Side-scan sonar for the Everyman
Posted on 05 March 2010
Written by Tim Coleman
Every angler can become a little more perceptive with the newest line of high-tech side scanners
Mark Bertini of Big Coppitt Key, Fla., has one in his 27-foot Contender to find wrecks in the Gulf of Mexico near Key West. Capt. Joe Huckemeyer of Hyannis, Mass., has one in his 100-foot party boat, Helen H, to find rocks, wrecks and fishy lumps in Nantucket Sound.
The "one" in both cases is the newest addition to the angler's electronic arsenal: side scanners.
Most fishfinders on the average boat in the Northeast look down on the bottom, much like shining a light from the second floor of a house. The spot of light on the ground or bottom, a narrow profile, is what shows up on the screen on most small-boat fishfinders.
Side-scan sonar shoots an electronic beam out to both sides of a slowly moving boat, greatly increasing one's ability to see more bottom, which greatly increases your ability to find new fishing spots.
A side-scan sonar is a unit made up of a small, torpedo-like "towfish" that is pulled behind a boat. The towfish is connected by a Kevlar cable to a receiver, usually a laptop loaded with software to read the bottom accurately at 300-plus feet on either side of the boat. Instead of seeing just the small circle of a fishfinder, a sonar "sees" a much broader expanse of bottom, locating wrecks no one knows about, rock piles, ledges or places where soft bottom has turned to hard patches - all spots where fish gather to feed.
Until now the only problem with such a unit was cost: up to $100,000 to purchase or $1,000 to $2,000 per day plus travel to rent a machine and an operator for a day. Needless to say, most anglers with homes and families didn't have the budget for sonar.
Enter the consumer side scanners, about the same size as a standard small-boat fishfinder, mounted in a console or near a helm, going for roughly $900 to $3,000 depending on the power output, manufacturer and bells and whistles. The transducer of such a unit shoots out a beam to either side of a boat moving along at striper trolling speed, picking up items on the bottom and revealing them on a screen.
"The new side scan products have transducers that are attached to the boat instead of pulling a towfish behind the boat," says Mark Gibson, Humminbird senior brand manager. "The advantages of this are that the system only takes one person to operate where the towfish systems take at least two people to operate (one to watch the display and one to operate the towfish by lowering or raising it out of the water using a wench). Also, by having the transducer attached to the boat, you don't have to worry about getting the towfish or cable hung on any structure in the water."
The picture scrolls by in two columns, each depicting the bottom features on either side of your boat. You'll see a blank spot right in the middle of the columns, the space right under your boat, because the machine is looking out to one side. We can add your regular up-and-down fishfinder to fill in this blank spot, the two machines not interfering with one another if installed according to spec.
Mark Bertini demonstrated his Humminbird unit last winter, if you can believe this, on a foggy day in the Gulf - each of us bundled up like we were on a striper trip in northern waters.
We ran over an area east of Smith Shoal Light where cement blocks legally dumped back in the 1980s create fish habitat in roughly 30 to 35 feet. As we slowly motored along, you could clearly see the blocks on the bottom. The picture is an almost, but not quite, photo-like look at what was beneath. At other times, looking for new fishing spots, it could make out individual fish swimming along plus the wreck of an old fishing boat in the same depth on the west side of the light.
Two months ago, I was out with Capt. Joe Huckemyer, leaving from his Hyannis dock at first light, scanning the bottom up to 175 feet out from the moving boat, checking out places all around Horseshoe Shoal. After an all-day scan, we'd uncovered five potential new sites for Joe's porgy trips in the spring, including what looked like rocks, the wreck of the F/V Dolphin and a low-lying structure we think is an old wooden wreck of some type.
To cover the same area of bottom with a systematic, mow-the-lawn search pattern using a regular, narrow-beam fishfinder would have taken - easily - three times as long. And by using the newer scanning technology in conjunction with a plotter set up only to show vessel track, a small boater can easily scan an area looking for new structures.
We should also mention that on the above trips we were using hang logs from commercial fishermen to guide us to suspected spots, but anglers can use the scanners just to scout out new areas on their own. One place that comes to mind is the rough bottom out to 120 feet deep off Misquamicut, R.I., home to some great porgy and sea bass catches during the summer through late fall. Boats equipped with scanners can zero in around lobster pot buoys usually set near structures, seeking out the rocks or other havens where lobster and sea bass hang out.
Boats down off New Jersey might turn on their scanners to maximum range looking for a small piece of debris away from a wreck that nature claimed or was scuttled by the state. While I think these scanners are a great boon to the average boater, it should be noted they are works in progress. Each of the two units mentioned above has limitations. Mark's smaller, less-expensive model starts to lose definition at the edge of its range in water deeper than 60 to 70 feet. If there is a little sea on, the unit also suffers. But on calm days, in ideal depth, it's a useful tool.
Joe's more expensive 1100 Series Humminbird units also has drawbacks. He says it begins to loose definition in water deeper than 150 feet. He also demonstrated bottom images that became elongated if he increased his speed or turned around the object, also distorting the image, causing a newcomer like me to question what I was looking at.
With those limitations in mind, it's advisable to make some trial runs with your new toy, making passes over a known shipwreck, seeing the difference between natural and man-made. Then make some passes over rocky bottom, either scattered boulders - a great spot for fluke - or areas where sandy bottom changes over to rocky ledges jutting upward, home to everything from porgies in the summer to blackfish in the fall.
As these scanners catch on with the fishing public, manufacturers are bringing out new models with improved features. As times goes on, I expect to see units that will record deeper with attention to accuracy even at extreme range from the moving boat, plus units that will record at higher speeds or perhaps slightly rougher sea conditions. Saltwater anglers in the Northeast, for example, regularly drop below 200 feet for cod off Massachusetts.
As it is now, many units have GPS interface along with depth, water temperature and boat speed displayed along with the twin scrolls of bottom information. Capt. Joe would like to see the dead space right under the boat narrowed down so he could use more of his screen to look out, a problem addressed by some 2009 models that offer down imaging: a split-screen version that lets you see the same picture-like images (under the right conditions) not only out a distance, but also right under the boat.
Overall, these units offer so much more, allowing you to see what the bottom looks like and to explore much larger swaths of it. I remember a veteran side-scan operator telling me his $65,000 unit peeled back the water, letting one peek beneath, missing nothing. The side scanners for small boats may not have that accuracy - yet - over such a broad range of bottom, but they are moving in that direction, narrowing the gap in technology and becoming a tool worthy of consideration.
This article originally appeared in the Home Waters Section of the March 2010 issue.