Go Fishing With German Efficiency!
In this article you get an introduction to fishing with a fish sonar. On one hand, the general basics of modern fish finding, and on the other, how to use a fish finder – technically. Such basic knowledge about fish sonars is the fundamental prerequisite for choosing a fish finder, which is well suited for your personal needs.
It is all too easy to take the wrong decision due to a lack of information and sink several hundred euros into the proverbial bottom of the sea. The first thing to consider when buying a fish finder is that it is designed for your preferred type of water.
Because it is unfavourable, if important functions are simply missing or other unnecessary ones have been expensively paid for. Once the device has been installed and used, it is usually impossible to return it.
The most important reason to familiarise oneself with the functioning of fish finders is to reduce the information gap between retailer and customer (you). Customers want to spend as little money as possible on the functions they need. The retailer, on the other hand, lives from sales.
That is why they often advertise fantastic new functions as virtually indispensable. However, only very few know, whether these are really necessary. So that you feel differently in the future, we have summarised (and explain) the most important functions of a fish finder in this article.
Table of Contents
How do fish finders work and how to use them?
The transducer is placed in the water and emits downward high-voltage pulses in the ultrasonic range. On their way down, the sound waves encounter obstacles such as
- objects floating in the water,
- the bottom
- or even fish – and entire schools of fish.
If a sound wave hits such a one – or at the latest the ground – then it is reflected to be received again by the transducer.
The sonar’s software then converts the received signals into an image and displays it on the screen. Based on the received signals, the software calculates whether it is a fish, branches or a hard or soft substrate.
How many watts should a fish finder have?
The more watts a sonar has, the higher is its transmitting power. Basically, more watts are always required in the USA than in Europe. The reason is quite simple. There are many and big competitions with prize money in the millions.
This means that the demands on the equipment are much higher, because every second in a three-hour competition counts. Here in Europe, competition fishing is banned in most states. And if not, then many competitions are more like a typical fishing club excursion with comfortable sitting on the edge of the water.
But now back to the wattage. The power of a fish finder is given in watts (RMS – Rout Mean Square), which describes the average value of the power of all frequencies. The wattage determines the strength of the signal that is sent to depth.
- Consequently, the deeper you fish, the higher the wattage should be.
- It also needs to be high if the frequency used is high.
You can compare this to calling a friend. The further away he is from you, the louder you have to scream. And, if you have a squeaky voice, you have to put more power into your voice to be heard (high frequency = Police Academy, Lawerne Hooks says hello).
Even medium-priced devices such as the Humminbird Helix 12 CHIRP MEGA SI GPS have a transmitting power of 1,000 watts (RMS) with legendary 8,000 watts (peak to peak).
Therefore it depends specifically on what you plan to do with the fish finder. Normally, the device automatically controls the wattage used according to depth.
- In shallow waters up to 50 m (165 ft), a low wattage of 100 watts is sufficient,
- while in deeper bodies of water the power must be fully exploited.
What is the best frequency for a fish finder?
Before we get into the functionality of CHIRP and photorealistic imaging, we need a fundamental understanding of how different frequencies work.
We’ll just do a quick overview of the subject here. If you want more comprehensive information, we recommend taking a look at our Ultimate Fish Finder Guide.
When a transducer sends a sound wave into the water, it’s called a “ping”. The sound wave (ping) is an audible tone created by a vibrating ceramic and has a specific frequency.
Pro and Cons of high frequencies
A 200 kHz wavelength is significantly shorter than one at 50 kHz (ultrasonic wavelengths range from 0.3 to 1.2 in – 7.5 to 30 mm), which means that an image produced at 200 kHz will be much more detailed than one produced at 50 kHz. This is because more sound waves come into contact with the object in question and are reflected back up to the transducer.
Most anglers underestimate the effect of sound waves. The respective frequency has a big influence on the distance at which individual fish are recognized as such at all. The difference here is enormous. At 50 kHz, fish closer than 50 cm (15.7 in) to each other cannot be detected as individual fish.
