To choose a fishfinder, consider the type of unit, size of the fishfinder’s footprint, resolution of the display, how much transmitting power you need, and what frequencies will work best in the inland, coastal or deep-water environment where you fish.
Combo, standalone or network fishfinder?
Three fishfinder choices are available; standalone fishfinders that perform no other function, combination products that also include a chartplotter, and fully-networked systems offering a smorgasbord of potential functions, all viewable through one or more multi-function displays. Some reasons to choose each type:
Standalone fishfinder: if you just want to see what’s below, dedicated fishfinders give the biggest display and the most performance for the least cost. If you have a small boat that you use for fishing small inland lakes or are on a limited budget, a standalone fishfinder is for you. Conversely, if your pilothouse has room for multiple displays, or if you just bought a new GPS, get a serious big-screen fishfinder. You can usually add a GPS sensor later to many units, turning them into chartplotter combos.
Combination fishfinder/chartplotter: combo units make sense for most owners of mid-sized boats. Use GPS for navigation to the fishing grounds, view both on split/screen, or view only the fishfinder. “Black box” sounder modules can turn many chartplotters into combo units, with the installation of a transducer.
Networked system: fully networked systems are available from all the major suppliers, and usually will support a huge range of data sources including radar, raster and vector GPS charts, video, and SiriusXM satellite radio. Your fishfinder, often an external “black box” module, is just one of these sources of data. Multiple display network systems are great for medium sized or large vessels. Capabilities get more amazing every year.
Garmin echo™ 300c standalone fishfinder: small footprint, bright color screen, dual-frequency transom mount transducer with up to 120° view.
Humminbird 597ci HD combo: compact 5" display with 640 x 480 resolution, plotter with optional Navionics mapping, dual frequency 50/200kHz transducer.
Lowrance HDS-10 Gen2 combo: big screen, NMEA 2000 networking, lots of included or optional transducers.
Where will your fishfinder be mounted? Typical fishfinders are mounted on a bracket or are flush mounted—installed in a dashboard, electronics mount like a NavPod, or a bulkhead. Bracket mounting allows you to install a larger display onboard a small boat where the dash lacks the necessary room, and allows the display to be removed and taken home for security.
To flush mount the fishfinder, choose a unit with a casing size that fits your location. This determines how big of a screen can fit. Most quoted screen sizes refer to the diagonal distance in inches across the screen.
More pixels—higher screen resolution and a big screen—allow you to see the air bladders of smaller fish. More shades of gray, or full-color presentation, provide a clearer image that’s simpler to understand. Your choices range all the way from four-level grayscale up to 16.7-million colors.
The resolution of a fishfinder’s display is what determines its ability to see fish near the bottom, to separate closely spaced targets from one another, and to see fish on the edges of “bait balls.” LCD displays are made of a grid of “picture elements,” tiny dots that individually darken when electrical current is applied, with their name shortened in common usage to “pixel.” More vertical pixels mean higher depth resolution, as each pixel represents less depth.
If your screen has 100 vertical pixels, and you search for fish in the 0' to 50' depth range, then each pixel represents 6" of depth. This blocky display won’t let you see subtle details. A display with 240 pixels in each vertical column will show about 2 1/2" of depth; one with 480 pixels will resolve to 1 1/4", giving you a clearer picture. The number of pixels in a screen’s horizontal axis determines how long objects stay onscreen before they scroll out of view, of significant importance with split-screen displays showing narrow columns of side-by-side information.
More pixels per square inch will provide better detail of structures, a better representation of what’s below you, and improved split-screen images. But remember: the contrast of the display must also be sharp in order to use the resolution. Like many features, you get what you pay for with display resolution—the more the better.
The power of a fishfinder—the strength of the “ping”—is expressed in watts RMS (root mean squared). Power is directly related to how well you see in silt-laden water, view down to greater depths, and successfully resolve separate targets and bottom structure. More power is better, so some manufacturers juice up the numbers by rating their product using peak-to-peak watts, which is eight times the RMS number. To avoid mixing apples and oranges, we use watts RMS exclusively. A 500-watt (RMS) fishfinder should have plenty of power for most coastal applications. Serious bluewater anglers should look for 1,000 watts or more. Inland lake fishers can see the shallow bottom with only 200 watts.
The latest broadband fishfinders, sometimes called CHIRP fishfinders, use a lot less power than their conventional alternatives, while at the same time giving far more detailed returns. You can learn more about this new (and more expensive) technology in our West Advisor on CHIRP Sonars and Broadband Radar.
Frequency of the transducer(s)
Fishfinders operate using a single frequency transducer, dual frequencies, multiple frequencies or a broadband CHIRP system. See our Advisor, Selecting a Sonar Transducer, for more about transducers. In general, higher frequencies give the finest detail resolution, the least background noise on your screen and the best view from a fast-moving boat, but don’t penetrate as deeply as lower frequencies. Shallow-water inland anglers generally choose higher frequencies of 200kHz, 400kHz or 800kHz. For maximum depth, use lower frequencies. We recommend 200kHz or higher for water depths up to 200' and 80kHz or 50kHz for deeper waters.
Looking to the side or straight down
DualBeam PLUS™, DownScan Imaging, Down Imaging, QuadraBeam PLUS™, Side Imaging, 360 Imaging™: fishfinder manufacturers offer the inland angler a growing (and often confusing) assortment of choices in frequencies, beamwidths, even the underwater direction you can look. Inland anglers who search for fish in shallow lakes don’t need the power to see down to 5,000', but can gain a big advantage by looking out to the sides, so Garmin, Humminbird and Lowrance have products using multi-beam transducers for that purpose. Here’s where the Marketing Jargon takes over, with names like StructureScan HD™ and DualBeam PLUS™.
To better understand this transducer mumbo-jumbo we’ll review some basic theory, courtesy of the folks at Airmar who make the transducers just about everyone uses:
- Higher frequency transducers have shorter wavelengths and more wave cycles per second, which means you can visualize more details (smaller fish) but have only shallow to moderate depth capacity. One sound wave at 200kHz is slightly longer than 1/4", so a 200kHz sound wave will be able to detect fish as short as a quarter of an inch. A 200kHz transducer has a range of only about 600'. High frequency provides a crisp, clear picture of the bottom with the tradeoff of less depth range.
- Lower frequency transducers, with longer waves and fewer waves per second, show less detail (larger fish) but carry more energy and penetrate to greater depths. One sound wave at 50kHz is slightly larger than 1", so a 50kHz sound wave will only detect fish if their air bladders are large, slightly longer than an inch. Lower frequency won’t provide as clear of a picture, but will operate effectively in the depths of the ocean or Lake Michigan.
- Dual frequency transducers use the same piezoceramic element (a sort of vibrating crystal) to send and receive pulses of more than one frequency (sometimes simultaneously). Dual beam or QuadraBeam transducers use multiple elements, sometimes aimed in different directions
- Low frequencies typically use wider beams, helping you to find large objects, like structure where fish hide. High frequencies let you zero in on the fish right below your boat.