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Electronics

Touching Bottom

Touching Bottom

Bathymetric systems are opening a seemingly magic 3-D window to the seafloor.

By Capt. Karl Anderson — June 2006

   
Courtesy of Furuno

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• Part 1: Touching Bottom
• Part 2: Touching Bottom

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Information is key to successful fishing, and the data that today’s powerful electronics can show you will make a big difference in how well you do. When this information is blended with situational experience and instinct, the odds of your being on the fish and in the bite are greatly increased. Top captains are continually processing the data at their fingertips to help them tune in to an interesting area or even specific species. The real trick here is to learn what data to look for and what valuable information you can glean from your boat’s electronics.

There are few offshore fishing situations that don’t rely on some type of bottom structure. In the past captains had to rely on what they saw on their echosounders to get a picture of the bottom or structure underneath the hull. Today several fantastic 2-D and 3-D bathymetric systems and software programs actually plot readings from your echosounder every few feet, creating real-time data that is drawn out over your existing electronic chart and rendered to show bottom relief and structure in a 3-D image. By using the bathymetric chart information, you’re able to find details about a seafloor that previously appeared smoothed over.

Bathymetric contour lines are much like the isobars on a weather map: The closer the isobars are, the stronger the winds; the farther apart, the calmer the winds. With contour lines, relative closeness indicates the steepness at which the bottom climbs or falls off; lines farther apart indicate a more gradual slope.

The beauty of these programs is that data saved from the echosounder enables you to create and recall the bottom you’ve covered. This can be an eye opener for even the most seasoned skipper. If you’re scanning a feature like a pinnacle or trench, it can eventually become a 3-D image that you are able to manipulate. You can even alter the view so you’re looking at it as if you were standing on the seafloor, look down a trench or up at a pinnacle and see how high it stands off the bottom, or spin the image and view the pinnacle from the direction the current hits it to give you an idea of how the water flows around it and where bait may congregate.

Or let’s say you’re looking at a wreck that you went over earlier in the day and have covered several times. Each time you go over it, more detail gets filled in. Eventually you can put together enough of the pieces of the puzzle to look at the wreck relative to the current and view the bottom structure around it. Then you can fish it according to where the best marks on the echosounder are relative to the wreck as it sits on the bottom. The same benefit holds true for any bottom structure, including ridges, drop-offs, canyons, edges, walls, pinnacles, trenches, crevasses, obstructions, rises, and valleys. When viewed in 3-D, you can see these features in a degree of detail that allows you to make your trolling tack or bottom drops more efficient, as you now have the knowledge of how the current and tide will affect your approach.

Using the bathy information available in chartplotters linked with GPS, you’ll enjoy a kind of position accuracy relative to features or contours that you never imagined was possible. Several manufacturers—including Nobeltec, Furuno with its MaxSea program, and Simrad with its Olex system—have intuitive and highly detailed systems that provide excellent information to help you better understand what’s under your keel. Both the MaxSea and Olex systems are PC-based and require a personal computer or laptop onboard to run the software. Depth and position data are input via NMEA connections from an echosounder and GPS source.

Next page > Part 2: Touching Bottom > Page 1, 2

This article originally appeared in the July 2006 issue of Power & Motoryacht magazine.

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