boaters generally use latitude and longitude as the frame of reference. Using these coordinates is similar to using the intersection of two streets to define a specific location. This is your frame of reference, and it is especially important if you are using a GPS to help you navigate. Your GPS provides a very precise position as a point in three-dimensional space, but it has no inherent knowledge of what is there. The GPS uses a model of the Earth to relate this point in space to a set of coordinates which include latitude, longitude and altitude. The GPS latitude and longitude values identify your location on the chart. (Altitude is not normally a factor in marine navigation.) Once you have the coordinates, you can find where you are and what is around you by plotting these coordinates on your chart. You will get a chance to do that in this session.

Plotting Tools
In order to work with your chart, you will use some basic plotting tools. The lines that you draw must be accurate, because any error can be reflected by a substantial difference in location when you are on the water.

In this session, I will use the USPS Rectangular Course Plotter, a clear plastic device approximately 4 inches wide by 15 inches long. It is imprinted with a series of lines parallel with the long edges and two half-circle segments similar to protractor scales for measuring directions. You will use this plotter to draw course lines and measure course directions, or to lay out a course in a specified direction.

Other plotting tools are available, including parallel rules, rolling parallel rules, and protractors with movable arms.

A protractor plotting tool is often included among the materials for basic plotting courses. These tools ate inexpensive and reliable. If you’re in cramped quarters or on a small charting table, protractors can be less cumbersome than parallel rules. Plus, because a protractor scale is printed directly on the plotting tool, you won’t need to access the compass rose for angles. This added flexibility is especially helpful when lack of space forces you to do your plotting on a folded chart. Murphy’s law being what it is, the compass rose is always folded underneath and therefore inaccessible. There is also a two-piece protractor with a swinging arm. For now, lets focus on the one-piece rectangular plotting tool.

This simple, rectangular, see-through-plastic template was designed by the United States Power Squadrons. Two protractor scales and parallel lines are printed on the template with one for use with latitude lines and the other (printed in reverse order) for use with longitude lines.

Course and bearing directions can be determined by using the scales on a protractor plotting tool. You need to align the bullseye with a grid line while you have the plotter aligned with the course line. You can align the top of the plotter or any of the printed parallel lines with the course line. Finally you read the course direction from the appropriate protractor scale. Which scale to use? Use common sense. This simplistic compass rose (upper right) provides you with a sense of direction. Any course or bearing toward the top right of the chart will be between 0° and 90°. By the same token, any course or bearing toward the bottom right will be between 90° and 180°. Toward the lower left will be between 180° and 270°. Finally toward the upper left will be between 270° and 380° (0).

To plot a course, align the course’s starting point (whether a navigation buoy or simply a waypoint on the plotter edge, orient the plotter’s bull’s-eye on a latitude or longitude line as appropriate, and read a direction in degrees true from one of the protractor’s scales. This device takes some practice in order to avoid reading or using the wrong scale, and it requires those pesky conversions between true and magnetic bearings and courses, which you can avoid by using parallel rules. Nevertheless, these plotting tools are the least expensive and among the easiest to use once you are comfortable with the conversion between true and magnetic, as we have discussed in TVMDC.

Tool Kit
You should put together an onboard kit of tools to support your navigation tasks. In addition to plotting tools and dividers, consider including a drawing compass, a calculator, a notebook for keeping waypoint information and calculations, a collection of fine tipped pencils and water proof sleeves for charts.

As you gain experience, you will find that some tools work well at home or on a chart table and others are easier to use on the boat, where space and flat surfaces are limited. On the water you will lay out the directions of sighted bearings and plot them to help identify your location. The USPS Course Plotter represents a good compromise for use in both locations.
Dividers are the second major plotting tool. They are used principally to measure distances or plot coordinates. Several types of dividers are described in the reference text. The simplest form consists of two arms ending in points and joined at the other end with a friction pivot. Once set, good dividers will not change their setting without some moderate effort; this allows you to accurately transfer a measurement from one place on the chart to another. You will mainly be using the latitude and longitude scales and possibly the distance scale as references for your dividers.

Accuracy is important. On a 1:80,000 scale chart, your pencil line width on the chart can represent over a hundred feet on the water. Generally, you will be asked to strive for course lines drawn with a sharp, medium-soft pencil to an accuracy of 1° of angle and one- tenth of a nautical mile in distance.

Using GPS as your Primary Position Sensor Much of traditional navigation is based on techniques to locate your current position. With GPS, that information is available continuously and with great precision, freeing you to concentrate on your other navigational duties. However, you need to understand and appreciate what GPS does and its limitations.