This is directly dependent upon distance resolution and should be a point of interest for anyone who owns or is looking to buy a fish finder. In our book the ultimate fish finder guide, we go into great detail on the subject of distance resolution.
Individual soundwaves impact a given object much more often at higher frequencies than at lower ones. In terms of imaging, this results in much more detailed fish finder images.
If you have problems to understand how the sound waves work, take a sheet of paper and draw points on a line at a distance of 7.5 mm / 0.3 in (200 kHz). Next to it repeat the same thing with a distance of 30 mm / 1.2 in (50 kHz). Now place an object – like your key – on the points. You will see that at a distance of 7.5 mm / 0.3 in many more points hit the key than at 30 mm / 1.2 in (shorter wavelength = higher frequency at the sonar).
Pros and Cons of low frequencies
A low frequency offers advantages especially in deep waters. Since the wavelength of 50 kHz is bigger than high frequencies, the water offers less resistance and you can reach a greater depth.
In the same way, the ground conditions can be visualized better, because the sound waves can penetrate deeper into it before they are reflected by the substrate.
Among other things, this is important for fishing at big depths of more than 300 meters (1,000 ft), such as in the coastal regions of many seas.
At these depths, the sound waves of a 200 kHz frequency will often not reach the ground, so there can be no echo. As a result, the screen remains blank and shows nothing at all.
Comparison between high and low frequencies:
Let’s take a high frequency of 200 kHz and a low frequency of 83 kHz as an example.
Pros of 200 kHz:
- More detailed images and information.
- Small obstacles are detected.
- Narrow beam angles that cover the depth better.
- Fish, that are close to each other are displayed as individual fish crescents.
Cons of 200 kHz:
- The small beam angle also scans a small area.
- Any information outside of the transmission cone is not captured.
- Not suitable for big depths (150 m / 490 ft and more).
Pros of 83 kHz:
- Big area covered by the sonar (mostly 60° beam angle).
- Can be used for bigger depths.
Cons of 83 kHz:
- The information of the scanned area is not so detailed.
- Schools of fish are often only displayed as a dense cluster of dots.
- In bigger depths there is too much information, which cannot be displayed.
What is the best beam angle for a sonar transducer?
The transducer is responsible for the frequency transmitted and the beam angle of the resulting sound waves. Put another way, at what angle do the soundwaves leave the transducer? The ceramic bonded to the transducer is usually round and coated on two sides with an electrically conductive material. A ceramic designed for 200 kHz / 20° has a diameter of 1 inch (2.5 mm).These ceramics get smaller every year, but their miniaturization is ultimately limited by the laws of physics.
How does a transducer crystal look like - and what practical difference do different size aperture angles make?
Many common fish finders operate at a frequency of 200 kHz and have an beam angle of 20° to 28°.
At a depth of 33 ft (10 m), soundwaves emitted at a 20° beam angle hit the bottom with a diameter of 11.5 ft (3.5 m), which equates to a surface area of about 100 sqft (9 sqm).
For reference, 100 sqft (9 sqm) is roughly the size of a small bathroom. At a depth of 33 ft (10 m), a ceramic with a beam angle of 60° produces a sound wave that enlarges to 38 ft (11.5 m) in diameter by the time it reaches the ground.
This means that the fish finder scans an area of 1120 sqft (104 sqm) – roughly equivalent to the area of a large apartment. Let’s take the opportunity to put these numbers into clearer perspective.
Imagine a 1120 sqft (104 sqm) apartment on the second floor of a building. There’s a big pike or bass located in that apartment’s kitchen. Your fish finder is located on the fifth floor, pinging and relaying the resulting image to you above the water.
A fish: 33 feet (10 meters) down in the water
Whoa! The depth finder display is showing a large fish arch at a depth of 33 ft (10 m).
- What to do now?
- Get out your best bait and cast?
