By Ben Ellison
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CHARTING YOUR COURSE By Ben Ellison |
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PREVIEW
So many buttons, so little time. The modern day navigator has powerful electronic tools, but all too often has not had the time (or the will) to master them. Old salts grouch about how the traditional skills are being forgotten, and they are not just being nostalgic. Twain Braden, of the Ocean Navigator School of Seamanship, says, “In terms of what we're capable of, we're far in advance of the old days; today's electronics give the big picture, and we can plan rather than react. But, in terms of skill and judgment, we're not as good as we used to be.”
Delivery skippers regularly step aboard yachts equipped with electronics worth ten of thousands of dollars, but are dismayed when they can't find a pencil sharpener on board. Let's take a look at today's navigation electronics with a particular eye to the usefulness of a sharp pencil. |
Boaters have a choice of traditional GPS or two newer variations, DGPS and WAAS. The “D” in DGPS stands for Differential and means the equipment receives an additional positioning signal from a land-based beacon. WAAS (Wide Area Augmentation System) substitutes additional satellite signal' for DGPS land signals. A GPS position has little value until it's related to that mother lode of navigational data – the nautical chart. The most basic technique is to read the latitude and longitude markings along the edge of a paper chart, and then use parallel rules, or a similar device, to plot your position. It's disconcerting how many inexperienced navigators don't know how to do this, usually because they've always cruised with the aid of a chartplotter. A wise navigator will carry paper charts as well and know how to use them. |
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Navigation instructors have a couple of other reasons to get their students to do traditional plotting and waypoint GPS simultaneously. For one thing, they are independent techniques, and therefore check each other. If your plotted and GPS courses and distances don't correspond, you messed up either your pencil plotting or your waypoint entry. A central tenant of smart navigation is to find ways to catch mistakes before they catch you. Another important principal is to carefully examine the waters you'll be passing through, a practice encouraged by laying your proposed track on chart. More than one boat has gone up on the rocks while right on a (poor) track to its GPS waypoint.
A further exercise is to lay out a whole series of tracks, key in the various waypoints, and build a 'route' in your GPS. Electronics dealers report that many owners never use the route function, and wonder why. Once set up, most GPS units will automatically switch from one course leg to the next as you pass each waypoint, freeing you to pay attention to the helm or just relax. Plus, you can notate the chart with the short route and waypoint names you program into the GPS, and they'll be much easier to use at a later date.
You may well find these exercises time consuming and tedious, and you'll likely want to know how to program waypoints more easily. We'll get to that, but the first task is understanding and mastering the GPS. At some point you will have to obey the number one appeal of electronics service personnel – Read the (expletive deleted) Manual. Understand that your GPS is actually both a data receiver and navigational computer whose interface is limited to just a few keys and a small screen; the most brilliant software designer can't make all it's functions and options obvious to you. You need to learn numerous acronyms and menu trees, perhaps even make notes for yourself.
During your study, you'll probably find some pleasant surprises, like a buried menu where your GPS will predict the sun rise and set for your location, or a database of navigational aids that you can list by 'closest' and choose quick waypoints from. You can find that your GPS has a 'get me home' function, turning a saved track of your voyage into a “cookie crumb” route back to where you started. You'll discover how to decode your GPS's 'satellite status' screen, not exactly essential information but useful to sensing the unit's accuracy at any given time.
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You may also find unpleasant surprises in a technology so young – such as your GPS uses different acronyms and terminology than we've been using in this article. Who's to say that SOG (Speed Over Ground) shouldn't be called SMG (Speed Made Good), or even that a 'waypoint' isn't a 'landmark'? Firm standards haven't yet materialized, and you may well have to open the manual when you switch from one unit to another. In fact, we've seen GPS units from the same manufacturer with the same model number that had significantly different key names and menu systems!
