Guest editorial
Issue 93 : Nov/Dec 2013
The chart plotter has evolved into a wonder that has simplified navigation and route planning beyond the dreams of sailors of old. Over the last decade, chart plotters have become less expensive and the chart sets now cover even the most remote areas of the world. It is rare to find a cruising sailboat without one. With the advent of navigation apps for tablets and smart phones, many cruisers have two or three aboard.
Five years ago, after delivering a friend’s boat that had a chart plotter aboard, we decided to join the electronic navigation world. Next, we bought an iPad and navigation apps and charts. It’s a marvel to see at a glance exactly where we are and to plot a course by simply moving a cursor around and dropping a waypoint. The chart plotter makes navigation so trivial it’s easy to become complacent and to overlook other navigational tools. Therein lie the dangers.
Many electronic charts are based on chart surveys done before the advent of the GPS. While your GPS will locate you on the earth’s surface to within a few feet, your chart might be off by as much as half a mile. The chart plotter could show your boat as being well clear of an off-lying danger when you are about to hit it. Many times, our chart plotter showed Nine of Cups being high and dry in the middle of an island when we were safely anchored in 50 feet of water a fair distance off the beach.
Electronic charts are usually accurate except for an offset. If you can determine what the offset is, most newer chart plotters allow you to correct for the offset. If your radar image can be overlaid on the electronic chart display, you can determine the offset by measuring the difference between the positions shown for the same landmark by the radar and the chart plotter. If not, you can use basic coastal navigation skills to determine where you are relative to the chart and then calculate the offset.
Many cruisers are so confident in their chart plotters they no longer invest in paper charts. Paper charts may be expensive, but it’s important to have the paper charts necessary to complete a passage. At an absolute minimum, we have a small-scale passage chart or charts of the area we will be sailing. We also try to have large-scale charts of ports we will visit.
Our appreciation for paper charts is based on the ease of creating a route on a chart plotter. If we’re sailing a passage between ports, we have a tendency to zoom in to a high-resolution view of the port at each end to plot waypoints and then zoom out to review the route connecting them. This low-resolution view of the route will often miss small hazards along the route. For example, the 1,000-nautical mile passage from Luganville, Vanuatu, to Bundaberg, Australia, passes right through Chesterfield Reef. This reef is clearly marked on the paper charts for the area but is only shown on the higher-resolution views on our chart plotter. Sailing onto this reef at 6 knots would certainly spoil your night watch.
Even if you painstakingly view your route at high resolution, you could miss hazards lying just off your route. With a motor vessel, this might not be a problem, but sailboats don’t always sail the rhumb line.
In the days before chart plotters, my wife, Marcie, and I spent time calculating waypoints and plotting routes together. That made both of us familiar with the route and potential hazards. Since plotting on the chart plotter is a quick, one-person activity, only one of us reviews the route when planning. To ensure we’re both prepared, we each review our planned route on the paper chart prior to any passage.
There is the possibility of losing electronics due to a lightning strike or because of an electrical or equipment malfunction. We have a couple of handheld GPS units aboard as backup. With paper charts and a GPS, we’d be no worse off than we were before adding the chart plotter, and I still have my trusty sextant, although I’m a bit rusty with it.
We’ve cruised areas like the fiords of New Zealand, canals of Patagonia, and rivers and estuaries of Tasmania where a chart plotter provides little or no detail. There, we found cruising guides and local charts to make navigating possible and we’ve sometimes made copies of hand-drawn charts or obtained mud maps from fishermen and other yachties.
A final shortcoming with chart plotters is that it’s not uncommon to meet a fellow cruiser who’s heading somewhere you’ve been or coming from a place you’re planning to go. It’s very pleasant to spend an evening going over charts and exchanging information on anchorages and navigation. We usually make pencil notes on our paper charts and cruising guides. We don’t know how to add little notes to our iPad charts, but even if we could, it just wouldn’t be the same.
Thank you to Sailrite Enterprises, Inc., for providing free access to back issues of Good Old Boat through intellectual property rights. Sailrite.com
