Fish Finder Transducers 101: Choosing The Right Transducer (2024 Guide)

Featured Image - fish finder transducer
Fish finder transducer

There comes a point in the life of all anglers when owning a fishfinder is necessary, particularly for boaters in saltwater and fresh water who need to find fish in such huge areas. But, buying the right fishfinder isn’t easy as they are quite complicated bits of electronics. 

When I started fishing some 20 years ago, I never quite understood the relationship between a fishfinder and a transducer and how important the transducer was to finding fish.

A few years in I realized that the transducer was the key to finding fish, the world of fish finders became so much clearer and I could pick the exact one I needed without much research. 

Join me as I run through everything you need to know about fish finder transducers so you can buy the right one on your first go. 

What is a transducer on a fish finder?

A fishfinder comes in 2 parts, a display and a transducer that are connected to each other via cables or over Wifi, depending on the model of fishfinder you buy or own. 

Garmin FishFinder And Transducer

A transducer is the part that looks for fish underwater. It then sends what it finds to the fishfinder monitor, which will process the information and give you high resolution images of what is under your boat. 

What does a transducer do on a fish finder? 

The transducer is responsible for scanning the underwater world with a beam of waves to pick up all the detail of what is under your boat. It’ll work out the water depths, the bottom features, detect fish targets, and other objects like drop offs or fallen trees for you to see on the monitor

How important is the transducer for a fish finder to work? 

The transducer is incredibly important for a fishfinder to work. If your transducer doesn’t work, nothing is scanning under the water and you’ll be staring at a fishfinder with a blank screen seeing no images whatsoever. 


If your transducer is broken your fishfinder is broken, one can’t work without the other. It would be like having a camera with no lens. 

How does a fish finder transducer work?

A fishfinder transducer works by scanning under the water with a beam of sonar waves. The device converts electrical pulses into acoustic energy or sonar waves and transmits these waves into the water hitting any objects that it comes into contact with. This might be fish, the bottom, structure like fallen trees, drop offs, and debris like seaweed. 

When the beams of sonar waves hit these objects, they bounce back and return to the transducer, which allows it to create an image of what is down there, kind of like echolocation, which you end up seeing on the monitor/display. 

Lowrance Sonar Diagram
Lowrance Sonar Diagram

The beam of sonar waves can range from high frequencies to lower frequency waves. Lower frequencies penetrate into deeper water using a narrow beam angle. With a narrow beam, you’re hitting greater depths but picking up less detail. While higher frequencies don’t go to such a depth, they pick up more detail using a wide beam, and when used together like in dual frequency transducers, they create an image with a lot of detail. 


Not all fish finder transducers are capable of dual frequency though, for example, CHIRP sonar transducers send out multiple frequencies, lower and higher frequencies simultaneously. 

What is inside a fish finder transducer? 

A fishfinder transducer is filled with various electronics that aren’t worth going into as it requires an engineering degree to understand how they all interact. 

The main component in the device that gives it the ability to convert an electrical current into sonar waves and reflected sonar waves into an electric current, is the piezoceramic element, without which, a transducer will not function. 

The piezoceramic element can be in the form of a disc, or multiple discs that form an array, depending on the power of a transducer.

How fragile is the transducer on a fish finder?

They can be quite fragile. For example if you drop your transducer on the dock when mounting it, the piezoceramic element might break and if this happens, it won’t work. The same goes if it hits a coconut when you’re driving your vessel around. 

Will any transducer work with any fish finder?

No, you will need to use a transducer that matches the capabilities of the display unit. If the fish finder transducers and display are capable of different power and frequencies, then one can’t talk to the other. 

FishFinder On A Boat

This means your display isn’t going to understand the signal the transducers send it and the display won’t be able to build an image for your screen. 

How to determine what transducer is needed for a fish finder? 

Every fishfinder display or screen device will come with a manual. Within that manual, you’ll find a description of the compatible power transducers that will work with the display. 


You shouldn’t find yourself in this position though as most fish finders come with transducers, so you shouldn’t have to buy one separately. 

What transducer fits a wide eye fish finder? 

Wide eye fishfinders are made by Humminbird and you can find any type of transducer to fit the display unit but it has to match the fish finder’s power rating. But, power ratings vary depending on the wide eye display, so you’ll need to look at the manual to work this out. 

Understanding the different types of fish finder transducers

There are quite a few different types of fish finder transducers out there, some have more power and some have just enough, and to know which one is right for your vessel, you’ll need to know about all the options and here they are. 

What is a transom transducer? 

