Gone are the days of positioning your boat solely relying on shoreline structures for reference. Modern sonar and GPS combos can turn an aquatic abyss into a visible underwater metropolis revealing a fish’s travel routs, feeding area and home. The level of features you may need or want largely depend on your style of fishing.
If you prefer to fish in a nostalgic sense, just using a basic sonar unit will do you just fine without getting too technical. Weekend and avid anglers may want a sonar/GPS combo with some extra features and a medium-sized display to make family outings more successful. For guides, professional anglers and those who just want the latest and greatest – you’ll be able to trust top-of-the-line units offering the bells and whistles to enhance how you make your living on the water.
With everything to consider, finding the perfect sonar unit for your style of angling may seem like the proverbial needle in a hay stack. Reading this buyer’s guide will allow you to confidently shop a seemingly complicated piece of equipment.
Let’s simplify this, sonar is just sound at a frequency that isn’t audible to us. The acoustic properties of water and the instrumentation used allow us to see what lies beneath based on how the sound reverberates around and through objects below. Before we get into the nitty gritty, here are a few basics to understand.
- Low-hertz sound travels farther than high-hertz sound. However, low-hertz provides less detail. Think low for deep water, and high for shallow.
- For the sake of sonar, sound waves are measured in the cycles of valleys and peaks and how close or far apart they are over a period of one second. These are measured in Hertz. For sonar, you may only need to know that kilohertz or kHz is 1,000 hertz, and megahertz (MHz) is 1,000 kilohertz. This is part of how a transducer’s output is measured.
- There are three schools of sonar based on how Hertz are used — traditional, CHIRP and ultra-high frequency. All other technologies take one of these three ways Hertz are manipulated and use various software and directional positioning to create the picture.
Based on the water temperature, turbidity and general murkiness, the sound sent out of the transducer needs to be tuned for the water you’re on for optimal clarity. The three options of how Hertz are used also require the transducers capable of creating the sound, which we’ll touch on later under the ‘Transducer’ section. How the view is displayed on your screen largely depends on the manufacturer’s software programs, and we’ll talk about this in ‘Viewing and Directional Sounding.’
Traditional, or standard sonar shows arches or pixels organized in a fish-shape, typically against a white background. The transducer pings at a set frequency. Screens are fast at displaying information. However, there is a short learning curve to understand what is being displayed, depending on how you have the frequency and sensitivity set, fish may appear the same as the cover they’re in or a patch of milfoil may show like a school of fish. It all depends on how your sonar unit is tuned. As far as sound goes, think of it as monotone.
Now if traditional sonar is monotone, CHIRP is it’s Grammy-winning-vocalist cousin. Standing for Compressed High-Intensity Radiated Pulse, CHIRP uses an incredible range of frequencies to create an image. A traditional-sonar’s best setting for a particular body of water may be 135kHz. With CHIRP, the transducer will send rapidly increasing and decreasing frequencies. Let’s say the transducer operates at 77/200kHz, the first ping will be 77, then 78, 79, 80 and so on. What’s the benefit? Increased definition and target separation. This lets you pick out fish
that may be hiding in cover, discover bait fish that otherwise might not have been detected, or see individual fish within a school or hugging the bottom.
CHIRP is developed by manufacturer’s in two different ways. Real chirp happens in the transducer, where it will ‘ping’ at an accelerating, then decelerating frequency as mentioned above. The second way is through the software within the computer assuming what it is looking at. In this way, the transducer may only ping at one frequency and the computer will fill in the rest on your display. While CHIRP transducers may be more accurate, both are effective at showing target separation and distinguishing cover, forage and predatory fish.
Ultrahigh-Frequency Scanning Sonar
As mentioned before, sonar is just sound, and ultra-high frequency is the dog whistle of the three. The waves of sound sent from low frequency like traditional sonar and CHIRP have peaks and valleys really far apart. Ultrahigh-frequency scanning sonar has peaks and valleys extremely close together, when peaks and valleys are close together, the incredibly high frequency increases detail to an image-like quality. Manufacturer’s brand this “Imaging”, “Scan” or “Vü” based on the increased detail. If traditional sonar and CHIRP ranges from about 50 to 200kHz, imaging sonar operates from about 450kHz to over 1MHz. For some manufacturers, this frequency of sonar is also CHIRP-capable for increased detail. Because the hertz are so high, distance is limited. This type of sonar is only capable of a total width of up to 800-ft. and depth of 400-ft. The higher the hertz, the shorter the reach, but greater detail.
Viewing and Directional Sounding
Now that you understand how sonar works, the next step is understanding the point of view you’re scanning from.
