Kristian Ferrell
Boat stringers are the wooden support structures underneath the deck of a boat, similar to the joists that hold up the floor in a house. They are foundational to the structure and quality of the boat, so they require regular maintenance and checks. The most common repairs associated with fiberglass boats include fixing damaged or delaminated stringers, which can be caused by disintegration of the stringer core material, impact damage, and fatigue from normal use. Repairs can be complex, so it is important to understand the extent of the damage and the type of wood used. In some cases, a complete stringer replacement may be easier than a partial replacement, and it is critical to replace the stringer in the exact same position. After repairing or replacing the core material, the fiberglass skin must also be replaced.
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What You'll Learn
Diagnose the problem and assess damage
Diagnosing the problem and assessing the damage is the first step in repairing fibreglass boat stringers. Boat stringers are structural support members that are oriented parallel to the long axis of a boat hull. They are responsible for stiffening unsupported flat hull sections, supporting cockpit and cabin soles, and distributing high load concentrations from engines and other mechanical systems.
To diagnose the problem, start by inspecting the boat for any signs of damage. Common causes of stringer failure include disintegration of the stringer core material, impact damage from slamming and grounding, and fatigue from normal use. Impact damage usually results in visible fractures in the wood, while rot will affect the integrity and strength of the wood. If the damage is limited to a small section of the stringer, you may only need to replace the affected area. However, if the damage is more extensive, a complete stringer replacement may be necessary.
In some cases, the damage may not be immediately apparent, especially if it is hidden underneath the fibreglass skin. To get a better look at the stringers, you may need to cut "access holes" in the hull liner or cabin sole. Use a mirror and flashlight to inspect the area for any signs of damage. It is important to note that repairing wood rot damage requires a different set of steps and products specifically designed for addressing rot.
When assessing the damage, pay close attention to the type of wood used in the stringers. In older boats, the stringers are typically made of wood, while modern versions may use manufactured fibreglass molds. If you are unsure about the type of wood, it is recommended to consult a professional. Remember that the replacement stringer should be made of similar material and dimensions as the original to maintain the balance of the construction.
After diagnosing the problem and assessing the damage, you can move on to the next steps of repairing or replacing the boat stringers.
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Prepare surfaces and mark the area
Preparing the surface of a fibreglass boat for stringer repair is a critical step in the process. It is important to ensure that all surfaces are clean, dry, and sanded. Use paper towels to wipe down the area, removing any traces of dirt, oil, or other contaminants. This step is crucial, as any remaining contaminants can weaken the bond between the new stringer and the hull. Once the area is clean, use a grinder to smooth out any sharp edges or rough surfaces. An 80-grit sander can be useful for this step.
After the surface is prepared, it is important to mark the location of the outside surfaces of the stringer. This step ensures that the new stringer is replaced in the exact same position as the old one. Make reference marks away from the repair area, so they remain undisturbed during the surface preparation and bonding process. These marks will guide you when removing the old stringer and installing the new one.
Additionally, it is recommended to mark the damaged stringer's position before removing it. This can be done by using a pencil or a marker to outline the stringer's shape and location. It is also helpful to mark the core/hull joint, which can be done by using a grinder to cut a small tab without cutting into the hull laminate. These marks will ensure that the replacement stringer is installed in the correct position and orientation.
Accessing the stringers can also be a challenge. In some cases, you may need to cut "access holes" in the hull liner or cabin sole to reach the damaged area. These holes can be filled with access covers, which are available for purchase. Using a mirror and flashlight can also aid in inspecting hard-to-reach areas. Overall, taking the time to thoroughly prepare the surfaces and mark the area is crucial for a successful stringer repair or replacement in a fibreglass boat.
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Remove the stringer and core
Before removing the stringer and core, it is important to prepare the surfaces. All surfaces should be clean, dry, and sanded. Remove any traces of contamination by wiping the surface and drying it with paper towels. Mark the location of the outside surfaces of the stringer. It is often critical that the stringer gets replaced in the exact same position it was located in previously. When you remove the old stringer, you will need reference points to locate the new one. Locate the reference marks far away from the repair area so they will not be disturbed when you prepare the area.
In some cases, you may need to cut "access holes" to get a good look at your boat stringers. Use a mirror and flashlight to look for obvious fractures in the stringer, delamination of tabbing and core away from the impact point, and inspect the tabbing where the stringer attaches to a bulkhead or transom.
Once you are ready to remove the stringer and core, use a grinder to cut the tabbing at the core/hull joint but be sure not to cut into the hull laminate. Save any large pieces of the core you remove. They can be used as patterns and will speed up the fitting of the new core.
