Restoring Wooden Boats: Replacing The Bottom

Wooden boats are beloved by many, but they do come with their own set of maintenance challenges. One of the most daunting tasks for wooden boat owners is replacing the bottom of their vessel. This is often necessary when normal bottom maintenance is no longer sufficient to keep the water out, or when extensive repairs are needed due to rot, damage, or leaks. The process of replacing a wooden boat bottom can be complex and time-consuming, but with careful planning and execution, it is achievable for both novice and experienced boat builders.

Drilling and marking framing positions

Drilling and marking the framing positions is a crucial step in the process of replacing a wooden boat bottom. Here are some detailed instructions to guide you through this complex task:

Step 1: Inspect the Framework

Before marking and drilling, it is essential to thoroughly inspect the framework for any signs of damage or deterioration. Look out for issues such as the boat spreading apart, broken or cracked frames, rot, or oil-soaked frames. Mark any frames that need to be replaced or repaired. It is generally recommended to replace rather than repair questionable frames to ensure the structural integrity of the boat.

Step 2: Prepare the Work Area

Ensure that your boat is securely supported and braced before beginning any drilling or marking. This will help maintain the stability of the boat during the process. Use cross braces and additional supports as needed, especially if you are working on a larger boat.

Step 3: Identify Framer Positions

Locate the positions where the new frames will be installed. This typically involves marking the locations on the inside of the boat where the frames will be attached. Use a combination of measurements, templates, and visual alignment to identify the correct positions for the frames.

Step 4: Mark and Drill Pilot Holes

Once you have identified the correct positions, use a pencil or marker to mark the spots where the screws or fasteners will go. Use a drill to create pilot holes at these marked locations. Ensure that the drill bit size matches the screws or fasteners you will be using. Drill the holes with precision to avoid any misalignments during the installation process.

Step 5: Prepare the Frames

If you are using steam-bent oak frames, as is common in wooden boats, you will need to prepare the frames before installation. This involves cutting and shaping the frames to fit the specific contours of your boat. Mark the frames for any necessary cuts or adjustments based on your unique boat design.

Step 6: Install the Frames

With the holes drilled and the frames prepared, you are now ready to install the new frames. Align the frames with the pilot holes and use clamps to hold them securely in place. Once the frames are positioned correctly, you can drill and fasten them permanently using appropriate screws or fasteners, such as silicon bronze screws.

Remember to work systematically, replacing or repairing one frame at a time to maintain the structural integrity of the boat. Always follow best woodworking practices and safety guidelines when working with power tools and chemicals.

Removing the existing bottom

Step 1: Flip and Brace the Boat

First, you need to flip the boat upside down and brace it securely. For smaller boats, this can be done with the help of several people. For larger boats, consider using slings. Proper bracing is crucial to ensure stability during the removal process. Use 2x4s to fasten the boat from frame to frame, just below the sheer plank. Additionally, fasten a 2x4 from the stringer to the cross brace. The number of braces will depend on the size and type of boat.

Step 2: Remove the Existing Bottom Planks

Start by locating the screw holes. Use a sharp scraper to remove paint along the frame line until you find them. Drill around the screws using a large plug cutter (1/2" diameter). Drill out all the screws, then remove any excess wood around the screw heads. If the screws are stubborn, use a vise grip to remove them. Once all the fasteners are removed, take out the planks. If you plan to use them as patterns for the new bottom, number them before removal.

Step 3: Remove the Inner Layer

Now, remove the inner layer of the boat bottom. This step is relatively straightforward compared to the previous one.

Step 4: Inspect the Framework

Inspecting the framework is critical to the restoration process. Check for signs of spreading, broken or cracked frames, rot, and oil-soaked frames. Use a sharp awl to poke for soft spots. Mark any damaged frames for replacement and address the underlying causes to prevent reoccurrence. Consider replacing questionable frames instead of repairing them to ensure a longer-lasting restoration. Disassemble and seal all the frames with "Sikaflex" or "3M 520."

Step 5: Disassemble and Refasten Bottom Frames

Check the fairness of the bottom, ensuring there are no significant problem areas. Refasten all intermediate frames that connect to the chines and stringers. Remove the frames, clean and inspect them for decay, then apply a layer of caulk (Sika or 5200) to both surfaces before refastening. Repeat this process for all intermediate frames and those that fasten to the side frames at the knees.

