A nautical chart is a map of a particular waterway. Good charts show shoreline and land features, water depth, channel markers, hazards, and other navigational aids to make sure you safely get to your boating destination. Chart plotters are Global Positioning System (GPS) based devices that store electronic versions of nautical charts and display them on a screen, with the position of your boat indicated by a blinking boat icon. In other words, a chart plotter not only shows you a chart, but it shows exactly where you are on the chart in real time. Chart plotters also allow you to plot courses for your journeys by setting waypoints to indicate your destination. The GPS function of chart plotters can measure the speed of the boat, and can provide an ongoing estimate of your arrival time at your waypoints.
To a large degree, electronic chart plotters have revolutionized commercial and recreational navigation. In addition to helping you get from point A to point B, chart plotters can also be used to set alarms if you stray too far off course (or start to drag your anchor at night), can be integrated with VHF radio, autopilot, radar, and fish finders to help manage just about all aspects of your trip.
Added features bring added costs, of course, and you may not need them all. This means that determining the right chart plotter depends a lot on how you plan to use your boat. Here are a few things to keep in mind.
In general, a larger display is better. It is helpful to be able to view your position at a glance, rather than have to peer at a small screen to find your location. It is typically recommended that you get the largest display your helm station can accommodate. Convenience and safety are the main factors. Being able to quickly determine your position makes navigation easier and minimizes the time you have to take your eyes off the water around you.
The resolution of the chart plotter screen is also important as it determines the level of detail that will be easily visible. Resolution is measured by the pixel count, with more pixels being better. Low-end chart plotters provide only a few hundred pixels. You will need to know how the screen looks in bright sunlight and when wearing polarized sunglasses, especially if the helm area of your boat is not well shaded. Many displays fade dramatically when viewed from an angle in bright sunlight. Again, you want to get the information you are looking for as quickly as possible.
Dash or Bracket Mounting
There are two ways to mount chart plotters — dash or bracket. Large boats typically have enough space to mount a chart plotter flush on the helm dashboard. Smaller boats may require a bracket to hold the chart plotter in a location that makes it easy to use while underway. A dash mount is usually preferable for a cleaner look, but the mounting method has no impact on performance. If your boat requires a bracket mount, this may be a situation where a bigger plotter is not necessarily better, as it can be cumbersome to mount and manage a large screen on a crowded helm area.
Chart Plotters with Radar
If you boat often at night or in low visibility conditions (fog, rain), you may want to consider a unit that incorporates radar as well. Chart plotters only help you see your position and the course you are on. They do not help you see other boats that might be in your path. Radar can be costly, though, so if you are a fair-weather day boater, you probably do not need to make that investment.
On long journeys, autopilot can be very helpful. You can set your course and focus on the conditions around you rather than checking your position every few minutes. In open water, you can relax a bit more, but of course you always need to be on the lookout for debris or other hazards.
If you plan on fishing, you may want a fish finder. The quality and reliability (in terms of being able to truly find fish) of fish finders are subjects of great debate. Integrating a fish finder with a chart plotter enables both to be displayed on a single screen.
While chart plotters are extremely helpful, like all electronics they can fail, crash, or be rendered useless if the boat loses power. For this reason, it is important to keep your paper charts handy, and know how to use them. (See our previous article, How to Read a Nautical Chart.) Also, when you are travelling long distances, it is actually easier to plan around distant destinations using paper charts. Yes, you can scroll forward on a chart plotter to see well beyond your current location, but getting the journey into a single view will likely require one or more paper charts, and a single view is very helpful when planning your trip.
Some boaters get fanatic about navigation electronics. Dig deep enough, and you will find many more features and benefits offered. Others are purists, and prefer to rely on charts and manual instruments like sextants to ensure that they are not dependent on technology to ply the waters. Only you can determine what is right for your boat and your boating plans.