Marinetalk is supported by its audience. When you purchase through links on our site, we may earn an affiliate commission. Learn more

What is a Stringer on a Boat? & Other Related Information

Fact checked by William Hart

what is a stringer on a boat

Along the longitudinal center of a vessel, you will find one line running from the bow to the stern. This line is the hull stringer, looking like the backbone of a boat. It holdsthe boat structure and connect other boat’s parts, such as ribs, bulkheads, inboard engines, and fuel tanks.

This article will explain the question “What is a stringer on a boat?” and guide you through examining the stringer’s condition before making a purchase decision.

Table of Contents

 Stringer on a Boat: What’s It?


Hull stringers are vulnerable to mold and mildew since they lie underneath the bilge, which holds stagnant water from your vessel. The repair cost for such damage can run into thousands of dollars. You don’t want to buy a used boat, then find out it has rotten stringers.

What is a Stringer?

The stringer on a ship is the longitudinal line in the center of a boat. It runs from the bow to the stern, connecting the ship’s ribs and bulkheads—the walls inside the hull that separate it into cavities. It serves as the boat’s spine and thus is vital to maintaining a robust boat structure.

Manufacturers also place a keel underneath the stringer to strengthen the construction. A boat stringer system is a grid that firmly holds the deck, hull, and stern in place regardless of the treacherous marine conditions.

On modern boats, you will find other components installed along the stringer, such as the bilge, inboard engine, fuel tank, storage space, and anchor rope.

Since a boat’s strength depends on the stringer’s condition, offshore fishing boats and cargo ships must be equipped with the best stringers to withstand storms and heavy rains.

What is a Stringer Made From?


Stringers can be from wood, wood laminated with fiberglass, PVC foam laminated with fiberglass, solely fiberglass, or solely aluminum.

  • Wood

Wood has been a popular boat stringer material since the old times. It is often treated with varnish or epoxy to eliminate mold growth and increase its durability.

Though wooden stringers construction is undemanding and affordable, the maintenance costs turn out to be rather expensive. The material will fail the test of time, even when covered in protective coats. Soon, the owner will have to replace the entire stringer.

At times, boat builders place hats on top of wooden stringers to protect them against the elements. But as technology advances, more effective options are available.

  • Fiberglass-encapsulated wood and PVC foam

Boats without wood stringers can have fiberglass-encapsulated wood or fiberglass-encapsulated PVC foam. Such stringers last much longer than wooden ones and offer the resilience of fiberglass without adding weight. (Fiberglass is one of the heaviest materials.)

When using PVC foam in replacement of wood, manufacturers can increase the buoyancy of the vessel and stabilize the temperature inside it.

The same technology is also applied to fiberglass fish boxes, which are initially PVC foam covered in fiberglass. These boxes insulate the fish from the outer environment, keeping them cold and fresh for long periods.

  • Fiberglass

Some stringers are constructed solely from fiberglass. The material is sturdy, enduring, and low-maintenance. Fiberglass stringers can be constructed in separate molds and then attached to the boat’s frame. This allows builders to control fiberglass boat stringers thickness and conformity.

  • Aluminum

Aluminum is lighter and more flexible than fiberglass but still offers the benefit of metal—mold-resistance, long lifespan, and little maintenance required.

However, aluminum stringers bond to the hull by welding, which makes repairing or replacing them extremely difficult.

How Does It Work?

Stringers connect the ribs, bulkheads, bow, and stern together, creating a robust grid system that can withstand the pressure of strong waves and wind. Imagine it as your boat backbone; the vessel can’t stand properly without it. It also provides stability, seakeeping ability, and incredible strength.

Stringer Maintenance and Repair

When a boat collides with an obstruction or another vessel, the owner tends to check only the hull. However, as the hull’s core, the stringer might receive a higher impact. Even robust metals like fiberglass and aluminum can crack under the force of a collision.