Step 6: Seal and Prime the Frames

Seal all new frames with a penetrating sealer, such as "Smith Systems." After allowing the sealer to dry, prime all new frames with a suitable primer, such as Red Lead Primer. However, do not prime the bottom surface of the frames that will be in contact with the new bottom.

By following these steps, you will have successfully removed the existing bottom of your wooden boat, setting the stage for the next steps in the restoration or replacement process.

Inspecting the framework

Signs of Boat Spreading Apart:

Look out for signs of the boat spreading apart, such as intermediate frames no longer tight against the chines. This indicates that the structure is no longer securely held together and requires attention.

Broken or Cracked Frames:

Inspect all frames for any damage, such as cracks or breaks. If you find a damaged frame, mark it for replacement and investigate the cause to identify any underlying patterns or issues.

Rot:

Use a sharp awl to poke the wood and check for soft spots, which indicate rot. Mark any areas of rot for replacement. Rot is typically caused by fungicidal microorganisms that thrive in moisture, so it's important to address this issue.

Oil-Soaked Frames:

Clean all frames with a strong solvent to remove any oil. If you find that oil is beading up again the next morning, mark that frame for replacement. Oil can indicate a problem with the frame's integrity and may affect the adhesion of the new bottom.

Disassemble and Inspect Bottom Frames:

Disassemble the bottom frames to inspect them more closely. Check for any problem areas, such as uneven scarph joints or signs of rubbing or chafing that suggest movement. Refasten intermediate frames and apply a layer of caulk to both surfaces before reinstalling.

Seal and Prime New Frames:

After making necessary repairs and replacements, seal all new frames with a penetrating sealer and prime them with a Red Lead Primer. Do not prime the bottom surface of the frames, as this will come into contact with the new bottom.

Inspect Transverse Frames and Floors:

Pay close attention to the transverse frames and floors. Check for any signs of rubbing, chafing, or softness. These areas are prone to wear and tear and may require reinforcement or replacement.

Check for Movement and Softness:

Use a screwdriver to gently pry under the frames, especially where they are through-bolted to the floors. Any movement or gap between the planks and frames indicates fastener problems. Test the wood for softness near the mating surfaces, particularly near the keel and along the garboards.

Inspect for Cracks:

Look for cracks in the frames, especially at the ends. Cracked frames weaken the structure and will need to be replaced or reinforced.

Tap Planks for Soundness:

Use the handle of your screwdriver or a wooden mallet to tap the planks and listen for any dull sounds. Sound planks should ring; a dull thud suggests rot or loose fasteners.

Check Fasteners:

Inspect fasteners for integrity, especially metal ones, as they are subject to corrosion. Look for discoloration, rust, or green copper oxides around fastener heads. Water stains near fasteners indicate potential leaks. If there is softness in the wood around bolt heads, it suggests that water is causing corrosion and the fasteners may need replacement.

Inspect Keel and Rudder:

Pay close attention to the keel and rudder, as these are critical for the boat's stability and manoeuvrability. Check the underside of the keel for any damage that could indicate grounding. Inspect the rudder blade for splits and the fittings for wear and corrosion. Ensure the rudder has minimal play in the bearings.

Check for Leaks:

Inspect seams and joints for any signs of leakage, especially in high-stress areas like chines and where the transom intersects with the bottom and side planking. Leaks can endanger fasteners and lead to further deterioration.

Bulkheads:

Don't forget to inspect bulkheads, as they are structural elements. Look for any signs of looseness, rot, or damage and replace them if necessary.

Deck Inspection:

Walk on the deck to feel for soft or springy areas. Pay attention to areas around fittings, such as stanchions, as looseness can indicate water penetration. Tap the deck with a screwdriver or mallet to identify any bad spots.

Remember, when in doubt, it's better to replace a questionable frame rather than repair it. By thoroughly inspecting and addressing any issues with the framework, you will ensure a strong and long-lasting foundation for the new bottom of your wooden boat.

