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Marine Product Guides >

Fish Finder Guides

  • How does the Sonar Works?
    The word "sonar" is an abbreviation for "SOund, NAvigation, and Ranging". It was developed as a means of tracking enemy submarines during World War II. A sonar consists of a transmitter, transducer, receiver, and display.
    In the simplest terms, an electrical impulse from a transmitter is converted into a sound wave by the transducer and sent into the water. When this wave strikes an object, it rebounds. This echo strikes the transducer fish finder  , which converts it back into an electric signal, which is amplified by the receiver and sent to the display. Since the speed of sound in water is constant (approximately 4800 feet per second), the time lapse between the transmitted signal and the received echo can be measured and the distance to the object determined. This process repeats itself many times per second.
    The frequency used by typical sonar is between 50-200 kHz. Although this frequency is in the sound spectrum, it's inaudible to both humans and fish. (You donít have to worry about the sonar unit spooking the fish - they canít hear it.)
    As mentioned earlier, the sonar unit sends and receives signals, then ďprints?the echo on the display. Since this happens many times per second, a continuous line is drawn across the display, showing the bottom signal. In addition, echoes returned from any object in the water between the surface and bottom are also displayed. By knowing the speed of sound through water (4800 feet per second) and the time it takes for the echo to be received, the unit can show the depth of the water and any fish in the water.
  • What is transducers?
    The transducer for fish finder  is the sonar unit's "antenna". It converts the electric energy from the transmitter to high frequency sound. The sound wave from the transducer for  fish finder   travels through the water and bounces back from any object in the water. When the returning echo strikes the transducer for  fish finder  , it converts the sound back into electrical energy which is sent to the sonar unit's receiver. The frequency of the transducer for fish finder must match the sonar unit's frequency. In other words, you can't use a 50 kHz transducer or even a 200 kHz transducer for  fish finder   on a sonar unit designed for 192 kHz. The transducer fish finder   must be able to withstand high transmitter power impulses, converting as much of the impulse into sound energy as possible. At the same time, it must be sensitive enough to receive the smallest of echoes. All of this has to take place at the proper frequency and reject echoes at other frequencies. In other words, the transducer must be very efficient.
  • Is water temperature is the big factor for fishing?
    Water temperature has an important influence upon the activities of all fish. Fish are cold-blooded and their bodies are always the temperature of the surrounding water. During the winter, colder water slows down their metabolism. At this time, they need about a fourth as much food as they consume in the summer.
    Most fish don't spawn unless the water temperature is within rather narrow limits. The surface water temperature gauge built into many of our sonar units helps identify the desired surface water spawning temperatures for various species. For example, trout can't survive in streams that get too warm. Bass and other fish eventually die out when stocked in lakes that remain too cold during the summer. While some fish have a wider temperature tolerance than others, each has a certain range within which it tries to stay. Schooling fish suspended over deep water lie at the level that provides this temperature.
    The temperature in a lake is seldom the same from the surface to the bottom. Usually there is a warm layer of water and a cooler layer. Where these layers meet is called a thermocline. The depth and thickness of the thermocline can vary with the season or time of day. In deep lakes there may be two or more thermoclines. This is important because many species of game fish like to suspend in, just above, or just below the thermocline. Many times bait fish will be above the thermocline while larger game fish will suspend in or just below it. Fortunately, this difference in temperatures can be seen on the sonar screen. The greater the temperature differential, the denser the thermocline shows on the screen.
  • Why is placement of transducers so important?
    For optimum performance, the transducer  for fish finder   must be in direct contact with the water at all times. Air bubbles and/or turbulence across the transducer will degrade its ability to transmit and receive signals. Acoustic noise-which is always present-can interfere with the operation of the transducer for  fish finder  . While ambient noise cannot be controlled, carefully selecting the transducer mounting location can minimize the effect of vessel-generated noise. The lower the noise level the higher you can set the gain setting.
  • Where is the best place to place my thru-hull depth transducer?
    Choose a location where the water flow is smoothest with a minimum of turbulence and bubbles (especially at high speeds). The transducer for  fish finder   needs to be continuously immersed in water and the sounder beam unobstructed by the keel or propeller shaft. Make sure that there is adequate headroom and there is a minimum deadrise angle.
  • How do I select my transducers?
    Transducer Guide
    To select the transducer for  fish finder   that's best suited to your needs, you need to consider the transducer's operating frequency, cone angle, and type of installation.


