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Before You Buy Guide: Understanding Fish Finders And GPS

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There’s nothing more relaxing than a day out on the water.  The gentle movement of the boat, the sun, and breeze moving over the water.  These things make it hard to want to ever go back to civilization. And catching a few big fish sure would be the icing on the day’s cake.  There’s no better way to improve your odds when dropping a fishing line in the water than with a fish finder.
One that works that is.  The last thing you need is to get out on the water to find out your fish finder doesn’t work the way you had intended.

What Is A Fish Finder

A fish finder is an electronic device that uses sonar transmission and reception to track objects such as fish in the water.  The fish finder sends out pulses of sonar. These pulses bounce off objects in the water and the fish finder receives the pulses that have bounced back.  Based upon how the pulses are received, the fish finder shows the objects which reflected the pulses on its screen. That’s sonar.

If you’re anything like me, you’ve played with echos at one time or another.  You know, when you go into an empty stairwell and no one else is around. You make a sound to hear the echo in the stairwell.  When I was a kid, I thought this was really neat and anytime I noticed I was somewhere that produced the echo effect, I had to call out the “Echo”.  Likely, you’ve done the same at some point or another.


The science of using sound waves and their subsequent reflections.  This is sonar. And this is what fish finders use. Sound waves well beyond our hearing range are transmitted and the reflections are mapped out on a screen for your convenience.  Knowing where those fish are hanging out can make all the difference when dropping a line into the water.

Sound waves are represented in this graphic illustration.

A Brief History Of Sonar

Sonar, or echo-location, has been around a lot longer than people would typically think.  Nature invented it first, long ago before we (humans) did. Animals like bats and dolphins both use sound echolocation.  It wasn’t until 1906, when Lewis Nixon, an American naval architect, invented a form of sonar. His sonar was for the purpose of detecting icebergs. 


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Since its invention, sonar has been widely used around the world.  Naval forces from every country which use boats likely use sonar in one form or another.  It is essential in locating things like mines, underwater missiles, and submarines, so you can see the value for military applications.  And, oh yeah, it works great to find fish as well.

Global Positioning System or GPS

Most decent fish finders also incorporate GPS technology.  GPS or Global Positioning System is a technology that utilizes satellites for navigation.  It is owned by the United States and consists of at least 24 satellites. It was originally used by the Department of Defense but was turned over for civilian use back in the 1980s.

How GPS Works

GPS works by having a device read signals broadcast by about 30 satellites which orbit the Earth.  At any point on the planet, there are at least 4 satellites covering every place on Earth. These satellites are orbiting our planet at about 20,000 km up.  And they each broadcast the signal which your GPS device can pick up. The device then does the work of calculating your location, based upon the signals it has received from at least 3-4 of the satellites.

Common Features To Look For In Fish Finders

Some good features to look for in a fish finder are:

  1. GPS – always handy to know where you are.
  2. Backlit screen – if it’s dark out, the screen has to light up, right?
  3. Battery Life – if your fish finder runs on its own batteries and not the power of the boat, like for a handheld unit for example, how long will the batteries last?  If the fish finder has to plug into something to charge, you’ll need to make sure you also buy a power supply like a battery pack or charging pack. If the unit takes normal batteries, then how long one set of batteries lasts will determine how many more you need to purchase both as a back up and also to power the unit the next time out on the water.  These batteries or power packs aren’t free so you need to factor this in when deciding which one to purchase.
  4. Portability – Okay, this won’t matter if you’re mounting the unit to your boat.  But if you intend to use the unit in a canoe or kayak, and then maybe out on a small fishing boat, you may not want to mount the unit permanently.  So, this is where it would be important to know just how portable the unit really is. For example if the batteries last 2 hours and you’re going on the water for 8 hours, then you need to carry a bunch of extra batteries, then it’s not so portable anymore.
  5. Bluetooth/Wifi – This is good if there’s a good app that can go with the device.  This is good to download maps and updates to the unit using your smartphone.  As long as you have a signal, you can download a new map.  
  6. Distance/Depth – This is one of the most important factors for me, when determining a good fish finder.  The distance and depth with which a fish finder can work is like looking at how far you can see.  In fact, it’s almost the same. The further the unit can pick up fish, the further away you can pick up fish.  
  7. Accuracy – Can the unit distinguish between a group of small fish or a big fish?  To what accuracy the unit operates determines how focused your vision is, metaphorically speaking of course.  But again, I don’t want to throw a big lure in the middle of a bunch of fish no bigger than the lure themselves.  I want to throw my big lure in front of a big fish, so I want to know if its a group or a big one.

Types Of Fish Finders

Portable Fish Finders – Top Rated 2019

Garmin Striker 4 with Portable Kit

The first on our top rated list is the Garmin Striker 4 including the Portable Kit.  This is an Amazon best seller, and for good reason.  It’s cheap and works really well. Here’s a few key points:

Battery Life.  Decent.  This unit can go out on the water for a full day and into the evening before you get a battery warning.  Unless you’re staying awake on the water for 24 hours straight, this unit works just fine.  

Screen.  Great.  Totally customizable.  You can make it have a split screen, customizing your view exactly the way you want it.  


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Features.  For the price point, this unit is fantastic.  Not only is it ridiculously customizable, you can set waypoints, set alarms, and more.  This unit can do most of the things a fish finder 4 times as much money can do. It’s just a really good unit.  It even has a cool beeper to warn you when you come across fish. This unit makes fishing foolproof. Well, nearly foolproof.  It can’t handle your fishing rod for you but it can do almost everything else. There’s a reason this is a top rated product in that price range.

