Safe Navigation in Poorly Charted Waters

While we’re in the middle of lining up a series of tests of electronic navigation devices and systems, I’m reminded how easily these devices can leave novice navigators unprepared for the real-world problems that they will face during a long coastal cruise or ocean crossing.

While we are truly entering the golden age of mapping the earth’s surface, chart accuracy remains a problem as you venture off the beaten track. As Ralph Naranjo reported in his outstanding report in the April 2016 issue of Practical Sailor, today’s navigators still require a range of traditional skills, published sources, and equipment to solve a navigational puzzle. A bottom-scraping cruise I took along the ever-changing coast of Southwest Florida reiterated some key points regarding coastal navigation.

1. Carefully plan your route ahead of time. Plug in your waypoint “bread crumbs” well in advance, not the night before you leave. Whether you are using coordinates or the map cursor to place them, double check their positions, using an appropriately scaled and up-to date chart (see #2 below). Make sure the routes connecting two waypoints lead safely clear of reefs or other hazards, and allow plenty of room for any chart inaccuracies. In addition to the navigator, I like to have at least one other crew-member check the waypoints. It not only puts another set of eyes on this vital information, it familiarizes them with the route should the navigator be unable to perform their duties. These waypoints, of course, should not be considered etched in stone. Currents, wind will effect your actual course, requiring route changes, and you may discover the route you plotted from the comfort of your marina slip did not take into account a new wreck, or a bridge under construction at your destination.

2. Don’t knock printed charts. Printed charts have much to offer, especially when planning routes, or making significant routing changes. At the very minimum, a printed small-scale planning chart for the area you are sailing should supplement your digital portfolio. As anyone with a chart-plotter knows, zooming out to planning scale on a vector chart often results in key obstructions disappearing from view, making it too easy to lay a course that intersects with known hazards. This is exactly the type of oversight that led to the grounding of Vestas Wind. Detailed, large scale printed charts of your destination, and of key “emergency” ports along your route can greatly reduce stress when Murphy’s Law takes hold. If the navigators at the highest level of ocean racing can make routing mistakes, we can, too.

3. Use multiple reference guides. U.S. Coast Pilots, their foreign equivalents, and updated cruising guides can save a lot of headaches, especially when making final approaches to gunk holes that neither printed nor digital charts have portrayed accurately. Two inlets we used during our short cruise were clearly mischarted, as shifting sands had not only reoriented the charted channel position, but also made the fixed navigational aids misleading.

4. Seek out reliable local knowledge. Local professionals, the U.S. Coast Guard, and online resources like Active Captain can be an important source of information when navigating areas that are known for shifting shoals. In most popular ports, tow boat operators and local marina operators are standing by on VHF to help guide sailors around known dangers that are not on charts, but even these sources should be cross-checked whenever possible. Ideally, your sources should be knowledgeable owners of boats with a similar draft to your own.

5. Use your senses. As much as possible, the navigator should try to time challenging navigation when natural forces are in working in his or her favor. A rising tide, good visibility, relatively calm water, and plenty of sunlight at your back can turn a tricky cut into Easy Street. Favoring the windward sides of narrow, shallow channels means that if you do go aground, there is less risk that you’ll be driven further into shoal water, and it will be easier to extricate yourself.

6. Dial in your electronics. Depth and radar alarms can be an extremely useful asset in scenarios where the bottom contours are prone to shifting, or where some features are poorly charted. They can be even more helpful if you’ve optimized the settings. For example, a deeper than normal sonar alarm setting can alert you sooner when you are creeping toward the shallow side of a channel with sloping sides. Properly adjusted, todays hi-definition radar can pick up fish traps as well as channel markers.

7. Approach with caution. Fortunately, much of the sea bottom in popular cruising areas are sand or mud, and most cruising boats can take an Intracoastal Waterway soft-grounding without harm. So long as you use a slow speed, backing or kedging off can be a simple operation. Of course, the stakes are much higher in many places, making a cautious approach even more advisable. Not allowing plenty of sea room between the boat and poorly charted reefs has caused the unfortunate end to many cruising dreams (see my related post on the wreck of a 46-foot catamaran in French Polynesia in 2017).

8. Have an exit strategy or alternative anchorage. Don’t be so rigidly fixed to your cruising plans as to put your boat and crew at risk. Try to anticipate any challenges an upcoming obstacle might present and discuss in advance with your crew what will be expected if you suddenly find that seven-foot channel depth is reading five feet on your sounder.

In the debate over paper versus digital charts, it is easy to forget that the most important navigational element on board is neither your chart or your plotter, but the captain and crew. Making sound decisions requires having good information, and as the navigators rule asserts, you should never rely solely on a single source for that information.