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What is the difference between a depth sounder, fishfinder and sonar transducer?

Each are transducers that are installed in the hull or inside the hull or on the outside of the hull. The transducers are designed to convert a signal that has been sent by an electronic transmitting device, into an acoustic wave and direct it toward the seabed. The transducer also gathers the reflected wave back into an electronic signal, which is then displayed on the transmitting device. This happens as many as 40 times per second.

A fishfinder and depth sounder are similar but there is one big difference. Both map the seabed and record depth, but a fishfinder will locate fish at the same time. Sonar is a term that covers both.

1. Depth sounders use 50 KHz frequency and a broad beam to measure bottom depths. Features of 50 KHz sounders are; deeper depths, wide cone angle around 35 degrees, less definition and more noise.

2. Fishfinders use higher frequencies (192 or 200 KHz) and a narrow beam (around 6 to 22 degrees) to produce a higher resolution echo. This higher resolution is better at locating smaller targets. Features of higher frequency sounders are; shallower depths, narrow cone angle, better definition and less noise.

3. Dual frequency sonars can show both the high and lower frequencies at the same time. The reason for dual sonar is that the 50 KHz signal has much greater depth capability, while the higher frequency will show more detail.

Sometimes if you buy a fishfinder you will get a transducer in the package. There are many choices of transducer so you may want to buy the transducer separately, to better match your needs.

Transducer Selection

When selecting the correct transducer the 3 considerations are frequency, cone angle and installation type. As we noted before frequencies can be high, low or dual. The frequency of the transducer needs to match the frequency of the machine you are using to display the signals. A 200 KHz sonar machine needs a 200 KHz transducer.

Cone angle The wider the cone angle the greater the covered area, at the expense of depth capability, since it spreads the transmitters power out. Narrow cone angle transducers penetrate deeper than the wide cone. The narrow cone transducer concentrates the transmitters power into a smaller area. For shallower water use a wider cone angle.

Transducer installation Which installation is better, a thru hull installation, an in hull mounted or transom mounted transducer. Without going into all the reasons, the best are a thru hull transducer properly installed and aligned. Next is the transom and finally the in hull transducer, also called the shoot through transducer, which sends its signal through the hull skin.

Transducers need to be vertically aligned. If you have a deep V hull the transducer will not be pointing down, so special mounting is required.

Location of a transducer is important. The transducer must be in an area of clean water. Disturbed or cavitations water contains bubbles and this will confuse the sonar.