Repairing and Replacing a Boat Stringer

boat stringer replacement

The stringers on a boat are under a lot of stress. If they are damaged or rotted, you have to replace them. Most fiberglass boats’ stringers are made of a wood core covered with a fiberglass skin. Damage can occur from the impact or rot of the wood core. It is essential to look for these signs and repair the stringers when they are damaged.

Core Material

A boat’s stringers are its backbone, supporting the rest of the hull and providing structural strength. While durable, they can be damaged by exposure to the elements at sea and from their weight and movement. The damage to the wood core of a stringer can lead to water and rot within the hull, which is why it is important to inspect them regularly. Click this link to learn more


Boat stringers are usually constructed of an active wood core covered by a fiberglass skin. When they are damaged, the fiberglass skin can tear and leave an opening for water or rot to enter the hull. This is a common problem for older boats that have not been maintained well, or even by newer boats that have been neglected after a few seasons of use.

While there are boat stringers made of metal, most are constructed with a wood core that is encapsulated in fiberglass. These are called fiberglass-encased wood (FEV) stringers. While they are still vulnerable to rot, it is not as common for them to be damaged by the elements or by their own weight.

When a boat’s FEV stringer is damaged, it is best to replace the entire section rather than just the skin over it. The reason is that the replacement must match the original construction, which requires the new stringer to be of the same species and dimensions as the old one.

There are many types of foam available as the core material in boat stringers. Some of the more common are polyvinyl chloride (PVC), styreneacrylonitrile (SAN) and polyetherimide (PEI). These foams come in various densities from less than 30kg/m3 to over 200 kg/m3, and can be manufactured in different thicknesses.

Other high quality core materials include Nomex honeycomb and aramid/Kevlar honeycomb. These cores are more expensive but offer better physical attributes, longer life spans and lower weights than other foams.

When installing a new core section, it is important to properly prepare the surfaces for bonding. Ensure that all surface areas are clean, dry and sanded before installation. Apply a liberal amount of thickened epoxy/406 mixture to one side of each contact area. Press the section into place, making sure to align it correctly. Clamp the section in position and clean up any excess epoxy before it cures.

Fiberglass Skin

In modern fiberglass boats, wooden stringers are often covered by a grid of fiberglass fabric that provides strength. In older fiberglass boats, wood is the main ingredient of the stringer, but the overall structure is encapsulated with fiberglass and resin. The fiberglass layer protects the wooden stringer from water and allows for a quick repair of rot or damage. In either case, a rotten or damaged stringer will need to be replaced before it is weakened further and the boat deck becomes unstable.

Wooden stringers will rot quickly, especially if they are exposed to bilge water on a regular basis. They will also become damaged from the wear of holding up the weight of the hull. This makes them a vital part of the structure that needs to be checked regularly for signs of damage or rot. Inspecting your boat’s deck for signs of sagging or areas that feel less secure is a good indication that the stringers have been damaged or rotted.

When inspecting a used fiberglass boat, find out when the stringers were last repaired or replaced. This will help you determine if it is worth the time and money to buy this boat or move on to another one that has better boat stringer condition.

If you are repairing an existing fiberglass stringer, prepare the bonding surface by wetting it with an epoxy/404 High-Density or 406 Colloidal Silica mixture. This will fill voids and provide a smoother finish for the new fiberglass skin to adhere to.

Cut a piece of fiberglass cloth that is large enough to wrap the entire length of the stringer and extend several inches on either side. This is called tabbing and helps to spread the load from the stringer over a larger area. It also ties the stringer to the hull or bulkheads. For best results, step the tabbing edges to keep them from peeling back and creating a weak point. Lastly, mark the position of the old stringer so you can place the replacement in exactly the same location. Be sure to place the marker far enough away from the repair area so it won’t be disturbed when you prep the area for bonding.


The structural nature of boat stringers makes them susceptible to damage from a variety of sources. Whether the damage is from impact, corrosion or just wear from holding the hull up against external pressure, boat owners need to look regularly for damaged areas of the stringers. When repairing or replacing a stringer, it is important to follow the original construction as closely as possible to ensure that the replacement stringer will be strong enough to handle the loads placed on it.

The most common damage to boat stringers is from impact. This may result from collisions with docks or other boats, or it can be caused by dragging gear over the stringers. In this case, it is important to look for fractures in the stringer and any delamination of the fiberglass skin around the impact area.

Another common source of damage is rot. Wood cores are susceptible to rot from water leaking through fasteners and from the tabbing of the stringer to bulkheads or transoms. If a wooden stringer is showing signs of rot, it is important to take action immediately before the rot progresses.

When replacing a stringer, it is important that the new stringer be constructed of the same type of wood that was used in the original construction. This is especially important if the old stringer was wood encapsulated in fiberglass. It is also important that the new fiberglass be applied at the same thickness as the original.

It is also important that the new stringer be positioned in the same location as the original. This is particularly true of boat stringers that support engines or other equipment. If the new stringer is not located in the same place as the old one, the load that it must carry will be distributed unevenly, causing the hull to sag or crack.

Lastly, it is essential that any replacement stringer be secured to the hull with fasteners that are suitable for the job. There are a variety of fasteners available, from basic chrome plated brass to high-strength stainless steel. When determining which fasteners to use, it is important to consider the amount of torque that will be applied to the fastener and the number of cycles the fastener will need to survive in service.


Stringers, also known as floor joists, are long lengths of wood or fiberglass that, along with the boat’s ribs and bulkheads, create a grid for supporting the decks of a boat. As such, they are subject to a lot of stress and may require replacement over time. Although many boat owners consider themselves handy, replacing a boat stringer is usually beyond their skill set and a job best left to professionals. Fortunately, the process isn’t too complicated. Using the right tools, and following some basic tips, anyone can replace a boat stringer.

The first step in a boat stringer replacement is to remove the old one. Depending on how well it was laminated and how long the wood has been submerged in water, this can be as simple as ripping out the remaining piece. Alternatively, it might be necessary to cut out the old stringer and grind away the remains. Either way, this is a messy job that requires some patience and a fair amount of cleanup.

Once the old stringer is removed, it’s essential to examine it for damage and rot. A rotten boat stringer should be replaced, especially if it is wood encased in fiberglass because water can seep into the wood and cause more extensive damage. It’s often easier to detect a wooden rotting stringer than a fiberglass one because water will show up as brown spots on the surface of the stringer.

When replacing a boat stringer, it’s important to use the same type of core and fiberglass used in the original construction. It’s also important to fit the new stringer in the same location as the old one. Finally, the resulting composite should be as thick as the original material so that it provides as much strength as possible.