GPS, or Global Positioning Systems, are satellite-based navigation systems developed by the U.S. Department of Defense for military purposes&#;but they're familiar to most of us as the navigational system used by our phones and cars. Whether you&#;re talking about the GPS on your , in your car, or a marine GPS for boats, all these units receive radio signals from multiple orbiting satellites to determine your position.
There are currently 30 active GPS satellites in orbit, plus some extras reserved as spares in case one or more satellites has mechanical difficulties or is damaged. By knowing the position of a minimum of three of these satellites, and calculating the time differences between the transmitted signals&#;which are moving through space at over 186,000 MPH&#;your GPS receiver can determine its exact position anywhere on earth.
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The more satellite signals your GPS receives, the more accurately it can calculate that position, and while accuracy depends on a number of factors ranging from atmospheric conditions to receiver quality, when many multiple satellites are in view a common GPS receiver can typically put your position within a 16-foot radius. High-end receivers with dual channels can get significantly more accurate.
Originally boating GPS units displayed your position in latitude and longitude, and while that information can still be displayed, on most modern marine GPS people use a digital chart to see where they are&#;much like you can look at a street map showing your position on your cell . A GPS that can display charts is called a &#;chartplotter&#; or &#;GPS/chartplotter.&#; And in recent years digital charts have become much more comprehensive in the areas they cover, have improved detail levels, and better accuracy. In fact, many modern chartplotters also allow you to improve the digital charts you look at in real-time as you operate your boat, by matching up your GPS position with depth soundings taken by your fishfinder.
Navigating with GPS is usually the most efficient, easiest way to navigate a boat, but far too many people use it as a graphical representation rather than a numeric one. You can display a digital chart on your GPS unit, and steer the boat in such a way that the boat icon at the center of the screen points in the correct general direction. But you&#;ll steer much more accurately if you instead use a dedicated &#;steering screen&#; that gives you the numeric compass heading you want to follow, the course you&#;re actually steering, and an arrow or indicator that tells you whether to steer to port or starboard to get back on the most direct course.
Be sure to read Marine Navigation: How to Navigate a Boat to get a more complete picture of navigating boats both with and without GPS. And remember: while most of us do depend on GPS to navigate our boats most of the time, no one should ever rely on it 100-percent. Like any electronic system GPS is subject to failure and you&#;ll need to know how to get back home when your electronics let you down.
Learn More: Marine Navigation: How to Navigate a Boat
Even boaters who never leave sight of land should have a GPS/chartplotter aboard, on just about any boat. You never know when you&#;ll encounter fog, or a mechanical issue forces you to stay out late and navigate home in the darkness. And at times like those, you&#;ll be quite relieved you have GPS aboard. Plus, today&#;s units are so inexpensive (you can get a basic GPS/chartplotter for just a couple hundred dollars) that there&#;s really no excuse not to have one.
Wait a minute&#;your already has GPS, so why get another one just for your boat? That&#;s a good question, particularly because you can use a number of boating apps to more or less turn your into a mini-chartplotter. Cell phones, however, have a number of drawbacks:
So while having a cell with a navigational app loaded up can come in handy and is a good back-up to have aboard, it should never be depended upon as your main navigational tool.
Anchor Alarm
A feature of GPS that&#;s useful to boaters in particular is the ability to set an &#;anchor alarm.&#; You can establish a geofence around your boat while it&#;s at anchor, and if the anchor drags or the line comes loose and your boat goes through the geofence, your GPS will sound an alarm.
Security System
Some of today&#;s systems also allow you to interface with your boat&#;s GPS from afar, via an app on your cell , so it acts as a security system. You can set that geofence up around your boat, and if someone tries to steal it, you&#;ll get a text alarm as soon as it moves out of position.
Additional Features
If your GPS is &#;networked&#; (wired to the other electronics aboard the boat) it can also fulfill a number of additional functions.
To learn more about GPS and see the government&#;s official statements about it, read FAQs, and more, visit the official U.S. Government GPS website.
Read Next: 5 Best Marine Navigation Apps for Boaters
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Navigating a boat is absolutely, positively nothing like navigating a vehicle on land. There are no roads, few signs other than basic navigational markers outlining major channels, and you may have to contend with fog or an inability to see land or landmarks. In fact, it takes years of accumulated knowledge and advanced learning to become a marine navigational expert. But don&#;t let that deter you&#;just as long as you have a firm grip on the basics, learning how to navigate a boat in most inland and nearshore waterways in normal weather conditions is a piece of cake. We can break it down into these simple steps...
