Mounting Transducers: Aluminum Boat Bow Installation Guide

Mounting a transducer on an aluminium boat can be a complex task, but with the right tools and careful execution, it can be done successfully. Transom-mount transducers are a popular choice for boaters due to their user-friendly installation and removal. When mounting a transducer, it is important to consider the type of boat, size, hull material, and intended use. Aluminium boats, in particular, require extra care to seal any drill holes properly to prevent corrosion. In this guide, we will cover the step-by-step process of mounting a transducer in the bow of an aluminium boat, including choosing the right location, tools, and installation techniques. We will also discuss troubleshooting tips and best practices to ensure optimal performance and accuracy of the transducer.

Use a mounting plate to minimise drilling into the transom

Using a mounting plate is a great way to minimise drilling into the transom when installing a transducer on an aluminium boat. This method is especially useful if you have multiple transducers to mount, as it can be a nerve-wracking process.

A mounting plate is a small, inexpensive piece of polyethylene plastic or a similar durable, synthetic material. It allows you to fasten your transducer to the hull without having to drill multiple holes. All you need to do is attach the plate to the hull with two small screws and a little marine silicone adhesive. This adhesive helps seal the holes and keep the plate in place.

Using a mounting plate gives you the freedom to adjust or move your transducers without putting more holes in your transom. This is particularly useful if you need to fine-tune the placement of your transducer to get the best performance. With a mounting plate, you can make these adjustments without causing any damage to your hull.

When installing a mounting plate, it's important to take extra care when drilling the holes for the screws. Measure the length of your screws minus the thickness of your mounting bracket, and mark the necessary depth on your drill bit with a wrap of painter's tape. This will help you avoid drilling too deeply into the hull.

Additionally, when tightening the screws, it's best to do so by hand rather than using an electric drill or driver. This will help you avoid stripping the screws, especially when tightening self-tapping screws into fiberglass below the waterline.

By following these steps and using a mounting plate, you can minimise drilling into the transom of your aluminium boat while still securely installing your transducer.

Avoid drilling too deep by measuring screw length and marking drill bit

When mounting a transducer on an aluminium boat, it is important to avoid drilling too deep into the hull. Drilling too deep can cause damage and create potential sealing issues, which can lead to corrosion problems. To prevent this, it is crucial to measure the length of the screws you will be using and mark the drill bit accordingly.

Measure Screw Length:

Before you start drilling, carefully measure the length of the screws you will be using to secure the transducer. You want to ensure that the screws are long enough to hold the transducer securely in place but not so long that they penetrate too deeply into the hull.

Mark Drill Bit:

Use a piece of painter's tape or a marker to indicate the desired depth on your drill bit. Wrap the tape around the drill bit at the measured screw length minus the thickness of the mounting bracket. This marking will serve as a guide to ensure you don't drill deeper than necessary.

Choose the Right Drill Bit Size:

Select a drill bit that is slightly smaller than the diameter of your mounting screws. This will create a tight fit for the screws and help ensure a secure installation. A snug fit also helps to avoid enlarging the holes and reduces the risk of water seepage.

Gather the Right Tools:

It is important to use a manual screwdriver or wrench to tighten the screws by hand. Avoid using electric drivers or power tools for tightening self-tapping screws into the aluminium hull. This will help prevent stripping of the screws and provide better control over the tightening process.

Seal the Holes:

After drilling the holes, apply a quality marine sealant to the screws and fill the pilot holes. This step is crucial, especially for holes below the waterline, to prevent water seepage and potential corrosion. Recommended sealants include lower-strength polyurethanes like Sikaflex 295 UV and 3M 4200, or synthetic rubber formulations like Sudbury Elastomeric Marine Sealant.

Test and Adjust:

Once the transducer is mounted, test its performance in shallow water before venturing into deeper areas. If you notice any issues with the readings, you can make fine adjustments to the transducer's position by loosening the bracket screws and moving the transducer slightly. Remember to re-tighten the screws securely after each adjustment.

