We cruised along at roughly 20 knots in a 2- to 4-foot chop, and the Simrad BSM-2 Broadband Sounder we were testing never lost the bottom and the screen never turned into a wash of rainbow-colored lines.
The bottom-lock was certainly impressive, but wait a second, was that some structure we just cruised over? No problem. The captain of the boat, Bill Dobbelaer, who is also the sales manager of Gray Taxidermy and a longtime offshore and deep-drop fisherman, hit the backtrack button, rewinding the image on the screen to the exact rock pile we had just run over. He placed the cursor on the structure, got a waypoint, turned the boat around and we had just found yet another possible fishing spot.
“I've been fishing here a long time, and I'm now finding stuff I never knew was out here,” Bill says. “This new technology is going to really change the game.”
Simrad's BSM-2 doesn't just use one frequency to pull up a bottom image, it uses Frequency Sweeping Pulse Compression technology — also known as “CHIRP.” Coupled with the new lineup of broadband transducers introduced by Airmar, this new platform creates an image that is free of any noise. The clear images create more separation on the marks, allowing you to spot individual fish from other targets and the bottom.
We pulled up onto one of Bill's spots. It was a small wreck consisting of a downed Cessna plane. The wreck was tiny, even smaller than the 40-foot Topaz we were riding on. Bill drifted across the wreck and slowly motored along each side of it as we watched the screen on the sounder. With the BSM-2's zoom feature we focused on the bottom 200 feet of water and could make out the wings of the plane and the fuselage as it sat on the bottom. It was also super evident which side of the wreck the fish were holding on. And here's the best part, we were in more than 500 feet of water.
The BSM-2's CHIRP function uses longer pulses, resulting in improved definition at greater depths. This eliminates the surface and turbulent water clutter as well as interference within the water column to give you an easier-to-interpret image. You never have to crank up the gain to get a good separation of targets. There simply is no need. You can pick out the predators from the bait and see if that's a rock on the bottom or a big fish.
“CHIRP was actually first used in radar technology,” says Lucas Steward, Navico product manager. “It was used in commercial applications for sonar, but you never saw it in the recreational lineup because the original transducers were too large.”
The new line of Airmar transducers work with next-generation CHIRP, FM, and Spread-Spectrum fish finders. Frankly, it's the transducers that have made these new sounders possible.