Installing Trim Tabs: Aluminum Boat Upgrade Guide

Installing trim tabs on an aluminium boat can be a challenging task, especially if you don't have access to the inside of the transom. While some people suggest using backing plates, others recommend simply drilling and tapping holes in the transom and using stainless machine screws for a secure fit. It's important to ensure that the tabs are not flush with the bottom of the hull, as this can slow down the boat's top speed. Additionally, it's worth noting that trim tabs can void the warranty on some boats, so it's important to check with the manufacturer before making any modifications.

Choosing the right trim tab size and material

When choosing the right trim tab size and material, there are several factors to consider.

Firstly, the size of the trim tab will depend on the size and type of your boat, its top speed, weight distribution, the type of water navigated, and your specific needs. As a general rule, for every foot of boat length, choose at least one inch of trim tab span on each side. So, for a 22-foot boat, the trim tab system should be at least 24" x 9", while a 36-foot boat would require a 36" x 9" trim tab system. It is also recommended to opt for the widest trim tab span that can fit, as this will create greater lift.

In terms of material, trim tab plates are typically made from cast aluminium, fabricated stainless steel, GRP, or composite materials. When choosing the material, it is important to consider the stresses and strains that the trim tab will endure. For aluminium boats, it is recommended to "insulate" stainless steel trim tabs from the aluminium hull by placing a sheet of thin nylon or other non-conductive material between the mounting plates and the boat to prevent corrosion.

Accessing the inside of the transom

If you don't have access to the inside of the transom, you have a few options. One suggestion is to bond a piece of 1/8 to 1/4-inch aluminium to the hull with an adhesive sealant and self-tapping stainless steel screws. This will provide more support for the screws holding the trim tabs. Another option is to use stainless steel rivet nuts to attach 1/8-inch aluminium plates to the transom, along with an adhesive sealant. This method provides secure anchor points for bolting on the trim tabs.

It is important to note that some boat manufacturers, such as Alumacraft, may void your hull warranty if you install trim tabs. Always check with your dealer and manufacturer before proceeding with any modifications.

Using a backing board

Drill and tap holes in the transom and backing board, then use stainless machine screws of the appropriate size to attach the trim tabs. If you use stainless screws, make sure you have enough of them and that they are the right size to hold the tab. As a rule of thumb, you should have a screw about every two to three inches.

Before installing the screws, drill a pilot hole about 1/3rd the size of the intended screw. Carefully screw it in, being careful not to over-tighten and strip it out. Once you've done this for each screw, remove them, apply a waterproofing compound to the holes and screws, and then put everything back in place for the final installation.

If you are unable to access the inside of the transom, you could consider bonding a piece of 1/8 to 1/4-inch aluminium to the hull with JB weld and then using self-tapping stainless steel screws to attach the trim tabs. However, keep in mind that this method may not be approved by the boat manufacturer and could void your warranty.

Drilling pilot holes

First, you need to decide on the placement of your trim tabs. Measure and mark the spots where you will drill your pilot holes. It is important to ensure that the holes are evenly spaced and lined up correctly. The spacing between each hole should be about two to three inches. Once you have marked the spots, you can begin drilling.

When drilling pilot holes, it is important to use the correct drill bit size. The pilot hole should be about one-third the size of the intended screw. This will ensure that the screw fits snugly and securely. Start by drilling a pilot hole at the first and last marked spots. These pilot holes will help hold the trim tab in place while you drill the rest of the holes. Insert screws into these pilot holes to secure the tab temporarily.

Now, carefully drill the remaining pilot holes. Take your time and ensure that the drill bit is perpendicular to the surface for accurate holes. Once all the pilot holes are drilled, remove the trim tab and set it aside.

Before inserting the screws, it is important to waterproof the holes. Apply a waterproof compound or sealant to each hole and on the back of the trim tab. This will help prevent leaks and ensure a secure installation. Now, coat each screw with the waterproofing compound as well. Insert the screws into the pilot holes, taking care not to over-tighten them and strip the threads. Use a cordless drill with a low clutch setting to tighten the screws gently and gradually increase the torque until they are just tight.

Finally, remove the screws once again and apply a generous amount of waterproofing compound to the holes and screws. Re-insert the screws for the final installation, making sure to fill all the holes and coat the screws completely. This will ensure a watertight seal and secure the trim tab firmly in place.

Waterproofing the trim tab

First, determine the location of the trim tab on the transom, ensuring symmetrical alignment. Mark the mounting holes according to the manufacturer's specifications. It is recommended to use a thin piece of plastic or nylon as a spacer between the trim tab and the mounting bracket to prevent corrosion caused by contact between dissimilar metals. Seal this spacer to the aluminum boat with a waterproof compound to prevent water from getting between the plastic and the boat.

Next, attach the trim tab using the provided brackets and hardware, ensuring they are securely fastened. When drilling the mounting holes, use a pilot hole about one-third the size of the intended screw. Carefully screw it in, being careful not to over-tighten, as this can strip the hole. Remove the screw, apply a waterproof compound or marine-grade caulking to the hole and screw, and then reinstall the screw. Repeat this process for each screw, ensuring that all holes and screws are filled and coated with the waterproofing agent.

After all screws are in place, remove them one by one, apply waterproofing, and then reinstall for a final time. This will ensure that the trim tab is securely attached and properly sealed against water ingress.

Additionally, consider applying a protective coating to the trim tab to prevent corrosion, especially if the boat will be operated in saltwater environments. Regular maintenance, including rinsing the trim tabs with freshwater and inspecting for any damage, will also help extend their lifespan and maintain optimal performance.

Frequently asked questions