Remember that all GPS does for you is provide a 3-dimensional point in space that corresponds with your current location. Your GPS receiver compares this point in space with a mathematical grid that represents the surface of the Earth. Using the grid, the point is converted into a latitude and a longitude (coordinates) on the Earth , plus an altitude. For marine navigation, you are not interested in altitude, which generally is less accurate than your horizontal position.

It is essential to bear in mind that GPS has no inherent knowledge of what is located at that spot or in its immediate vicinity. Your charts provide that critical information. You need to plot the coordinates reported by the GPS on the chart to gain a sense of the local terrain and features.

Your GPS receiver contains a miniature navigation computer that takes the position information and provides a great deal more information that is useful to your navigation. Specifically, GPS can compute your motion; and it can compare your current location with one that you have stored in the GPS as a way- point.
GPS computes your actual course over the Earth’s surface (or Track) by comparing your current location with your position just seconds ago. By doing this, the GPS can also compute which direction you moved and how fast you moved that way. These are reported as Course Over Ground (COG) or Track, and Speed Over Ground (SOG) or Speed.

GPS compares your current coordinates with those of a point you have stored in the unit. These points are called waypoints and are used for navigation. By making the comparison, the GPS computes the bearing from your current location to that point, and the distance between them. Figure 4-33.
Skill — Plotting on a Chart

This skill is required in order to take the GPS coordinates shown by your GPS unit and determine the position on the chart. Refer to Figure 4-18.

You will execute the following steps:
1. Obtain the GPS coordinates from the GPS screen in the Figure. GPS units display latitude and longitude as dd° mm.mmm’.
2. Write down the coordinates, rounding thousandths of minutes (or seconds, if used) to tenths of minutes.
3. Examine your chart and approximate the general location of the coordinates by use of the latitude and longitude scales.
4. Locate the position in degrees, minutes, and tenths that corresponds with the latitude position shown on the GPS screen. While you can measure these in either order, in this exercise you will start by measuring the latitude of the position.
5. Set one point of your dividers on the position of latitude as identified on the scale and extend your dividers so that the other point is set on the nearest horizontal grid line (parallel of latitude). Preserve this setting.
6. Lift the dividers and move them to the left or right, along the same grid line, to the area you approximated the GPS position to be located.
7. Place one point on the grid line of latitude and set the other point on the chart in the direction of the coordinate. Draw a light pencil line parallel to the latitude line for reference.
8. Repeat this process for longitude using the nearest vertical grid line (meridian of longitude) for reference.
9. Place one point of the dividers on the spot determined to be the point of longitude scale and the other on the nearest vertical grid line.
10. Transfer this setting to the grid line in the area you approximated the GPS position to be located. Draw a light pencil line parallel to the longitude line for reference. 11. Mark the GPS coordinate where the two pencil lines intersect. 12. Label the GPS position with a dot surrounded by a small circle. Labeling should indicate how the position was determined (GPS) and the time the coordinates were obtained from the GPS screen (e.g., 1000 GPS).

EXERCISE I can’t scan a full scale chart for us to use for exercises so I can only give examples. Wish we had a classroom setting!
GPS indicates a boat’s position by longitude and latitude, and a navigator must be able to plot GPS coordinates to determine a position on a chart. You will need your dividers and a chart. Plot and label the GPS Coordinates.

Time Coordinates
1000 41° 43.787’ N; 072° 02.325’ W (examples)
1. Round the minutes to 43.8’ and 02.3’ and plot the position.
2. Approximate the location of the coordinates by looking at the latitude and longitude scales on the chart.
3. Open your dividers and on the latitude scale on the side of the chart, place one point of the dividers on the position of 41° 43.8’ N, and the other point on a latitude grid line.
4. Lift the dividers and move to the general area of the coordinates. Place a divider point on the same latitude grid line and set the other point down on the chart (the two points must be aligned vertically with the direction of the latitude scale) and draw a light pencil line.
5. Next, perform the same function only using the longitude coordinate and the longitude scale at the top or bottom of the chart. Open your dividers and on the longitude scale, place one point of the dividers on the position of 072° 02.3’ W, and the other point of a longitude grid line.
6. Lift the dividers and move to the general area of the latitude pencil line. Place the first divider point on the same longitude grid line and the other point on the chart directly to the left or right of the first point (the two points must be aligned horizon tally with the chart’s longitude scale) and draw a pencil mark. The two pencil marks should cross. If not, recheck with your dividers.
7. Mark and label the GPS coordinates with a dot surrounded by a small circle. The time of the fix is shown in the 24-hour format, followed by the letters GPS. The labeling indicates the fix was determined at 1000 by GPS.

