Fish Finders For Boats: Essential Facts You Need Before Buying

When buying a fish finder for a boat, you need essential facts before buying; otherwise, you may not buy the correct one. Lucky for you, I will provide the details to ensure you get the right one for the job and at the right price.

Garmin Striker Plus 5cv with Transducer

Whether you are after a depth sounder fish finder or searching for the best deal on fish finders, I hope my article will be of great help. There is an abundance of information on fish finders for bass, pontoon, kayaks, shallow water, and hundreds of other variations on the same topic. Whatever your reason is for reading this article, I am sure it is time well spent.

An online friend of mine recently bought one for his small fishing boat and used it as a depth finder as much as anything. The fish finding side helps great, but he seeks out those slightly deeper channels to concentrate his fishing. Have you a preferred way of using them?

If you are boat fishing, you may have noticed the advantages of using a fish finder. Detecting schools, depths, and water temperatures are all good ways to better your chances of getting a great catch. But what exactly is a fish finder, and how do you use it? This article will go over the definition of fish finders and look at their types, features, and reading them. 

So what are the essential facts?

Here are the essential facts that you should consider before making your fish finder purchase:

  1. What is a fish finder?
  2. What types of fish finders are there?
  3. What frequency do fishfinders operate at?
  4. Are fish finders waterproof?
  5. What do fish finders show?
  6. How do I read a fish finder?
  7. Do fish finders show water temperature?
  8. Are portable fish finders any good?
  9. How to set up a portable fish finder?
  10. Do fish finders come with a GPS?
  11. Are all fish finders waterproof?
  12. How are fish finders powered?
  13. What are the fish finder brands available?
  14. Fishfinder sizes available for the angler

Below I will now go into these fish finder essential facts in more detail for you:

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What Is A Fish Finder?

A fish finder is a tool used for detecting underwater life using waves of energy. This energy can be converted from a transmitter into sound. It is broadcasted from a transducer (usually located on the bottom of a boat or watercraft) to be reflected on underwater surfaces. 

Once the sound energy is reflected off an underwater surface, it is bounced back in the transducer’s direction, where it is received and converted into an observable form on a display screen. Fishfinders use sonar principles and technology.

What Types Of Fish Finders Are There?

Fish finder types are varied, but can generally be divided into types of features, scans, displays, and capabilities.

Fishfinder features

Fish finders can be divided into three feature categories:

  • Standalone – this fish finder only displays underwater objects, including depths, fish, and the underwater floor. 
  • Combination Fish Finder/Chartplotter – has an underwater display, as well as charts, maps, and GPS navigation, and
  • Networked Fish Finder – includes the underwater display, maps, charts, GPS navigation, satellite radio, video, and capability to be used through cell phones or computers. 

Generally, standalone fish finders are for small vessels, while networked fish finders are for large fishing boats. A combination of fish finders can equally come in handy on both.

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Fishfinder scans

Fish finders scan in three main ways:

  • Two-Dimensional (or 2D) scans – displays simple shapes and the underwater floor in a left-to-right scrolling orientation,
  • SideScan or Side Imaging – maps transducer waves that go out perpendicularly to your boat in a wide-sweeping fashion,
  • DownScan or Down Imaging  has transducer waves that are aimed directly down, underneath your boat. Shows a photorealistic profile of the underwater surfaces.

In general, 2D-scan fish finders are less detailed, while SideScan and DownScan fish finders display much more detailed pictures. 

Fishfinder displays

Fish finders typically have LCD displays, in either black or white (grayscale) or in color. 

LCDs are a grid of electric “picture elements,” or pixels. Generally, the more pixels you have per square inch vertically or horizontally, the better quality your picture will be. 

It is recommended to have a fish finder with at least a 240 (height) x 160 (width) pixel display – but much higher pixel displays should be considered.

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Fishfinder capabilities

Fishfinders operate at different wave frequencies. Generally, higher wave frequencies provide more accurate readings – and less background noise. 

However, high frequencies do not penetrate as deeply as low frequencies do. For this reason, high frequencies are generally reserved for shallow or inland fishing – and low frequencies for ocean fishing.

A recent development in transducer technology is CHIRP (Compressed High-Intensity Radar Pulse). CHIRP operates on bandwidth, or a range of frequencies, rather than one specific frequency. As a result, it can produce high-quality, detailed scan displays.

What Frequencies Do Fish Finders Operate At Typically?

Fish finders usually operate at frequencies of 200, 192, 83, or 50 kilohertz (kHz). 

That said, the ideal fish finder frequencies for freshwater fishing are 200, 400, or 800 kHz.

For saltwater fishing in depths up to 200 feet, 200 – 800 kHz finders are recommended. For depths greater than 200 feet, frequencies of 80 or 50 kHz can be used. 

CHIRP devices operate at bandwidth ranges of 40 to 75 kHz or 130 to 210 kHz. These are very powerful, accurate frequencies for depths up to 10,000 feet. 

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Are Fish Finders Waterproof?

Fish finders should be generally waterproof.

To determine a fishfinder’s waterproof abilities, look for the Japan Industrial Standards (JIS) or International Protection (IP) rating codes. 

JIS ratings range from 0 to 8. The higher the number, the more waterproof the device is. A JIS-6 device is considered watertight, for example, and a JIS-8 device is considered submersible under continuous pressure. 

