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Using paper charts in the digital age

2013 June 17

Good seamanship dictates that a chartplotter is no substitute for paper charts

Navigation is loaded with cool gizmos these days. The technology is great and getting better every day but it shouldn't replace paper charts and basic navigation skills. Rather, paper charts form the foundation for all the cool toys.

Redundancy is one of the best reasons for augmenting electronics with paper. Electronics can and do fail. Batteries die, electrical systems fail, boats get hit by lightning, a wave may break in the cockpit dousing sensitive electronics. Political and military situations in the world can impact electronics too; GPS can be shut down or regionally blocked on the decision of the government.

Equally important is the situational awareness that paper charts offer. Situational awareness describes a process or philosophy of gathering complete objective data about your immediate environment and using it to make the best decisions that you can. Fixating on blinking numbers on a GPS, or a little icon of your boat sliding across a sea of blue provides some data but not enough. Plotting your position on a chart and examining all the chart data in the location provides more. "Getting your head out of the boat" and looking around, taking landmark bearings and celestial sights gives a bit more. Combined you have a pretty complete situational awareness and can make good decisions.

I have a simple, informal process developed over years of passagemaking that I've pared down to the bare essentials.

My passage planning starts on paper, which I find convenient as well as ensures that I have the correct charts for the passage. I sketch in my waypoints, draw a proposed course line and review all the navigational details along the way. Charts contain an amazing amount of data but some of it is cryptic. A great book to assist in decoding all the detail on a chart is Nigel Calder's aptly named How to Read a Nautical Chart. Once I have my passage sketched, I transfer the waypoint data to my GPS and organize it into routes for easy use.

There seems to be an assumption that paper charts are less accurate that digital versions, but in general this is not true. Navigating solely with paper charts and dead reckoning can be less accurate than using GPS, but the paper chart data is as accurate as digital. Navigational data is largely funded by government agencies the world over with the primary product being the paper chart. The same data used to produce the charts is used for digital charts and in some cases the digital charts are actually scanned from paper charts. The key to navigational data quality is to use the latest and best available, whether paper or digital.

Navigational data is funded and produced for the benefit of commercial traffic, so you will find more and better data in areas with lots of shipping. Once you are off the beaten path you may find that sketch charts from cruising guides are a better source of data for the cruising sailor, as the data is often gathered by many cruising sailors over a number of years. This crowd-sourced data seldom makes it into commercial paper or electronic charts.

Another caveat for digital charts is to use the chart at the scale it was intended. Chartplotters are able to greatly magnify chart detail with zoom functions. Increased magnification can also magnify any chart errors, sometimes with disastrous results.

Modern GPS units provide lots of information, and many will plot that data graphically, but for my use I need just five pieces of data from the GPS; latitude, longitude, course over ground, speed over ground, and the time of day. Latitude and longitude are pretty self-explanatory, this is your location on Earth. In the past this was hard-won data that took hours of celestial sight reduction and careful recordkeeping to get within a couple miles of your position. Now we have the luxury of getting it at the push of a button. You can think of COG and SOG as your "true" course and speed, without regard to current. I keep a log of the basic GPS data on a legal pad, drawing five columns and writing in headings for time, lat, lon, COG and SOG. I typically make a log entry every hour, more often if I am somewhere with lots of hazards or if I get bored. This level of detail is what is available from a traditional dead reckoning paper plot, with the added benefit that the position, course and speed are GPS accurate.

Since my paper log contains all my accurate DR data, I can easily create a paper chart plot from it. I typically just plot my positions and note the time. If I need to know the speed I can get it from the log or calculate it from the time-distance deltas on the plot. I will typically measure the course directly from the chart line if needed. I try to transfer my positions to the chart every couple hours, but even if I get lazy I always have the data in the log. Each time I plot, I am forced to look at the chart and this opportunity lets me gather a little data about the area I am in, forcing me to note critical data about nearby hazards or interesting historical data about the area.

This may be a contentious statement, but I set up my GPS to use true course and I plot in true. I find it easier all around and, to be honest, I tend to do my long-term navigation using COG rather than looking at the compass. I use my compass to steer a straight course when hand steering, but I just use it as a relative course, typically not even paying close attention to the numbers. If I need to actually navigate with a compass, in the event of a GPS failure, I calculate variation and deviation.

GPS does a great job navigating to a waypoint, but often doesn't directly warn you that you are off your intended course. Take, for instance, a course from Florida to the Bahamas across the Gulf Stream, in which you leave Miami and aim directly for a waypoint in Bimini. Your GPS would happily show you the course when you leave and would continue to tell you the course as you make your journey. It wouldn't directly tell you that you are making a large arcing course to north as the Gulf Stream sets you miles off course, adding many miles to your trip. That large arc could take you 30 or more miles to the north and then the return trip to the south would have you pretty much directly opposing the stream. Making the situation worse, that large arcing course could take you over hazards that should not have even been on your intended path. The GPS is not providing you inaccurate data; it will always give the correct course to the waypoint, but given all the inputs of your situation it is not the course that you want to steer.

A better way to approach that passage would be to do some paper-based approximations during your planning. Bimini is roughly 48 miles away and you know the Gulf Stream will be with you most of the way (the stream generally starts a couple miles offshore and flows to within a few miles of Bimini). The stream flows at 2 to 3 knots to the north, and you know that it will take at least 10 hours to make the crossing. Based on this, the stream will impact your voyage roughly 30 miles (3 knots for 10 hours) to the north, so you need to aim at a point 30 miles south of Bimini. A quick measurement on the chart will show you where to steer and you can enter that waypoint into your GPS. On the passage, you will log your progress and plot as you go. Your course should be leading to Bimini and a quick check with the GPS will verify the COG is roughly aiming at Bimini. You can adjust the course as you go, and log the results.

On the softer side, combining paper and electronic navigation ties nicely into the traditions of sailing. A paper chart, dividers and parallel rules have been the tools of the trade for hundreds of years-it just feels right to use them.

Prudent navigation requires basic paper chart skills and is very nicely augmented with technology. Aside from the navigational benefits, using paper charts leaves lasting evidence of a passage, nothing warms the heart on cold winter night better than reviewing a coffee-stained chart detailing a previous summer passage.