Transducer design also determines the width of the signal, or its beam angle. The wider the beam angle, the greater the amount of water that is covered by each ping. A wide beam angle lets you search more area but the resolution of its return image will in all liklihood be lower. A narrow-beam-angle transducer typically scans a smaller area with higher resolution so it’s generally used in shallow water, while a wider-beam angle unit yields greater coverage and less detail, so it’s usually used in deeper water.
Another key factor in the quality of the information is resolution—the amount of detail in the image. This is primarily determined by the speed at which the sounder module pings: A low ping rate will usually produce an image that looks blocky or “pixelated” and is often an indication of a low-quality design.
How and where you mount your transducer also determines the quality of the image. It cannot read through bubbles, so any turbulence caused by irregularities on your boat’s hull will adversely affect the system’s performance. In selecting a location you’ll want to keep the transducer away from anything that disturbs water flow: through-hull fittings, water intakes, and steps and strakes. Conversely, you should keep the transducer away from the area ahead of propeller because the turbulence it will invariably generate can cause propeller-blade cavitation. (Troubleshooting tip: If your sounder works well when your boat is not moving but doesn’t when she’s underway, you should immediately suspect the depth transducer installation.)
Since the sounder module is separate from the display (and the transducer) it can be as large as necessary to generate the power required for the job and can be mounted in any location that’s isolated from noise generated by other electronics. But the actual depth the system can read also depends upon the quality of the water beneath the boat, the type of transducer, and the installation. That’s why many electronics manufacturers do not quote a maximum depth their sounder module can measure, but instead provide a typical value that the system should be able to achieve in good water.
In selecting a networked sounder you have a basic decision to make: If your primary objective is fishing, select your sounder module first, then use that manufacturer’s network components and displays. If you’re mostly going to be cruising, any sounder module that can work at the depths you cruise at should work well, since detail probably won’t be a big issue and you’ll be able to focus on each system particular features.
This is also where the advice of an independant electronics professional can be an invaluable help. Or you can visit my Web site, www.navigate-us.com and review the “Guidance” and “Compare” sections, which will also help you narrow down your search.
Furuno, (410) 479-4420.
Raymarine, (603) 881-5200.
This article originally appeared in the March 2009 issue of Power & Motoryacht magazine.