Applying epoxy and glue

When applying epoxy and glue to a wooden boat, there are several steps to follow. Firstly, it is important to select a suitable epoxy resin. There are two main types of epoxy resin used in boat building: polyester and epoxy. Polyester resins are cheaper but not suitable for building with wood, so epoxy resins are recommended due to their superior ability to bond with wood. When choosing an epoxy resin, opt for a well-known brand of marine epoxy to ensure quality. Additionally, consider the potential health and environmental risks associated with epoxy resins and take the necessary precautions.

Once you have selected the appropriate epoxy resin, follow these steps for application:

• Prepare the surface: Ensure that the wood is clean and free of any contamination such as oil, wax, or moisture, as these can prevent the epoxy from adhering properly. If necessary, sand the surface to create a smoother finish.
• Mix the epoxy: Epoxy resins come in two parts: the resin and the hardener. Refer to the manufacturer's instructions for the correct mixing ratio and ensure thorough mixing. Only mix the amount of epoxy that you can apply within the pot life, which is the interval after mixing when the epoxy can be applied.
• Apply the epoxy: Using a brush, roller, or other suitable tool, apply a coat of epoxy to the prepared surface. Make sure to work in a well-ventilated area and follow the safety instructions provided by the manufacturer.
• Allow curing: After application, give the epoxy enough time to cure. The curing process can take several days, and the boat should not be used during this period.
• Sanding and finishing: Once the epoxy has cured, you may need to sand the surface to smooth it out and prepare it for painting or varnishing. Remove any dust or debris before proceeding to the next step.
• Painting or varnishing: Apply a coat of primer or paint suitable for use on epoxy surfaces. Follow the manufacturer's instructions for the best results.

In addition to using epoxy for repairs, it can also be used in the stitch and glue method of boat building. This method involves cutting and stitching together pieces of plywood, then gluing them using epoxy. The epoxy acts as a strong adhesive and helps to seal the seams between the plywood pieces.

Finalising the new bottom

Preparing the Framework

Before installing the new bottom, it is essential to inspect and address any issues with the framework. This includes checking for signs of the boat spreading apart, broken or cracked frames, rot, and oil-soaked frames. Replace any questionable frames rather than repairing them to ensure the longevity of your new bottom. Disassemble and seal all the frames with a penetrating sealer, such as "Smith Systems," and prime them with a suitable primer like Red Lead Primer.

Selecting the Right Plywood

When it comes to choosing plywood for your boat's bottom, avoid using standard marine plywood from local lumber yards. Instead, opt for a specialised product like "Okoume" plywood by "Shelmarine." This plywood is designed for boat construction and ensures the necessary durability. Calculate the required amount of plywood by dividing the length of your boat by 8 and then multiplying by 6.

Installing the Plywood Layers

The installation process typically involves using three layers of 6mm plywood for a typical runabout boat under 20 feet in length. Start by applying a generous coat of epoxy, such as "West," to each sheet of plywood and let it dry overnight. Wash the sheets with soap and water, scuff them with 80-grit sandpaper, and install the first layer with the grain running fore to aft. Ensure the pieces are no wider than two to three frame widths for easier bending. Dry-fit all the pieces before permanently fastening them, and remember that all joints must end on a frame.

Fastening and Epoxy Application

Apply a coat of epoxy, such as "3M 5200," to the frames, chines, and keel. Place the plywood down and secure it with silicon bronze fasteners, such as 14-gauge 1 1/4" silicon bronze ring shank nails. For the second and third layers, rip the plywood into 6" widths and apply them diagonally to the keel at a 45-degree angle. Mix epoxy with an additive like "WEST SYSTEM 403 Microfibres" to achieve a mayonnaise-like consistency. Apply this mixture to the boat and fasten the plywood strips, ensuring that epoxy squeezes out to cover all edges.

Final Coats and Painting

Once all three layers of plywood are installed, apply at least five additional coats of epoxy over the bottom. Look for any imperfections or high and low spots, and mark these areas for correction. Sand the bottom again and mix epoxy with a fairing compound to fill in any imperfections. After sanding these areas, apply two coats of a suitable primer, such as Red Lead Primer, followed by two coats of bottom paint.

Post-Installation Checks

After completing the installation and painting, allow the epoxy and paint to cure fully. Check for any remaining twists in the boat, as these can be challenging to correct once the bottom is installed. Ensure the boat is properly supported and levelled, and make any necessary adjustments to the chocks or supports.

Frequently asked questions