An electronic chartplotter combines a nautical chart image with a vessel's precise geographic position and provides the helmsman with a superb real-time picture of the navigational situation. Some systems further enhance the level of situational awareness by incorporating information from the vessel's sonar and radar. These systems are powerful enough to create the illusion that everything the helmsman needs to know is right there on the screen, a great advantage, provided the user recognizes that there is no substitute for keeping a sharp and continuous visual lookout. Whether you are piloting an aircraft or a boat, getting "head down" is a bad idea.

Remember, regardless of the level of sophistication of the display system, the information you see is only as good as the input data. While position data derived from a GPS may be excellent, your charts may not be up to date and can contain significant errors. Atmospheric and aquatic conditions may degrade data from the sonar and radar. Any significant lag in the system's magnetic heading sensing can create errors during turning maneuvers.With that caveat in mind let's examine today's chart plotter field.

Plotters can be classified in two groups, dedicated hardware/software packages or as software designed to run on desktop or notebook computers. Each type offers advantages and limitations. In general, the special-purpose, hardware-based equipment is easier to install, easier to use and on many recreational vessels will be better suited for real-time use at the helm. This is especially true of installations that are exposed to the weather and occasional immersion. The display screens of the dedicated hardware systems tend to be smaller but brighter than those of notebook or office-type computer installations (although modified computers and various sizes of sunlight-viewable screens are available and are a worthy solution).

Systems based on software that's designed to run on a standard computer operating system, such as Windows, or on a Macintosh computer often provide a wider range of navigation options than those in dedicated chart plotters. Such programs let you plan your trips on the computer at home and then transfer those plans to the equipment on the vessel. Software updates are usually more likely to be made available for programs designed to run on general-purpose computers than those used in packaged chartplotter hardware.

Hardware-based chartplotter systems are typically ready for use right out of the box. Some units require insertion of a chart cartridge, others have all US waters already installed. (It is always desirable to be able to update any built-in cartography.) Many units have built-in GPS receivers, some with the antenna contained in the display housing, others designed to work with a remote antenna/receiver (the GPS's "engine" is now a micro-chip set and small enough to be built into the antenna, eliminating the need for a coaxial cable to carry the RF signal to the plotter housing). If you choose a unit with a built-in antenna, be sure that its antenna always has a clear view of the horizon. The hardware is typically hardened for use in the marine environment, in many cases extending to total waterproofing. The operating systems employed in hardware-based plotters dispense with a hard-disc drive, an advantage in environments that subject the hardware to strong vibrations and shocks.

Hardware-based systems are available in a wide range of prices and levels of performance. Display screens range from a few inches (as in a handheld computer) to more than 12 inches diagonal. In addition to the basic navigation/charting facility, a number of supporting operating modes may be available, such as calculation of fuel consumption with display of nautical miles per gallon. Content of the display screen frequently includes data from the radar and sonar, plus the option of video from a variety of sources. While chart plotters are available with display screens as large as 20 inches, a very large screen is not absolutely necessary, even a small display provides an excellent picture of a vessel's navigational situation. However, for real-time piloting in which the chart image is being used for precise navigational guidance, such as entering a harbor surrounded by poorly charted shoals, a large screen will quickly prove its worth by making it easier to integrate what is on the screen with what you see ahead.

A chartplotter may offer a number of display choices, including various split screens, which show chart data along with sonar, radar and navigational data, plus video from any one of a number of sources. Some installations give you the option of watching real-time TV programs. (If the helmsman aboard the boat you're on is using the chartplotter to watch TV while under way, GET OFF.) In most cases, a dual display will be more than sufficient, perhaps the chart and radar information or the chart and fishfinder data. Displays that overlay radar on the chart image can be useful, however their value will be very limited unless the vessel is equipped with an accurate, fast-response heading sensor. Any errors in the heading data, including those that occur when the vessel is turning, have the potential of creating a totally confused image. Separating the radar information from the chart image may be the better way to go. If you plan to cruise offshore, you may prefer the navigation display. It does not rely upon a chart image, and it displays a full range of data about your present position, speed, course, time and distance to the next waypoint.

Chartplotters comprised of special-purpose hardware running a generally invisible operating system are usable only for the range of purposes provided by the manufacturer. Software upgrades may occasionally be available, but most systems will be retired from use with the original operating system and software intact. Software that's meant for a general-purpose computer, on the other hand, offers a very wide range of capabilities. The variety hardware available includes standard notebook or desktop computers or hardened versions of these machines. Give first priority to the display screen's suitability for the specific installation. Check the screen's readability indoors and out. Judging the readability indoors using a bright light to simulate sunlight is rarely satisfactory. The total quality of ambient light at the helm of your boat-including brightness and the dispersion of the source-will determine how well you can see the screen. The most challenging lighting conditions can occur in the shade of a bimini top, where the ambient light comes from everywhere.

Any computer used on a vessel must be designed to provide a high degree of protection from shock and vibration. In this regard the notebook computer may be superior to a desktop machine. Hardened notebook computers offer superior environmental protection, often including sealed exterior openings and water-resistant keyboards. On larger vessels, a standard desktop machine can be installed on shock mounts in a well-protected location belowdecks and be connected to a suitably rugged keyboard and display at the helm. Dedicated chartplotters usually avoid the potential damaging effects of shock and vibration by avoiding the use of a hard drive.

Most of the chartplotter software requires a Windows operating system. (See the sidebar below for a list of programs). Some are complete with chart catalogs, others require the purchase of cartography at additional expense. Programs designed for use with Macintosh computers are once again available and can be attractive for mariners who prefer Apple Computer hardware and its latest OS-X Unix-based operating system.The attractiveness of two of these programs is enhanced by their ability to use official US Government charts that can be downloaded without charge from the NOAA website. (Vector S-57 charts are already available on the Web site, the raster-scan chart catalog is now available as well).

Selecting a chart plotter for your boat can be a fascinating, very pleasant, educational but time-consuming task. Plan to spend as much time as you can in a store that has a wide range of units on display-when they won't mind if you stay and play for a few hours. Don't expect to be able to appreciate the values and detriments of any one product or piece of software after only a few minutes. If you have friends whose boats are equipped with recent versions of the equipment in which you are interested, ask them to show you why they chose the equipment. Listen intently and if possible accompany them on a voyage. Consider that they will naturally defend their choice of equipment or software. You are about to make a significant investment and need to form your own well-informed opinion. The range of products available-dedicated chart plotters and software systems that run on Windows or Macintosh-is long and constantly expanding. A check of any catalog or a Google search for chartplotters will reveal a seemingly endless list of vendors and equipment. A few are listed in the sidebar.

Regardless of your choice of hardware/software, be sure the installation properly supports the equipment. You'll need a reliable source of electrical power, preferably from a circuit that is separate from any other consumers. It should be capable of supplying at least 12 volts at all times (even when the battery voltage drops to 11.8 volts-the fully discharged voltage of a deep-cycle battery). Provision of a special Navigation/Communication electrical bus, a NAV/COM bus, supported by a back-up battery can be a very worthwhile investment in navigation safety and peace of mind.