The majority of the time, the sonar you are looking at is historic. Your boat has passed a point when the transducer sent out a ping, it reverberated to the receiver, then the processor inside the head unit projected it on the display. While the processor inside the display is largely in charge of how sonar is perceived, changing the direction of the sounding can alter what you see on the screen. You can see off to the sides, change a cone angle, point it ahead to see what’s coming or even find transducers that sweep to get a bird’s-eye, 3-D view of the lake bottom.
Real-time and forward-facing sonar shows you what is happening or about to happen. In fact, the first sonar units ever were real time — they were called “flashers” and are still the most common sonar on the ice. Granted, they’ve had some major updates since the 1960s, and we’ll touch on that in the ‘Ice’ section below.
Global positioning satellite (GPS) is what eliminates having to position your boat using objects on the shoreline as points of reference. Sonar units equipped with GPS mapping allow precise, repeatable boat placement on any body of water.
Whether your combo’s GPS receiver is internal or you have to use a puck, its refresh rate, or how many times position changes on the screen in one second, is measured in Hertz. A simple rule of thumb is if the GPS has a 5Hz. receiver, it refreshes about five times a second on your screen. 10Hz is close to 10 times a second. Consider this refresh rate on your screen when your throttle is wide open. If you can’t see hazards on the water, you may be able to see them in time on your GPS, depending on how zoomed in you are.
When sonar units come with GPS, they often include a base map, usually just an abundance of shorelines without any cartography, or minimal at best. Using a mapping card with preloaded contours for your area expands detail and accuracy down to sub-1-ft. increments in some instances for popular lakes, rivers and reservoirs.
Aside from just showing you contours of the lake bed, GPS software may use your sonar features to map out other fishing factors, like bottom hardness, vegetation and to custom create precise topography. These features reveal where fish could be staging, traveling through and feeding.
Some premium mapping cards also include online updates and possible viewing on your laptop or desktop. This would allow you to do some homework for your next trip out.
Display size, display technology and functionality are the three major factors to consider when deciding on a sonar unit for your craft. The display should be considered after determining the sonar and GPS features you need. If the features don’t measure up to your style of fishing, the display’s size, technology and functionality is null.
You know your fishing style. This should dictate the features you’ll be looking for in a sonar and GPS unit. For more effective shopping, ask yourself these questions:
- Where and how is the display being mounted? Is it at the helm or at your feet on the bow? Will it be flush-mounted or on a gimbal?
- What are the functions you will need to view simultaneously? GPS and sonar? Multiple GPS and sonar? Sonar, imaging and GPS?
Generally, the farther the screen is from your face, the larger you want it to be. Same is true the more features you need view simultaneously. Consider the view you like and where you prefer to mount the screen. It shouldn’t strain you in any way to look at it while fishing or driving your boat. The opportunities for mounting the display vary by the type and size of your vessel.
The larger and later-model your boat, the more likely it is to have the space to flush mount a sonar unit into the bow and console. Jon boats and V-bottom hulls up to 18 ft. may allow you to place the display how you like, while a bay or bass boat may be fairly specific on where electronics should be mounted.
You know your style of fishing; do you know what you should be looking at to match that style of fishing? Depending on the screen’s size, you might want to find a display that allows splitting the screen up to view things like sonar, imaging, and GPS simultaneously.
With televisions going ultrahigh definition, it should come as no surprise sonar screen technology is advancing at almost an equal pace as well in much the same way. Pixels are getting smaller. Backlighting is becoming more efficient and brighter. Processing power needs to increase with greater capacity, detail and speed capability. Having a transducer that’s able to pick up reverberation well enough to produce high-definition images is useless without the screen being able to display it.
Typically, you’re going to be looking at this screen when the sun is high and bright. When the sun comes through the living room window, your TV can get a nasty glare. It’s no different with a sonar display, so look for screen technologies that will reduce this glare. Some companies formulate their glass with coatings and integrated treatments to combat glare. But, for the most part, glare is combated by brightening up the backlighting to surpass the light from the sun when it can. Make sure to check the brightness levels in the store to know what you’re getting.
Also, when you venture into a Cabela’s or Bass Pro Shops retail experience, ask for an associate to power up the display you’re looking at outdoors if possible, so you can see it in the same light you’ll be using it in.
Chances are, if you use a smartphone, you’re already well on your way to familiarizing yourself with touch-screen and hybrid displays. Hybrids use both keypads and touch-screen technology. You have the option to control the unit one way or the other. What’s the benefit? Using touchscreens has become intuitive for many people through daily smartphone use. They also make navigating through menus incredibly fast. Having a reliable-through-all-conditions keypad is an added option that ensures display control in inclement weather.
Don’t rule out just having the keypad-only option either — they have their place. Anglers have been accustomed to keypads since graphs first hit the scene. They’re more inexpensive to purchase and operate. Keypads are also reliable in any weather, so you can operate them easily with bulky gloves on.
