Marine Electronic GPS

Most serious ocean fishermen wouldn’t dream of heading offshore without their high-tech marine electronics, especially their electronic chart plotter and digital cartography.  Why?   Because they count on their marine chartplotter and electronic charts for a wealth of information that helps them find and catch more fish.

In growing numbers, freshwater anglers are also “tuning in and turning on,” spurred by increasing availability of smaller sized, affordable electronic chart plotters and fishing charts for popular freshwater lakes and rivers.  For about the cost of a high-performance stainless prop, freshwater anglers can install a GPS/chart plotter and add satellite boating navigation and detailed waterway maps to their arsenal of weapons.

Today’s best marine GPS receivers can pinpoint your position to within three meters anywhere in the world, allowing you to navigate with accuracy and – most importantly – return to “fishy” areas.   And with the proliferation of inexpensive, hand-held GPS units that can fit in a tackle box, many fishermen are “steering by the numbers” to do just this.

Using an electronic chart plotter, however, adds a whole new dimension.    Electronic chart plotters add marine map technology capable of showing your boat’s position and movement over a digitized map of the lake or river’s bottom.  Depending on the level of detail, this digital cartography can include submerged creek channels, drop-offs, points, brush piles, sunken islands and other structure items that are critical to fishermen.

With a little imagination, it’s easy to see how a real-time representation like this can help the freshwater anglers.   By really knowing the layout of the lake and where your boat is positioned in relation to key structure, you can spend more time fishing where the fish are.  And by correlating what you see on the electronic chart plotter with information from your depth-sounder, you won’t have to wonder what’s under your boat.  In fishing, knowledge is confidence.  And confident anglers catch more fish.

Of course, an electronic chart plotter can only provide as much detail as is contained on the digital cartography it is running.   Companies like C-MAP have come a long way in the development of extremely detailed electronic charts for the nation’s most popular freshwater fishing areas.   The company’s MAX Lakes catalog of specialized freshwater fishing charts was developed with one purpose in mind — to help freshwater anglers catch more fish.  Today, C-Map MAX Lakes fishing charts are available covering  thousands of popular lakes and waterways in every U.S. state.

There are many ways savvy fishermen use this electronic chart data to their advantage.  For example, walleye anglers can use their electronic chart plotters to focus and fine-tune their trolling presentations.  Successful walleye trolling is based on precise boat positioning, boat speed and bait presentation, and a plotter gives you an extra high-tech tool.   If the fish are hanging along an edge or suspended over an underwater riverbed, you can position your boat precisely, track your progress on the map and make adjustments for wind and current.

Say you’re a bass fishermen, and you’re working a steep drop off a submerged point with a pig-and-jig or live bait.  Same idea – you can monitor your boat’s progress in relation to the shoreline and the bottom, and make small adjustments as necessary.   And with the accuracy of today’s marine electronic GPS, you can keep working productive water by marking where you hookup and returning to this area through subsequent drifts.

These are just a few of the ways an electronic chart plotter and specialized fishing charts can make a wizard out of any freshwater fisherman.   Whether the name of your  game is largemouth, walleye, trout, crappie or stripers,  C-Map charts will help you catch more fish.    Visit your boat dealer or electronics store and get turned on to the world of electronic charts.  

Electronic charts keep you on the right side of the line – and the law.

Anybody who fishes ocean waters off California is aware of the state’s Marine Life Protection Act (MLPA) and what this law means to recreational anglers. In a very complex process, various groups have been working on ways to achieve the conservation goals of the act, which was passed to protect the state’s marine resources. What this will mean to the layman is a growing network of no-fishing and/or restricted fishing zones up and down California’s 840-mile coast.


Southern Californians are familiar with this already; Marine Protected Areas have been in place around the Anacapa, Santa Barbara, Santa Cruz, Santa Rosa and San Miguel Islands for several years. Closures are on the way for the rest of the state, as well as an even greater network of no-fishing zones for Southern California islands and coastline areas. Battle lines are being drawn right now, with a variety of competing marine maps vying for the approval of the state Fish and Game Commission.

However these marine maps end up coming out, it will be the fisherman’s responsibility to know and obey the law. There aren’t any floating warning signs telling you where you can or can’t fish, and printed charts with GPS boundaries of closed areas aren’t much use either. 

Without a doubt, an electronic chart plotter with updated digital cartography is the best way for anglers to remain inside the law — and outside closed areas. A marine chartplotter will allow boaters to graphically see their GPS position relative to specific closed areas (most electronic GPS units allow users to customize the electronic chart display to mark general boundaries on the marine map.

Since the first closures were put in place around the Channel Islands several years ago, C-Map charts by Jeppesen Marine have had existing no-fishing zones clearly marked in red. This means that boaters can fish with confidence that they won’t accidentally cross into areas that could cost them a hefty fine. By using the electronic chart plotter’s proximity alarm feature, they can be alerted if they get too close, even if they are off the bridge and busy fishing in the cockpit.

Another advantage C-Map charts offer is the confidence to fish in close proximity to these closed areas, while remaining legally outside. These areas were selected because they are productive fish habitat — and anglers without this electronic edge are often too concerned to take their boats anywhere near them. I’ve experienced this first hand, catching quality bottom fish in an area adjacent to (but safely outside) the Carrington Reef closure area at Santa Rosa Island while other boats chose to steer clear of the whole area.

