Transom Talk: Choosing The Right Board For Aluminum Boats

Aluminium boats often use plywood to provide rigidity to the transom. However, the plywood is susceptible to rotting. To prevent this, boat owners can treat the wood with sealants such as epoxy resin, spar varnish, or Thompson's water seal. Some opt for solid wood such as white oak, mahogany, or teak, which are more resistant to rotting but can be pricey. Others choose to forgo wood altogether, instead using fibreglass resin, or aluminium.

Marine-grade plywood

• Strength: The plywood's multiple layers, or plies, are made from strong woods like Douglas fir, bonded together with waterproof glue. The higher the ply count for a given thickness, the stronger the material.
• Resistance to warping and cupping: The extra plies in marine-grade plywood contribute to its overall strength and stiffness, making it less prone to warping or cupping over time.
• Durability: Marine-grade plywood is designed to withstand water damage. It is constructed from rot-resistant wood, often with more layers than regular plywood, and a waterproof adhesive. This makes it ideal for boats, as water can find its way into most areas of a vessel.
• Longevity: The combination of strong, rot-resistant wood and waterproof glue means that marine-grade plywood can last for decades if properly sealed and installed.

When using marine-grade plywood for a boat transom, it is important to seal it with epoxy and fill any holes with thickened epoxy to prevent water intrusion. Additionally, applying a thin layer of fibreglass cloth over the plywood can further enhance its durability. While marine-grade plywood may be more expensive than other options, its superior qualities make it a worthwhile investment for boatbuilding and repair.

Epoxy resin

When it comes to repairing or replacing the transom board of an aluminium boat, there are a few options to consider. Firstly, it is important to note that the wood used should not be pressure-treated as the chemicals used in the treatment process can react negatively with aluminium. Instead, exterior-rated plywood, such as BCX, or natural woods like white oak, mahogany, or marine ply are recommended. These woods provide strength and rigidity to the transom and can be sealed and protected using epoxy resin.

There are different types of epoxy resin available, including casting resins, coating resins, and adhesives. For boat transoms, a marine-grade epoxy resin is recommended. This type of resin is designed to withstand the challenges of marine environments, including exposure to salt, water, sand, sunlight, oil, and other chemicals. Marine-grade epoxy resin can be used for structural components, repairs, waterproofing, and sealing. It is important to follow the manufacturer's instructions for mixing and application to ensure optimal results.

When working with epoxy resin, it is crucial to consider temperature and humidity as they can significantly impact the working time, cure time, and the final characteristics of the cured resin. Warmer temperatures accelerate curing, while colder temperatures slow it down. Additionally, high humidity levels can cause the finish to cure cloudy. Therefore, monitoring and controlling temperature and humidity during the application and curing process are essential for achieving the desired results.

Spar urethane

When it comes to the type of board used for an aluminium boat transom, exterior-rated plywood such as BCX is often recommended. Some boat owners also use white oak, mahogany, or marine plywood, sealing it with epoxy or spar urethane.

For unfinished wood, it is recommended to apply a sufficient amount of spar urethane to seal open joints, edges, and end grains. After the first coat, the surface should be lightly sanded to ensure even finish and proper adhesion for additional coats. A second coat is then applied, and a third coat is recommended for exterior surfaces or previously unfinished wood. After the final coat, it is important to allow adequate curing time before normal use.

White oak

However, white oak can be difficult to source in the right size and type. For instance, white oak plywood is not commonly available. When using white oak, it is important to seal the wood properly to prevent water damage and ensure longevity. This can be done with a penetrating epoxy sealer, spar varnish, or polyurethane.

When replacing a transom board, it is important to consider the thickness of the wood, as well as the type of sealant or glue used. It is also crucial to avoid using pressure-treated wood, as the chemicals used in the treatment can corrode aluminium, leading to perforations in the transom.

In addition to white oak, some boat owners opt for exterior-grade plywood, such as ABX, Arauco, or BCX, which is sealed and coated with epoxy resin or spar varnish. Others choose to use composite materials, such as Coosa board or aluminium, which do not require sealing and are more resistant to water damage.

Overall, white oak is a suitable option for boat transoms, but proper sealing and installation techniques are crucial to ensure the longevity of the wood and the integrity of the aluminium boat.

Solid fibreglass

To replace the transom on an aluminium boat with solid fibreglass, you will need to follow these general steps:

• Remove the old transom: This may involve cutting or prying out the old transom, depending on how it is attached to the boat. Be careful not to damage the surrounding areas of the boat.
• Prepare the surface: Clean and sand the area where the new transom will be installed. This will help ensure a strong bond between the fibreglass and the boat.
• Cut the fibreglass: Measure the area where the transom will go and cut the fibreglass to size. It is important to be accurate in your measurements to ensure a proper fit.
• Apply resin: Use a suitable resin, such as epoxy or polyester resin, to bond the fibreglass to the boat. Follow the manufacturer's instructions for mixing and application.
• Lay up the fibreglass: Place the cut fibreglass into the resin-coated area and smooth out any air bubbles or wrinkles. You may need to use clamps or weights to hold the fibreglass in place while the resin cures.
• Finish and seal: Once the resin has cured, you can finish the transom by sanding, painting, or applying a gel coat to match the rest of the boat. You may also need to drill holes for mounting the outboard motor.

It is important to work in a well-ventilated area when working with fibreglass and resin, as the fumes can be hazardous. Always wear appropriate safety gear, including gloves, eye protection, and a respirator.

Frequently asked questions