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Boat Stringers Repairing And Replacing 101 [All You Need to Know]

If you have a boat, you are aware of just how much stress and pressure that a boat goes through. 

Boat Stringers Repairing And Replacing

Boat stringers, in particular, are one of the most crucial parts that need proper care and upkeep to stay afloat. What gives the hull of the ship its structural integrity are these stringers that form a grid pattern beneath the deck. 

These beams are made of a variety of materials that are designed to go the distance. However, after regular wear and tear, even these materials are susceptible to breaking down. 

That is why keeping them in tip-top condition is so important. As a piece of the ship that supports the deck, a stringer’s role in the ship is crucial. 

If you don’t know where to begin repairing or replacing your boat stringers, worry not. Our comprehensive guide will cover everything. 

With that, let’s get into it!

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Boat Stringers Repairing And Replacing

Boat Stringers Repairing And Replacing

Stringers And Their Importance

If you are unfamiliar with stringers, then maintenance can be confusing. There are terminologies that you need to be aware of to understand what you need to do. 

Understanding what a stringer is and why it is so important is an excellent place to start before working on the stringers. Essentially, stringers are what keep the hull, cockpit, and engine supported above the ship’s hull. 

So, it is clear why they are so crucial for any ship and they are attached to the ship’s hull, running parallel to the long axis of the boat. Now, the individual stringer’s construction in a fiberglass boat is composed of a core and fiberglass skin on top of it. 

Fiberglass is used to protect the core from external contaminants and damage. There are multiple layers of fiberglass that make up this skin that spans the length of the core and over the edges. 

Stretching the fiberglass skin beyond the ends of the core serves the purpose of attaching the stringer to the hull. And the extension of fiberglass is known as a tab. Tabbing allows the stringer to accommodate a heavier load, giving it greater structural integrity. 

Types Of Cores

Stringers are not uniform in length and dimensions as they stretch across different lengths of the boat. As such, some stringers are more integral to supporting sections with a heavy load compared to sections with lighter loads. 

When it comes to this distinction between stringers, the cores used within the stringer can vary. They are all made of the same type of wood but have different dimensions. 

There are active core stringers that support heavier loads and act as the primary structure. On the other hand, inactive core stringers are not as integral to keeping the hull supported and only help keep the form of the fiberglass skin. 

Moving on, active core stringers are usually composed of solid wood or pressure-treated plywood. These cores need to be durable as they bear the full weight of the hull and other loads on the boat itself. The heavier a load to be held, the denser and thicker the active core will be. 

Additionally, the fiberglass skin on an active core stringer is thinner as compared to that of an inactive core stringer. As the core takes up a larger area, the space for the fiberglass skin is less. Essentially, the fiberglass skin only acts as the attachment of the stringer to the hull. 

Naturally, inactive cores are made of a lower density material than active stringers. Stringers with this kind of core do not bear much load and rely on the fiberglass skin to support themselves. 

Usually, these cores feature a cardboard tube, low-density foam, or have no core at all. After all, the actual core doesn’t matter; it is essentially a thick fiberglass skin to lend support. 

When Do You Need To Repair Boat Stringers?

Deciding whether your boat stringers need repair or replacement can determine how much work is required. 

If your stringers are made of wood (an older type of material), then look for signs of rot and water damage. This can manifest itself in brown spots on the surface of the material. 

Furthermore, you can simply notice if the deck feels less stable, a sign of a faulty stringer formation. Walking across the deck or cabin has a minor degree of flexing underneath the feet. 

In order to fully gauge the extent of the damage in the stringer, drill a few access holes into the hull liner or cabin sole. This gives you a better view of the condition of your stringers. 

Impacts and rotting are two of the most common types of damage when it comes to stringers. Identify the source of the weakness in the stringer formation; which stringer, in particular, requires maintenance. 

Fractures and splitting away at the tabbing of the stringer are two clear signs that a stringer has taken impact damage. One common area where impact damage is made evident is at the tabbing. There is usually a wearing away of the epoxy resin laminate, so inspect the tabbing portions of the stringers thoroughly. 

Wooden cores are susceptible to rotting if they become exposed to moisture. This can occur when the laminate surrounding the core is worn away or leaking at the tabbing joint. 

Additionally, the fiberglass skin is prone to becoming internally detached from the core. To determine if this is the case, use a small hammer to tap the surface of the stringer lightly. If you hear a dull sound when you tap the suspected area of damage, then it means the fiberglass has become detached. 

Repair Or Replace?

Once the source of contamination in the stringer has been assessed, you need to make a plan of how to deal with it. You can either deal with just the problem area or replace the entire stringer. 

Of course, not every contamination or damage will merit an entire repair job. If there is minimal damage or just a small area affected, an anti-rotting formula can be used. 

However, repairing the stringer ensures a foolproof solution to contamination. Furthermore, if there is considerable damage to the stringer, then you may have to fix it or get a professional to do the job. 