By carefully measuring screw lengths, marking your drill bit, and following these steps, you can effectively avoid drilling too deep when mounting a transducer in the bow of your aluminium boat.

Avoid electric drivers when tightening screws

When mounting a transducer on an aluminium boat, it is important to avoid using electric drivers when tightening screws. This is because self-tapping screws can easily strip when too much force is applied. To avoid this, screws should be tightened by hand. This is especially important when working with fiberglass below the waterline, as gelcoat cracking can occur, which can lead to water penetration between the gel and the fiberglass.

To prevent gelcoat cracking, it is recommended to run your drill in reverse once the bit reaches the fiberglass. This will help to create a smooth, chamfered edge around the hole. After drilling, a countersink tool can be used to carefully refine the edges and create a neat finish.

The use of a quality marine sealant is also important to prevent water ingress. Sealants such as 3M 5200, Sikaflex 295 UV, 3M 4200, and Sudbury Elastomeric Marine Sealant are commonly recommended for this purpose. It is also worth considering bedding the entire transducer bracket in sealant to prevent crevice corrosion.

When working with aluminium boats, it is crucial to remember that transducers require a clear path for the sonar signal through the water. In-hull transducers are generally not recommended for aluminium boats due to signal interference with the metal hull. Therefore, a transom-mounted transducer is often the best choice, providing a direct and unobstructed path for the sonar signal.

Seal installation by coating screws and filling holes with marine sealant

When mounting a transducer on an aluminium boat, it's important to seal any drill holes properly to prevent corrosion. Here are detailed instructions on how to seal the screws and fill the holes with marine sealant:

Tools and Materials:

• Marine sealant (such as 3M 4000 UV, 3M 5200, or Boatlife Life Seal)
• Screws
• Drill
• Drill bits
• Screwdriver
• Wrench
• Tape
• Level
• Marker
• Epoxy or adhesive (optional)

Steps:

• Gather your tools and materials.
• Confirm the location of the transducer, ensuring it is away from any obstructions, in a spot with minimal turbulence, and not in the path of the propeller.
• Place the transducer and bracket temporarily and mark the screw positions, ensuring level alignment.
• Drill holes at the marked spots using a drill bit slightly smaller than the mounting screws for a tight fit.
• Apply marine sealant to the screws, coating them generously.
• Insert the screws into the holes and tighten them with a screwdriver or wrench.
• Apply a bead of marine sealant around each screw head to fill the holes and create a watertight seal.
• Use your finger or a small tool to smooth out the sealant and remove any excess.
• Allow the sealant to cure according to the manufacturer's instructions.
• Re-tighten the screws if needed.
• Route the transducer cable to the fish finder display inside the boat, avoiding pinch points, and secure it with clamps or ties.
• Test the transducer setup in shallow water before going out deeper to ensure it is working correctly.

Note: Always wear safety glasses while drilling and follow tool safety guidelines.

Level the transducer with the transom waterline

To level the transducer with the transom waterline, you must ensure it is parallel to the waterline when the boat is in the water. This is crucial for accurate and uninterrupted readings.

On V-bottom boats, it can be tricky to get the transducer level with the waterline when viewed from the back. This is because they rarely sit level on trailers. You can use a horizontal line on your transom (e.g. the bottom edge of a jackplate) and a framing square to adjust the side-to-side level of the transducer.

If your transom has a straight, horizontal line across it, such as a bottom paint line, a boot stripe, or an aluminium transom cap, you can use this to your advantage. Use this line and a framing square or similar tool to mark a vertical line, then line up your transducer bracket with this line. If there is no obvious horizontal mark, you can use a string to mark a line across the transom from one chine to the other.

It is also important to ensure the transducer is parallel to the bottom of your hull. This ensures consistent water flow over the transducer's face and avoids air bubbles. You can achieve this by aligning a straight edge with the hull bottom and matching the angle of the transducer.

Frequently asked questions