No: Hold on a minute – we only know that the fish is located in 33 ft (10 m) depth. However, the fish finder can’t tell us if it’s in the kitchen, the bathroom or some corner of the living room.
Choosing the right frequency and beam angle is therefore incredibly important. If you want to get out on the water, find fish and *BAM* hook a three-feet-pike, you should know that a high-quality fish finder isn’t enough on its own.
Depth sounder systems are often misinterpreted in terms of their complexity and physical limitations.
How to use multiple frequencies at the same time?
Depending on its design the crystal of the transducer can support multiple frequencies – and sometimes even multiple aperture angles. One common depth finder transducer configuration is
- to have a 200 kHz signal transmitted at a narrow angle
- and a 83 kHz signal transmitted at a wide angle.
The benefit of this configuration is that the 200 kHz signal delivers detailed images from the area under the boat, while the 83 kHz signal scans fish in a wide area around the boat. You get a nice, panoramic view of what’s going on underwater. For example, Hummingbird fish finders allow you to display the frequencies separately on-screen.
What is the Dual Beam function of a fish finder?
The Dual Beam function allows you to combine the signals of both frequencies (at differing beam angles) in one on-screen image. A fish finder with Dual Beam is great for beginners, as they provide a great deal of information in one place and won’t confuse you with too many different imaging modes.
If you want a more sophisticated and varied fish finder experience, individual frequency imaging modes and beam angles are the way to go.
Dual Beam is a great solution for trolling, because it combines the benefits of both frequencies and partially eliminates their respective drawbacks. The simultaneous, divided display of both frequencies would be the best configuration for its use.
Beam angle and scanned diameter
The following table shows you how to approximate the scanned diameter of your fish sonar. You can use this information to determine the area currently being displayed on it’s screen. The area covered by tit’s sound waves is calculated as follows:
(Diameter) d = 2 * tan(α/2) * h (depth)
|Depth||Transduction cone diameter at 20° aperture angle||Transduction cone diameter at 60° aperture angle|
|16 ft / 5 m||5.74 ft / 1.75 m||18.9 ft / 5.75 m|
|33 ft / 10 m||11.5 ft / 3.5 m||37.7 ft / 11.5 m|
|66 ft / 20 m||23 ft / 7 m||75.5 ft / 23 m|
|100 ft / 30 m||34.5 ft / 10.5 m||113,2 ft / 34.5 m|
How is a fish crescent created by a fish sonar?
- A fish enters the beam angle – and subsequently the distance from the fish to the transducer is measured. The signal is then continuously interpreted and displayed.
- Then the fish moves into the direction of the boat, effectively shortening the distance to the transducer. Its image moves upward, with its peak indicating its true depth (in other words, its closest position relative to the transducer).
- The fish then slowly leaves the sonar cone and moves away from the boat. The distance increases again, and the displayed points move downward.
The perfect fish arch however is a rarity
Much more often, fish wander around in the transduction cone or move along the length of the boat. Each of these circumstances cause different types of fish arches to be displayed on your depth finder.
They might have a particularly thick or thin side, or one end of it might be missing altogether. Additionally, arches might stack up on one another.
You therefore have to ask yourself a number of questions:
- Which ones are predators, and which ones are prey?
- If the large arches are predatory fish, how do I catch them?
- Are they located to the right or the left of my boat?
How to interpret fish finder images
- The task at hand: Interpret the fish arches displayed on your sonar screen – and decide based on that interpretation, whether the fishing spot is worth the effort.
- Note: The importance of the speed, with which the boat moves is often underestimated, nevertheless does it influence the size (and form) of the fish arches.
A lot of fish finder owners tell us that they stroll around until they can see nice, fat fish crescents on their displays. Only then do they stop and start fishing. We however believe this is one of the primary reasons that fuel – and potential fishing time – is wasted. The upshot is that you spend less time actually catching fish.