Closures like these will begin expanding up and down the state in 2010. Additional Marine Protected Areas totaling as much as 400 square miles are in the works for the Southern California region alone, depending on which marine map gets approved. Other coastal states, as well as the federal government, are also looking at similar networks of protected areas and fishing closures to manage marine resources. Don’t think this trend only applies to the Golden State. 

Like it or not, more closed and restricted areas are in our future. Having a marine electronic GPS and quality electronic cartography will become increasingly important as the wide-open ocean becomes less open to anglers.  This is why I’m glad that Jeppesen Marine updates its navigational charts and fishing charts at least twice each year.  As a law-abiding boater and fisherman, I want to be sure I’m navigating with the most accurate electronic chart data available.

When I went to sea in the early 1970s, the state-of-the-art for maritime navigation on the open ocean was to make imprecise estimates of a ship's position through celestial observations of the sun, moon, stars and planets. Using a sextant, we would measure the angle of a celestial body above the horizon and then laboriously work through complicated trigonometric functions to translate those measurements into lines of position on a plotting sheet — often an hour or more after the sight was taken. Between celestial fixes (which could be several days) we used dead reckoning to estimate our position.

I got a thrill out of pacing the bridge wing at dawn and dusk with a sextant, stop watch and starfinder, trying to pick out Sirius, Kochab or Alpheratz. I felt an almost mystical bond with the ancient Arab astronomers and mathematicians who first figured it all out back in the Middle Ages.

Now, of course, we still look to the skies for guidance. But instead of the stars, we use radio signals from satellites to fix our position on the earth's surface. While I still feel a certain level of nostalgia for the "bad old days" of celestial navigation and dead reckoning, it's undeniable that marine electronic GPS has made a tremendous difference in maritime navigation and an inestimable contribution to safety at sea. Electronic GPS provides a real-time, constantly updated, highly accurate ship's position, liberating the navigator from the need to plot fixes and dead reckoning tracks onto paper navigation charts. Electronic GPS is the fundamental enabling technology that permits us to navigate on C-Map electronic charts.

So how does GPS work? I hope you won't mind if I oversimplify what is actually a very complicated process. Basically, a GPS receiver calculates its position through triangulation — that is to say, by crossing three or more lines of position. Each GPS satellite transmits a radio message that contains both its position in space and a super-precise time signal. The satellite signal is transmitted in a form known as a pseudorandom code and a GPS receiver generates an identical pseudorandom code. By matching the received code with its own generated code, the GPS receiver is able to determine the distance to each satellite. It does this by measuring the elapsed time it takes the signal to transit from satellite to receiver. (The radio-wave signal travels at roughly the speed of light — 186,000 miles per second.) With three satellites, you can thus determine your position in two dimensions, which is fine for surface navigation. With four or more satellites, you can compute a three-dimensional fix. (The fourth signal yields altitude.)

In my next blog, we'll look at GPS errors and how they can be minimized through differential techniques.

In the meantime, you can read a good tutorial on basic principles of GPS on the Trimble website at www.trimble.com/gps/howgps.shtml. Trimble was originally a pioneer in electronic navigation instruments, but has since given up its marine navigation business in favor of highly precise GPS-based surveying technology.

In a fast-paced modern age, sometimes we long for simpler ways. That is part of the lure of sailing — being out on the water, in the sun, the wind ruffling my hair. This idyllic picture makes it easy to get sucked into a fantasy that the old ways were better. That is until you realize that some of the old ways were darn hard work!

Would I, for example, exchange my modern electronic cartography or GPS charts for the romantic notion of navigating by sextant? There is a delightful definition of the sextant in Beard and McKie's Sailing: The Fine Art of Getting Wet and Becoming Ill While Slowly Going Nowhere at Great Expense:

"Sextant: an entertaining, albeit expensive, devise which, together with a good atlas, is of use in introducing the boatman to many interesting areas on the earth's surface which he and his craft are not within 1,000 nautical miles of."

In sailing navigation, the sextant is used  to locate where you are by measuring how far a celestial object is above the horizon. The angle of object-to-horizon and the time when you take the measurement are used to calculate a position line on a navigation chart. You first decide what celestial object to use, depending upon the time of day and what objects you can see clearly. For example, sight the sun at noon. Then, with the sextant set to zero, you slowly move the arm of the sextant down until the reflection of the object just kisses the horizon. The angle shown on the sextant's scale provides the altitude that you use along with the exact time of sighting to calculate the ship's location.

Unfortunately, there are any number of problems that can "muddy the waters," so to speak. Finding a celestial object on cloudy days or overcast nights could be one. By the same token, the horizon may not be visible. Because a sextant is a delicate instrument, its arc could be warped by changing temperatures or could be bent if dropped. Then there is the issue of mathematical aptitude that could allow errors to creep into my calculations...

Hm-m-m. Perhaps the old ways are better left to stalwart old salts who have a bit more time on their hands. I think I'll stick with my handy marine electronic GPS and relax with a cool lemonade.