Pre-voyage Planning is the process of navigation that can be thought of in three stages—planning, navigating underway, and periodically double-checking your courses, positions, and chartwork. The planning stage—the topic of this and the following segments is essential to ensure your safety. You need to select your courses, check them for hazards, and adjust them to avoid obstacles. Even if you normally boat in an area you know well, it’s possible to be caught at sea under adverse conditions with restricted visibility. Careful planning can help you avert discomfort or even disaster in a situation such as this.

The simplest preplanning method involves working with paper charts and pushing buttons on your GPS receiver. Another method, described later in this chapter, eases some of the button pushing by using a computer to upload waypoints and routes into your GPS. A third method, planning directly on digital charts, is presented in the following chapter. Whatever method you choose, pre planning is a good off-the-boat activity that can be done in the evenings or during the off-season.

You should not say, “well lets go home now, I marked where we departed from”, and go straight there, unless you know your position and that nothing is obstructing your path home. Have a leg programmed out of your channel to head for in known deep water and then follow your departure leg back in.

Planning and Paper Charts
The chart is your security blanket and the navigator’s most essential tool. It provides the key information you’ll need to plan and enjoy safe boating. Of course, local knowledge and personal observations will enhance your navigation, because charts are not infallible and cannot show everything. You may know from prior experience or the advice of a local fisherman that aligning a particular red barn in front of a particular white church steeple puts you on the best course through your harbor inlet, but you won’t find the barn on your chart (though the steeple might be noted). Nevertheless, it’s amazing how much information is on a chart, and how seldom it’s wrong. It’s essential that you have the latest version of the charts for your area.

Criteria for a Safe Course
The fundamental premise when using GPS is that you will first pre-qualify safe paths, then follow those paths when you’re proceeding from one place to another on the water. The same principles apply to pre-qualifying an area in which to meander without fear of encountering unseen hazards. So, what is considered safe?

DETERMINING SAFE DEPTHS
Obviously, you won’t go far if your boat has run aground. Thus, adequate depth is the first feature you’ll look for to pre-qualify a safe path. But what is adequate? The answer depends on two factors: the characteristics of your boat, and the characteristics of the seabed. Each sounding shown on a chart represents a measurement of the bottom depth at a particular location. When enough soundings are assembled, a contour line of constant depth can be drawn using the soundings as a reference. All soundings are referenced to a standard datum, which for most NOAA charts is mean lower low water. (MLLW). This means that each sounding on a printed on a chart represents nearly the shallowest you can expect to find at that location.

Isolated Hazards can be natural or man made. Outlying rocks are a common example of the former. If you drained all the water from a bay, it’s underlying topography would look much like that of the surrounding land, with hills, valleys, and rocky outcrops whose peaks might protrude above the surface or lurk just below for the unwary boater. As with wrecks and other man-made hazards, rocks are classified as exposed, covered, and covering.
In addition to wrecks, man-made hazards include old pilings. These, in fact, represent one of the greatest hazards to boats, because they can easily penetrate a hull. Lake Erie is full of them.

SHOALS, or circumscribed shallow areas, are in effect the tops of underwater hills. Often, shoals lie along a line, not unlike the spine of a miniature mountain range. Sometimes, though not always, they are rocky. Main channels frequently run parallel with shoals. Often, the shortest path between two points lies across intervening shoals. Be fore attempting such a path, take special care to ensure adequate water depth. (Lake Erie Island area is full of shoals and shallow reefs).

CLEARANCE OVERHEAD
The final consideration for pre-qualifying safe paths is vertical clearance. Will your boat fit under bridges and overhead cables? Generally, one of the manufacturer’s specifications for your boat is bridge clearance. Remember, this measurement is taken from the waterline to the highest part of the boat’s structure as it leaves the factory. You have likely added antennas, radar, outrigger poles, and so on. You will need to consider the additional heights of these objects when planning your passage. If they can be lowered, make a note on your chart as a reminder.

The clearance printed on the charts is generally referenced to mean high water (MHW), or occasionally mean higher high water (MHHW). Check your chart legend for the datum used. Just like timing a passage over shallow water, you might be able to pass beneath a low bridge by using the tides to your advantage.

In some waters on the Intracoastal Waterway along the U.S. East Coast, for example you will encounter bridges that can be raised or drawn or swung open to provide clear passage. Generally, their heights when closed are shown on the bridge itself as well as on your chart. You also may find a depth of water scale on a bridge abutment. You should be certain of your boat’s actual bridge clearance and plan carefully so as not to unnecessarily cause the operator to open the bridge or, even worse, attempt a passage you can’t clear.