Fish sickles are fine, but ground imaging is even more important: It is this information that can reveal truly promising fishing spots. A quality fishing spot is what leads to success in the sport, and it’s the thing that separates the winners from the losers.
Finding fish is definitely an exciting topic, but it’s so broad that we’ve dedicated two whole chapters of our book to it (chapters 4 and 7). Have a quick look here to check it out. You can download over 20 pages for free.
What can you see on a fish finder’s screen?
How to read a fish finder? Its images are always read from right to left. In the following picture, you can see a traditional 2D sonar. This means that the information is gathered by a conical sound wave field and subsequently processed and displayed. What you see on-screen is already in the past. The most recent information is always located on the far right side of the screen.
Real-time information (on what is presently in the transduction cone) is displayed exclusively in the A-Scope or RTS readout, assuming you have them activated on your depth finder.
The display of a fish sonar is divided into the following information sets:
A. Color scale (yellow = strongest echo, dark blue = weakest echo)
B. Setting-dependent (A-Scope or RTS)
C. Ground line
D. Individual fish
E. School of fish
F. Surface disruptions
G. Current water depth
H. Current boat speed (km/h or mph)
I. Current water temperature (°C or °F)
J. Current transducer frequency
What is CHIRP and is it worth it?
Conventional transducers emit sequential soundwaves of a single frequency and convert the returning echoes into an image. Things are different with CHIRP. Here, the transducer simultaneously emits multiple soundwaves of differing frequencies and analyzes the returning echoes. The higher frequencies are more sensitive, while the lower ones penetrate farther into the depths. Taken together, they create a much more detailed image. CHIRP stands for Compressed High-Intensity Radiated Pulse, and it represents the state-of-the-art when it comes to depth finder technology.
How does the Down- and SideScan sonar work?
What are DownScan Imaging, Down Imaging, ClearVü and DownVision?
What are StructureScan, Side Imaging, SideVü and SideVision?
- StructureScan Imaging (Lowrance)
- Side Imaging (Humminbird)
- SideVü (Garmin, DownVü until 2016)
- SideVision (Raymarine)
How to maintain a fish finder?
When should I replace my transducer?
Under normal use conditions (regular fishing trips from spring to fall), a plastic transducer should last approximately 6 to 8 years. After that point, its performance will diminish noticeably. You most likely won’t notice this at first, because the image details deteriorate little by little. Therefore it’s hard to make a comparison, as you probably won’t have a record of the image quality from when you first bought the depth finder.
We always use the following tried-and-true method: Right after you get a new fish finder, switch all automatic settings over to manual. Then
- Make notes of these settings and
- take a photo of the display.
After (at most) 5 years, set the device up in the same way and get that photo out – it will be easy to tell if the image quality has changed.
Incidentally, if the image quality has diminished, you’ll have the perfect argument to present to your better half as to why you need to buy a new depth finder or transducer!
Does a fish finder insurance exist?
Depth finders are an ideal target for thieves. As on one hand they are easy to steal and on the other they bring in plenty of cash on the second-hand market. Especially, if they are rather new or equipped with a large screen. Unfortunately, you can’t insure a depth finder on its own.
However, they are covered by your boat (or boathouse) general liability insurance. In cases of break-in/theft or damage during the course of a break-in, your insurance will pay out according to the conditions of your policy. For a claim to be acknowledged, the depth finder and other electronic components need to be registered as inventory with your insurance company. Additionally, you should always make sure to keep your purchase receipt in a safe place.
If you have an expensive transducer, you furthermore have to report any instance of ground contact with your insurer. If the transducer breaks at some later date – and the failure can be traced back to an unregistered instance of ground contact – the insurer will not accept your claim because you are required to report any possible damage as soon as possible after it happens.
Typical failures that are made with fish finders?
A fish finder’s transducer emits sound waves (just like a ferroelectric speaker) and transmits them toward the ground. The sound waves that are reflected back to the transducer are converted into data that is displayed as a image on the screen. All kinds of factors influence those sound waves on their way to the ground and back.
