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  • Post last modified:September 3, 2022
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Fish finders are pretty much a must-have on a fishing boat these days.

They let you see what’s underneath your boat, the structure, your bait, and the fish.

A fish finder needs a transducer to work.

What Is a Transducer and How Does It Work?

Transducers are electronic devices converting electrical energy into sound waves. These sound waves are reflected by an underwater object and return to the transducer, which sends them to the fish finder for processing.

A transducer allows the fish finder to generate live images of the bottom, underwater objects and the fish.

Built-in Transducers

Many expensive trolling motors today have a sonar fully integrated with the lower unit. The wiring runs through the shaft, and the connectors are shielded to minimize interference.

But what if your trolling motor doesn’t have a built-in sonar?

Well, you’ll need to find a place to mount your transducer somewhere on the boat or on the trolling motor itself.

Why Mount a Transducer On a Trolling Motor?

There are several pros and cons of this solution:

Advantages

  • Easy to install
  • Images from the bow of your boat, rather than behind
  • When in anchor mode, you can easily point your transducer in any direction

Disadvantages

  • Extra cable to deal with. It can easily tangle if you don’t fix it properly
  • You can only use it when the trolling motor is in the water
  • You can hit underwater objects with it

Choose the Right Transducer for Your Motor

The first thing to do is to find a compatible transducer that will work with your fish finder.

Next, you’ll need to decide where to mount it.

Can you put a transom mount transducer on a trolling motor?

Absolutely, but you’ll need a bracket to keep it in place.

Transom-mount transducers are designed to be installed on flat surfaces.

Some metal brackets are easy to bend into the round shape of the trolling motor. You will need a hose clamp to fix the bracket to your motor’s lower unit.

A better option is to get a transducer mounting kit. This will ensure your transducer is firmly attached to the motor’s lower unit.

Pick the Right Mounting Bracket

For most trolling motors and popular fish finders, you will find a suitable mounting kit.

This can remove the guesswork: will it fit?

For example, this one:

Mounting a Transducer Step-by-Step Process

1. Choose the mounting position

The transducer mounts under the trolling motor, usually between the motor’s skeg and the prop.

Placing the transducer after the motor’s skeg will protect it in case of impact.

If you mount it in front of the skeg, you should allow the transducer to pivot to the back in case of impact. The transducer should clear the prop in this position to prevent damage.

You should not overtighten the bolts, as this can break the mount when hitting an object.

2. Mount the transducer to the motor

You can use a stainless steel hose clamp or a nylon cable tie.

Cable ties can slip in case of impact protecting the transducer.

If you use a metal hose clamp, make sure the end doesn’t stick out. Clip off the remaining part, otherwise, it can attract weeds.

3. Check the trolling motor in stow position

Make sure the transducer mount doesn’t touch the trolling motor mount.

The motor should be resting on it without the mount rubbing against its mount.

4. Route the cable up the motor shaft

It’s best done with zip ties. Make sure the cable is tightly attached to the shaft.

Pay special attention to where the lower part of the shaft meets the outer tube.

You need to allow extra cable there before fixing it. This lets the motor freely turn left and right when you steer it.

You also need to leave enough slack for depth adjustment and deployment.

The cable should not prevent the motor from moving up and down.

This is especially important if you have an electric-steer motor, such as the Terrova.

These motors move left and right, up and down on their own. Any zip tie in the middle of the shaft can prevent them from doing so.

In this case, you can only fix the cable at the very bottom of the shaft and close to the motor head. This will allow it to move freely, although you need to allow a sufficient amount of cable.

Does it matter which way a transducer faces?

Most down imaging transducers should be facing downward, without any tilting. This will give you the most accurate sonar readings.

If you have a forward-looking sonar, it will need to face toward the front. That usually means attaching the transducer to the shaft rather than the lower unit.

Reducing Interference

Trolling motors are a source of electromagnetic interference.

Interference can affect the transducer, especially as the motors are getting more powerful and packed with electronics.

Sometimes you can dramatically reduce the interference by properly grounding your system.

In other cases, you will need to find the possible sources of interference and eliminate them one by one.

Alternatives

Transducers can also be mounted thru-hull or on your transom.

They can also be removable.

Thru hull transducers are the most difficult to install, and involve making a large hole in your boat. For this reason, most people choose them for depth sounders rather than fishing.

Mounting Transducers on the Transom

As we’ve illustrated above, you can attach a transom-mount transducer to your trolling motor.

What about using it directly on the transom it was designed for?

Pros

  • You can use your fish finder when the trolling motor is stowed
  • Easier to install and manage cables
  • Work great if you fish from the stern

Cons

  • You need to drill a hole in your transom (although there are some screwless transducers available)
  • Not great if you fish from the bow

Portable Transducer Brackets

Another option is to use a removable transducer bracket.

There are extremely easy to install; all you need is to clamp the on to your transom.