Transom mount transducers are transducers that are installed on the transom of your boat. They come with transom mounts that you screw into the transom and attach the units to, from which you have the ability to adjust the angle of the beam


These are the most common type of transducers out there and can be mounted to any hull material. 

What is a 4-pin transducer?

4-pin transducers are transducers that have a 4-pin port for connecting the transducer to the screen cable. You can get converters that change the cable from 4 to 6 or 8 pin, so no matter what you can always match different pin displays to different pin transducers. 

What is a us2 transducer? 

US2 (Universal Sonar 2) transducers are trolling motor transducers that are built into the lower unit of a trolling motor. The transducers are fully protected and all the wiring runs inside the indestructible composite shaft, making it neat and tidy, ideal for anglers fishing in shallow water. 

What is an HDI transducer on a fish finder? 

Hybrid Dual Imaging (HDI) transducers are made by Lowrance and feature both Lowrance Broadband Sounder PLUS Exclusive DownScan Imaging in one of their units. 

Lowrance HDI Transducer

Together, they give you amazing detail, wide-coverage, and great target separation by using multiple frequencies. This kind of unit makes fishing easy for anglers. 

What is a through-hull transducer?

Thru-hull transducers are transducers that you mount in through the hull of boats. They come in a housing that is then put through the hull and mounted flush or semi-flush to the hull. Through-hull transducers must be positioned in front of the propeller, rudder, keel or anything else that may create turbulence.

These are the hardest types to install in boats and would require a fairing block which allows the transducer to be mounted properly, but they give more detail than others. 

What is an in-hull transducer? 

In-hull transducers that you mount in the hull of a fiberglass boat which then shoot their sonar sound waves through the fiberglass hull. This removes the need to drill holes through the hull and you can install the units without taking boats out of the water and there will be nothing poking out the hull either. 


In-hull transducers don’t work on boats with aluminum hulls, steel hulls, or in foam sandwich/hulls that have air pockets, as the sonar doesn’t go through hulls like this.

What is a tilted element transducer? 

Tilted element transducers are a type of thru-hull transducer that is tilted to accommodate the deadrise of the boat, to ensure the beam goes straight down, less interference and gives you accurate sonar readings. 

This all gives the units the ability to give excellent depth readings at a high speed of up to 30 knots

How does a fish finder side scan transducer work? 

Side-scan transducers work by sending out high frequencies of sonar beams to the port and starboard side of boats. Instead of scanning down like normal transducers, these transducers are scanning to the side to find fish targets for anglers sitting in shallow water near the surface. 

What power does a fish finder transducer connect to?

Transducers get their electrical power from the displays they are connected to. The displays are connected to a house battery on the vessel and transfer this power from the battery to the transducers. 

If you are using a portable fishfinder, the power will be in the form of a rechargeable battery within the housing. 

How to install/mount a fish finder transducer

Transducer Using A Sternsaver Glue on Mount

Tilted Element & Thru-hull

Mounting tilted element and thru-hull transducers require you to first remove the boat from the water after which you will need to: 

  • Drill a hole in the boat for the mounting location to fit the unit 
  • You must make sure the hole is in the right mounting location of the boat where the transducer is fully submerged at all times in the water and is away from bubbles – usually aft of the bow
  • Once the unit is in place, make sure it’s lined up straight for accurate readings and a good beam angle. 
  • Then seal it with a sealant to make it waterproof. 

This is a very big picture method, as it’s far more complicated than this, here are the full details

Transom Mount

Transom mount transducers are one of the easiest to install as they go on the outside of the boat on the transom. Here is how you do it. 

  • When installing a transom-mount transducer, make sure it is mounted in an area of the transom with the least amount of disturbed water or turbulence to avoid interference.
  • Take the mounting bracket and place it on the starboard side of your transom at least 15 in. (38 cm) away from the propeller blades, and mark 4 holes below the waterline to match the transom mount bracket. 
  • Drill 4 holes in the marked areas and then screw in your mounting bracket to the transom.
  • Seal the holes with sealant
  • Attach the transducer to the mounting bracket
  • Connect the cables from the transducer to the monitor 
  • Adjust the angle of the transducer to be parallel with the waterline
  • Test and re-adjust as necessary 


These are ideal for use on small center console fiberglass boats with inboard-outboard, outboard and jet drive propulsion systems as they don’t take up much room. They are also perfect for pontoon boats as the transom is submerged on those vessels unlike the majority of the hull. 


Mounting an in-hull transducer is not easy, requires quite a lot of skills and you might need a fairing block.


