By Emmett PorterFish finders differ in the sonar they use, the extra features built into the unit, and how the transducer mounts. This guide sorts those types using a sonar explainer published by one electronics maker, Lowrance, and the owner’s manual for one GPS fish finder, the Garmin STRIKER Vivid, as examples. Sonar is a technique that sends a signal, or ping, underwater and then receives its echo. According to Lowrance’s sonar basics guide, the echo is created when the original signal bounces off the bottom and objects in the water column between the transducer and the bottom. For fish-finding, sonar displays fish as an arch shape, a partial arch, or a straight line, depending on how the fish and the boat move. Without sonar, it is much harder to locate fish or the structures they hold near, such as rocks, drop-offs, ditches, trees, and logs.
Lowrance explains that traditional broadband sonar sends single-frequency pings at 200 kHz, 83 kHz, or 50 kHz. High frequencies (200 kHz) yield the best resolution, while low frequencies (50 kHz) can reach greater depths. CHIRP sonar, by contrast, continuously sweeps through a range of frequencies, typically 28 to 51 kHz (Low), 85 to 155 kHz (Medium), or 140 to 250 kHz (High), which creates a more complete picture of the bottom and objects in the water. The beam angle also matters: traditional sonar transmits sound waves in a cylindrical cone. A 200 kHz transducer often has a cone angle of less than 20 degrees, so in less than 10 feet of water the cone diameter on the bottom is less than 3 feet across. As a rough guide, the wider the beam angle, the lower the resolution.
Sonar Technologies and Views
Lowrance’s guide describes several sonar types. CHIRP sonar gives clearer views of individual fish targets, even close to the bottom or in tight schools. Down imaging (Lowrance calls it DownScan Imaging) produces photo-like images of rocks, trees, bottom composition and other structure directly beneath the boat. Side imaging (SideScan) shows up to 600 feet to each side of the boat, which lets you cover more water and look at areas too shallow for the boat, such as next to the shore. Live sonar delivers real-time images of fish swimming around structure and responding to a lure. Lowrance also describes a three-dimensional view of fish, structure and bottom contour, and a mode that combines down imaging with CHIRP fish arches.
The Garmin STRIKER Vivid owner’s manual describes similar sonar capabilities when a compatible transducer is connected. The manual lists four basic styles of sonar views: a full-screen view, a split-screen view combining two or more views, a split-zoom view, and a split-frequency view that displays two different frequencies. Its down-imaging sonar, which Garmin calls ClearVü, emits a beam similar to the shape of the beam in a copy machine, unlike the conical beam of traditional transducers, providing a clearer, picture-like image of what is beneath the boat. Its side-imaging sonar (SideVü) shows a picture of what lies to the sides of the boat, useful as a search tool for structures and fish. A flasher page shows sonar information on a circular depth scale, indicating what is beneath the boat in real time, with colors representing different strengths of the sonar return.
Transducer Mounting and Installation
Lowrance states that a transducer is the physical product that supports sonar technologies, commonly installed on a boat’s transom, inside the hull (shoot-thru hull or thru-hull), or on a trolling motor. Lowrance says its transom-mount transducers use a design that lets water pass smoothly over the face of the transducer when the boat is on plane. Lowrance recommends attaching a plastic plate to the hull first to avoid drilling holes directly into the transom and to improve water flow. Trolling motor mounts use a bracket designed for the transducer. A shoot-thru hull installation epoxies the transducer to the floor of a fiberglass boat, transmitting through the hull. A thru-hull installation requires a hole in the bottom of the boat, and a fairing block is cut to match the deadrise of the hull so water flows smoothly. For vee-shaped hulls, the deadrise angle must be accounted for to align the transducer beam vertically, ensuring the return signal is picked up efficiently.
The Garmin manual adds that you may need to set the transducer type manually if you connect a transducer not included with the chartplotter. Options include Dual Beam (200/77 kHz) or Dual Frequency (200/50 kHz). The manual warns that manually selecting the wrong transducer could result in damage or reduced performance, and recommends using Auto Detect when available.
GPS, Mapping and Navigation
The Garmin STRIKER Vivid manual explains that the device includes a GPS receiver that must collect satellite data to establish the current location. Once acquired, you can mark waypoints, create routes, and navigate to destinations. Its Quickdraw Contours mapping feature lets you instantly create maps with depth contours and labels for any body of water. While recording, a colored circle around the vessel icon indicates scan quality: green for good depth and GPS position at speeds under 10 mph, yellow for speeds between 10 and 20 mph, and red for poor depth or GPS position or speeds above 20 mph. The manual estimates you might be able to record about 1,500 hours of data onto the device with a single-beam sonar.
Comparison of Sonar and Unit Types
| Sonar or Unit Type | What It Shows | Notes |
|---|---|---|
| Traditional Broadband Sonar | Fish arches, bottom depth, structure | Single-frequency pings (200, 83, 50 kHz). High frequency for resolution, low for depth. (Lowrance) |
| CHIRP Sonar | Higher resolution fish targets, bottom detail | Sweeps a range of frequencies for better target separation. (Lowrance) |
| Down imaging | Photo-like images of structure directly below boat | Garmin describes a beam shaped like the one in a copy machine. (Lowrance, Garmin) |
| Side imaging | Images to each side of the boat, up to 600 ft per side | Useful for searching large areas and shallow water near shore. (Lowrance, Garmin) |
| Live Sonar | Real-time views of fish and lure movement | Shows fish responding to a lure in real time. (Lowrance) |
| GPS combo unit | Sonar views plus waypoints, routes, Quickdraw contours | Allows mapping and navigation. (Garmin manual) |
| Flasher | Real-time sonar returns on a circular depth scale | Colors indicate different strengths of the sonar return. (Garmin manual) |
Power and Local Rules
The Garmin manual’s troubleshooting section says the device needs at least 12 Vdc to turn on, and that a good fuse in the power cable reads 0 ohm on a multimeter. It also reminds owners to be aware of local regulations on sonar frequencies: for example, to protect orca whale pods, you might be prohibited from using frequencies between 50 and 80 kHz within half a mile of a pod. For reading what the screen shows, see our guide on how to read a fish finder.
Frequently Asked Questions
What is the difference between CHIRP and traditional sonar?
Traditional sonar sends a single-frequency ping, while CHIRP sweeps through a range of frequencies. According to Lowrance, CHIRP delivers higher resolution views and better target separation, creating a more complete picture of the bottom and objects in the water column. Garmin’s manual adds that CHIRP can distinctly identify individual fish in a school and generally performs better than single-frequency applications.
What is a flasher view?
The Garmin STRIKER Vivid manual describes a flasher page that shows sonar information on a circular depth scale, indicating what is beneath the boat in real time, with colors for different strengths of the sonar return. Our ice fishing flasher vs fish finder guide compares stand-alone flashers with fish finders.
How do I mount a transducer on my boat?
Lowrance outlines several methods: transom mount, trolling motor mount with a bracket, shoot-thru hull installation epoxied inside a fiberglass hull, and thru-hull installation with a fairing block. The key is to align the transducer so the sonar beam points straight down, accounting for the hull’s deadrise angle. For transom installs, Lowrance recommends attaching a plastic plate to the hull first.
For more guides on choosing and using fish finders, visit our Fish Finders category. You may also find our articles on fish finder sonar types, how to read a fish finder screen, kayak fish finder setup, and ice fishing flasher vs fish finder helpful.
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About Emmett Porter
Emmett covers beginner & family fishing, comparing specs, features and long-term owner feedback to help readers choose with confidence.