Types of transducers
Going back to the Sonar section to when we talked about the four basic sonar types (Traditional, CHIRP and Ultrahigh Frequency); they each require a transducer with those capabilities. Granted, the more advanced the transducer, the more likely it is to be able to ping at several of these frequencies and directions required. A transducer made to use ultrahigh-frequency pinging will generally have the capability to scan with traditional sonar as well.
Directional sonar (forward facing or bird’s-eye viewing) requires another kind of transducer made to face and scan in that direction.
Mounting position and options
There are three basic positions to be concerned with: through-hull, transom mount and trolling motor mount.
The most common and economical is the transom mount. Transducers are mounted on a bracket, which is then attached to the transom by screws directly through the transom itself, on a transducer mounting plate made to reduce the number of holes in the hull or a suction cup in the case of portable sonar units.
Attaching a transducer on your bow-mounted trolling motor will actually put you on top of the fish. This is such a benefit to anglers that the big manufacturers have integrated transducers into the motor’s head as an option on many models. If your trolling motor doesn’t have this capability or the correct transducer installed, there are many universal and make-and-model specific options to secure any kind of transducer that isn’t a through-hull mount.
Through-hull mounts, more commonly found on salt water vessels, benefit the user by working at nearly any speed. Transom-mounted ‘ducers generally stop reading the water correctly after a certain speed — it varies with every boat because of how water flows out from under the hull. The construction of these transducers are hull-type specific and can either be mounted against the bottom of the hull on the inside of the boat, or actually be mounted through the hull where the transducer is out in the elements.
Transducers are just speakers with the capability to hear like a microphone simultaneously. Your stereo in your car has tweeters for high-pitched sounds, mid-sized cones for treble and crisp tones while the subwoofer produces the bass. Transducers work in their operating frequency in much the same way.
When you hear a car with a loud stereo coming down the street, the first sound you hear is the bass. Bass has a very low frequency, but carries longer distances and passes through denser objects with ease. Next you’ll hear the vocals, or the middle-range instruments, you may hear it through the car doors or in your garage, but not through the walls of your home. Cover under water becomes more defined but the transducer’s effective range is shortened in this analogy. Finally, you will hear the treble and high-pitched instruments when the car is closest. These frequencies offer the highest detail, but don’t travel well at distances beyond a close range.
The ping that comes from a transducer, is just a sound with a certain pitch and volume tuned to reverberate through the water in a way that a processer can produce a picture based on what is picked back up. Every body of water is different. While one lake may be experiencing an algae bloom, the next closest lake may be gin clear. Or while one has turned over, the next lake may still be in its summer phase. Will you have multiple brands of sonar on your boat? All of these factors affect how you tune your sonar’s operating frequency to get the clearest view on your display.
Simple concept. The wider the cone, the more water you cover. Here’s a rule of thumb for determining what cone angle to use — the greater the depth, the narrower your cone, or the shallower your depth, the wider your cone.
Pythagoras is going to help you catch fish. Never thought you’d have to use this formula again, did you? If you feel a cold sweat triggered by trigonometry class flashbacks, don’t worry. We’re going to make this simple with an in-the-field example and give you the answers in the chart below. The Pythagorean Theorem (a2 + b2 = c2) will allow you judge how wide of an area you’re seeing below the boat, so you can adjust the transducer, then target your casts, or plan a trolling path on the go.
Using the chart below, let’s say you’re using CHIRP sonar while drop-shotting on a 20-ft. rock pile for smallmouth bass and you have your cone angle set at 20°. All the fish you see hugging the bottom are within a 7.05-ft.-dia. circle. Or, they’re within a 5.28-ft.-dia. circle if they’re suspended 5-ft. off the bottom.
Scanning sonar that shows views on the sides or a bird’s-eye view behave more like a sweeping wall of 180° or 360° and do not need to be concerned with cone angle since they cover the entire water column.
Sound spreads out. Just because the cone is set to 20°, doesn’t mean sound only occurs within the cone. When fishing, be conscious of this residual sound.
Simply put, this is how manufacturers measure the signal power of a sonar unit’s transducer. They are displayed in two fashions — RMS (root-mean-square) and peak-to-peak power. The maximum power output of a sonar unit is measured in watts. It helps to think of the sonar system like a stereo, because electrically speaking, they work in such similar ways. The transducer is the speaker, display is the head unit, frequency is the pitch, and the peak-to-peak power or RMS is the maximum volume. Peak-to-peak power determines how deep a sonar’s transducer is effective to at a certain frequency. Generally speaking, the more powerful a sonar, the greater depth it can read.
Understanding the following terms will help you make more informed decisions when comparing sonar units side by side.
- Alternating current (AC) – Electrical current can alternate directions in regulated intervals, flowing one way or the other. Strength and frequency are easily adjustable.
- Direct current (DC) – Electrical current only flows one way. Strength and frequency vary little or not at all.