Deeper PRO+ Smart Sonar – GPS Portable Wireless Wi-Fi Fish Finder for Shore and Ice Fishing

Next we have the Deeper PRO+ Smart Sonar – GPS Portable Wireless Wi-Fi Fish Finder.  This neat little unit is castable and is intended to be used from a shore or dock.  But obviously this unit could also be used off your boat. 

The deeper pro comes with three positions to put the eye bolts for casting.  These are intended for long cast, short cast and straight down like you would if you were ice fishing for example.

The Deeper PRO+ works paired with your smartphone, using the downloadable app.  The app is easy to use and gives a surprising amount of options.  

This fish finder is a neat little toy, but it will never be able to do what the Garmin does.  Also, if you really want to be efficient, you need to have a fishing rod and line setup with a decent test on the line just for using the Deeper PRO+.  This now adds more to the cost of using this unit as with the Garmin, there is no need to cast out the unit. But, unlike the Garmin, this unit can be used from a canoe, kayak, or on foot from the shore.  So basically, if you have a boat, skip this unit. If you have more of a need for a portable unit you can use from shore while on foot, then this unit may be the one for you.

LUCKY Portable Fish Finder Handheld Kayak Fish Finders Wired Fish Depth Finder Sonar Sensor Transducer for Boat Fishing Sea Fishing

This is the bargain price unit.  Coming in at under $50, this unit by Lucky has some decent reviews.  This fish finder can tell you depth, it has an alarm to let you know when fish are near, it will even tell you the water temperature.  

So, this unit is portable but it is also wired.  The wire has a distance of 26 feet, so you can mount on any small boat, canoe or kayak.  The Lucky has a boasted depth range of 328 feet.  The unit has a built in battery pack that states that it lasts about 5 hours.  This would be the kind of unit you use for a bit, find the fish, turn it off and fish the spot for a bit, then turn back on after a while.  Not the kind of unit you want to leave on unless your planning on only going fishing for a few hours. With a little smart planning, you can likely make this unit work for you for a day if you are turning it on and off.  


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One thing I’m not a big fan of with this unit is it’s lack of customization.  After using the Garmin, all other portables just don’t make the grade. This unit feels slightly cheap, but hey, you get what you pay for.  If you’re looking for an entry level fish finder on a budget, then this is the one for you.

Stationary Fish Finders

Humminbird HELIX 5 Fish Finder

This acclaimed fish finder boasts a 5 inch display, CHIRP dual beam PLUS sonar, and a precision internal GPS chart plotting with built-in Anima cartography.  This is the unit if you own a half decent boat and you’re looking for a good entry level nav system.  

The Helix 5 by Humminbird combines the convenience of both a fish finder and a GPS chartplotting navigation system.  

One feature I really like about the Helix 5 is that it has a MicroSD card slot.  So, you can add a memory card to add maps, save waypoints and so on. That makes it super handy for going back out to find your favorite fishing spots.  When you find a great spot, add and save a waypoint and next time plot a course right back to your spot. It’s just that simple.

Lowrance HOOK2 5 – 5-inch Fish Finder with TripleShot Transducer and US Inland Lake Maps Installed

Next for the stationary fish finders we have the Lowrance Hook 2.  This 5 inch screen fixed fish finder has some striking graphics and is another easy to use unit.

The Hook 2 has some really easy to follow menu setup so you aren’t wasting time messing around with settings.  The sonar is auto-tuning which again takes another burden off your shoulders.  

With the extra wide CHIRP angle, this unit gives you nearly double the coverage of conventional fish finders.  And with the downscan, sidescan and CHIRP views, it covers all the bases.  


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Built in GPS is, of course, standard on the Hook 2 as well, allowing for easy navigation including waypoints and follow trails.  Given the US inland lakes map pre-installed and you’re good to go. But if you aren’t doing a US trip, don’t worry because the Hook 2 also comes with a build in SD card slot so you can upload your own maps, upgrade the software and so on.

One thing I really like about the lowrance is that you can get this unit in several different sizes, depending on your needs.  And also depending on your budget of course as the 12” screen version is over a thousand dollars. But, if you have a decent boat and you want some decent toys, then maybe the bigger version of the lowrance is the one for you.  They come in the following sizes:

Down Scan vs Side Scan Fish Finders vs CHIRP

Down Scan

Sonar that images what is beneath the boat

Down scan, down imaging, down picture, you may have heard these terms before.  Some are trademarked but all are terms used for basically using sonar to see what is beneath the boat.  Some forms of this work better than others, but the point is that they scan for fish and depth beneath the boat.

Side Scan

Sonar that images what is to either side of the boat.

This type of sonar fish finding is the scanning of a certain range to either side of the boat.  A good fish finder should have a decent range in 360 degrees around the boat, in my opinion. And the greater the accuracy combined with the greater the range makes the best fish finders.


Compressed High-Intensity Radiated Pulse


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Okay, that’s a mouthful. Basically, it’s like this.  With sonar, certain frequencies produce clearer images but only at a short range.  Other frequencies produce a slightly more distorted or ‘fuzzy’ image, but they do so at a much greater range.  Traditional sonar would be a single or even dual or triple pulse with one, two or three frequencies to attempt to determine the best image and result.  CHIRP uses a varying frequency longer pulse to exponentially determine clarity and range and thus provide a much greater range and more precise result that traditional forms of sonar.  CHIRP is new tech and you want it. It makes it so much better.


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