If your boat has wooden stringers, you should regularly check for signs of decay, such as brown dots and softness. When you notice any damage, take steps to repair or replace the stringer before it is too late. The stringer is key to the hull strength, so never leave it out of your maintenance checklist.

In addition, you should keep the bilge area nice and dry because the stringer lies directly underneath it. You can’t stop water and oil from accumulating in the bilge, but you can pump and clean it thoroughly after each fishing trip.

Frequently Asked Questions


How do you tell if your boat stringers are bad?

Regardless of stringers’ sturdiness, they are damaged from time to time. The most common culprits are rot and cracks from impact. Are your boat stringers rotted? How to tell if they are in bad condition?

You should lift the hatch, gain a closer look at them, and search for damage signs. The symptoms of bad boat stringers include mold spots, cracks, and fractures. If your boat doesn’t have a hatch, you might have to cut through the deck to gain access to the stringer.

Can boat stringers be repaired?

Yes, they can. Repairing boat stringers cost and approach will depend on your boat size, structure, and engine type. But rest assured that a crack doesn’t mean you have to replace stringers in a boat.

Can you change part of a boat stringer?

Yes, you can, but it also depends on the condition and type of your stringer.

Decay and moisture spread rapidly on wood. So when mold and mildew invade a wooden stringer, you might have to replace it entirely.

However, you can repair one part of a fiberglass boat stringer. When replacing stringers in fiberglass boat, the technician will cut the damaged section, place a new core in its position, and bond it to the boat’s frame. The same procedure can be used for replacing stringers in a ski boat.

Nonetheless, the new core must have an identical boat stringer design, type, and size to the old one. Stringer is the boat part that you never want to alternate.

How much does it cost to fix a stringer on a boat?

The cost of repairing a boat stringer depends on its size and material. The larger the stringer, the more money you have to spend. Additionally, replacing a fiberglass stringer is usually more expensive than a wooden one.

The estimated cost runs from $1000 to $10,000. But the price to repair complex stringer systems of large boats can exceed $10,000.

How to inspect the wooden core of a stringer?

When you spot a crack on wood or wood-encapsulated fiberglass stringers, you need to inspect further. When the protective coats deteriorate, moisture can penetrate the wood and spoil it from the inside out.

Examine the core by drilling into the wood and then accessing the wood bits. Soft and soggy wood splinters indicate that the stringer is rotten. You should call a boat service to discuss the best approach. If the wood turns out to be in good condition, seal the hole with epoxy or varnish before closing the hatch.

The steps to replace part of a boat stringer

Replacing a boat stringer requires practiced skills and heavy-duty equipment, thus we don’t recommend you carry out the steps at home. But here is the procedure technicians will use when you service your boat.

  • Step 1. Clean and wipe dry the stringer and the area around it.
  • Step 2. Mark the deteriorated section with a sharpie.
  • Step 3. Cut and remove the deteriorated section with a grinder. This step must be done carefully to avoid damaging the deck.
  • Step 4. Cut a piece of wood or mold a fiberglass core following the damaged section’s dimensions. The new core’s material must be identical to the previous one.
  • Step 5. Sand the new stringer, wipe away the dust, cover it with epoxy resin, and firmly press it into place.

What are composite boat stringers?

Composite boat stringers can be made from Kevlar, carbon fiber, and epoxy, which eliminate many disadvantages of traditional materials, such as short lifespan, vulnerability to weathering, and heavy weight.

You will find composite materials more flexible and lightweight but still strong and long-lasting. Plus, you won’t have to worry about mold, mildew, or moisture.


To sum up, what is a stringer on a boat? It is the longitudinal line placed on the keel to strengthen the hull, connect the ribs and bulkheads, and create a robust boat structure. The health and lifespan of your vessel depend on the stringer system.

It is critical to equip yourself with knowledge before purchasing your first vessel. The water is fun and exciting, but only when you come prepared. So, don’t hesitate to browse our website for more boat information! See you next time!

5/5 - (2 votes)