Navigation
By Carl Robertson, Robertson’s Marine
Utah Boating Guide
Originally published Apr 01 2000
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For most of us, navigation is pointing the boat towards that certain spot of beach across the water and dropping the throttle down. Between here and there we look for green water (shallow stuff) and dodge the cross traffic along the way. Generally, that will work, but an understanding of navigation by instruments is important. If you boat a great deal, the time will come when you will be caught out on an unfamiliar large body of water after dark, in the fog, or heavy rain. Your ability to get back to a safe harbor, especially on the larger lakes and reservoirs, might fully depend on your understanding of basic navigation skills and your ability to use navigational tools and devices.
There are three essential questions one answers during navigation: Where am I? Where do I want to go? and How do I get there? The first question, Where am I? (position), seems so elementary. But keep in mind that any navigation should always be started from a known position. Navigating with perfect precision from a wrong position will always end at the wrong destination, often with dire consequences.
Second, Where do I want to go? (destination), is usually expressed as a distance and direction (range & bearing) from your position. This information is usually measured or estimated from a chart or can be computed by knowing the coordinates (latitude and longitude) of the destination. When someone says the best fishing is two miles straight out from the boat ramp, they have given you the destination as range and bearing.
Third, How do I get there? (route). This one is usually easy: a straight line. Point the boat in the direction you wish to go, drive the appropriate distance, and you are at the destination. But as anyone who has ever tried to follow a straight line from Bullfrog to Wahweap knows, this is not always possible. Sometimes changes of direction are needed to avoid obstructions, or just to follow the path of a river or channel. These changes of direction occur at “waypoints,” which are intermediate points followed along the route to the final destination.
Navigational Tools
One of the most important navigational tools you can have is a chart of the lake or body of water that you are boating on. A good overall picture of the area, terrain, and structure is essential to finding your way around. These charts come in a variety of forms: road maps, topographical maps, true nautical charts, electronic database maps, and of course, the sketch on the back of the napkin that shows where uncle Ed’s favorite fishing hole is. You will typically not find true nautical charts for the waters of Utah, with the exception of the Great Salt Lake. What you will find for many of the larger bodies of water, however, are topographical maps with contour lines that extend below the water. These maps show the water displayed at some calculated level. You should keep in mind that water levels vary throughout the year, and the chart/map you are using may not accurately display the level at the time you are using it. The chart shows a birds-eye view of the body of water that you are operating on. Depending on the quality of the chart you are using, it may show launch ramps, marina facilities, waterway marking buoys, and/or water depth indications.
Buoys and waterway markings are the equivalent to road signs and traffic indicators that we use on water. The regulatory markers are used to provide information. The lateral markers are used to show the general path of the channel or river. Keep in mind that the buoys and markers are frequently moved out of place by storms, waves, or high wind conditions, and should never be relied upon to be precisely in the correct position. Because of this, danger markers and lateral markers should always be given wide berth on the safe side when maneuvering around them. Also keep in mind that lateral markers are arranged so that the red buoy is on the starboard side of the channel, when returning to the source of the water (upstream); or, on the starboard side, when returning to a harbor from the lake side. The red buoys should always be to the right when returning. (Red, Right, Returning).
Knowing what to look for above the water can tell you a great deal about what is below the water. The Bullfrog Marina area can have many submerged hazards; the buoys tell you where they are. (Photo: Chad Booth)
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There are three types of magnetic compasses commonly used in boating: a needle compass, a card compass, and a digital read-out compass. They all operate a little differently.
A needle compass consists of a magnetized needle mounted on a pivot at the center of a fixed graduated card, which permits the needle to swing freely in the horizontal plane. The needle always points to north. To operate the compass, you line up the north markings on the case with the needle. Once aligned with the needle, the markings on the case indicate which direction you should travel. These types of compasses are small, inexpensive, and reliable instruments, but difficult to use on a moving boat.