Additionally, replacing the stringer is another route you can take that is guaranteed to take care of the damage. This maintenance method is more costly and time-consuming but also ensures the stringer formation is the best that it can be. 

It is important to note that replacing a stringer requires you to use the same wood type as the original stringer. Matching the cores will help maintain even support across all the stringers and deck. The dimensions and position of the replacement stringer are other considerations that need to be matched in both stringers. 

Taking the consultation from a professional is recommended to determine what type of core your stringer has. As a general rule of thumb, it is always a good idea to talk to someone who knows what they’re doing. This is especially important if you choose to do the maintenance work yourself instead of outsourcing it. 

Repairing A Boat Stringer

Once you have confirmed the condition of the stringer, you can begin working on repairing it. Before working, it is a good idea to understand the composition of the stringer. This helps make working with this complex structure much more manageable. 

Fiberglass boats have a fiberglass skin that surrounds a core material (usually wood). This core is known as an active core stringer as it is what gives the stringer its strength. The wood is the support with the fiberglass layer acting like a protective layer. 

Additionally, the fiberglass skin is what attaches the stringer to the boat. Any damage to this layer can result in structural damage to the hull and allow seepage. As such, making repairs as and when needed is essential to keep the boat in good condition. 

  1. Prepare The Fiberglass

Strips of fiberglass need to be cut to accommodate the stringer cores. This new layer of fiberglass needs to cover the span of the existing stringers, so cut it according to the thickness of the one being repaired. 

For your first strip, ensure the fiberglass covers the entire length of the stringer and then some to accommodate the tabbing. The following strips will be smaller in size, about an inch or a half-inch with every subsequent strip. 

By tapering the new fiberglass strips, a more robust stringer formation is created. Weight is distributed across the structure evenly to the tabbing ends. Therefore, stepping the edges of the fiberglass is essential to keep the strength at an optimal level. 

  1. Prepare The Surface

Now that the fiberglass strips are ready, the stringers themselves need to be prepped for the new layers. Any contaminants on the stringer can affect how well the fiberglass adheres to the active core. 

Dust, grime, and oil or gasoline stains need to be removed before any repairs can be done. Use a degreaser and a solvent to wipe away these contaminants. After the solvent is applied and wiped off, quickly dry the surface with a towel to prevent seepage. 

Additionally, the stringer needs to be prepped to allow the fiberglass skin to stick to it. This can be done with a 50-grit grinder to give a texture to its surface. 

In the event that the stringer already has a fiberglass layer, use a 12-to-1 bevel tool to adhere the new layer to the pre-existing ones. As fiberglass is rigid, bending it around the corners of the stringer can be difficult, so round off the top edges of the core. 

Furthermore, the inner corners of the active cores toward the hull and bulkhead need rounding out. These are areas of critical structural integrity and require special attention due to their unique shape. 

  1. Apply The Fiberglass Layer

With all the preparation work completed, the fiberglass is ready to be installed onto the stringer. 

Begin with the longest stringer and place it over the corresponding stringer. Apply a layer of resin and hardener mixture over the entire piece and allow it to seep into the strip and wood. 

Repeat this process for every stringer, working towards the outside of the boat. Waiting between applications on different stringers is not necessary. You can place the new fiberglass strips one after the other across the stringers. 

Allow each initial layer on every stringer to reach its initial cure before applying another coating. Repeat this process until you reach the desired thickness of the stringer. Furthermore, being able to place the strips one after the other immediately removes the need to sand between coats. 

Once you have applied every strip of fiberglass, pour a few more epoxy layers to create a final protective layer. It is at this point that the epoxy resin should be allowed to dry and cure fully. 

  1. Finishing Touches

At this point, you can also add an aesthetic touch, if you so choose, to your stringers. Marine-grade epoxy-based formulas can add a pop of color to the boat. 

Furthermore, painting the outer surface of the epoxy resin is another possibility in customizing the stringers. Just make sure you wash and sand the surface before applying anything to it. Primer is another necessary step to make sure the paint adheres well to the stringer. 

However, if you wish to leave the resin as is, it is entirely acceptable as the stringers are not on display. As these are located underneath the deck in the bilge, the finish of the stringer will not always be visible. 

Additionally, the same applies to cleaning up the epoxy resin layers. Imperfections and sharp corners are unavoidable when doing the repairs yourself. If you want a clean look, then an 80-grit sander can even out the surface well. 

Replacing A Boat Stringer

Replacing stringers is not as complicated as it may seem. Completely replacing a stringer is often seen as less of a hassle than just repairing it. 

The logic behind this is that there may be additional damage within the stringer that is not obvious right away. Therefore, replacing the entire stringer is the safest bet to make sure there are no further repairs needed. 

  1. Prepare The Surface

Similar to the process of only repairing the stringer, clean the surfaces of the stringer of contamination. Dry and sand the stringer before working on it to have the best quality result possible. 

