Chuck Husick: Techno-Talk, September 2003 BoatUS Magazine - Updated June 2009

Navigation and Plotters

All navigation begins with plotting your position on a chart. Until about 1993, most mariners were using paper charts and the traditional plotting tools: pencil, divider, parallel rule and protractor. A few were using an electronic chart table that automatically interfaced paper charts with Loran C or GPS receivers (KVH Quadro Electronic Charting System, $649 in 1994). However, 1995 signaled the future with the Garmin GPS MAP 220, a 16-color chartplotter for $2,198.

Fourteen years of progress in electronic cartography, the ever increasing availability of low-cost, high-speed microprocessors, cheap memory and liquid crystal displays that can be seen even in direct sunlight, have totally changed the marine navigation world, both for ships and for the recreational mariner. The big ship version of the recreational vessel chartplotter — the Electronic Chart Display and Information Systems (ECDIS) — is now a legal substitute for the paper charts normally carried on such vessels. Smaller commercial vessels will soon be permitted to follow suit and use chartplotters with electronic cartography in place of the now mandatory paper charts.

While use of electronic navigation systems in the commercial world is regulated by the federal government, recreational boaters are free to adopt new technology as fast as it emerges from the laboratory. We now enjoy, or are confronted and perhaps confused by a dizzying array of electronic navigation equipment. Choices include handheld GPS/Chartplotters, GPS equipped Personal Digital Assistants, the iPhone, dedicated chartplotters, multifunction display systems that combine chart navigation with sonar and radar data and powerful navigation software desktop and laptop computers.

The chartplotter you choose should match the way you intend to use it. The display screen of chartplotters used at the helm must be visible in every on-water lighting environment, direct and indirect sunlight (the latter can be as much a problem the former) and in night operation, where even a minimal amount of light can be too bright. The screen must be large enough to make chart details clearly visible at arm’s length. Refocusing your eyes to see too small a screen can be a dangerous distraction while underway. Screen redraw time must be no more than a few seconds to allow switching scales or panning across a chart with minimum delay. At this time the Furuno NavNet3D system provides the most advanced screen image presentation in part by eliminating the customary pause for screen re-draw entirely, making it possible to seamlessly scroll or zoom the chart image.

A handheld plotter used at the helm for real time navigation should be powered from the boat’s electrical system and securely mounted in the primary viewing area. All electronic equipment used at an exposed helm should be waterproof. Plotters used for real time navigation should be controlled by dedicated keypads with perhaps a few “soft” keys. The “pull down” menus common on PC-based plotters can be hard to use in other than calm water.

Technology now allows graphic display of an amazing (an possibly bewildering) amount of information including: a chart, radar, sonar (depth information and/or a fishfinder display), GPS or Loran C navigation information, hull speed, wind velocity, water temperature and, in some areas, information from local radio linked sources such as PORTS and National Weather Service radar images. The critical challenge is to limit the on-screen information to a few really usable combinations. Excessive clutter will diminish the value of the information and in the worst case mislead the user. Displays that overlay radar data on a chart image must be used with special caution. Correct registry of the chart and radar data requires a source of accurate, minimum lag heading information. The simple magnetic flux gate sensor used in many autopilots is rarely good enough for this purpose. Some of the most advanced systems obtain heading information from a GPS compass which provides a number of advantages including little or no time lag, immunity to influence from local magnetic fields and the ability to deliver true-north information, eliminating the need to compensate for local magnetic variation. 

While general purpose computers running charting software can provide a very powerful navigation aid, they are best used on an enclosed bridge or at a chart table as an adjunct to navigation. The ability of these computer-based systems to monitor numerous ship systems makes them very attractive for larger yachts. The GPS equipped Apple iPhone and some similarly equipped PDAs can provide quite useful chartplotter capability in an internally powered, handheld package. The iNavX application available for the iPhone ($50) presents a full function chartplotter with the capability of wirless download of any US raster chart. When in cell phone range the phone's Safari web browser can be used to connect to and display real-time National Weather Service Radar images.

Regardless of the type or configuration of electronic chart and navigation aid you select, always remember that the prudent navigator never relies exclusively on any one source of navigation information. No matter how precise your position information appears, it may not match the charted position of dangers to navigation. Although today's electronic equipment and the GPS is very reliable there is always a chance that something will malfunction. When voyaging offshore or in unfamiliar areas it's a good idea to Keep an updated log of positions or note the information on a paper chart. Without electrical power the navigation screen will become a blank, suddenly displaying what can only be called terra incognita. Whenever you are at the helm you need to minimize your head-down time as much as possible. In boats as in airplanes, use your neck to move your primary navigation safety sensors: your eyes.