- Peat-to-peak power – An AC measurement of the maximum watts flowing one direction, to the maximum watts flowing in the opposite direction. Also known as ‘total swing’. If a sonar unit shows 2,400 watts of peak to peak power, that means the maximum wattage flowing one way is 1,200 watts to 1,200 watts flowing the opposite direction.
- Root mean square (RMS) – DC voltage that produces the same power output in watts as the AC voltage. It is also 0.707% of the maximum power rating.
- Watt – The standard unit of power in the International System of Units (SI) equivalent to one joule per second and equal to the power in a circuit in which a current of one ampere flows across a potential difference of one volt.1
- Volt – the standard unit of potential difference and electromotive force in the International System of Units (SI), formally defined to be the difference of electric potential between two points of a conductor carrying a constant current of one ampere, when the power dissipated between these points is equal to one watt.1
There are several ways to network sonar units. Unit to unit, unit to smart device/computer, unit to trolling motor, unit to engine, camera connection and Ethernet boxes.
Unit to unit
- How: By cables plugging into the back of the display or an Ethernet box
- The benefit: This allows units to share mapping and transducers to expand your sonar and GPS potential.
Unit to smart device/computer
- How: Wi-Fi or ANT+ technology through your Bluetooth®-enabled smartphone, tablet, or home computer. Sometimes there is a corresponding app and an online subscription through the manufacturer.
- The benefit: Mid- to high-end modern sonar units allow software updates through this connection. This keeps your sonar relevant longer, given the pace of technology improvements.
Unit to trolling motor
- How: Usually through a cable matched by manufacturer.
- The benefit: Simply put — better and easier boat control. GPS-enabled trolling motors are becoming increasingly common. Networking the two electronics allows them to communicate about heading, following contours, returning to productive spots and more.
Unit to engine or outboard
- How: Two ways: 1. Universal NMEA 2000/183 cables from the back of the display to your outboard, I/O or inboard’s computer. 2. Hydroulic mechanisms that drive the outboard via control through the sonar unit.
- The benefit: With NMEA connections, you now have a digital dashboard that can tell you far more about your engine than your vessel’s gauge cluster. You can also network sonar units to share transducers as well. By directly connecting your motor for operational control through your sonar unit, you can troll with unparalleled precision.
- How: By cable, type varies by manufacturer.
- The benefit: Control your action camera easier, so you can take more innovative and accurate shots of your fishing adventure. Or, use an infrared camera to view the lake through the fog to make your morning run safer.
- How: By Ethernet cable. Some manufacturers may use another type of cable connection
- The benefit: Consider this method when connecting more than two sonar units, or more than two transducers between two units. The benefits are the same as a unit-to-unit connection when you increase the number of components in the network.
Ice and Portables
Two types of fish-finding electronics dominate the ice: flashers and screen units optimized for the cold. Water is at its most dense state at 38°F (this is why ice floats). Ice electronics are calibrated and built to be used in this kind of water and weather.
Ice transducers sit inside of an augured-out hole in the ice. They stay suspended in the hole near the surface by a stopper on the cable and a gimbal or a large float surrounding the cable.
Most of these units are powered by a sealed 12-volt, 9Ah lead-acid battery; however, there are lithium batteries or power packs available for some manufacturers.
Flashers use a spinning wheel display with lights that flash on when the transducer pings a fish, your lure, cover or structure. The flashing lights on the wheel give you info in real-time, so you can watch fish react to your lure. To read a flasher, imagine it as a clock where 12:01 is the surface, and 11:59 is the bottom of the water column. Depth markers on the wheel or a digital readout tell you how deep you are seeing fish or your lure. Multiple colors also tell you the strength of the return signal, usually in a three- or five-color palette. The meaning of each color varies by brand. You can find the meanings on each manufacturer’s site, but it’s best to check one out at your nearest Cabela’s or Bass Pro Shops.
Because anglers can fish around each other in close proximity, look for an interference rejection setting when shopping for a flasher. This will eliminate distortion these units experience when picking up another unit’s sonar signals.
Screen units optimized for hard water operate nearly identically to their open-water cousins. The sonar shows fish arches or lines in much the same way, so really what you see on them is historic. However, depending on the manufacturer, different screen modes may allow you to see a digital version of a flasher wheel.
Screen units may also offer GPS capability with cartography options like their open-water versions, which is useful when trying to follow a moving school of fish around the lake.
Portable units are the same as the open-water screen units optimized for ice fishing with different screen modes. They are powered in the same manner, with sealed 12-volt batteries or power packs. Also, portable sonar units and ice-fishing units may be mounted the same way — on a gimbal with a handle for carrying — but the transducer is mounted on a suction cup or a separate gimbal that clamps onto your boat’s transom or gunnel.
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