Buying The Perfect Fish Finder: (How-To Select Guide)

Searching for a new upgrade for your fishing success? In this article we will cover how to select a fish finder to enhance your angling.

What’s A Fish Finder?

Simply put this is a marine electronic device. It uses sonar to show a graphic depiction of what is under the vessel. Below is what you need to determine to select a fish finder in no particular order:

picture of s fish finder on a boat showing sonar reading

  • Pick a type of unit
  • Ensure the mount size of the fish finder is appopriate
  • Select a level of screen resolution
  • How much output power you need
  • Which transducer frequencies you require based on where you fish

Outdoors Informed is reader supported. We independently research and rate every product. When you buy through a link on our site, we may earn an affiliate commission. However, our opinions and evaluations are our own. Outdoors Informed does not accept free products from manufacturers. Learn more.

Share This Article:
Table of Contents

Types: Standalone, Combination, Multi-Use

The first step to select a fish finder is to choose the types of unit. There are three main versions available, for example the standalone fish finder.

  1. Standalone: A single use model performs no other function. These give the best performance to cost ratio if all you want is to see what’s under your boat. For small vessels and buyer with a limited budget the standalone unit is for you.
  2. Combination: This model adds in either GPS or a chartplotter for navigation. For the price this type is best for owner of mid-sized watercraft. Combining sonar and navigation will make finding fishing ground that much easier. It also allows you to view both on split screen, or view only the fish finder.
  3. Multi-Use: The third and most expensive are multi-use networked systems. These provide a huge range of onboard data. Select this category if you own a large vessel and want all your info in one jam packed unit.

Fish finder Considerations

The next steps to select a fish finder are for you to determine what angling features are most important for you. Brands offer anglers a growing choice in how you can see what’s displayed under your boat. Fish finder quality is all about sonar, transducer frequency and output power.

What Is A Transducer?

selective photo of a black and yellow colored transducer

This is an essential component for every fish finder. A transducer is the physical part which sends out and receive sonar waves. When the reflection data returns, it transfers into the display unit. This is the place the signals get processed into a picture which you can see and understand.

Where do you mount a transducer for a fish finder? The easiest way is on the transom of a boat, which is fine for small to medium watercraft. Another option is the trolling motor mount. For larger boats a through-hull mount is common.

Expect exposed mounts to be plastic, this material is compatible with most boat types. For thru-hull or in-hull mounts you need to consider the hull material. Metal and fiberglass hulls need plastic housings. While aluminum or steel hull need bronze housings.

Transducer Frequency Explained

As I said, a fish finder needs to use a transducer to use sonar, and there are four types to choose from. Either a single frequency transducer, dual-frequency, multiple-frequencies or a broadband system.

Which frequencies the transducer uses, will reveal different amounts of detail on screen. High-frequencies will give terrific detail, but won’t penetrate deep into water. Likewise, low-frequencies like a 50kHz pulse pierces further deeper but displays less detail.

Shallow-water inland anglers should select higher frequencies, such as 200kHz, 400kHz or 800kHz. In contrast, open ocean fishing is better served using lower frequencies. A 200kHz or higher (up to 800kHz) will function for water depths up to 200 feet. For deeper water move to a 80kHz or 50kHz.

What’s Output Power?

Also called transmit power, this is the strength or amount of sound energy pushed into the water. Expressed in watts RMS (root mean squared). For fishing, choosing output power relates to three factors. First, more power allows the user see in murky water. Second, it delivers views at deeper depths. Third, more transmit power helps separate fish and bottom structure.

It’s common to see a 500-watt (RMS) unit. This will have plenty of power for typical inshore coastal use. Yet for open ocean anglers, you may need 1,000 watts or more. For lake fishermen, you might only need a 200 watts transducer to see the shallow bottom.

What Is Sonar?

It’s a technique that uses sound waves to “see” in water. First, understand that anything that moves in a wave (e.g. sound, light) can reflect off objects. Sonar fires sound waves forward and then uses microphones to “listen” for reflections. It measures how long it takes to echo, which can determine how far away and in what direction objects are. More about the type of sonar to consider after I explain frequency and output power.

a black colored fish finder with yellow colored display showing sonar returns


Types Of Sonar:

There are four main types of sonar that marine technology uses. Some units only use one type, while more expensive models have all four.

Conventional Fixed-Frequency

Older models use this 2 dimensional method, the main downside to this type/method is ambiguous imagery. Using single pulse or tone bursts of energy means this version is high in power, but very short in duration. As a result, it limits the total amount of sound that’s transmitted into the water column. Using a single frequency limits the clarity and resolution of the image.

Thus, what’s shown on screen becomes harder to recognize. You could have the catch of a lifetime or a hook a bunch of weeds.