When you consider vertical clearance, don’t forget about overhead cables, especially on inland waterways. Of ten, these may be low enough to present a hazard, and many carry high voltages.

HORIZONTAL CLEARANCE
Just as you need a safe margin between your keel or running gear and the seabed, you need to plot courses that maintain a safe horizontal margin. You need ample room to steer around obstacles. Wind and waves can cause small deviations from course, so your paths should be wide enough to allow for this. Also, typical GPS accuracy is within 50 feet of your true position. When planning, check along your intended path to ensure safe waters a little more than ten times wider than that GPS error to either side. To make planning easy, look at the latitude scale. Because one minute of latitude is a nautical mile (about 6,076 feet), one-tenth of a minute (the smallest tick mark) is roughly 600 feet. Using this handy reference for perspective, you can scan your projected path on the chart and confirm that the horizontal clearance on either side of the course is at least as wide as the smallest increment on the latitude scale.

Of course, this assumes that, when underway, you will periodically plot your GPS positions. Plan to plot your GPS position about once every hour, or more frequently if you’re traveling fast or in foul weather. While you’re at it, try to verify your GPS-derived position through independent means. In the event of a failure, this may be the only information you have.

Steps in Pre-voyage Planning on a Chart
It bears repeating: Before you do anything, you need a set of charts for your boating area. With charts in hand, study them in the comfort of your home. Preplanning waypoints, legs, routes, and avoidance waypoints will vastly simplify your navigation underway.

FIGURE 5-10. Planning on a chart involves plotting lines between your starting point and your destination. You need to measure the coordinates of these end points to enter them as waypoints. A scan along the line indicates the potential for hazards. If potential dangers are identified, you must create intermediate waypoints to build a route that avoids the obstacles.

Here are the recommended steps for programming waypoints: First, locate your home port and other ports you wish to visit.
Buoys around these ports will become way- points.
Second, locate hazards—places where the water may be too shallow and must be avoided. This information will help you prepare safe routes or avoidance waypoints.
Third, plot a sequence of straight-line paths on your chart that will take you from your home port to other points of interest. For safe and confident navigation, these paths will ideally begin and end at prominent navigation aids—preferably ones that emit noise and/or light and are surrounded by safe water. Alternatively, you can plot waypoints just offshore from prominent landmarks fronted by safe water. Given a dearth of likely looking nay aids and landmarks, you’ll have to rely more heavily on latitude/longitude way- points in featureless waters.

Next, invent short names for each of the connecting waypoints.
Then note any landmarks you’ll be able to use for visual reference while running between waypoints. Charted towers, standpipes, tall buildings, and light houses can help you verify your position or guide you to safety if your GPS fails.
Now, using your plotting tools, measure the coordinates of each identified waypoint. Be sure to double-check each set of coordinates to avoid mistakes. To keep track of these coordinates and other useful information, create a written table with columns for waypoint name, latitude, longitude, and comments.

Finally, once the waypoint table is complete, enter the data into your GPS. This can be done manually on the GPS or by using a computer. I will discuss both approaches later on.

FIGURE 5-11. Record your waypoints on a tablet or in a log book. Waypoints should be named to reflect their location and features. The latitude and longitude for each should be recorded along with summarized details. Always double-check the accuracy of your coordinates. A simple slip of a digit can place you in peril.

GPS receivers usually allow you to enter six to nine characters for each waypoint’s name along with an accompanying symbol. You should develop a naming and symbol convention that works for you. Because there are many buoys labeled R “2” or G “1,” you will need to distinguish among them. Generally, you’ll find it easier to locate waypoints in your GPS memory if you develop regionally based nomenclature. Let’s say you’re plotting the waters around Newport, Rhode Island. You could name each waypoint with the prefix NPT” followed by an identifier such as “R2” for red buoy number “2’ hence “NPTR2.”

Most GPS sets alphabetize the waypoint names, so using regional prefixes will ease the task of finding waypoints later by grouping those for a particular area. Avoid beginning a way- point name with a number. Most GPS receivers assign numbers to newly marked waypoints, and you’ll want a way to clearly distinguish your established waypoints from more transitory ones.
Next, you may wish to mark danger areas such as isolated rocks or wrecks. Use the same regional prefix (“NPT”) for these locations, but also add another character such as “D,” for danger (With the “D” in place, your danger waypoints will also be alphabetically grouped within their region.) Then add identifying abbreviations such as “RKS” for rocks or “WRK” for wrecks (hence “NPTDRKS” or “NPTDWRK ). If there is more than one rock to mark near Newport, simply add a number (“NPTDRKS2’9.

