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How to Mount a Transducer on a Fiberglass Boat Properly

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how to mount a transducer on a fiberglass boat

Properly positioned transducers can map every object under your boat, taking your boating and fishing game to the next level. Installing a transducer on a fiberglass boat is not an easy task. In this article, we will provide a detailed guide on how to mount a transducer on a fiberglass boat, including all types: in-hull, thru-hull, and transom mount.

In-hull and transom mount transducers can be installed without drilling holes on the boat’s hull. However, thru-hull transducer installation requires more complex and technical steps. In short, the general steps are:

Table of Contents

What You Will Need


1. Transducer

There are three basic types of transducers: in-hull, thru-hull, and transom mount. Each type has different functions and installation procedures.

  • Transom mount: This transducer style is easy to install, simple to use, and inexpensive to maintain. They can be used for both outboard and I/O-powered vessels of multiple materials, including fiberglass. However, transom mount transducers are relatively small and limited in power, normally around 600W. They are commonly used for smaller fiberglass Jon boats.
  • In-hull: As the name implies, these transducers are mounted inside the hull. When in use, they shoot the signal through the boat’s bottom. Since in-hulls don’t immerse in water, they are usually more durable and easy to attach or detach. The downside is signals can be blocked by the boat’s bottom, causing misinformation. In addition, they can only be installed on vessels with a solid fiberglass bottom.
  • Thru-hull: A thru-hull offers outstanding performance in tracking undersea objects. They can provide amazingly clear signals with small target separation. This style is often for larger fishing vessels and professional offshore use. There are many different materials for through-hull transducers. To prevent corrosion caused by dissimilar metals, you should purchase in-hulls with bronze housings for a fiberglass boat.

2. Mounting tools

No matter what transducer you choose, you need a bevel gauge to measure the boat’s deadrise angle. Other than that, gather the following tools for each type.

  • Transom mount transducers

Get a Stern Saver glue-on transducer mounting system. Basically, it’s a board that can be adhered strongly to the boat. The kit comes with everything you need: one board, adhesive, mounting spike, template, sandpaper, alcohol pads, and rubber gloves. Also, prepare a hand drill to make holes on the board to attach the transducer.

  • In-hull transducers

You need to test an in-hull before installing, and prepare a sealable and thin plastic bag. You will fill it with water to perform the test.

For installation, the required tools are sandpaper, alcohol pads (or isopropyl alcohol and a few pieces of cloth), marine adhesive, cable ties, propylene glycol, and petroleum jelly.

  • Through hull transducers

Through hull transducer mounting requires more professional skills and techniques. You will need to work with hole saws and electric drills. Each transducer model has different pilot holes, you should prepare drill bits accordingly. If you intend to install a thru-hull with a fairing block, you will need a band saw or table saw to cut it.

Other than that, the necessary tools are similar to those of an in-hull installation: sandpaper, alcohol, marine sealant, and cable ties.

3. Boat layout

A crucial part of transducer mounting is determining the accurate location. A high-quality transducer won’t function well if placed incorrectly. Hence, grab your watercraft’s structural design. Additionally, you need the electrical system layout to know where to avoid when drilling.

4. Safety gear

Last but not least, prepare goggles and a mask to protect yourself from flying splinters.

Steps to Install a Transducer on a Fiberglass Boat


Step 1: Determine the transducer position

Each transducer type has different position requirements.

  • Transom mount transducer: The rule is to mount it to the starboard side (the right side of the boat when you stand facing the bow). There is less turbulence caused by the propellers on this side. You want to find a location that is as far away from the engine lower unit as possible while still allowing the transducer to be immersed in water at all times.
  • In-hull transducer: The location of an in-hull transducer depends on the type of hull and propulsion. For inboard planing hulls, you can place the transducer ahead of the engine and prop shafts. For displacement hulls, the position should be on the vessel forward. However, on outboards and sterndrives, the device should be located on the aft. Most importantly, the in-hull must be as close to the centerline as possible.
  • Once you’ve got a location, test the transducer. Connect the device to the fish finder, hang it overboard and take note of the result. At the same site, fill the plastic bag partially with water, place the device inside, then tighten the bag. After that, press the transducer against the hull. The reading should be similar to the previous result. If not, you need to find another location.
  • Through hull transducer: This type of transducer is for larger ships with multiple structural designs, so we can’t provide specific position guidelines. In general, choose a location that is away from interference and turbulence caused by machinery or radiation sources. The device must be continuously under the water. Do not mount it where it might be damaged while trailering, hauling, or launching.

Step 2: Measure the deadrise angle

Use a bevel gauge to measure the deadrise angle of the selected position. You will need to mount the transducer in correspondent to this angle to assure its best performance.

Step 3: Mount the device

  • Transom mount: Once you find the right spot, start by sanding down the area. Then, adhere the board that comes in the Stern Saver kit onto the boat, following the product’s instructions. After 12 hours, the board is set. You will need to drill holes in the board to mount the transducer. Make sure the transducer is angled properly.
  • In-hull: First, sand down the area and wipe off the excess with alcohol pads to mount an in-hull. Then, place the device, and seal it in place with marine adhesive. Finally, pour propylene glycol into the housing and lubricate the O-ring with petroleum jelly.
  • Thru-hull: The procedure to mount a thru-hull is more complex. First, cut a hole that fits the device from outside the hull with a hole saw and drill. If you choose to use a fairing block, cut the fairing following the deadrise angle using a bandsaw or table saw. Wipe off the excess, then fit and secure the transducer with marine sealant.

Step 4: Set the cable

The last step is to set the cable under the boat’s floor and connect them to the fish finder terminals. Secure the wirings with cable ties if needed.


Installing a fishfinder on your fiberglass boat doesn’t always require a professional. With proper products and techniques, boat owners can do it themselves. But always remember to put your safety first, especially when working with hole saws and electric drills.

Hope you like this article on how to mount a transducer on a fiberglass boat. If you have installed a transducer before, please share your knowledge and experience in the comment section. Learning from a fellow boat owner is always exciting. We look forward to hearing from you!

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