  1. Mark Off The Stringer

To make sure the replacement stringer is placed in the correct position, mark off the old stringer’s position. Keep the mark away from the area to be replaced to keep the surface of the stringer intact before installing the new stringer. 

  1. Take Out The Old Stringer

Now that the surfaces and stringer have been marked off, the stringer can be removed. We need to replace the entire stringer, so the core needs to come out as well. A grinder can help you get to the tabbing where the stringer is attached to the boat. 

While cutting away at the tabbing, be sure not to dig into the hull’s laminate surface. Once the stringer is removed, take note of how thick the fiberglass skin layers are. The replacement stringer needs to have the same thickness to be a perfect repair. 

  1. Make A New Core

With the old stringer removed, the replacement stringer can begin to be made. The first step is to create a new core and build up the rest of the stringer around it. 

It is crucial to use the same type of wood as the other stringers in the boat to have the same structural integrity. Try to match the exact dimensions of the old core when cutting away the wood for the new one. 

  1. Prepare Surfaces For Bonding

Before the surfaces can be joined, they need to be prepared for the adhesive. This can be done by creating a surface that the glue can hold on to. Sand down the surfaces with 50-grit sandpaper to create a rough texture. 

Repeat this step for the bonding surfaces of the hardwood or epoxy stringer. Once all the surfaces are sanded down, clean away the dust and dirt. The surfaces are now ready for bonding. 

  1. Installing The New Stringer

Epoxy resin is used as the bonding agent here due to its durability and versatility. In the application process for epoxy resin, the surfaces need to be wet to have proper adhesion. Wipe down the surfaces where the adhesive is to be applied with a damp cloth; this means the core and hull. 

Only one of the surfaces needs to have epoxy on it, so it’s up to you whether you put it on the core or hull. Insert the new stringer into the hull and press down until the epoxy is squeezed out from the joint. 

Use this excess epoxy resin to shape a fillet against the intersection of the stringer and hull on both sides. You can use more epoxy resin to fill in the fillet if there is not enough. Try to have a 12 mm radius on both sides. These fillets will increase the structural integrity of the stringer.

  1. Apply A New Fiberglass Skin

Now that the stringer is installed, clean up any excess epoxy before it dries. With this, the stringer has been replaced. All that is left is to replicate the thickness of the fiberglass skin on the old stringer. 

Follow the steps in the repairing section of the guide to building up the fiberglass skin. Remember to match the exact thickness or be as close to it as possible. This will give you better structural support to your deck. 

  1. Further Maintenance

Whether you are just repairing or completely replacing a boat stringer, it is important to keep an eye on them. If you have carefully worked on your stringers, then there should not be any further complications. 

However, the role of a stringer is one of the most critical parts of a boat. Making sure there are no further problems can be worthwhile. Your boat’s quality and durability will be immensely better with a solid stringer formation. 


Working on the maintenance of your stringers can be a time-consuming process. To ensure you have the smoothest process when working, learn as much about the process beforehand as possible. 

Keep in mind these tips before you start working on the stringers to be better prepared once you do begin. 

  1. Diamond Cutter

While it is not necessary, having a diamond cutter wheel attachment on your grinder can make cutting away easier. Whether it is the fiberglass skin or the stringer itself, it will help give a clean and easy cut. 

  1. Shape The Stringers 

Shaping the stringers with fiberglass layers should be done as carefully as possible. Having uneven surfaces can make the stringer bear too much or too little weight. This causes inconsistent weight distribution and can damage the hull or deck. 

  1. Safety Equipment 

Safety gear is an absolute must before working on the stringer in any capacity. There are dangerous materials involved in the maintenance, like fiberglass, so safety is definitely a priority. 

Safety glasses and a respirator, as well as latex gloves, can keep these irritants and dangerous particles away from sensitive areas. Additionally, wear long sleeves to protect your skin from flying debris. 

  1. Measurement 

Replication of the original stringer’s dimensions is crucial to maintaining the correct weight distribution across the stringers. If the repair job does not follow the same dimensions of fiberglass or core, it can result in further damage to the surrounding hull and deck. 

Furthermore, the positioning of the stringer needs to remain constant if you are doing a complete replacement. The size and shape of the stringer determine how much load it bears, so keeping it in the same position is critical. 

  1. Maintenance 

Not only is stringer maintenance a time-consuming process, but it can be quite expensive. Ensure you are set up with an adequate budget and time to work on the project before beginning any work. 

Wooden boats on the lake. Nepal evening.

Wrapping Up 

Now that you are aware of stringers and how to care for them, we believe that you can maintain the boat. 

It goes without saying that keeping your stringers in working condition is incredibly important. You wouldn’t want any of them to give way while on the sea. 

Hence, make sure you are regularly checking for damage even after finishing repairs or replacements. Vigilance is essential not just while out and about on the water but also while the boat is docked. 

So, keep an eye on the outside and inside of your boat for a safe boating experience.