IP ratings are similar in that they range from 0 to 8 (8 being the most water-resistant).

Generally, look for IP or JIS ratings above 6 for fishfinders – but this need may depend on your usage.

What Do Fish Finders Show?

Fish finders will generally show:

  • Depth – The depth of the underwater floor, or the range of the finder itself,
  • Fish – Traditionally, the arches map a fish’s air bladder. This is how fish finders detect fish,
  • Underwater contours – Including the floor, debris, and schools of smaller fish, 
  • GPS positioning – Including charts and maps, and 
  • Water Temperature – The temperature right underneath the transducer. 

Of course, more advanced finders will have more features. 

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How Do I Read A Fish Finder?

You will see a profile view of the underwater floor for most fish finders – with the objects mapped first traveling from left to right on your screen. Your current position will be the rightmost area of your display.

Pronounced arches will reflect large fish underneath you, while small dots reflect smaller schools of baitfish. More advanced fish finders will make individual large fish in schools visible as well. 

For SideScan fish finders, you will see a dual-sided map of your underwater environment. Your position is at the top of the screen, and the contours of the underwater floor are mapped underneath this. 

Areas closer to the center of the screen reflect the water and fish nearer to the surface (and your boat). Like profile-view finders, large fish in SideScan finders will appear as pronounced arches.

Do fish finders show water temperature?

Yes, most of them show the temperature, and many of these will enable you to know the temperature at certain depths. This will enable you to find a warm spot in cold water and a cooler spot in warm water. This can make a good selection area for fishing and playing the waiting game.

I have found that fish will find a temperature range they prefer and stick to it as best as they can as they feed. Follow their methodology, and you could catch more on your next trip out. Sometimes it is good to think outside the usual box we find ourselves in.

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Are portable fish finders any good?

I find they are a handy gadget to have when fishing an expanse of water from a boat, and you would like to know where the fish are before you cast out. When I fish a lake from the bank, I will often choose the position I believe is best and wait it out. This, however, will depend on how I feel and my determination to catch.

Often I am happy just to be at the waterside dipping my line.

How to set up a portable fish finder?

For this explanation on setting up the fish finder, I shall use the very popular Garmin Striker 4 with Transducer, 3.5″ GPS Fishfinder.

Assembling the Mount

Before you can assemble the mount, you must have a Phillips screwdriver.

  1. Insert the handle into the two openings on the portable mount.
  2. Attach the handle to the portable mount using two M4×0.7×40 screws and M4×7 mm nuts.
  3. Install your fishfinder or chart plotter mount on the portable base.
  4. See your fishfinder or Chartplotter installation instructions.


The transducer can be configured in two ways. You can configure the transducer with the included suction cup mount for use on the side or bottom of your boat. You can also configure the transducer with the included float for ice-fishing or dockside use.

Floating the Transducer

  1. While holding the transducer arm in one hand, it takes the transducer cable’s length and makes a loop.
  2. Insert the loop into one end of the float until the loop extends out of the opposite end of the float.
  3. Ensure the cable’s length between the float and transducer is long enough so the transducer can be suspended below the water or ice.
  4. Thread the transducer through the loop at the end of the float and pull tight.

Mounting the Transducer with the Suction Cup

If you purchased the transducer separately from the portable kit, before you can mount the transducer on the transducer arm, you must find the packaged hardware with the transducer.

  1. Attach the suction cup to the transducer arm using the shorter screw.
  2. Pull the transducer cable back and insert the transducer or transducer mount into the transducer arm. If possible, insert the transducer cable through the notch and opening in the transducer arm.
  3. Place the washers on the outside of the transducer arm.
  4. Insert the longer screw through the washers and transducer or transducer mount.
  5. Fasten the screw with the wing nut.
  6. Attach the suction cup to your boat.
  7. Align the transducer parallel with the waterline. (Source)
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Do fish finders come with a GPS?

Yes, the better quality ones will have a GPS facility as part of the functionality they provide. Some of the low priced ones may not have this extra benefit. The great part of having the GPS is that you can store your location for future fishing trips if you had a successful time. Well worth the extra few coins, in my opinion.

Are all fish finders waterproof?

No, they are not generally waterproof unless they are of the type used directly in the water. What I am referring to is the ball or tube-shaped type that is cast out. The monitor side will remain with you onboard, obviously. The monitor will not be waterproof but should be able to cope with rain. A cover to protect your investment would, of course, be advisable.

How are fish finders powered?

The fish finders have a lithium battery fitted. Most are rechargeable for ease of use, and they can be trickle fed with a charge whilst in usage. The Garmin referred to earlier has a current draw at 12 volt: 0.23 Ampere.

What are the fish finder brands available?

Some of the popular brands I have found on amazon include the following:

  1. ReelSonar
  2. Garmin
  3. Deeper Start
  4. Eyoyo
  5. Humminbird
  6. Lowrance

More brand names are available, but these are selected from the most popular sellers when writing this article.

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Hopefully, you now have a better idea of fish finder types and how to use one. Though fish finders can vary, their basic principles remain the same – and knowing these principles can make a more successful boat fishing trip. 

I hope this list has been an excellent start for you in getting some ideas. Now, feel free to enjoy catching your favorite fish species of fish the rest of the year.

FTC advertising disclosure:

This post contains affiliate links, which are unmarked ads, and I will earn a commission if you shop through them, but your prices will not be affected.

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