To help fix these issues traditional sonars use dual-frequency or even triple-frequency transducers. Doing so delivers a decent combination of depth and detail.


CHIRP is an acronym for Compressed High Intensity Radar Pulse. Unlike conventional single frequency sonar, CHIRP sweeps a continuous range of frequencies. CHIRP devices send a signal that sweeps upward. From 40 to 75kHz, 130 to 210kHz, or other frequency ranges.

During a single transmission it sends out quick pulses moving from low to high frequency. This continuous sweep of frequencies provides a much wider range of information. Which in turn, creates a clear, high-resolution image.

The ability to identify a single fish, or separate fish from bottom structure, is a matter of inches. Rather than of several feet with traditional fish finders. Another bonus of this type is that CHIRP can use low and high frequencies at the same time. This allows it make swift changes from high to low frequency, so it can scan the water without alerting fish.

Which CHIRP Frequency Range Is Best?

  • High (150–240 kHz) is for inland and freshwater. Great for lure tracking, identifying bait fish or for targeting fish near bottom structures. Choose this for depths under 600-feet.
  • Medium (80–160kHz) displays a wider coverage area. Best for scanning large areas fast, showing larger fish arches. Doesn’t provide as much detail as high CHIRP for seeing small objects. Another good option for depths less than 600-feet.
  • Low (below 80 kHz) for blue water use over 600-feet deep. Delivers spectacular depth performance (up to 10,000 feet). Plus it can mark targets at all depths in the water column.

Down Imaging

Closeup photo of a Lowrance Fish Finder displaying downscan imaging

As you might have guessed it, this method scans below your boat, much like conventional sonar. This name is a registered trademark of Humminbird marine electronics. Other brands call this sonar similar names, like Garmin calls it DownVü. Lowrance calls their version DownScan imaging.

Like traditional 2D sonar, sound waves get shot straight down into the water. But unlike 2D, it’s very thin, and doesn’t widen as it travels down through the water. Using a narrow cross-section view generates a much higher target separation.

Moreover, it’s common for the frequency range used for Down Imaging to be 800 kHz and 455khz. Thus, this technology is best in shallower waters. The 800khz beam delivers sharp image resolution. While a 455khz beam gives the best image quality and depth.

Imagine your boat over a structure, and you want to know the distance to throw a jig lure. Using this type of sonar would be ideal for this instance.

Side Imaging

As the name sounds, this type utilizes a transducer to shoot two sonar cones sideways from each side of a boat. As well as, sonar waves pointed downward at a shallow angle. This type is a great addition to use with 2D or down scan.

For terminology, Humminbird calls it side imaging. While Lowrance calls it side scan, and Garmin’s name is Sidevü.

It’s best for scanning large bodies of water to look for fish holding structure. This is why anglers often call it structure scan, another confusing turn of phrase right?!

Like down scanning, side imaging uses short wavelengths of 455, or 800 kHz. Which is great for generating high resolution images, but poor for deep water visuals.

Deep waters don’t mean this isn’t a capable tech. With a range of up to 200 feet on either side of your boat. It can actually scan a total of about 400 feet of bottom structure total.

Imagine using it in a large lake, river, or coastal water and finding a rock ledge or submerged tree. You can move to the spot and further investigate with 2D or down image to get super detailed results.

360 Degree Imaging

Similar to side views, this category relies on sideways beams of sonar. Yet differs as the transducer nose cone will rotate in a 360 degree motion. As a result, it “sees” in all directions that surround the boat. Think of it as having a multi-directional side scanner when your vessel isn’t moving.

The main advantage of this software, is the act of surprise to catch fish before spooking them. Being able to expand your field of view in the water without having to move the boat is a huge plus.

Live sonar

Fish finding technology has evolved from determining bottom depths and locate structure. Unlike older versions that show historical data, this version gives updates in real time. This is the latest and greatest technology, so expect to pay a price for it.

Garmin calls this LiveScope, Lowrance is Active Target and Humminbird with MEGA Live. This greatest advantage of live sonar is the ability to make an accurate placement a lure in front of a fish. As well as, keep the lure in the fish’s strike zone. It can also discern a school of target fish from a group of bait fish. Live versions aren’t great for making large area scans for structures but are great when you do find fish.

Ice Fishing Sonar Flasher

black ice fishing flasher on a icy background

For people who want to select a fish finder for ice fishing, you could choose a sonar flasher for vertical fishing. Like live sonar, they show sonar returns in real time.

The actual way they show the results are different than fish finders. A flasher has simplified dial with multicolored lights to represent sonar detections. Which can be a bit of a learning curve, to new fishermen.

