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April 30, 2009

New Advances in Chart Overlays

Overlays offer key details from top to bottom

I've spent many days fishing on blue water and green, though now I primarily work the sounds and marshes near my coastal Georgia home. Many of my friends, who also fish inshore, find it easiest to tune their electronics to show basic fish-finder and plotter   windows, and then never deviate.

But my, what they're missing!

That goes double for offshore fishermen whose distance from land makes them all the more vulnerable to weather and sea conditions.

Today's multifunction displays allow anglers to see the three-dimensional ocean world from the sky to the surface to the seafloor and see where their boat floats within that world. They do that using the magic of chart overlays.

Anglers can overlay several real-time feeds, such as radar, Automatic Identification System (AIS), Mini Automatic Radar Plotting Aid (MARPA) and Sirius/XM WX satellite weather, on their chart-plotter picture, as well as multiple static or semi-static feeds, such as sea-   surface temperature charts, tide, wind and current information, fishing contours and satellite photos. How much detail you can overlay depends mostly on the hardware, but software options also vary when it comes to what static data you can buy.

The newest, most expensive multifunction displays obviously offer the greatest variety. But a surprising number of overlays come on the new, though smaller and less expensive units too.

Constant Feed
Capt. Steve Bent - who charters the 34-foot custom sport-fisherman Free Spirit out of Egg Harbor, New Jersey - overlays his Raymarine HD Radar with MARPA onto his E-Series chart plotter primarily for safety reasons. He wants to see what lies in his path when the light dims or the world grows foggy.

"With MARPA, I can follow 12 targets out to 10 miles," Bent says. "It gives you the target speed, course, range and bearing to him. If you highlight it, it draws a vector line so you can see how he moves in relation to you."

To properly line up that radar image over the plotter on the display, the subject boat needs a heading sensor or a digital radar sensor if the multifunction unit uses digital signal processing. Heading sensors usually come with autopilots. But if the boat has no autopilot, the captain can buy a separate electronic compass/sensor for about $500 to $1,000.

Ken Cirillo, business development executive for Jeppesen Marine, makers of C-MAP cartography, says that radar can pick up water cresting a shoal off his Massachusetts home shores. That picture overlaid on a plotter can highlight  contour lines. He says when radar picks up bird flocks, the overlay helps confirm or refute the targets.

The radar overlay also helps Bent and other captains look at rain and squall conditions within a tighter radius to their boats than they can see with weather-service overlays. Anglers can determine the actual direction a nearby rain cell may be moving and plan to fish spots outside its path.

An AIS unit, connected to a multifunction display, overlays its targets in a fashion similar to MARPA. But it offers more information on the type and size of vessels in your neighborhood.

Many larger commercial vessels must carry AIS transmitters by law, but recreational vessels may or may not. Savvy captains use AIS overlays to find bait and fish.

"A number of trawlers and boats are scallop or squid fishing up here, and many have AIS transmitters," Bent says. "You pull up AIS and click on an icon, and it tells you what the boat is and IDs it. Last summer when we were fishing bluefin, knowing where these boats were was important. When they were shucking scallops, they would hold tuna around them."

Capt. George Mitchell, a tournament pro and charter captain who fishes southeast Florida and the Bahamas, uses his Furuno NavNet 3D and AIS unit to find anchored ships. "We look at the mouths of the major inlets for anchored freighters (using AIS). These are often hot spots for baitfish," says Mitchell. "Then we pull alongside the ship and hail it on the VHF to see how long it's been at anchor.

"In the northern Gulf, we like to find new research vessels (using AIS) that may have moved into an area since the last time we were there. These can sometimes be hot spots for pelagics."

Taking Temperatures
Perhaps the most important overlay for anglers may be the electronic sea-surface temperature charts from subscription services. While Sirius and XM WX provide real-time weather information, they can only update the temperature charts once or twice a day.

"You can visually see where the temperature breaks intersect with structure and where the boat is right on top of that," says Capt. Mark DeBlasio, who operates the Canyon Runner out of Port Pleasant, New Jersey, and uses Sirius weather overlays on his Northstar 6100. "There are also times when we can't get a clear satellite shot for several days -when it's cloudy. But halfway into the trip, we get a clear shot. That has proven valuable."

DeBlasio also uses Sirius' live buoy reports to find wave heights and wind directions at different spots, and he watches the live Doppler radar that depicts fronts approaching from a distance.