NavNet | Transducers

Furuno offers a wide range of matched, high-performance transducers for virtually every type and size of boat. While you don't need to know how a transducer works to get the most out of your Fish Finder, a basic understanding of the variables goes a long way toward selecting the right transducer for your needs. Let's take a look at those variables and learn what makes a transducer 'tick.'

There are a wide variety of transducers available for Furuno Fish Finders, but all of them operate on the same principle. Your fish finder applies an electrical pulse to the transducer, where an array of piezoceramic discs vibrate, sending out an acoustic signal - a tick - into the water column. This tick occurs at a specific frequency (or range of frequencies - more on that later) and travels outward from the element in a vaguely cone-shaped pattern called a beam. The sound wave encounters objects within the beam, and the transducer receives the reflected echoes from those objects. Finally, the transducer sends that information as an electrical signal to your Fish Finder to process into a picture of the underwater world on your screen.

The time from when the sound wave is generated to when the return echo is received tells us the depth at which a target is encountered, and the strength of the reflected echo tells us about the target’s size and density.

Frequency

When an electrical pulse is applied to a 200kHz transducer, it vibrates at a frequency of 200,000 cycles per second, generating 200,000 individual sound waves.

Short-wavelength, high-frequency transducers produce sharp images, while low-frequency, high-wavelengths “see” deeper in the water column. This means the lower in frequency you go, the deeper your Fish Finder can reach for the same amount of power.

For recreational and sportfishing applications, the 50/200kHz pairing of frequencies offers a balance suitable for both shallow and deep water. The 200kHz frequency produces crisp images in shallow water while the 50kHz frequency allows you to “see” deeper.

Beamwidth

The transducer's beamwidth is the effective angle the sound wave covers. This is important because it determines the area in which your Fish Finder can “see.”

As frequency increases, beamwidth generally becomes narrower. Think of it as focusing the beam of a flashlight. As you adjust the lens, the beam delivers more energy to a smaller area. Remember that low-frequency wavelengths “see” deeper in the water column than high-frequency wavelengths, so a boost in power is not always necessary to detect fish in deeper water.

TruEcho CHIRP

CHIRP, or Compressed High Intensity Radar Pulse, has been used by the military, geologists and oceanographers since the 1950’s. This technology has become available for widespread use on personal vessels, and it’s taken the sport fishing world by storm. CHIRP transducers employ sinusoidal waveforms with a pulse frequency that increases or decreases linearly over time.

Wait, what?

In plain language, the elements in a CHIRP transducer vibrate across a range of frequencies. The transducer begins vibrating at a low frequency which is modulated upwards to a higher frequency throughout the duration of that pulse. Sonic information is sent and received at each individual frequency in the range, and a single CHIRP sounder can transmit and receive information across as many as 90 different frequencies.

Here’s the exciting part: the energy CHIRP transmits into the water can be up to 1,000 times more than that of a regular Fish Finder. This means more energy is focused on the target, resulting in a Fish Finder that can deliver up to 5x greater resolution and depth capability.

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Side-Scan

While a standard Fish Finder scans directly beneath your vessel, Side-Scan shows you what is on both the port and starboard sides of the boat. Side-Scan allows you to see the shape of structures for fishing inshore or along the coast. This helps you identify bottom structure not shown on your navigation charts and avoid the risk of collision by unintentionally drifting into shallow areas. You can also identify the presence of fish targets around structures before casting your lure or jig.

Side-Scan has a reputation for producing near-photo-quality images, making it simple to instantly identify what you see on the screen. This heightened resolution is due to the very high frequency range that most Side-Scan systems on the market operate in. Remember that the cost for those high-resolution images is range, and most Side-Scan equipment available for the fisherman is effective only at very short ranges and very slow speeds. This is why Furuno offers a choice in Side-Scan frequencies, with CHIRP options of 230kHz or 445kHz center frequencies from thru-hull, paired, or transom mount transducers.

Multibeam Sonar

Standard transducers have a beam angle of 40˚ or less. When a target is encountered anywhere within that beam, the Fish Finder will know its depth, but not its location port-starbord within that beam. The DFF3D Multibeam Sonar transducer covers a 120-degree swath using 41 individual beams. Not only can you see fish to port, starboard, and directly beneath the boat for nearly 1,000 feet, you can pinpoint where they are around you. Knowing both the depth and direction of your targets, the DFF3D's four operating modes give you more insight into your fishing operation than a standard Fish Finder can deliver.