A card or mariner’s compass has a card with the degrees printed on it. It has bundles of parallel magnetic needles attached to the underside of the compass card, which pivots about its center in a glass-covered bowl. There is a black vertical line, known as the lubber’s line, drawn on the inner surface of the glass bowl that surrounds the card. The course of the ship may be obtained by reading the number of degrees on the card opposite the lubber’s line. Remember that the degrees on the card are printed in the opposite direction of a needle compass. You do not try to keep north on the compass card pointed to the north. To operate, you simply steer to the heading. The lubber’s line indicates your direction of travel. This is the most common type of compass found aboard boats. It is very reliable, slightly more expensive, and with its internal dampening, much easier to use aboard a moving vessel.
The most simple compass, from an operator’s point of view, is a digital compass. These compasses use a fluxgate sensor that reacts with the earth’s magnetic field to determine direction. It tells you what direction you are heading in degrees, with north reading at 0 degrees, east at 90 degrees, south at 180 degrees, and west at 270 degrees.
A magnetic compass points towards the magnetic north only if it is placed in an area that is free of magnetism, and if no iron or steel objects are nearby. Iron and steel objects deflect the magnetic needle, and an error known as deviation occurs. To correct deviation, the needle compass must be moved to an area without magnetic influence (not always possible). The card compass must be compensated, which is done with a system of adjustable magnets arranged to compensate for the disturbing influences. The digital compasses are usually self compensating; you steer the boat around two very slow 360 degree turns, and the electronic compass will sense the deviating influences and automatically cancel them out.
Another factor that affects readings of true north is the angle between the magnetic north and true north. The magnetic field of the earth is not lined up with the true north/south axis of the earth. This angle between the two is called the magnetic variation or declination. The degree of this angle varies in amount, depending on where you are at. Most charts will provide you with the angle of magnetic variation for the particular area that relates to the map. However, for the most part, the variation in Utah is 14 degrees east. This means to obtain the Magnetic direction (what you will see on your compass) from the True direction (what you will measure from the map), you will need to subtract 14 degrees.
A compass can be used to determine both heading and position. Heading is taken directly from the compass as outlined above. For positions, you can take readings of the directions to prominent landmarks, reverse them (subtract or add 180 degrees), and then transpose them to a chart as directions from the landmark. With two or three of these readings, the intersection of the lines of position show your location on the chart.
The compass (to measure which direction you are going), combined with a speedometer and a good watch (to calculate time and distance), are the basic instruments that have served mariners for hundreds of years. The use of these instruments should be understood, even though the real fun and ease of navigation is with new electronic devices.
Electronic Navigation Systems
There are two widely used types of electronic navigation systems. They vary only in features that the individual devices have and the method that they use to determine your position.
Loran is a system of radio transmitters around the nation that send out synchronized signal pairs from Loran stations. By measuring the time difference (TDs) between the master station and the slave, the Loran receiver can calculate your position. On modern Loran receivers this calculation is done automatically and your position is displayed as a latitude/longitude. The system is marginally useful at ground level in Utah. There are many areas of no signal, due to terrain and weather conditions, and the signals that are received are subject to propagation errors that reduce their accuracy.
GPS (Global Positioning System) uses the Department of Defense’s Navistar satellite network. The GPS unit receives coded signals from the satellites, and using precise timing, calculates the position of the receiver by triangulation. The GPS system has many advantages over Loran.
GPS works anywhere, from Bird island in Utah Lake, to the Canary islands in the south Atlantic, and every point inbetween. It is a truly global system. Using 21 satellites, the GPS system is accurate to within a few meters, anywhere in the world.The system works in all weather conditions. It is a three-dimensional system that provides not only latitude and longitude but altitude as well.
Other than the way they determine position, electronic navigation systems share features common to all, with a few extras for the high end units. Most include these items:
- Receiver for position determination (Where we are).
- Waypoint and route storage (Where we want to go).
- Navigation computer (How do we get there).
- Plotter or mapping device-graphic representation of where we are going or where we have been.
