Treating Wood Transom On Aluminum Boats: A Step-By-Step Guide

Aluminium boats often use plywood to provide rigidity to the transom. The ply runs across the width of the transom, and its height depends on the boat's design. Over time, the wood can rot and will need to be replaced.

When replacing the wood, it's important to avoid using pressure-treated wood, as the treatment chemicals can react with and damage the aluminium. Instead, exterior-rated plywood, such as BCX, can be used. The wood should also be sealed to prevent water damage. Some options for sealing include epoxy resin, fibreglass resin, spar varnish, and polyurethane.

Avoid pressure-treated wood

When repairing or replacing the transom on an aluminium boat, it is important to avoid using pressure-treated wood. While it may seem like a good idea to use wood that has been treated to last longer, pressure-treated wood and aluminium are actually a very bad combination. The most common types of pressure-treated wood contain copper, and when copper comes into contact with softer metals like aluminium, it causes corrosion.

Over time, the chemicals in the treated wood will leak out, and the copper will eat holes in your aluminium boat. Even if you don't see an immediate reaction, you will likely start to notice pitting, indentations, and other early signs of corrosion. These issues will only get worse over time and could eventually render your boat unsalvageable.

Instead of using pressure-treated wood, it is better to use regular exterior plywood that you seal yourself with a product that doesn't contain copper. You could also avoid using wood altogether and opt for aluminium sheets, which are lightweight and won't rot like wood.

If you're set on using treated wood, it is possible to create a barrier between the treated wood and the aluminium to prevent the copper from leaching out. However, this may require extra work and money, and even paint may not be enough to keep the copper from attacking the aluminium. It's also important to coat or cover the bolts used to secure the wood, as they can also corrode over time if they're in direct contact with treated wood.

In summary, it's best to avoid using pressure-treated wood on your aluminium boat altogether. By choosing an alternative material or taking the necessary precautions, you can save yourself a lot of headaches and avoid costly repairs in the future.

Use exterior-rated plywood

When treating a wood transom on an aluminium boat, it is important to never use pressure-treated wood. All non-treated wood will eventually rot, so it is recommended to use exterior-rated plywood, such as BCX.

Exterior-rated plywood is generally B- or C-grade and is sanded on one side. It is typically composed of five plies of southern yellow pine, bonded together with waterproof glue. While it is thinner than 23/32", it is still referred to as 3/4".

When using exterior-rated plywood, it is important to seal the wood to ensure that it lasts. This can be done by coating the wood with epoxy resin, such as Total Boat penetrating epoxy sealer, Raka epoxy, or polyester or vinlyester resin. You can also use a homemade sealer with linseed oil and other similar products. It is also recommended to seal the edges of the plywood with glue.

After sealing the wood, you can attach it to the boat using stainless steel bolts. It is important to pre-drill the holes and seal them with resin or sealant before drilling to prevent water seepage.

Using exterior-rated plywood and properly sealing it will help ensure that your wood transom lasts for a long time.

Seal with epoxy or fibreglass resin

To treat a wooden transom on an aluminium boat with epoxy or fibreglass resin, follow these steps:

Firstly, ensure you are using exterior-rated plywood for your transom. Marine-grade plywood is ideal, but exterior-rated plywood will also work. Fill any voids in the edges with an appropriate filler, and coat all sides of the plywood with epoxy or fibreglass resin. This will seal the wood and protect it from water damage.

When coating the plywood, you can use a paint roller or brush to apply a thin coat of epoxy or resin to all sides of the plywood. Allow the first coat to dry, then apply a second coat. You may need to sand the plywood between coats to ensure a smooth finish.

If using epoxy, look for a clear penetrating epoxy sealer, and follow the manufacturer's instructions for mixing and application. You can also use a marine enamel paint to provide additional protection and a finished look.

If using fibreglass resin, it is important to use fibreglass cloth or mat in conjunction with the resin. The cloth provides strength and helps the resin bond to the wood. Apply a thin coat of resin to the wood, then lay the fibreglass cloth over the top. Use a roller or brush to work the resin into the cloth, ensuring that it is fully saturated. Allow the first coat to dry, then apply a second coat.

When installing the transom, use stainless steel hardware and seal all holes with a marine-grade sealant before inserting screws. This will help prevent water ingress and protect against corrosion.

By following these steps, you can effectively treat and seal a wooden transom on an aluminium boat using epoxy or fibreglass resin, ensuring a long-lasting and durable finish.

Avoid galvanic corrosion

To avoid galvanic corrosion, it is important to carefully consider what materials you put in contact with the aluminum on your boat.

Firstly, never allow aluminum to come into contact with treated wood. The wood preservative used in treated wood corrodes aluminum. Instead, opt for exterior-rated plywood like BCX or marine-grade plywood. You can also use alternative materials such as Coosa Board or starboard.

When it comes to hardware, use aluminum or marine-grade stainless steel. 316 stainless steel is the best match for aluminum in a marine environment. It is a non-magnetic austenitic chromium-nickel stainless steel that contains up to 3% molybdenum, which helps limit corrosion in saltwater environments. If 316 stainless steel is not available, 304 stainless steel is often used on aluminum boats with no apparent ill effects.

Additionally, always wash your boat down after use in saltwater. Rinse out the bilge and anywhere else where water could pool. This is because, without an electrolyte, galvanic corrosion does not occur. Seawater is an excellent electrolyte, so make sure to give your boat a good rinse with freshwater after each use.

Other tips to prevent galvanic corrosion include:

• Only use paint and coatings designed for use with aluminum.
• Do not exceed 1,300 millivolts of impressed voltage when protecting the aluminum.
• Repair cracks and scratches that expose the bare aluminum.
• Do not use an automotive battery charger on the boat.
• Do not use any lubricant containing graphite as it can contribute to galvanic corrosion.

Use stainless steel bolts

When treating a wood transom on an aluminium boat, it is important to use the right materials to avoid corrosion and ensure longevity. While stainless steel bolts are safe to use, there are some important considerations to keep in mind.

Firstly, it is crucial to understand that stainless steel and aluminium are dissimilar metals, and when they come into contact, a chemical reaction can occur, leading to corrosion. This is why it is essential to use a sealant or marine caulk/sealant like 3M 5200. Applying a generous amount of sealant to the bolts before installation will act as a barrier, preventing direct contact between the stainless steel and aluminium and inhibiting corrosion.

Secondly, when drilling holes for the bolts, it is recommended to pre-fill the holes with resin or marine sealant. This step ensures that no water can seep into the inner layers of the wood transom, causing potential damage over time.

Additionally, it is worth noting that stainless steel bolts should be used in conjunction with stainless steel nuts and washers. Using different metals together can create a battery-like effect, leading to further corrosion issues. Therefore, maintaining consistency in the type of metal used for all hardware is vital.

Finally, when tightening the bolts, it is important not to over-tighten them. Stainless steel bolts are softer than mild steel, and excessive force can cause them to snap. Applying a moderate amount of torque will ensure a secure fit without risking damage to the bolts.

By following these guidelines, you can effectively use stainless steel bolts to treat a wood transom on an aluminium boat, ensuring a long-lasting and secure installation.

Frequently asked questions