Also, on most GPS receivers, you can mark locations on the Map Screen by choosing from a number of different symbols. Use these symbols to clearly differentiate between hazards and navigation aids. For instance, most GPS units offer icons such as a skull and crossbones. This sober image is perfect for marking hazards. Use a distinctly different set of symbols to mark land-based objects such as towers or buildings.

For regions of shallow water, you can add imaginary buoys at key locations if real buoys are lacking. By labeling them “R” or “G” (for “red” or “green”), you will know on which side of them you need to stay. Append with something such as “I” for imaginary before any identifiers or numbers of your choice (“NPTIR3”). Mark and label these points on your chart.

Many GPS models will automatically assign a route name in this construction: name of the starting waypoint {hyphen} name of the ending waypoint.
This makes the route name clear and unambiguous. As a further convenience, many of these same GPS models can even reverse the order of the waypoints if you opt to take the route in reverse order.

Usually you will use GPS as your primary position reference as well as your navigation computer on the water, but you first need to understand what it is telling you. Your GPS receiver makes an excellent navigation tool. GPS provides precise position on a continuous basis, and your receiver uses that information to provide a great deal of other useful information. However, it is essential that you understand what your GPS can and cannot do.

What GPS can do
The primary purpose of the Global Positioning System is to provide position. Your receiver converts that position into a format that is useful to the boater.
Your GPS will:
1. Provide position in latitude and longitude. Computations within your GPS receiver will also enable it to:
2. Provide a course to steer, if waypoints are used.
3. Provide estimated arrival time at destination.
What GPS cannot do:
GPS ‘s only source of information is from the constellation of satellites. Therefore, it has no inherent knowledge as to what resides at the position it provides. As a result, GPS cannot:
1. Warn of hazards.
2. Determine water depth.
3. Your source of information for the local environment must come from charts, your personal observations, and other instruments on the boat.
FIGURE 5-12. Your GPS can execute a route—a preplanned sequence of legs. To build a route, select the New Route Screen and begin by entering the departure waypoint. Then, enter each subsequent waypoint. The GPS computes the course for each leg and its distance.

CREATING ROUTES
To ease your tasks on the water, it makes sense to create routes or route segments using your newly entered waypoints. By accessing the route function within your GPS, you can select waypoints in a desired sequence and thus build a route. Most GPS sets allow you to enter roughly twenty waypoints for each route and can store as many as fifty routes. Usually, the GPS automatically names the route by using the first and last waypoint names. Unless you have a strong reason for changing it, the default naming scheme is preferred. Now you have created a personal waypoint logbook for your boating area with the information stored in your GPS. By identifying and programming a substantial number of waypoints, you have constructed a frame of reference to compare with visible objects and hazards while on the water.

Plotting on a Chart
Because we are using paper charts in this training exercise, it’s important to be comfortable with techniques for plotting courses and bearings on a chart. The basic tools were discussed earlier.
It’s wise to thoroughly annotate your paper charts with the information stored in your GPS. This includes labeling the waypoints in the same manner. By the way another advantage of waterproof charts (other than the obvious) is that they usually can be written on, erased, and annotated at will without damaging the chart.

Summary of Plotting Lines

I have described several types of lines that you will plot on your charts—some in advance and some while you go. Here’s a quick summary:
Ahead of Time
Course—a solid line representing your intended path on the water, labeled with the direction and distance of the leg.
Range—a dashed line between two charted objects— generally ashore or in shoal water—that is then ex tended over navigable waters, where it switches from dashed to solid. A range is labeled with its bearing. Government-established ranges are pre plotted on charts; you can add your own ranges as desired.

While Underway
DR—a solid line representing your estimated progress on the water. A DR is based on the course steered; its length is the distance traveled as estimated from speed and time of travel. [B]Bearing[/B]—a solid line representing your observation of a landmark or navigation aid labeled with the time of the observation and the bearing direction in degrees.

Plotting a Course
In the “Planning and Paper Charts” section of this chapter, we drew straight-line segments on the chart along pre-qualified paths that avoid obstacles. We then measured the coordinates of the end points of each such leg and programmed these into the GPS as named waypoints. Finally, we programmed routes by calling up waypoints in a desired sequence.

Plotting falls into two main categories:
Prevoyage plotting and plotting that’s done underway Intended courses (legs, waypoints, routes) are preplotted. Ranges are preplotted. On the water, you plot bearings to match your observations, and a DR (dead reckoning) plot to back up your electronic navigation. These courses and bearings have been measured in degrees true using the chart grid for reference.

