The Ultimate Guide To Replacing Boat Floor Stringers

Boat stringers are integral to a boat's structure, providing support to the deck, hull, and other components. They are often made of wood, wood encapsulated in epoxy and fibreglass, or entirely of fibreglass. Over time, wooden stringers can rot, compromising the integrity of the boat's hull. Replacing boat floor stringers is a complex process that involves cutting off the deck, measuring and cutting new stringers, removing the old stringers, grinding and sanding the hull, preparing the surface for bonding, installing the new stringers, applying the fibreglass skin, and finishing. It is important to mimic the boat's original construction as closely as possible to ensure the safety and structural integrity of the vessel.

How to identify rotten boat stringers

Boat stringers are an essential structural component of a vessel, providing support for the deck, hull, and other boat components. They are often made of wood, wood that has been fiberglassed, or entirely of fiberglass. Over time, wooden stringers will rot, and even fiberglass stringers can become damaged. As stringers are integral to the safety of your boat, it is important to routinely check for damage and replace them if necessary.

• Look for brown spots on the stringers, indicating that water is weeping from the inside out.
• Check for soft spots on the deck or impact damage.
• If your boat has wooden stringers encased in fiberglass, you can drill a small hole through the fiberglass into the wood core. If the wood shavings are wet or rotten, the stringer is damaged and needs to be replaced. Be sure to reseal the holes afterward to prevent water penetration.
• Use a moisture meter or moisture tool to test the wood for water damage.
• Look for discoloration, peeling glass, and soft spots.
• Check for delamination of the fiberglass from the deck or transom.
• If your boat has engine mount bolts, try removing one bolt at a time and reinstalling it. If the bolt turns endlessly without tightening, it may indicate a rotten stringer. Alternatively, stuff a paper towel into the bolt hole and check if it comes out wet.
• If your boat has a fuel tank built into the deck, there is a risk of cutting into the tank or its lines when cutting the deck to access the stringers.
• If your boat has a plywood deck, it is likely that you will need to destroy and replace it during the stringer replacement process.

Tools and materials needed to replace boat floor stringers

Before embarking on the project of replacing your boat's floor stringers, it's crucial to gather the necessary tools and materials. Here is a comprehensive list to ensure you have everything you need for a smooth and successful process:

• Plywood board or plank: Marine-grade plywood is highly recommended due to its durability and resistance to water damage. Ensure you have enough plywood to cover the entire area of the floor stringers.
• Plastic sheet and marker: These are required if you need to create a template for ordering custom flooring.
• Circular saw or jigsaw: You will need a power saw to cut through the existing flooring and shape the new plywood planks accurately.
• Safety goggles and gloves: It is important to prioritize your safety by wearing protective gear, including goggles and gloves, when operating power tools and handling materials.
• Pry bar or crowbar: This tool will help you carefully lift and remove the old flooring without causing damage to the surrounding structure.
• Marine-grade adhesive: A high-quality adhesive designed specifically for marine use is essential for securing the new flooring in place.
• Epoxy resin: Epoxy resin will be used to coat the plywood planks, making them more durable and water-resistant.
• Screws: Stainless steel screws will be used in conjunction with the adhesive to attach the new flooring securely.
• Measuring tape: Accurate measurements are crucial for ensuring a precise fit for the new flooring.
• Drill: You will need a drill to create holes for the screws when installing the new flooring.
• Fiberglass mat and resin: Fiberglass provides an additional layer of protection and enhances the durability and water resistance of the new flooring.
• Sealant: A marine-grade sealant is necessary to seal the edges and seams of the new flooring, preventing water intrusion.

Additionally, you may require other tools and materials depending on the specific needs of your project. It is always a good idea to have some extra supplies on hand to address any unexpected issues that may arise during the replacement process.

Once you have gathered all the required tools and materials, you can proceed with the replacement process, following the steps outlined in other sections of the guide. Remember to work carefully and seek professional advice or refer to your boat's manual if you have any doubts or concerns.

Steps to replace wooden boat floor stringers

Step 1: Cut off the deck

This is a tricky part as cutting too deep, especially near the sides and bow, can pierce the hull. First, check if there is a fuel tank built-in and be cautious of wiring or cable runs. Delicately drill a hole in the deck to measure its thickness. Set the saw blade to cut through that depth and no more.

Step 2: Measure and cut the core for new stringers

Duplicate the old stringers as closely as possible. Make an initial rough cut, then modify as needed by putting the new stringer core next to the old one. Don't forget that the fiberglass skin will increase the size of the stringer. Cut a sample of the old fiberglass stringer skin to ascertain the thickness of the glass used and the number of layers you'll be adding.

Step 3: Remove the old stringers

The wood inside the old stringers has likely turned into a gelatinous mess, so you will mostly be dealing with the fiberglass shell. Depending on how well the boat was laminated, it may be possible to simply rip or bang out the remainder. Otherwise, shave them down along the hull and then grind away the remnants.

Step 4: Grind and sand the inside of the hull

To get a good secondary bond between the new stringers and the hull, you need to create a clean surface. Grind away all the glass from the old stringers and then sand the area thoroughly. Be careful not to apply too much pressure in one spot for too long, as you may grind through the hull.