If you are replacing a section of plywood stringer, use a minimum of an 8-to-1 scarf bevel. For a 3/4”-thick piece of plywood, this equates to a 6″ long bevel. When repairing hardwood or highly loaded core areas, use a longer 12-to-1 scarf angle. When cutting scarfs, keep in mind that the longer the scarf angle, the greater the joint surface area, and the stronger the joint. All joints in fiberglass skins should have a 12-to-1 bevel or overlap. Forming the scarf bevel on the new piece of wood is easy. You can use typical cutting tools with the piece of wood supported on a workbench.
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Repair or replace the stringer
Boat stringers are the wooden support structures underneath your boat deck that help to keep your boat afloat. They are essential components that provide structural integrity to your boat. Over time, wear and tear can lead to issues with the stringers. The usual causes of stringer failure are disintegration of the stringer core material, impact damage, and fatigue from normal use.
Before starting any repair, it is important to diagnose the issue and understand the extent of the damage. Look out for any bulges or cracks on the surface or in the tabbing. Tap the stringer surface with a hard object to hear a change in sound. Typically, a damaged stringer will sound flatter or hollow, or there will be no sound at all. When you've identified the damaged area, mark it out. If the damage is extensive, you may need to completely replace the stringer.
To repair a damaged stringer, you will need to cut away the damaged area, being careful not to cut into the surrounding unaffected areas. Sand or scrape out the damaged material and use a vacuum to clean the area and remove any debris. Prepare the surfaces by sanding and cleaning with water or a solvent to remove dust and contaminants. Let the surface dry completely before applying resin and fiberglass.
You can use a polyester resin, vinyl ester resin, or epoxy resin for the repair. Vinyl Ester Resin and epoxy resin are more waterproof than polyester resin, but any can be used. Apply the resin using a paintbrush or roller to the fiberglass, then apply the fiberglass to the damaged area. Let each layer cure before adding another layer until you achieve the desired thickness. Finally, let the area cure and replace the fiberglass skin if needed.
In some cases, it may be easier to replace the entire stringer rather than repairing a section. When replacing a stringer, it is important to use a similar material and dimensions to the original stringer to maintain the balance of the construction. Mark the location of the outside surfaces of the stringer and remove the damaged stringer and core. Use a grinder to cut the tabbing at the core/hull joint, being careful not to cut into the hull laminate. Bond the core with a resin/hardener mix, then push the new stringer into position. Replace the fiberglass skin, and your deck will be fully supported again.
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Finishing touches and maintenance
Once you have repaired or replaced your boat stringers, there are a few final steps to take. Firstly, it is a good idea to smooth out any sharp edges with an 80-grit sander. Since the repair area is mainly in the bilge area, where there is little light and appearance is not a priority, you don't need to do much in the way of finishing. However, if you want a more finished look, you can paint the repaired area. Choose a paint colour that matches the surrounding area, prepare the surface by washing it, then sand the epoxy surface. Remove any dust and apply a primer before painting with a topcoat.
After completing the repair or replacement, regular maintenance and inspections are key to ensuring the longevity of your boat stringers. Keep a close eye on the area for any signs of problems. A good replacement should last a long time, but extra attention to the stringers is always worthwhile, as they are foundational to the structure and quality of your boat. Their role in providing structural support means that strong stringers will extend the life of your boat. Regular checks and maintenance are an essential part of owning a boat, and issues with stringers are common, so it is important to be vigilant.
If you are unsure about any aspect of the repair or maintenance process, it is always best to seek a second opinion from a professional. Boat stringers are an important structural component, and incorrect repairs could lead to further damage. It is also important to use the same type of wood and dimensions as the original stringer when making replacements, as using different materials can upset the balance of the construction.
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Frequently asked questions
Boat stringers are structural support members that are situated underneath the boat deck. They are similar to the joists that hold up the floor in a house.
First, you need to diagnose the problem. Look for damage by opening a hatch or cutting access holes in the hull liner or cabin sole. Common causes of stringer failure include disintegration of the stringer core material, impact damage, and fatigue from normal use. Once you have identified the issue, you can follow a seven-step method to replace the stringer:
- Prepare the surfaces by cleaning, drying, and sanding.
- Mark the area of the damage.
- Remove the damaged stringer and core.
- Replace the stringer, ensuring it is in the same position as the previous one.
- Replace the fiberglass skin.
- Finish by sanding and painting if desired.
- Maintain and regularly inspect the area for any problems.
It is possible to repair or replace only the damaged portion of a stringer. However, in many cases, a complete stringer replacement can be easier and more effective. If you are unsure, it is best to consult a professional.
It is important to use similar materials and dimensions to the original stringer to maintain the balance of the construction. For example, replace a wood stringer with another stringer made from wood.