Once a route is entered, most GPS sets provide you with the courses and distances between each of the way- points in sequence in that route. You’ll find it helpful to label the legs of the routes plotted on your chart with these values. To be consistent with navigation conventions, name the leg with the following elements: start with “C” for course, then add the three-digit direction, then finish with the letter “M” for magnetic (assuming you are using magnetic headings in your GPS). For instance, a course of 30 should be labeled “C 003 M.” Place this label near the beginning waypoint above the course line. To note the distance of a leg, start with the letter “D,” then add the GPS-derived number (usually expressed in nautical miles and tenths). This label should be placed under the course line, ideally near the center of the leg. As you add these labels, verify their accuracy with your plotting tools. Why do this if the GPS computes courses and distances for you? Well, this is another check on the accuracy of your entry for each waypoint.

By comparing your measured course direction and distance with that computed by the GPS, you gain confidence that you’ve measured, entered, and selected waypoints properly. (You’ll be amazed how many times you pick up an error in an entered waypoint by doing this.) Again, waypoint coordinates are just numbers until they’re plotted on a chart.

Most recreational boaters will want to label their plots with magnetic courses and bearings, as here. This enables them to relate to their compasses without further correction for variation. Directions labeled in magnetic should be annotated with an “M” suffix for clarity.

If you have a Maptech or other commercial chart book, you may find that some routes and legs are already labeled, along with waypoint coordinates. Most such books use magnetic headings and nautical miles. You will note that the reciprocal course heading is labeled at the other end of each line. The reciprocal is the course you steer from the opposite direction. To determine a reciprocal, either add 1800 to a course of less than 180°, or subtract 180° from a course of more than 180°. You can also use your GPS receiver to determine a reciprocal course simply by selecting the invert feature from its menu. Doing so will save you from entering your return trip as a separate route. Once inverted, the route will list the reciprocal course directions for each leg. Invert again to restore the original sequence.
Yet another way to find a reciprocal course is to place your parallel rules over the original course on the compass rose, then read the reciprocal from the other side of the rose.

For the most part, you probably will be working in magnetic rather than true. The language of the boat is magnetic; the language of the chart is true. You need to be comfortable with the conversion—which can be done mathematically by adding or subtracting local variation—or graphically (and more simply) using the compass rose. Let’s look at the latter first.

USING THE COMPASS ROSE
As described in previously, the compass rose (which is printed in multiple locations on your chart) provides the chart’s fundamental reference for magnetic directions. It is printed in a magenta ink that is distinctive when viewed with red light at night. (Navigators use a red light at night for illuminating charts and instruments, because this color has minimal effect on night vision, which is essential for keeping watch.)

The compass rose has two rings. The outer ring aligns with the chart grid of latitude and longitude lines—that is, with true north; the inner ring aligns with magnetic north. Within the inner ring is a legend that notes the local variation used for the chart. The variation describes both the magnitude of the difference in degrees and minutes between true and magnetic north for the charted location, and the direction of that offset, either east or west. (Magnetic north is moving, albeit slowly, so variation needs to be adjusted for this movement.) In addition, the legend identifies the date used for the variation and the amount by which it will change each year, east or west. You will need to adjust the variation accordingly if your chart is several years old and the annual change is significant.

Charts are printed with one or more compass roses. The compass rose has two rings. The outer ring is aligned with the chart grid and true north. The inner ring is aligned with magnetic north. A legend at the center of the rose provides the local variation and its annual change. The compass rose simplifies the labeling of courses and bearings and provides instant reference between true and magnetic north.

Many mariners use the compass rose for laying out or measuring a course or bearing. Because the rose is rarely if ever located where you want to plot or measure a course, devices such as parallel rules are used to transfer the direction to or from the rose, as described and shown in Figure 5-16. Make sure you read your direction from the compass rose going the right way—that is, by imagining your boat at the center and reading toward the rose in the direction of the course or bearing.

The compass rose can be used to measure or plot magnetic direction. With parallel rules, you can align one rule along the bearing to be measured and extend the other rule to align with the center of the compass rose. A magnetic bearing can be read directly on the inner scale. If the distance between the compass rose and the bearing line is too great, you can walk the parallel rules.

Another type of parallel rule uses a roller (Figure 5- 17) to pick up a desired direction from the compass rose and transfer it across the chart to where you are plotting. Typically, you will need a flat, stable surface for this device to work.

An alternative tool uses a roller instead of two rules. The roller allows the rule to glide across the chart without changing its orientation. In the left panel, the parallel rule is aligned with a bearing. In the right panel, the parallel rule has been rolled so that the straightedge aligns with the compass rose for reading the bearing.

