How to Choose a Transducer?

A fishfinder transducer is a device which is attached to your fish finder consol; it sends sound waves through the water and receives return echoes which enable it to determine the distance and size of objects under and around your boat – like fish and bottom structure. Some fish finder transducers read boat speed and water temperature too.

Choosing the right type of fish finder transducer is the key to getting the best performance out of your fishfinder and maximizing your fishing experience. With so many variations and factors to take into consideration it can be quite challenging choosing the fish finder transducer that perfectly suits your needs. We have outlined a few points for you to consider before you buy yours.

Ask yourself where you will fish, what type of boat you have, how big it is and how often it will be taken out of the water?

Where do you fish?

The frequency you require will be determined by the type of water you use your fishfinder in:

  • Fresh, clear or muddy water?
  • Shallow or deep water?
  • Salt Water?

What type of boat/hull do you have?

This will determine the installation method and equipment require for the best performance from your fishfinder transducer.

  • Inboard or outboard motor?
  • Large or small vessel?
  • Wood, metal or fiber-glass hull?
  • Positive ground system?

Do you require a portable fish finder transducer option?

  • Will you use your fishfinder on a friend’s boat?
  • Will you use your fishfinder from the shore?

What Type Of Housing Should I Use For My Fishfinder Transducer?

  • Fiber-Glass Hull: a plastic or bronze housing is recommended.
  • Wooden Hull: a bronze housing is recommended. Wood swells and contracts which could damage plastic housing.
  • Metal hull: For larger metal hulls stainless steel housing with a plastic sleeve to prevent electrolytic corrosion is recommended. A plastic housing is recommended for smaller aluminum vessels.
  • A metal housing should not be installed in a vessel with a positive ground system.

Where To Mount Your Fishfinder Transducer?

The general rule of thumb when deciding where to mount your transducer is to choose a location with minimal vessel-generated noise from propellers, shafts and other machinery. The flow of water over the transducer head should be as smooth as possible for the best performance. Your location should have a minimum deadrise angle (the angle of the bottom of the hull in a cross-section view of the boat)

Mounting Method One: Through The Hull (Thru-hull)

This method requires you to cut a hole in your hull and is the most involved method of installing your transducer, however when mounted correctly produces the most effective signal return. We recommend anti-fouling marine paint to reduce marine growth and algae on your sensor which you can get from any marine supply store.

Thru-Hull Transducer
Thru-Hull Transducer

You can flush mount your transducer which produces minimal drag and is recommended for smaller boats, sailing vessels and boats which are often transported on a trailer.
External thru-hull usually requires a fairing block to be installed to ensure your transducer is facing squarely downwards, and this is recommended for larger vessels.

Mounting Method Two: Inside The Hull (In-hull)

This method installs the device inside the bilge of a boat’s hull and sends it’s signal through the hull. This installation method is preferred by some as there is no drilling through the hull, no drag, the transducer is not exposed to marine growth, no risk of damaging the transducer during trailer transportation and the device can be installed while the boat is afloat.

In-Hull Transducer
In-Hull Transducer

These benefits do not come without a price, and that price is power loss. The signal will experience some loss when shooting through the hull material although most modern in-hull transducers are designed to compensate for this loss.

Most in-hull transducers are mounted inside a liquid filled tank – mineral oil or castor oil as these liquids are thick and are less prone to aeration.

Not all hull types are suitable for in-hull installation – wood, cored fiber-glass, aluminum or steel hulls act as a barrier against the acoustic signal. This method is recommended for solid fiber-glass hulls.

Mounting Method Three: Transom Mount

This method mounts the device to the back (transom) of the boat in contact with the surface of the water. This method is probably the quickest, simplest and cheapest, favored by smaller boats that are often transported by trailer. However, turbulence and bubbles from the propeller can cause poor performance if the device is not mounted correctly.

Transom Mount
Transom Mount

Most models come with an impact release feature, which allow the device to pivot up and out of the way when struck by an object. This method is not recommended for inboard motors or boats that regularly exceed 40MPH (35 knots)

It is recommended to mount on the starboard side of single drive boats as this minimizes aeration from propeller action. It should be mounted at least 3″ from the swing radius of the propeller.

Other Mounting Methods

Although the above three methods are the most common ways to mount your transducer there are other options available too. These include a portable option using a heavy duty suction cup which temporarily holds the device in place (at trolling speeds only). A stick on option; using very high bond tape for a super-easy installation. Some fish finder transducers are designed for mounting on a trolling motor.

Fishfinder Transducer Power And Frequency

Generally speaking the depth capability, accuracy and clarity of your sonar unit depends on:

  • The power transmitted – measured in watts
  • The frequency used – measured in kHz – kilohertz
  • The cone angle – measured in degrees
  • The method of installation

Water conditions also affect the clarity and depth capacity; all sonar’s will show deeper depth readings in clear fresh water than in salty or muddy water.

The strength with which the fishfinder transducer sends the signal is referred to as the power and is measured in watts. The higher the power the better your chances of getting a good return echo in deep water or poor water conditions. It also allows for better detail and structure definition.

The accuracy with which your fishfinder transducer detects bottom structure and fish targets is also determined by the frequency selected for the depth you are viewing.

Higher frequencies give you greater detail when detecting small objects over a small portion of water. Generally 200 kHz works better for views under 200 feet/60 meters. High frequencies typically show fewer undesired echo returns while showing better target definition.

For deeper water, a lower frequency is preferred. The beam is wider with a lower frequency and suited for viewing larger areas under your boat, however this also means less target definition. Although lower frequencies can see deeper, the picture may not be as clear and detailed as with the higher frequencies.

Many of the modern fish finder transducers have dual frequency capacities and allow you to view both the high and low frequency side-by-side on a split screen for both perspectives.

You should always match the fishfinder transducer frequency to the sonar unit being used.

Fishfinder Transducer Cone Angle

The transducer concentrates the transmitted sound into a beam which widens as it travels deeper, the cone angle of the beam determines the coverage area and detail of the underwater world.

Cone angles are generally narrower at high frequencies and wider at low frequencies.

Wide cone angles (lower frequencies) offer a larger view and detect fish around the boat and not just directly under it, yet they sacrifice resolution and exhibit less target separation.

A narrow cone (higher frequencies) concentrates its power into a smaller viewable area allowing for greater detail and exhibit greater target separation.

Therefore a dual frequency fishfinder transducer is a great option for deep water fishing; it allows you to view the general area over a large volume using a low frequency wide beam. For greater accuracy and clarity you can use the high frequency, narrow beam.

For shallow clear water fishing a single narrow, high frequency beam would be sufficient.

Previous ArticleNext Article