Or if you prefer a device that does more than just live sonar, there are ice fish finders. These generate almost the same result but their battery-life is much lower than a flasher. Which is a big deal in the frigid temperature that you encounter while out on the ice.

Cone Angle

Another important factor to consider for a fish finder is the angle of the sonar cone. This refers to the angle of the sonar beam as it’s leaving the transducer and transmitted through the water. The cone angle therefore determines the underwater area coverage. A wider/larger cone angle, will provide greater area coverage.

For example: one brand may have a 200 kHz frequency transducer may have either a wide (20°) or narrow (12°) cone angle. Another company offers a 50 kHz model with a 35° cone angle. Dual-beam transducer have the best on both worlds. Having both narrow (12°, 200 kHz) and wide (35°, 50 kHz) cone angles.

Most transducers come with cone angles that range from 9-degrees to over 60-degrees. A common range for mid-range devices are between 16 to 20-degrees. This range is an excellent choice new angling enthusiasts.

In general, a wide cone angle is best for fishing shallow to medium water depths. Whereas a narrow cone penetrates to deeper waters, but shows less due to their narrow beam.

Global Positioning System (GPS)

Most small standalone fish finders today, will include basic GPS. While combination and multi-use finders will definitely have GPS among over connectivity option. GPS is a bonus to locate your current position and leave a precise marker for next time. You also can mark docks, boat ramps and other locations on the water.

Keep in mind though, GPS pinpoints your location, but alone it doesn’t show it on a map. If you need an electronic map on your screen, you should select a fish finder with a chartplotter.

Display Size & Quality

overhead photo of 6 fish finders with different screen sizes

The display or screen is critical due to the fact it’s what translates the information to your eyes. It’s important that you select a fish finder that’s simple to set up, navigate, and is accurate too.

Moving on, when a manufacturer refers to screen sizes its diagonal distance. Measured in inches or centimeters across the screen. It’s obvious that a widescreen displays allow you to see more meaningful information. Especially if it’s capable to split the screen view. But remember that increasing the screen size, also increases the cost as well.

Another factor is screen resolution and how many pixels it will show. A pixel is a single dot on a screen, the more pixels, the more detail the display can put out. You should at least look for 240 × 160 pixels. Bear in mind though, at this resolution, it may compare to a game of Tetris instead of angling. When you do select a fish finder buy the largest and best quality (LCD if possible) display you can afford. Any model with more than GPS has many data sets on the screen, so that screens under 5-inches can be over cluttered.

Next you want to decide between color or black and white display. Color offers up to millions of colors and details while black and white screens have just 265 shades of gray.

Mounting: Footprint

Kayak anglers and small boaters should focus on footprint over everything else. Many companies will make you to buy extra parts, which is misleading. Head units often sit on a bracket or a gimbal that’s affixed to the boat.

Also, consider where you will mount the transducer. As mentioned before there are three type and each differ on installation.

  • Transom-mount: In this instance you get an adjustable-angle bracket. It gets screwed or bolted to the rear of the boat on the transom. The actual transducer hangs below and behind hull. It’s much simpler than the others, but is prone to crashing waves.
  • Thru-hull: Considered the hardest install, but tends to deliver the best signal quality. Sailboats and inboards often use thru-hulls.
  • In-hull: This is a special transducer for only fiberglass hull boats. The difference here is that it doesn’t actually come in contact with the water. Instead, you use silicone or epoxy glue it on the inside of the hull.

Durability & Water Resistance Ratings

As with any marine product, durability is a massive factor for life expectancy. The big issue to enhance durability is the water resistance. Understand that water-resistant doesn’t mean waterproof. Since fish finders are electronics, it’s vital they don’t let moisture inside. Pay attention to the JIS or IPX ratings of the fish finder you intend to buy.

Portable models get removed and stored in a fishing backpack or even a tackle box. So unless you a clumsy and let it fall overboard you might be able to get away with a lower rating.

While fixed units on smaller open boats, need grater water-resistance. Considered the installation and buy the highest IPX rating you can afford.

A rating of 4-IPX means a given device is safe from splashing water. Not a great option for a canoe or kayak. 6-IPX can withstand low to high-pressure jets of water. At 7-IPX you can dunk the unit up to 10 feet for 30 minutes. Rounding out the ratings is 8-IPX this one means it can be underwater for an extended amount of time.

While cheap overseas no-name brands are enticing, for durability, purchase from a well-known brand. Read the reviews for Humminbird, Garmin, Lowrance & Raymarine they are all popular brand names.

Finishing up: How to select a fish finder plotter

Now you should have all the information you need to select a fish finder that’s best for your fishing. Remember that the screen size and quality make reading the info easier. But the transducer type, frequency and sonar pay an equal part in your success.


black letter O green letter I

This website uses cookies to ensure you get the best experience on our website: more info