The receiver is automatic and usually easy to use. Just turn the unit on, and when the display stops flashing or the warning indicators go out, the unit displays your position. If the unit is turned off within 100 miles of where it is subsequently turned on, this process usually only takes a few minutes. If the distance is greater (as is the case when the unit is new), the process may take a little longer. Most receivers have an initialization process that speeds up the first acquisition, so consult your owners manual. Do not let this procedure intimidate you or take up valuable recreation time-you can usually bypass the procedure altogether by turning the unit on 20 minutes in advance and letting the unit figure it out by itself.
Waypoint and route storage are a little more complicated, although most manufacturers try to make this as painless as possible. Waypoints are usually entered into the system by one of four methods:
- Directly enter the latitude and longitude of the waypoint into the unit. This can be measured from a map or from a list of waypoints. This book includes a listing of the latitude and longitude of all the launch ramps in the state.
- Go to the spot and enter your current position as a waypoint. This is usually the easiest method, as most receivers have a one button capability to do this.
- Enter the waypoint as a range and bearing from your current position or from another waypoint. After this information is entered, the navigation computer on the unit will calculate the lat/lon of the new waypoint and enter it into the system.
- On units with electronic charting, you can position the chart cursor over the spot on the electronic chart where you want the waypoint, and the navigation computer will determine the lat/lon and enter it into the system.
Routes are entered as a series of waypoints that are already in the system, in the order that they will be used to navigate.
Once the position is determined and waypoints entered, you can utilize the navigation computer to calculate the direction and distance you need to go to reach your destination. This is performed with a “Go To” function. The receiver is told to go to the waypoint or to follow a route (series of waypoints). On most receivers this is usually a one or two button function. Simply point the boat in that direction and go. Once you are underway, the navigation computer will keep track of your progress, and display it as course over the ground (COG) and speed over the ground (SOG). The computer will also calculate an estimated time of arrival (ETA) based on your current course and speed. Keep in mind that although the COG function is normally displayed to look like a compass, it is not. This is only a calculation of where you are going based on previous positions. The unit does not know which way the boat is pointed, only a compass does. If you are on a steady course, COG is usually a good indicator of direction, but if you are rapidly changing direction or stopped dead in the water, this information will be wrong.
Most receivers have a plotting device-a graphic display of where you are, where your destination is, and where you have been. These plotters keep track of a trail, for a given period of time, of where you have been. This time the trail is kept is a function of how much memory the unit has and how often it plots a trackpoint (breadcrumb) on the trail. Although we do not have to worry about the birds eating our electronic breadcrumbs, we do have to worry about how many the unit can display. When the memory of the unit is full, it will start erasing the trackpoints at the beginning of the plot. These are the most important ones-where we started (and usually where we want to return at the end of the day). It is very good practice to read the manual and know how long the trail will last. I do not like to depend on this function for return trips on unfamiliar waters. I always mark waypoints along the path to use on the return, as they are a more permanent mark.
Most receivers plot this information on a blank screen, but the newer units that have electronic charting plot the information directly on the electronic map. This is a great help, as the plot does not have to be transposed to a paper chart, and one can determine very quickly where they are and where they are going in relation to surrounding charted features. These systems vary widely on the chart accuracy and detail, and wide berth should be given to charted land features.
Tips for using Electronic Navigation Systems
- Read the owners manual and become familiar with the use of the unit.
- Practice operating the unit on a clear, sunny day, and be proficient in its use. (A cold foggy night is not the best time to learn.)
- Always enter a “home” waypoint into the system. I like to do this just outside the entrance to the harbor. Do not place the waypoint at the ramp or dock, as you usually cannot go there directly from anywhere on the water. The ramp or dock is normally easy to find if you can get safely to the harbor entrance.
- If the unit is battery powered, carry spares. Murphy’s Law states that the batteries will always run out of power at a rate directly proportional to the rate at which the visibility is dropping.
- If you intend to use the trackplotter to find your way back, make sure it is set up to retain as much plot as you need.
- Remember that the direction function is only accurate if you are underway and on a steady course.
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