What Is a Cone Angle on a Fish Finder?

One of the most misunderstood parameters of the modern fish finder is the cone angle, and it might just be one of the most important. The cone angle can determine the area of water searched as well as the clarity and resolution of the results found. It can also directly lead to a more successful fishing trip when you know how and why to choose the correct one.

  1. How Fish Finders Work

    • A fish finder works on the same principles that a bat uses to "see" or that submarines use to find ships and other subs -- sonar. An underwater transducer called a hydrophone transmits a sound wave into the water beneath the boat, and when the wave hits a fish or other object, it is reflected back. Through computation, the size, location and composition of the object can be determined and displayed on the fish finder screen.

    What Cone Angle Means

    • When the transducer emits a sound wave into the water, the wave starts out roughly the size of the face of the transducer, spreading out in a uniform conical shape as it penetrates further into the water, much like an upside-down ice cream cone. The cone angle is typically measured at the point where the signal strength of the sound wave drops to half-power. This half-power measurement is typically listed by manufacturers as "minus three db" or "-3db," the scientific notation of one-half signal strength.

    Why Cone Angle is Important

    • Cone angle determines how wide of an area the fish finder can search underneath your boat. A wide angle will give a larger coverage area around you, but it will give less clarity and definition at greater depths. A narrow angle will show less of an area around you but will give more clarity at greater depths. Choosing the correct angle will depend on the expected depth of the fish you are looking for as well as the amount of physically moving the boat to search you wish to do.

    Frequency and Cone Angle

    • Cone angle works hand-in-hand with the frequency of the sound emitted by the transducer, and both must be taken into account. A high frequency combined with a narrow cone angle offers a very crisp and clear picture of what lies beneath your boat, although the picture will be of a very small area. Deep water fishing benefits from a wide cone angle and a low frequency transducer, allowing you to search a large area quickly, though not at as high of a precision level.