Using your parallel rules, confirm the GPS calculation of course direction for each pre-plotted leg on your chart as follows: Align one rule with the plotted leg, then walk the rules across the chart to the nearest compass rose and read the course in degrees magnetic from the inner ring.
Does the result agree with what your GPS is telling you? If so, the course direction calculated by the GPS is correct, and the plot can be so labeled. Now check the distance of the leg by walking it off with a pair of dividers, as de scribed previously. Does the result agree with your GPS calculation? Good; add the label and turn to the next leg of the pre-plotted route.

Are these courses now ready to steer? Yes, provided your steering compass doesn’t exhibit significant deviation errors that you can’t get rid of. See “Correcting for Deviation” later in this thread for more on this topic.

Measuring and plotting courses and bearing in degrees magnetic, as described above, is simpler than piloting by degrees true. When you confine yourself to the language of the compass, you sidestep the potential for translation errors.

The other approach, as mentioned, is to measure and plot courses and bearings in degrees true, then steer or sight their magnetic equivalents after adding or subtracting local variation (always) and onboard deviation (if necessary), as described below.
But why do things this harder way when it’s simpler to work in degrees magnetic using the inner ring of a compass rose? The short answer is that most small-craft navigators don’t. Nevertheless, the concept of converting back and forth between true and magnetic directions is one you should understand, even if only to recognize when the difference is about to affect your navigation. We have discussed the importance for converting, in detail, way earlier in the thread.
And there are practical reasons for knowing how to measure and plot courses and bearings from a chart’s grid of latitude and longitude lines. For one thing, the grid covers the entire chart and is always available to you, whereas the nearest compass rose is often folded underneath and there fore not conveniently accessible when you’re working on a small surface. Second, those who navigate this way all the time swear that it becomes so second nature as to be faster than using a compass rose. Well, maybe.

Finally, if your ship’s compass carries deviation on some headings, as described earlier, you’ll have to add or subtract these values from your magnetic courses no matter how you obtain them, in order to get courses to steer.

Because the technique for doing this is just like adding or subtracting variation to get from true to magnetic or back, you might as well learn it now.

If you don’t have it, go back and start reading, I can’t help a lot of things being reiterated and am not going to do them all or we will never get through this!
If you’re still not convinced, think of it like iodine on a cut—painful but good for you.

So let’s return to the routes you have pre-plotted on your local chart or charts in anticipation of a wonderful boating season, this time assuming that you’ve initialized your GPS receiver to calculate course directions in degrees true. As you call up each leg of a route in sequence, the GPS tells you its course direction and distance. As before, double check these numbers with plotting tools before labeling each leg. To do this, align one of the protractor plotting tools, (for example see prior post, Figures 4-23 and 4-24), with the plotted leg, then read its course direction in degrees true from the nearest parallel or meridian, as appropriate. Does the result agree with the GPS calculation? If so, add the label.

One kind of protractor plotting tool employs a pivoting arm (Figure 5-18). The protractor is aligned with the grid lines on the chart and the arm is set to the desired angle. Some of these plotters have an extra scale on the movable arm that allows you to adjust for the local variation between true and magnetic, making this a truly versatile tool.

A very useful plotting tool has a protractor scale and a pivoting arm. Parallel lines are printed along with the pro tractor on the fixed part. This is aligned with the grid lines on the chart, with the center of the plotting tool on your current location or the object being sighted. The arm can then be rotated to a selected angle so the line can be measured or drawn. Be cause the protractor is aligned with the grid, the direction provided is in degrees true.

For the moment, however, let’s assume you’re plotting in degrees true.
You’ve pre-plotted routes on your chart and calculated the course direction for each leg in degrees true. But before you can steer that course on the water, you’ll have to convert it to degrees magnetic, which is the language of your ship’s compass. Remember, local variation is the same for all boats in an area and on all headings. Your chart will tell you what the variation was at the time the chart was created. Assuming your chart is the most recent edition (as it should be), you can safely use the charted value of variation. This is an angular correction either east or west. You will need to add a westerly variation or subtract an easterly variation from each true course to get its equivalent magnetic direction.
Summarizing, the formula is: Reminder: True = + W or — E Variation = Magnetic Suppose, for example, your local variation is 15° W and you want to convert a course of 175° true to its magnetic equivalent. You add 15 to 175 and find that the magnetic course is 190°. If your local variation is 15°E, a course of 175° T would translate to 160° M. Westerly variation is added to a true course; easterly is subtracted. Some navigators find the expression “West is best; east is least” to be a helpful memory aid.

