Have you ever taken a minute to differentiate your left hand from your right? The difference is subtle, right? All the functions and features are the same—only a few small differences.
The same applies to fish finders and depth finders. They are slightly different forms of each other. Both the depth finder and the fish finder work based on sonar technology.
They both make high-frequency sound and wait for the echo to come back. When the sound wave reflects and returns, the machines pick them up and determine underwater objects.
But hey, as I mentioned before, there are slight but significant differences between them. And there are a few of them really.
A depth finder focuses on the deepest part of the water mostly, while a fish finder’s priority is more about the objects between. It gets more technical than that, though.
Difference Between Fish Finders And Depth Finders
Let me break it down into basics for ease of understanding.
How Do They Prioritize Different Objects?
It’s the frequency that enables these machines to do so. Generally, depth finders use relatively lower frequencies. Don’t get misled by the word ‘low’ here, though. This ‘lower frequency’ usually ranges between 50kHz and 200kHz.
Sound waves in this range tend to travel undisturbed for the most part, and thus help to generate a better image of the seabed.
Fish finders, on the other hand, use higher frequency sound pulses. The range varies more as well. Some fish finders may use sound pulses of 200kHz on the lower end of the spectrum, while the higher end can go as far as 800kHz.
Sound pulses generated by the device travel through the water at the same speed regardless of its frequency. When the sound wave hits any surface (any surface, big or small), the surface creates an echo, that travels back to the boat.
The quality of the echo depends on the frequency of the sound. How so? I’m glad you ask—time for science.
As I mentioned, the speed of sound doesn’t vary depending on frequency. But what varies is its wavelength. I’m not going deep into sound science territory.
Simply speaking, the soundwave with a lower frequency has a higher wavelength and tends to fly past small objects completely, when they should have absolutely hit them and made an echo.
Instead, a big part of the sound pulse ignores most floating objects (fish, or debris, or something else) and goes straight to the bottom. This makes for a good depth sounder.
Fish finders, on the other hand, use relatively higher frequency sounds, in other words, sound pulse with a very small wavelength.
These pulses struggle a lot to go past basically anything. Even objects with a very small footprint create echo strong enough to be read by the transducer and display as an object.
But you are not going to see any of those. Those will happen under the water, invisibly.
What Shall You See?
Well, on your display, you are not going to notice anything unless you put the two devices side by side. But if you do put two devices side by side, You’ll notice that the geography is the same, but the amount of detail is way different.
On your depth sounder screen, it’ll seem as if there’s hardly anything under the water. At the same time, it’ll look a lot livelier on the fish finder display.
Since the sound pulse of a depth sounder ignores objects with a small footprint by nature, very few objects will repulse enough echo waves to be read by the device.
The device is also tuned to ignore the weaker echo pulses, freeing most of its processing power for analyzing the bottom. They are thus giving you an empty and nearly barren water column to look at.
However, it won’t seem this way, until you compare it with the lively feedback produced by a fish finder. The transducer of a fish finder is tuned to pick up very small or even weak echo, giving you a visual of nearly all the objects underwater. Thus, it’ll look more populated and crowded on the screen.
More About The Sound
No, it’s not all about the sound pulses; there are other differentiating factors, but sound sure is a big factor. I’ll mention a couple more points. It costs more energy to generate higher frequency sound waves.
Now, it may not sound like a big deal, but when you are on a boat, in the middle of the ocean, for hours at a time, constantly keeping the device running, it will be a big deal.
And since fish finders use higher frequency sound pulses, they require relatively frequent battery recharge.
At the same time, even though it costs more energy, there are reasons to use a higher frequency sound. They provide a better resolution image of the scanned area as well as reduced background noise.
Besides packing the bare minimum, most modern devices come with other extra facilities.
Although the margin is getting thinner and thinner everyday between fish finders and depth sounders, there are still a few trends that most of the devices of the kind follow.
GPS integration is being inseparable with many tools nowadays. It’s such a commodity, especially for mapping tools. A depth finder is a mapping tool. But fish finders are not necessarily one. Therefore, built-in GPS integration is much more common to appear in depth-finders.
The attached display of the devices also varies quite a bit. A fish finder usually comes equipped with a relatively large screen with only one segment and showing one kind of information, mostly the vertical view of the underwater objects, because the detail is what makes this device useful.
Depth finders, on the other hand, are either much more basic with a 3-digit seven-segment display only or much more advanced having several segments on display partitioned from each other, and also simultaneously displaying different types of information.
As I mentioned briefly previously, depth finders usually tend to be either very basic build, with the bare minimum, or highly advanced machines. There’s not much choice available in between.
That’s because these devices are usually made either for starters or for specialists. It’s not a good idea to overwhelm a starter with a plethora of information, right? So, keep it simple.
On the other hand, an expert will want a plethora of information, if not even more. Fish finders are actually for neither. They are not for complete starters, who are still ‘getting-a-hang-of’ kayaking.
They aren’t for specialists either. They are for your everyday fishing trip, offering you just enough information that you need but not enough to overwhelm you.
In terms of technicality, in a way, fish finders make up the missing link between the lower-end and higher-end depth finders.
Well, that’s about it, really. I tried to cover the major differences between the two devices. Sure, there are more, and sure I did not go through all the small details, but those would make things more confusing if anything unless you are an expert on the topic.
Overall, both the devices are designed for their own purpose and the way they could work best. They both use sonar technology and work in the same way, and that makes things confusing between them. But honestly, they are like the two hands of yours, looks the same, but very different they are.
Surely, your left hand can do many of the jobs that are usually done by your right. Probably not as effectively or efficiently, but it can. To be honest, fish finder and depth finder can also be interchanged and still get by, but not quite satisfactorily.
There you have it—the difference between the fish finder and depth finder. See? It wasn’t that hard, was it?