Thursday, November 29, 2012


This week we navigate navigation.

Dead Reckoning:
Every boater needs to know proper navigation techniques to arrive at a desired destination safely and on time. The earliest ocean voyagers and explorers relied on a process known as “dead reckoning,” in which a vessel’s speed and heading were recorded each day, and an estimate of its current position was plotted on a chart. Prior to the invention of the magnetic compass, a course was steered relative to known stars or the position of the sun on the horizon. Speed was determined by dropping a chip of wood (a “chip log”) into the sea off the bow and timing exactly how long it took to reach the transom; since the boat’s length was a known, the speed at which the vessel passed the chip was recorded as an estimate of the boat’s speed. Of course, these primitive methods didn’t account for drift, currents or winds.

For thousands of years, accurate clocks and timepieces weren’t available aboard ships, so a “sand glass” (often erroneously known as an “hour glass”) was used. To determine speed the sailors used a 30-second sand glass, while a 30-minute sand glass was used to keep ship’s time. By the way, the content of the “sand” glass was usually not sand, but a mixture of ground-up seashells, stone, eggshells, marble or other materials that would be less likely to stick together. It wasn’t until the invention of the chronometer, (ship’s clock), that longitude could be accurately calculated. Today, a $10 electric watch is as accurate as a chronometer of the 18th century, which cost over 1,000 times more. By measuring the angle between the masthead and the sun at noon, the navigator could determine latitude. Until the 1920s, a sailor’s day changed not at midnight, but at noon.

Paper Charts:
Anyone piloting a boat should know how to read a paper chart, though as boats continue to get bigger, faster, and more expensive, operators are becoming less qualified. You should know how to plot a course from point A to point B without running aground or getting hopelessly lost if you lose sight of land. You should know how to use a protractor, parallel rulers for plotting bearing and direction, and a divider for measuring distance.

The use of paper maps or charts dates back to the very beginning of recorded history. Every seafarer drew his version of the coasts he sailed by and the harbors in which he sought shelter. As a ship approached coastal waters, a sailor would lower a lead weight on a line incrementally knotted in fathoms (6') to determine the “sounding” or depth. The weight on the “lead line” contained a hollow point that was stuffed with beeswax, so a sample of the bottom could be pulled up and recorded. Today’s nautical charts are the result of generations of mistakes, which you don’t need to repeat. A chart is cheap insurance. However, regardless of what the chart shows, don’t steer toward birds standing in the water!

The widespread use of the accurate, inexpensive national system known as GPS has given a false sense of navigational security to the digital generation. The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather, anywhere on Earth where there is an unobstructed line-of-sight to four or more GPS satellites. While aircraft positioning requires a “fix” on four satellites, boats only require three satellites to determine their position because elevation (altitude) is fixed at sea. The GPS system was originally developed by the military in 1973 and is owned and maintained by the United States government; it’s freely accessible to anyone with a GPS receiver.

Between 24 and 32 GPS satellites, in stationery medium earth orbit, broadcast radio signals from space, and each GPS receiver uses these signals to calculate its three-dimensional location (latitude, longitude, and altitude) and the current time. Each satellite contains solar-charged long-life batteries which power the radio station and an extremely accurate atomic clock. Long after the world as we know it ceases to exist, the GPS satellite stations will continue to broadcast to our radio-receiver GPS units.

You can spend thousands of dollars for built-in marine GPS units which have the ability to interface with other navigational instruments like radar, depth-finders, and autopilot, or you can purchase inexpensive hand-held marine units made by Garmin or Magellan, which will still get you there. Expect to pay about $100-$150 for these battery-powered units that are about the size of a smart phone. I used an entry level, hand-held Magellan GPS on a previous trawler for ten years…just try to avoid dropping it overboard!

Smart Phone GPS:
Cell phone manufacturers have been installing tracker chips in cell phones for years; this technology allows law-enforcement agencies to pinpoint the location of the phone. It was a fairly simple software step to turn the cell phone into a GPS-capable device. Now anyone with a smart phone can download navigation software and use their phone as a navigational instrument. The navigation application is primarily used for land-based location and directions. I don’t recommend using your smart phone as your primary GPS instrument. If you drop it overboard, you’re without an instrument; if you run out of battery charge, you’ve lost your ability to navigate.

If you want the best built-in GPS equipment for your boat, you can expect to spend $1,500 to $6,000+ for a unit which has plotter functions that allow you to program a course and track your progress in real time. A full-color monitor, often the size of a flat-screen television, will keep you in the channel and identify markers, buoys, and day-beacons. Many units also offer a satellite view option and a depth-finder interface which displays the contours of the bottom you’re passing over; additional software can look forward and to the side just like sonar. Most plotters also offer interfaces with radar and autopilot. The units offer audible alarms to alert you when you’re off course, need to change course, or are entering shallow water or pulling your anchor. By adding a Bluetooth interface or downloading additional software, you can access shore-based service facilities.

A tablet is a general-purpose computer contained in a single panel. Its distinguishing characteristic is the use of a touch screen as the input device. This lightweight, portable computer is a transitional device between a smart phone and a laptop. Popularized by Apple’s advertising campaigns, the first iPad revolutionized the computer industry. Though many manufacturers now offer tablets, the iPad’s clean lines, retina display and simple operating system have made it the number one choice in the market. Now that 4 generations and a mini iPad have been released, the iPad has become the go-to primary navigation instrument for many boaters.

I like the iPad 3 with wi-fi and cellular capability that allows you to operate the device as a full function GPS plotter. I also like buying refurbished equipment directly from the Apple store because it comes with a new guarantee. Expect to pay between $379-$679.

Expect similar prices on eBay for refurbished iPad 3 units:

You can mount the iPad on your bridge in a specially-designed bracket manufactured by the Ram Mount company for less than $50.
The iPad 3 has a 9.7 inch color screen with retina high-resolution display and a 10 hour battery life. (Add a solar charger). You can download “free” and “fee” marine navigation software; for reviews and to find the best application for your personal needs go to:

The added advantage of the iPad is that it’s multifunctional; when not navigating, it offers excellent video conferencing on, a high resolution still and video camera, a voice-activated recorder, and many of the features of a compact laptop—I use it with my wireless keyboard and mouse. Thousands of additional apps are available.

Closing Observations: 
As a former professor at the Merchant Marine Academy, I’m a big advocate of boat operation and safety courses. Learn how to navigate. Take courses offered by the US Coast Guard or your local Power Squadron; you can even take the course online at:

The waters in the Bahamas are so crystal clear that a lookout is often all you need to thread your way through narrow channels to pristine deserted islands. The rule of thumb when sight navigating is: “If it’s blue, you’ll float on through; if it’s brown, you’ll run aground; if it’s white…you might.”

The Treasure Coast


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