This article describes the basics of how to navigate in your own boat using either traditional paper charts or a chartplotter or charting app. Navigation skills are critical for sailors and other boaters to avoid problems with underwater obstructions and to reach the intended destination safely and efficiently. Many boats - and lives - have been lost due to poor navigation, even with modern electronics that most boaters now take for granted and feel confident will guide them faultlessly through the water. Regardless, attention and navigation skills remain crucial for boaters in all but the most known waters.
We'll look at the two most important dimensions of navigation: knowing where you are at any given moment, and knowing which way to steer to best reach the intended destination. Both aspects vary depending on whether you are using traditional paper charts or a chartplotter or app, but even with good electronic aids, most boaters still should understand the traditional methods simply because electronics so often fail in marine environments.
Traditional Navigation with Paper Charts
The safest thing is to always carry and know how to use paper charts, even if you use a GPS-enabled chartplotter or app. Have recent charts at the appropriate scale. Buy recent charts locally or download NOAA paper chart booklets and print them out yourself.
When in sight of land, maintain a sense of your current position at all times by observing aids to navigation (such as green and red buoys or the flash of a lighthouse or lighted buoy) and taking compass bearings to obvious shore features. For example, you might observe a water tower at 270 degrees and a small island at 40 degrees. Using parallel rules lined up with the correct angles on the compass rose on the chart, pencil in the bearing lines back from both these features, and where the lines cross is, theoretically, your approximate position. Three lines of bearing are more accurate.
To plot your course, pencil in a line from your present position to your destination, or to a point where you need to turn to avoid an obstruction, go around a headland or island, etc. (Such points are called waypoints.) Using the parallel rules, walk the line over to the compass rose to determine the direction to steer. Then use dividers or a ruler to measure the approximate distance to that point, and - assuming you know your boatspeed - determine the time it will take to reach it. You can then "dead reckon" your moving position along that line based on your speed and the passage of time. Continue to take bearings to confirm your changing position and to ensure you stay on the course line.
Never assume, however, that the boat is moving on your plotted course line just because you are steering in the correct direction. A current could be sweeping you off course to one side, and a sailboat always makes some leeway (side-slipping downwind). This article explains the basics of determining whether you are affected by a current and how to compensate for it to avoid potential hazards.
Navigation with Chartplotters and Apps
Chartplotters and navigational charting apps show your boat's position superimposed on the chart on the screen, making it easy to see where you are. With this information you can in some cases simply eyeball your destination and route and follow your progress safely over the chart. With more distant or complicated destinations you can enter waypoints into the chartplotter or app and build a route, which typically is shown as a line on the chart screen that you simply steer along. As long as you constantly observe your position on the chart and steer appropriately to avoid hazards, it would seem that little could go wrong. In fact, many boats still get in trouble by going off course unaware, due to less than perfect steering or a side current. Again, learn how to compensate for a current. Look behind you as well as ahead to detect whether you are still on the straight line between points, that you haven't been swept to one side possible toward unseen rocks. Even when using chartplotters many boaters have been swept off course and into a hazard simply because it can happen very fast and because many boaters do not bother to plot route lines that visibly demonstrate whether they are still on that straight line to the next waypoint. Overconfidence can cause many problems, especially in the minutes immediately following an electronics failure when you may need to act quickly to avoid a hazard. Experienced sailors using a chartplotter often still keep a paper chart in the cockpit so that they are able at any moment to switch to chart navigation skills if the plotter suddenly stops.
Other Aids to Navigation
Finally, it's a good idea to be aware of other aids to navigation, as used by traditional mariners for hundreds of years. This can be as simple as estimating current speeds by observing the action of moving water on a nearby buoy or lobster or crab pot float. When you are familiar with your boat's motion and speed, you can learn to gauge boatspeed by the appearance of water flowing past your hull - and use this same appearance to extrapolate the speed and effect of a current by observing the water flowing around a buoy.
Another navigational aid is the boat's depthfinder. Simply comparing your measured depth with the depth shown on the chart helps confirm your approximate position when using traditional paper charts. This article describes in more detail how to use your depthfinder for navigation. If you don't have a depthfinder on your boat, you can easily install an inexpensive one such as this model yourself. Even with a chartplotter, which can be off by short distances in showing your position, a depthfinder is often important for safe navigation.