If you’re a saltwater angler who is new to boat electronics you should get a pro to do it for you.

Here is a full description of how to do it. 

  • Pick an area inside the hull to install it, away from any water intakes and heat sources like inboard engines
  • Place the transducer in the water outside the boat and turn the fishfinder on to get a baseline reading
  • Take the transducer and place it in a bag full of water which is sealed
  • Place it on the hull where you intend to install it and turn on the fish finder
  • Make sure you’re not in shallow water, 25 ft and above is needed
  • Test the readings against your baseline
  • If it’s good, you have a good place to install it
  • Work out the deadrise of the hull (the angle of the V) 
  • Adjust the transducer mount to match the deadrise angle
  • Install the housing to the hull 
  • Pour 14 ounces of propylene glycol (non-toxic antifreeze) into the housing 
  • Add the transducer and match the deadrise angle 
  • Seal and plug in the cables

And here is a short video demonstrating how to install an in-hull transducer.

In-hull Transducer Installation

Trolling Motor

Trolling motor units are the easiest to install and here is how you do it. 

  • Take a stainless steel hose clamp and strap the unit to the opposite side of the trolling motor to the propellor
  • Make sure it’s parallel to the water 
  • Run the cables to the screen 
  • Secure the cables to the trolling motor shaft with cable ties 


This is the kind of transducer you would mount to a kayak, either on a trolling motor for the kayak or on a pole you lower down. 

Should the transducer be submerged?

Yes, every transducer has to be submerged or it won’t work as the beam can not travel through the air and be reflected back. Even in-hull units are submerged in liquid in their housing. 

How deep should a fish finder transducer be?

It just needs to be constantly submerged, there is no specific depth it needs to be at for its beam to function properly. In general, they are usually mounted between 0.5-1 ft under the water.

Which way to point the fish finder transducer?

Downscan or CHIRP sonar transducers should be pointed straight down as you want the beam to go down to the bottom to show you what’s under your boat while you’re fishing. 


Side and forward scan units usually also point down but the beam is fired out in a different direction, but you should check the manual if you have one of these as they differ. 

Why mount a fish finder transducer on the rear and not the front of a boat?

As I have already mentioned, for a transducer to send out its CHIRP sonar waves, it needs to be submerged. When a boat is bouncing around in waves, the front of it rises and comes out of the water, which, if the transducer was installed at the front, would cause it to leave the water also. 

When installed at the back, no matter what the waves are doing, the rear of the boat will always stay in the water, allowing the CHIRP sonar waves to always give you depth, bottom structure, and fish readings while you are fishing.

If you’re getting incorrect readings after installation, check out this guide on how to tell if a transducer is bad.


How do I fix the plastic transducer mount for my fish finder?

You can’t always fix a plastic mount as it depends on how badly damaged it is. If it’s not too badly damaged you can glue on some plastic parts to support whatever was broken before and then add the unit to it. 

What kind of sealant to use on a fish finder transducer? 

HA6 Marine Silicone Sealant
HA6 Marine Silicone Sealant

A good, marine-grade, silicone sealant such as Sika or HA6 is the best to use for installations. It will hold its seal well and stop any water from coming through. 

How to shorten the cable for a fish finder transducer? 

The best way to shorten the fishfinder cable is to coil the wire up and fasten it with cable ties. If you cut the wire and splice it, you’ll have broken and waterproof sealed cable and your warranty will be voided. 

How do I clean a fish finder transducer?

To clean a transducer, just rub it gently with a soft cloth and some dishwashing detergent. If the fouling is bad, gently scrub it with a green Scotch Brite pad being careful not to scratch the face of the unit. 

How do I read 2 transducers on one fishfinder?

You’ll need to first cable up the transducers to the head unit properly. Once this is done, you can go into the settings on your unit and select which transducer you want to see whether is your CHIRP or side imaging but you need a display unit that can handle this. 

When shooting thru-hull into the air, what should the transducer reading be on the fish finder? 

If shooting a thru-hull into the air you should have zero reading on the fishfinder as the transducer only works when submerged in the water. 

Sounding Out 

Thanks for reading my article, I hope you enjoyed it and now have a better understanding of transducers and how to ensure they assist with your fishing success. They are quite complex to install but once mounted, should work and show you the structure. 

If you found the article useful, please share it with your friends, and if you’re ready to buy a fishfinder with the best performance, check out my best fishfinder article for some top suggestions. 

On the other hand, f you’re more interested in an accessory that imrpoves your culinary experience on the sea, check this article.

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