    Most of the sonar units that we sell accessories for operate at 192 or 200 kHz. Some models use 50 kHz. A few are dual frequency capable, meaning they can use both 50 and 200 kHz transducers. Typically, high frequency for the  fish finder   units provide the best resolution and definition of structure and targets. They excel at showing minute details of the underwater world. 50 kHz units have much greater depth penetration capability, but show less definition.
    You must match the transducer's frequency to the sonar unit. For example, a 200 kHz sonar unit requires a 200 kHz transducer.
    Cone Angle
    A transducer's cone angle determines its coverage area of the underwater world. The wider the cone angle, the greater the area that's covered. We offer a variety of 200 kHz transducers for the  fish finder   with either a wide 20?(60?with high sensitivity settings) or narrow 8?cone angle. The 50 kHz transducers for the  fish finder   come with a 35?cone angle.
    Generally, use a wide cone angle for fishing shallow to medium depths, the narrow cone penetrates to deeper depths, but shows less fish and structure due to its narrow beam.
    The depth capability of your sonar units depends on its transmitter power, receiver, sensitivity, frequency, transducer, and transducer installation. Other things that effect depth capability are: water conditions and type, (all sonars will show deeper depth readings in fresh water than salt) and bottom conditions.
    Types of Transducer Installation
    Most of our permanent-mount transducers are designed for high-speed operations. For the best results, the transducer should be placed where a smooth, undisturbed flow of water will pass across the face of the transducer at all boat speeds. Read your transducer's owner's manual before installing the transducer.
    Transom Mount
    The transom-mount transducer for the  fish finder   is the most popular, and it's generally the easiest to install. The transducer design performs best when it is slightly below the boat's hull. A plastic transducer is recommended on aluminum or steel-hulled boats to avoid potential electrolysis problems.
    Mounting the transducer on the transom is recommended for outboard and stern-drive (I/O) powered boats only. Transom mounting is ideal for high-speed operation and models with the "kick-up" feature to prevent damage if the transducer strikes an object.
    Make certain that the chosen location doesn't interfere with the boat's trailer. DO NOT mount the transducer directly behind the ribs, or thru-hull fittings. Typically, on aluminum boats, mounting the transducer between two ribs works best. On all hulls, mount the transducer at least one foot away from the engine's lower unit. This helps to prevent air bubbles from the transducer for the  fish finder   interfering with the propeller.
    Periodically wash the bottom of the transducer with soap and water to remove any oil film or growth that may collect. Oil and dirt reduce the transducer's sensitivity and can even prevent its operation.
    Shoot-Thru-Hull Mount
    In this installation, the transducer is bonded to the inside of the hull with epoxy. Ideally, the transducer is placed in the aft third of the hull close to the centerline. The signal "shoots through" the hull with some loss of signal strength. This installation must be made in an area of the hull that is made from solid fiberglass, with no air bubbles or separated layers. If the hull is of multi-layer or "sandwich" construction, you will have to remove the inner layer of fiberglass and the wood or foam core to expose the outer layer of the hull. This type of mount is recommended only with 192 or 200 kHz transducers.
    Bolt-Thru-Hull Mount
    In this type of installation, a hole is cut in the hull and the transducer  for the  fish finder  is mounted through the hull by means of a threaded shaft and nut. If the boat hull has a dead rise higher than 10 degrees, fairing blocks made from wood or plastic must be fabricated so that the transducer will mount in a completely vertical position.
    On in-boards, the transducer must be installed ahead of the propeller(s), shaft(s), and engine water intake(s).
    If the boat's hull is made of steel or aluminum, use a plastic transducer to prevent electrolysis problems.
    Trolling Motor Mount
    The PD-W "pod" transducer is designed for mounting on an electric trolling motor. It has two slots for a hose clamp (which must be purchased separately). Transducers  for the  fish finder  can also be mounted on a trolling motor using the TMB-S trolling motor bracket. It's curved to fit the contour of most electric trolling motors.

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