If the water is warm and salty, the sound waves move more quickly and return to the transducer earlier than they would otherwise. This has an effect on depth measurements and can easily cause incorrect readings to be displayed. Furthermore, salt water has more suspended particles in it, such as plankton or other micro fauna, which can disrupt the signal. 50 kHz signals in salt water are not as easily interfered with as 200 kHz signals in similar conditions. When dealing with cool fresh water, sound waves take longer to travel the same distance – which obviously also has an effect with regard to depth measurements.
The most common mistakes why you get a poor sonar image?
1. The transducer has been mounted incorrectly – your fish finder is now transmitting sound waves either too far forward or rearward. The resulting echo is much weaker and more delayed than it should be, causing inaccurate depth readings and blurry images on-screen. Now, you’re missing all the fish.
2. The inclination of the transducer also varies depending on the speed of the boat. You should therefore always mount your transducer according to the directions in your user’s manual. Manufacturers furthermore often provide fitting jigs, which ensure a proper mounting.
3. The fish finder’s transducer can also be mounted too closely to the propeller, which causes the mass of air bubbles formed there (cavitation) to interfere with the displayed image. Because sound waves can’t travel through the bubbles, there are no measured values to be interpreted/displayed. The measured values within the cavitation zone are higher than the signals from the bottom (and even those from fish).
It’s pretty annoying to spend a lot of money for a quality fish finder, only to discover that it won’t display depth or any other signals. It’s even worse when you realize it’s your own fault. It’s also important to avoid mounting the transducer on sharp edges on the hull of the boat, as that can result in air turbulence as well.
4. On displacement-hull boats, the transducer should be mounted on the foremost third of the vessel. In this case, through-hull transducers should be used so that they are located far enough from the motor.
5. If your boat is gliding, you should mount the transducer as close to the center of the bottom as possible, to ensure contact with the water and minimize turbulences. If you want to get accurate information from your instrument, it is important that you mount the transducer correctly.
6. At low speeds, it’s usually not a problem to go for a stern-mounted transmitter, if you’re using one of the high-quality models found in our fish finder reviews. These units are robust enough and have special software to deal with the corresponding turbulence.
The most common operator errors
1. Your scroll or ping speed is too high. Almost every fish finder owner has, at some point, set the scroll speed or ping speed to maximum without thinking of the consequences. However lower scroll speeds increase the chances that you’ll find hotspots that you’ve missed in the past.
If you set your scroll speed to the lowest possible setting appropriate for your boat speed, you can get a great overview of the last two minutes of travel. The power of this one little setting can be enough to help you find the one hotspot that all other anglers have simply passed by.
External sources of interference
There are various external factors that can cause interference, including (but not limited to) other fishing boats. The wakes of passing vessels can cause your unit to deliver inaccurate readings. But because they are usually only temporary disruptions, this kind of interference however can generally be disregarded.
You may also experience electrical interference from your other onboard electronics. High-frequency interference is usually caused by the motor or generator. This kind of disruption usually manifest themselves in the form of inaccurate depth readings.
Other depth finders that are transmitting an identical frequency to yours can also interfere with your signal and produce inaccurate data. The kicker is, when all anglers position their boats near a hotspot and set their respective depth finders to 200 kHz.
This causes 200 kHz soundwaves to be distributed to all directions – that subsequently are collected and processed by the transducers on each and every boat. The problem is, that you don’t know, where the 200 kHz echo you are receiving originally came from. Not only does this produce inaccurate depth readings, it also shows fish where there simply aren’t any.
This brings us to the end of this article with the most important fish finder tips. If you now know how to use a fish finder, but are still unsure about which sonar to buy for fishing, you can a have a look at the other fish finder reviews in our extensive fish finder test (including the newest models of all important fish finder manufacturers like Garmin, Lowrance, Humminbird or Raymarine) or write us a short message. Have fun on your next angling trip and “Petri Heil” – Jens and Martin.