So you learn traditional plotting and how it relates to GPS, you read your manual, and you take command of your machine. Now you'll want to streamline the process of acquiring waypoints and building routes. There are numerous methods. Some chart reprints have the lat/long of significant spots printed on them, and there are even whole books of waypoints. These will save you the effort (and possibly errors) of taking positions off a chart, but not the drudgery (and possible errors) of keying in the data. A popular shortcut is to use the 'mark' function on your GPS (that's usually what's it called) to collect waypoints when you are actually at a particular place; of course that doesn't work to build routes into familiar waters, where they might be most appreciated. The ultimate way to program waypoints is by clicking on an electronic chart. |
Even a modern 10 inch color display can not show nearly the information that the human eye can quickly scan from a paper chart. You need to master all the ways your plotter can pan, zoom, and scroll in conjunction with your vessel. You might also investigate options to customize the display for better visibility, like eliminating soundings over a certain depth or changing color palettes. You should get a good grip on what scale charts are loaded into your plotter, and at what zoom levels they display. In a sense, chart scales are a relic of paper charting; but they remain an indication of how much detail is included. In other words, you may be able to zoom tight into a harbor on an electronic 1:80,000 chart, but it still won't have all the detail of the equivalent harbor chart. There are also some issues with the cartridge type charts most plotters use. They've certainly improved a lot from the days when navigators scoffed at their 'etch-a-sketch' look, but they still often lack some of the non-essential but useful data seen on paper charts, like land contours. It is also common for vectorized charts to use symbols for navigation aids that are quite different than those on our familiar NOAA charts. Strangely, even if you use the same chart cartridge, buoys may look different from one manufacturer's plotter to another. Usually you can get the buoy's complete description by moving the cursor over it, but it's smart to learn the plotter's symbol set to avoid confusion on the water. On the other hand, some contemporary plotters and cartridge charts go beyond paper charts, offering databases of marine facilities and graphic tide and current predictions. Of course, new features require that new menus be fitted into already complex interfaces; again, spending time with the manual is essential. You may be tempted to try an Electronic Charting System (ECS), in which the functionality of a plotter is harnessed to the power and flexibility of PC software and hardware. You can have a bigger screen showing raster equivalents of familiar paper charts. You can type in waypoint names with a regular keyboard instead of rotating through letter lists. You can probably call up extensive help files, perhaps even animated tutorials. Some GPS manufacturers offer simple, inexpensive mapping programs that you can load on your home PC, mouse click routes, and then upload them to your portable GPS via a data cable. At least one chart CD version includes a planning program that facilitates printing out charts at home with routes overlaid. For the most part, however, software developers are using the muscle of PC's to build chartplotters on steroids. In the ECS environment you can have a nearly infinite amount of information overlaid or windowed onto your chart. Anything that has geographical coordinates qualifies-aerial photos, topographic maps, tide and current predictions, marine facilities, pilot books and so on. Some ECS offer free weather downloads that displays on top the charts. Fisherman and explorers are smitten with bottom contour data displayed in3-D. At any rate, an ECS may have a more familiar and capable interface than a chartplotter, but it's also probably more complex. You'll have to do your homework to get the most out of it, and once mastered, you can expect some attractive new feature to come along. How about overlaying your radar image on top of an electronic chart? It's available in a couple of recent EC programs (and a few new plotter/radar units), and it's a terrific aid… if you have a firm foundation in chart and radar basics. |
First off, it's useful to understand how a radar 'sees', sending out circular arrays of microwave pulses of a certain vertical and horizontal beam width and then receiving back those pulses that bounce off something reflective. It's a crude sort of sight. The wide vertical beam needed to compensate for a vessel's motion also causes unwanted reflections from waves, or no sight at all if a vessels rolls or pitches too far. The relatively wide horizontal beam of many recreational-sized radars lacks resolution, making two vessels at a certain distance look like one. To an eye that sees only reflections, a sloping shore may be invisible, though a further-away bold shore is easily seen. Similarly, a wood or fiberglass vessel may generate only occasional blips while a steel vessel beam on at the same distance might look like an aircraft carrier. Radar units have various controls to help you optimize their version. 'Gain', essentially a volume control on reflected signals, is a critical adjustment, and may need tweaking every time you change the radar's range. Sea clutter and rain clutter are both useful filters for removing signals that cloak the more solid objects you're most interested in, but both can also reduce your unit's sensitivity. Nowadays, most radar units have automatic tuning circuits, but you may find yourself with an older unit with a 'tune' knob. Treat it with great respect; it controls how well your unit receives reflected signals and should be set carefully when a known target is in sight and other controls are minimized. The other important element to understanding your radar screen is 'relative motion'. The screen image is sort of a chart with you in the center, but it's swinging and sliding with your boat's track through the water. Cursors, Variable Range Markers (VRMs), and electronic Bearing Lines (EBLs), and 'echo' functions can all help you figure out if one of those targets is maintaining a constant bearing and decreasing range, i.e. is on a collision course. However, actually figuring out another vessel's true course and speed is complicated, though useful for making the wisest maneuvering decisions. Professional mariners learn to use paper 'maneuvering sheets' to plot radar targets at set time intervals and then apply their own vessel's course/speed vector to deduce the other vessel's true motion. There are numerous good books and courses on the subject. Starpath School of Navigation markets a PC radar simulator that will let you deal with busy traffic in the safety of your own home, even open a window to one side that shows every simulated vessel's true motion. Get comfortable with your electronics. Gather up all your manuals, some sharp pencils and paper charts and spend some quality time with the equipment. The electronics in your pilothouse are capable of doing a lot more than you realize. Not only will you get the most out of them, but also you'll know what to do if the equipment ever fails and you're left navigating by the seat of your pants. Originally published in Marine Electronics Journal, |
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