Step 5: Prepare the surface for bonding

Choose solvents and prep methods following the fiberglass resin manufacturer's instructions. Pre-prep a jig to support the stringers as the bedding dries. Using putty or epoxy and a fillet tool, create fillets at all 90-degree angles so the fiberglass has a radius to lie against.

Step 6: Install the new stringers

Bed the ply core in thickened epoxy or fiberglass putty, then put the stringers in place, adding the jig pieces to support them. While the epoxy or putty is still pliable, form a "fillet" (a radius) along both bottom edges of the plywood. Add more epoxy or putty to ensure the fillet is at least half an inch.

Step 7: Apply the fiberglass stringer skin

Cut fiberglass cloth to wrap the stringer and extend either side of it ("tabbing") the same amount as the original stringers. When applying multiple layers, make each consecutive layer about half an inch smaller than the previous one so the tabbing is stepped. Wet out the stringer cores with fiberglass resin, then center the first cloth layer over the core and wet it out. Apply additional layers while the resin on the previous layer is still tacky.

Step 8: Apply finishing touches

After the fiberglass has cured, sand or grind any jagged edges or fiberglass hairs until smooth.

Step 9: Replace the deck

With your new stringers in place, you can replace the deck, do some finish work, and then get back on the water!

Steps to replace fibreglass boat floor stringers

Prepare the Surfaces

First, ensure the surfaces are clean, dry, and sanded. Remove any contaminants by wiping the surfaces and drying them with paper towels.

Mark the Area

Before removing the damaged stringer, mark out its position so that you can replace the new stringer in the same location. Make these marks away from the repair area so they are not disturbed when the surface is prepared for bonding.

Remove the Damaged Stringer

Remove the stringer and core. Use a grinder to cut the tabbing at the core/hull joint, being careful not to cut into the hull laminate. Measure the thickness of the fibreglass skin for duplication.

Make the Core

Using the same type of wood as the existing core, cut a piece of timber to fit the size and shape of the core in the removed stringer. Dry fit and trim the new piece as needed for a snug fit.

Sand the Surfaces

Abrade the bonding surfaces by sanding with 50-grit paper and brush away any dust or loose material. For hardwood or epoxy-coated stringers, sand the bonding surfaces with 50-grit sandpaper.

Bond the Core

Wet all contact surfaces of the hull and core with a resin/hardener mix. Apply a liberal amount of thickened epoxy/404 High-Density or 406 Colloidal Silica mixture to one side of the contact area. Push the stringer into position with firm hand pressure. The thickened epoxy should squeeze out of the joint. Shape the squeezed-out epoxy into a fillet, and add more thickened epoxy to the joint if needed for a smooth 12mm radius fillet. Clean up any excess epoxy before it cures.

Finishing

Now that you have successfully replaced the stringer, finish by replacing the fibreglass skin.

Tips for finishing and maintaining new boat floor stringers

Finishing and maintaining new boat floor stringers is essential to ensure the longevity and integrity of your boat. Here are some detailed tips to help you with this process:

Tip 1: Choose the Right Materials

When finishing your new boat floor stringers, it is crucial to select the appropriate materials. For the stringers themselves, you can use solid wood, plywood, or fiberglass. If you have a wooden boat, the stringers should be painted, varnished, or sealed with epoxy. On the other hand, if your boat is made of fiberglass, the stringers are typically wood encapsulated in epoxy and fiberglass. Ensure that the materials you choose are of marine-grade quality to withstand the marine environment.

Tip 2: Address Any Rot or Damage

Before installing the new stringers, thoroughly inspect the surrounding area for any signs of rot or damage. Stress and water penetration can cause stringers to rot, compromising the integrity of your boat's hull. Look for brown spots on the stringers, indicating water penetration, or impact damage that may have occurred. If you find any issues, be sure to address them properly before proceeding.

Tip 3: Use Proper Techniques for Stringer Installation

When installing the new stringers, follow the original construction as closely as possible. Use the same type of wood or fiberglass and fit the new stringers in the exact locations as the old ones. Ensure that the stringers are securely bonded to the boat's hull, either with epoxy or fiberglass. This will ensure that they provide adequate structural support and can withstand the stress of waves and the weight of your boat.

Tip 4: Maintain and Inspect Regularly

To maintain your new boat floor stringers, keep your bilges dry and repair any fissures or cracks that may form. Regularly inspect the stringers for any signs of damage or rot. By staying on top of maintenance and addressing issues promptly, you can prevent more significant problems from occurring and ensure the longevity of your boat's structure.

Tip 5: Consider Additional Support

If your boat is larger or has inboard engines, consider adding a bulkhead or additional support structures to enhance the strength of the stringers. This will help distribute the weight and stress more evenly, reducing the chances of twisting or warping. Consult with a boat maintenance professional or engineer to determine the best approach for your specific vessel.

Tip 6: Seal and Protect the Stringer

Finally, properly seal and protect your new stringers to prevent water penetration and rot. Use epoxy or fiberglass to create a waterproof barrier around the stringers, paying close attention to the joints and connections. This will help extend the life of your stringers and reduce the need for frequent repairs.

Frequently asked questions