Next I'll see if the shoot-through works any better in low frequency mode than it did in high frequency. I shut down the unit, switch plugs one more time, and"¦nothing. In water over 600-feet it doesn't get a reading at all. If I move shallow to 600, wait for it to get a reading, then putt east, it holds a faint reading to anywhere between 660 feet and 800 feet before going caput. It never shows a separate target, and really isn't much use at this depth.FURUNOThe view on the left shows detail levels at 200-kHz, while the one on the right shows the same exact fish at 50-kHz, on this dual-frequency, split-screen unit.

There is one good thing I noticed about the shoot-through, though. Unlike the transom mount, and to a lesser degree the through-hull, the performance of the shoot-through is completely unaffected by the boat's motion. Since it does its pinging and its listening from inside the hull, this makes perfect sense.

POWER RATINGS

You may have noticed that one very important factor in depth penetration hasn't been touched on: wattage. Wattage is actually not the most important factor, because a unit's probing and listening power is effected by the transducer every bit as much as it is by actual wattage. In fact, doubling the transducer crystal's diameter has the same effect as quadrupling the output power. This happens because the larger the transducer, the more focused its beam – think of a flashlight set to spotlight, instead of flood. So, a machine pushing 200 watts through an eight-inch transducer will see just as deep as a fishfinder pushing 800 watts through a two-inch transducer.

Yeah, yeah, I know: you don't believe it. Neither did I. That's why I brought Lowrance big-wig Ron Webber with me on this expedition. He promised to prove it. Now that the transducers have been thoroughly tested, Ron hooks up a Lowrance LC-X 104 C to his laptop computer. He has the codes necessary to manipulate the unit's power output from 50 watts to 1,000 watts, on the spot.

Next, we hang a massive, grapefruit-sized 200/50-kHz through-hull transducer, on a temporary bracket mount, over the side of the boat. In 1,000 feet the LC-X 104 C had no problem touching bottom with 1,000 watts. As he backed the power down, the bottom reading lost color definition and got a little spotty. But even at 50 watts of output, the reading held. Just to prove his point, Webber then hooked up a $200 cheapo 100-watt unit. With the standard (one-inch crystal) transom-mount transducer, of course, we saw nothing. But when he hooked it up to the huge transducer hanging over the side, it got a solid bottom reading in 1000 feet.

ASSESSMENTlENNY RUDOWYup, there are sea bass down there! The through-hull transducer tells no lies.

Through-hull transducers do, according to traditional theory, provide the best performance – and this testing proved it to be true. Again holding to traditional theory, the transom mounted transducer gave us the second-best view and the shoot through provided the poorest view.

But also remember that transducer size plays a huge role in how effective your unit will be on the water. Of course, if you buy a fishfinder package from a big-box store or a catalog, you'll be stuck with the transducer the manufacturer supplies with the unit. If you want your rig to be as capable as possible, then make your purchase from a marine electronics specialist who can source the transducer separately. You can choose the type that best fits your application, and get the size you feel you need, instead of taking what came out of a box.

Back at the dock I don't even need to look at my notepad. The test results are that obvious. Transducer choice clearly dictates how well your unit will perform. The through-hull provides the best performance, in all depths and situations. A transom mount comes in second, providing good shallow-water definition and acceptable deep-water performance. The shoot-through is in last place. These will be useful as depth gauges but not as fishfinders used by anglers who want to actually catch fish.

Yes, all of these types have advantages and drawbacks. But if you want the ultimate under-water view, the evidence says it's time to cut a hole in your boat.