The Garmin 188C (left) is well-suited for boats with limited space on the pedestal or cockpit bulkhead. If you have the space, though, consider Si-Tex's Dynamic Duo (center and right)—a separate plotter and sounder combo that sells for about the same as the Garmin 188C.

Chartplotter/sounder combo units take up less space and usually cost less than separate pieces. But if the combo breaks down, you've lost two important instruments at once. Not good. Citing this Achilles heel, Si-Tex is pushing a two-unit system sold as the "Dynamic Duo" to give the consumer "the convenience and safety of two dedicated products at the low price of a combo unit." It's a compelling pitch, so we decided to test the product. And a good way to evaluate the Dynamic Duo—which consists of the Si-Tex ColorMax 6 chartplotter and CVS-106L sounder—was to match it against a proven combo unit from Garmin—the 188C. …