Thanks to modern tech, navigating with a modern GPS/chartplotter is a piece of cake. You can pull up an electronic map (though mariners always refer to their maps as &#;charts&#;), which shows your real-time position, speed and direction of travel, and more.
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Locating your position is as simple as looking for the boat icon and/or GPS coordinates on-screen. To get from point &#;A&#; to point &#;B,&#; all you&#;ll have to do is create a waypoint.
The most important thing about creating waypoints and routes and then navigating to them is to look closely at the chart, and make sure you won&#;t be trying to cross any major obstructions like a finger of land, restricted areas, or waters which may not afford your boat it&#;s minimum draft (how much water your boat needs to avoid running aground).
There are many other electronic items that assist in navigation, like radar and autopilots. But these are naturally a bit more advanced. What about using a navigational app on your cell ? There are a number that can prove helpful to boaters, including a wide range of iOS boating apps and Android boating apps.
However, boats and cell phones don&#;t always mix well; the moist environment and risk of shock damage are ever-present, and cell coverage can be sketchy or non-existent in many boating areas. As a result, you should never rely completely on a cell for navigating a boat.
Electronics can and do fail, so it&#;s also important to gain a basic understanding of the tools you need for analog navigation, and keep them aboard your boat at all times. These include:
With these basics, as long as you&#;re within sight of land and major landmarks you can figure out where you are and where you&#;re going.
Compass
A compass tells you which direction your boat is heading in&#;north, south, east, or west &#; as measured in degrees relative to magnetic north. There are 360 degrees representing a full circle. Zero degrees on the compass is north, 180 degrees points south, it&#;s 90 degrees to the east, and 270 degrees leads to the west. So a glance at your compass tells you what direction you&#;re travelling in, at any given time. When you steer your boat to a specific degree on the compass to maintain a straight course, you call this your &#;bearing.&#; So if you&#;re cruising to a restaurant for lunch and it&#;s directly to your north, you&#;ll be steering a zero-degree bearing. If it&#;s to your south you&#;ll steer a 180-degree bearing, and so on.
Charts
Charts are simply maps of the water and waterways, with special marking for water depths, channel markers, lighthouses, and restricted areas. NOAA produces charts for US waterways which can be viewed online for free, but to get printed versions you have to purchase charts or books of charts (for larger areas) from a NOAA certified agent. You can also pick up charts and chart books for your local waterway in virtually any marine supply store.
Parallel Rulers
Parallel rulers are two rulers attached by a pair of swiveling arms, so you can swing the rulers close together or far apart but they will always remain perfectly parallel. By doing so repeatedly, you can &#;walk&#; the rulers across a chart. Why in the world would you want to? Because it will allow you to determine the exact compass bearing of any course you may want to steer. All charts have a compass rose with all 360-degrees printed on them. Place the ruler on top of the chart, on the course line you&#;d like to steer. Then walk the rulers to the compass rose, and viola&#;you know what compass bearing you need to steer your boat on to run the course.
Dividers
Dividers have two arms that are attached at one end, and can be pulled apart to different widths at the other end. These are used to measure distance. All charts have a key which shows scale by miles and nautical miles. Hold the dividers up to the scale and pull them apart until the arms&#; width equals the chart scale for a mile or any increment of miles (it&#;s common to see one, five, 10, or even 20 mile increments depending on the scale of the chart). With the dividers set you can then use them to measure the distance between any two points on the chart.
With these tools in hand&#;or at the helm&#;you can accomplish the three most basic navigational tasks: figuring out where you are, where you want to go, and following a course to get there.
Where is Your Boat?
How to Navigate to Where You Want to Go
This is just a matter of identifying your location and destination, then determining the corresponding compass bearing between the two places. Set your boat&#;s compass to match the bearing, and you&#;re ready to get underway.
Following a Course
Now that you know how to get a bearing, following the course is easy&#;all you have to do is steer the boat to keep the compass on that bearing. You&#;ll notice that keeping a boat on course can be difficult, especially with smaller, faster boats, and if you can keep your path within five or so degrees of the intended course you should consider it a job well done. Now get out there, and navigate!
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