While correcting for local variation, you should correct for compass deviation too; indeed, the latter correction will apply even when your magnetic course has come from a GPS calculation or from a reading off a chart’s compass rose. Putting it all together, we get the formula TVMDC, which is the universal technique used to convert between true, magnetic, and compass directions.

Tips to remember:
1. Converting from true to magnetic Add westerly variation (going down); subtract easterly
2. Converting from magnetic to true Add easterly variation (going up); subtract westerly
3. Converting from magnetic to compass Add westerly deviation (going down); subtract easterly
4. Converting from compass to magnetic Add easterly deviation (going up); subtract westerly
For plotting, you will use only true or magnetic directions; most navigators choose magnetic for reasons already explained. Compass courses are steered but not plotted.

Plotting a Bearing
While on the water, you will have occasion to take visual bearings on charted objects to help you determine your position. We discussed bearings in the past and return to their use on the water in later chapters, so here we merely discuss briefly how to plot them. Remember, a bearing is considered to be a line of position and as such represents a line on which your boat is located. Because the observed object is charted and your boat is not, you will need plot the line using the object as the reference point. Still, the line is drawn toward the object, in the direction of the bearing, from the estimated location of your boat. It is labeled with the time of the bearing in four digits (24-hourclock) above the line and the direction of the bearing in three digits below the line. These labeling conventions are the same as for courses.

Plotting a Range
Ranges are plotted as straight dashed lines between charted objects with the line extending into the intended area of navigation. The portion of the range that is navigable is denoted by a solid line. The bearing of the range should be labeled on top of the line for ready reference on the water. If the range is charted, generally the bearing will be true. If you plot the range yourself, you can do so in degrees magnetic; just follow the bearing with the letter M Generally, the landmark to the rear will be taller, and the sight picture will be in a straight line, if you are “on” the range, the two objects will align. If you are to the left, the rear landmark will appear to the left of the one in the foreground. Plotting and labeling for true and magnetic directions are shown in Figures 5-13 and 5-14. Any charted object can be used in a range: a water tower, a church spire, a daybeacon, a bold bluff on one end of an island. With this in mind, you can plot strategically located ranges on your local chart while cruise planning. They’ll come in handy.

Entering Waypoints into Your GPS
As we saw earlier, cruise planning includes a process of plotting a network of safe legs on charts covering the area in which you intend to boat. These safe legs start and end at waypoints. In turn, each waypoint is referenced by a set of coordinates, specifically a latitude and a longitude. Getting all of that into your GPS can appear to be somewhat tedious, but it’s worth the effort. This is the information that makes your GPS so useful.

You’ve learned how to measure waypoints and construct a waypoint table of latitudes and longitudes. Using this table to manually enter waypoints into the GPS is perhaps the most straightforward method; however, there are alternatives. All of the methods are summarized below.

Manual Entry
Enter coordinates manually by accessing the New Way- point Screen. Using the cursor button, scroll down until the coordinates field is highlighted, and press ENTER. You will be presented with a single highlighted character. Use the cursor to scroll up or down to change the character (number) until it corresponds to your desired entry. Then the cursor to scroll right or left to change the values of other characters. When you’re satisfied with the entered values for latitude and longitude, press ENTER to accept. Scroll to OK or Save and press ENTER. Your GPS will assign a number in the name field. You can change the name (or the symbol displayed with the waypoint) in this field in the same manner as entering values into the coordinates field.

Scroll
An easier way to store coordinates in your GPS is to scroll the cursor on the Map Screen. The cursor’s coordinates are shown on the screen. Press MARK to access and edit the New Waypoint Screen, then save. On some GPS models, this is the method by which you access the New Waypoint Screen. Usually, it is quicker and easier to scroll to the general area of the desired waypoint, press MARK, edit the details of the coordinates until your satisfied, then save.

Bearing and Distance
As indicated earlier, it is wise to plot your course on a paper chart and label each leg with its course directions and distances. Now you can put that information to good use. With this technique you can accurately enter all the waypoints into your GPS without entering the coordinates for each one.
Start at one of the intersections for a group of legs and enter the waypoint coordinates for just that intersection.

Many newer GPS models provide a bearing and distance readout of the cursor position in addition to its coordinates, as described above. Akin to the scroll method you can use those readouts to enter other waypoints as follows.
Set the current location of the GPS in toe simulator mode (usually found in the menu). Select the newly entered waypoint as your simulated position. Now using the cursor on the Map Screen, scroll until the displayed values for cursor bearing and distance correspond with the course direction and distance of the desired leg. Press MARK and proceed with your naming. Repeat this step for any other legs that emanate from that starting point, or reset your simulated position to another intersection and continue from there.

To be Continued