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Dead Reckoning: Click any image below to enlarge
There is no question that electronic navigation is the tool of choice today and rightfully so. A competent navigator is not the skipper who can press a button and follow a command, but one who uses all the tools at his disposal to navigate his course safely and efficiently. Sitting at the helm enjoying the scenery, having a cocktail and looking at the GPS while you bend down to prepare the next drink depicts a beautiful fairy tale cruise. There are skippers that in a twelve hour voyage will never once look at his or her chart, relying solely on their electronic first mate to get the boat and crew to their destination safely. Learning and practicing some of the basic forms of traditional navigation will be rewarding as well as make you a safer, more competent navigator. Dead reckoning is the most basic and useful of these skills. GPS today should be used in conjunction with dead reckoning, not to replace it. Electronics are man-made and subject to failure without warning. If one were to voyage to the Bahamas with GPS only and it failed, the only information you would have is that you are in the Atlantic Ocean and traveling East. If you plotted a dead reckoning course and updated it every hour along with your GPS fix (any known position i.e. lat/long, channel marker, water tower), you would have a very accurate estimation of your position by doing two easy things: 1) looking on the chart and seeing where you were thirty minutes ago and 2) applying some simple math. Let’s talk a bit about dead reckoning and what it really means. Dead reckoning (DR) allows a
navigator to determine his present position by projecting his past The DR Plot... 
Maintaining a DR plot directly on a chart is important. Whether you make a plot on chart paper (chart-size paper with meridian lines pre-drawn to be labeled with lat/lon corresponding with the chart you’re currently working with to avoid writing directly on a chart) or not is personal preference. Set your rhumb line from a known position to your destination and DR at least two fixed intervals (if possible) ahead. If you are in open ocean, plot a DR at least four to five hours ahead. If you are traveling at eight knots not taking currents or other factors into consideration, you will travel approximately eight miles in one hour. In open ocean, on your chart you would plot out thirty-two miles along your rhumb line. This will show you any possible hazards to navigation along your course and about what time you may encounter them. You should DR every hour along with recording a GPS fix and compare the two. You will then quickly see if you are drifting off course. If you are coastal cruising, you can DR the same way except you will be able to DR to a fixed object (i.e. water tower). If you have a visible tower ten miles up your course and then another one twenty miles up, DR to both and you can then estimate when you will reach possible hazards to navigation. Again, you must DR along your rhumb line every hour with a GPS fix and compare.
Summary There are many advanced forms of DR plot that can be used. Regardless of what form of dead reckon you use the rules always apply and by practicing these skills, you will become a more comfortable and competent navigator that can still function when the GPS God dies. You can learn more about dead reckoning from any basic mariners’ navigation publication. Wayne Newberry, A two-time transatlantic veteran and twenty year trawler voyager aboard a 1969 Willard 36
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