The 3D sounder history provides an intuitive and easy-to-understand 3D seafloor image
Triple-Beam mode tells you not only the depth but also the direction (port/down/starboard) of fish targets
Cross Section displays the real-time sea column echo in a 120˚ swath
Side-Scan displays the shape and structure of targets both port and starboard

There are combination transducers available for the DFF3D that provide Multibeam Sonar elements along with standard Fish Finder elements in a single housing, eliminating the need for multiple transducer installations.

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Mounting Options

Depending on your hull, your transducer will installed in one of three ways: Thru-Hull, In-Hull, or Transom Mount. A fair amount of skill is required to achieve a proper installation, so if in doubt, don't go it alone! Consult your local Furuno dealer for assistance.

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Through Hull

Through-hull transducers require that a hole is cut in the hull, so their installation is more involved than a relatively simple transom mount. They are also more difficult to access for periodic cleaning, which they may require more often than a typical transom mount transducer. Owners of trailerable boats with through-hull transducers must be careful not to damage it when launching or loading the boat.

To keep the transducer facing squarely downward into the water column, a fairing block must be used. The fairing block is installed parallel to the flow of water to ensure proper boat handling, and this will not necessarily be the same from hull to hull.

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Transom Mount

Transom mounting is the simplest method of transducer installation and is most common among smaller boats. The transducer is installed on the transom, slightly below the waterline. The transducer face should be at a slight angle forward so as to reduce the effects of turbulence and aerated water.

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In-Hull

A third option when mounting your transducer is referred to as an in-hull, or shoot-through installation. An in-hull transducer is mounted on the inside of the hull. The transducer signal ‘shoots through’ the fiberglass and so the hull does not require a hole cut in it, although certain hull types may need to be bored out to remove any flotation material. When properly installed the effects of turbulence and aerated water are minimized. Because the transducer face does not touch water, there is no real maintenance involved with an in-hull transducer. These are compelling arguments for shoot-through installations.

These benefits do not come without a price, and that price is performance. The signal will experience loss when shooting through the hull material. This means that the performance of your fish finder will suffer. Most modern in-hull transducers are designed to compensate for this loss.

Boats with wood, aluminum or steel hulls will not be able to use in-hull transducers, as these materials act as a very effective barrier against the acoustic signal. Sound waves simply will not propagate through these materials. Only fiberglass boats, with no flotation core, can utilize an in-hull transducer. Fiberglass boats with foam or balsa cores or those with air pockets will need to be ‘dug out’ so that the face of the transducer touches the fiberglass. This can make installing an in-hull transducer a tricky proposition.

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Choosing a Mounting location

Choosing the optimal location to install your transducer is critical to getting the best performance from your electronics. Acoustic noise is always present, and these sound waves can interfere with your transducer's operation. However, carefully selecting your transducer's mounting location can minimize the effect of vessel-generated noise from the propeller(s) and shaft(s), other machinery, and other fish finders. The lower the noise level, the higher the gain setting you'll be able to use effectively on your fish finder.

As a rule, no transducer should be located near a water intake or discharge opening, directly aft of any lifting strakes, steps, or other obstructions or irregularities in the hull, or behind eroding paint (an indication of turbulence). Water flow across the transducer face must be as smooth as possible to get the best performance while cruising.

Always select a location where:

Water flowing across the hull is smoothest with a minimum of turbulence and bubbles
The transducer will be continuously immersed in water (not applicable for In-Hull models)
There is a minimum of deadrise angle
The transducer beam will not be obstructed by the keel or propeller shaft(s)
There is adequate headroom inside the vessel for the height of the housing, tightening the nuts, and removing the valve assembly and insert

Bottom Discrimination Transducers

Some features of Furuno Fish Finders require specific transducer configurations to operate, and we call these Bottom Discrimination Transducers. Let's take a brief look at those features, because you'll want to make sure you select a Bottom Discrimination transducer if you want to take advantage of them.

Bottom Discrimination

Bottom Discrimination indicates if the seafloor is made up of sand, mud, gravel, or rocks - valuable information that helps you locate rich fishing hot spots and boost your catch of the day.

* Bottom Discrimination feature works only with specific transducers. Check to ensure your transducer is compatible.

ACCU-FISH

ACCU-FISH™ is a proprietary fish size assessment function that assesses the size of individual fish size. Echo returns are evaluated based on strength and turned into fish size display on the screen. ACCU-FISH™ can detect fish size from about 4 inches (10 cm) to 6.5 feet (199 cm), in depths of about 6 feet (2 m) to over 325 feet (100 m).

In some instances, fish size indicated on the Fish Finder may differ from actual size. Please read the operator's manual carefully before using this feature.

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Transducer Guide