How Are Sailboats Made?

How Are Sailboats Made? | Life of Sailing

Last Updated by

Beth York

June 15, 2022

Sailboats have been around for centuries. While their general shape has not changed much, how sailboats are made has changed dramatically as manufacturing techniques have improved. Originally boats were made from a single tree trunk with the interior dug out to form the hull. As tools developed, hulls began to be made out of wooden planks and the spaces between them filled with organic material. With modern manufacturing techniques, sailboats are generally made out of a combination of natural and man-made materials. These new designs have created sailboats that are faster, more roomy, and safer than ever before.

Modern sailboats are made using a combination of fiberglass, resin, wood, foam, and metal. Technology has found its place within the boat building community and many hulls are partially built by machines. The majority of boat building is still done by hand e.g. electrical systems, rigging, carpentry, and fiberglassing.

As with any product, there is a great deal of variation in technique and method to boat building from company to company.  Typically, a mold is used to create the hull and deck pieces out of fiberglass. The fiberglass is laid in layers with foam or balsa wood sandwiched between.   A structural floor grid is laid into the hull to support the weight of the tanks and engine.

All cabin walls and cabinets are installed by carpenters at the factory.  Wiring for electronics and lights are placed between the deck layer and the cabin ceiling. The quality of the sailboat is dependent upon the materials used and the level of workmanship. The higher the price tag, the more expensive materials used.

My S2 sailboat is almost 40 years old and the processes that were used to create it have changed slightly over the years.  I have been in every nook and cranny in my boat and intimately know it's workings. Last fall I finally decided to take down the 38 year old headliner and paint the ceiling and walls. It was a huge job, but it taught me a lot about how my boat was made. I discovered that S2 installed the headliner prior to the chain plates and walls. This made it nearly impossible to fully remove every stitch of the old material. By understanding how sailboats are made, you can become more comfortable completing diy work!


Table of contents

History Of How Sailboats Are Made

The ancient Egyptians began building sailboats around 4000 BC.  Initially their boats were made out of gathered reeds. Later, their vessels were constructed out of chisel cut cedar wood planks. The planks were connected using wooden pegs or "wood nails" and rope. These planks were attached to a dug out keel section. Ancient Egyptians used oars to travel down the Nile and sails to return upriver. Their sails were made from animal skins, woven reeds, and later linen.

Vikings began building sailboats around 1000 years ago. These wooden ships were constructed using overlapping axe hewn planks which were connected using iron rivets. Sails were square shaped and constructed from wool dyed to identify the ship.

Wooden sailboat construction continued until the 1830s when iron began to be used. They continued to be made of wood, but were given a protective iron covering to improve their strength as warships. This is where the term 'iron clad' originated.

Eventually steel took the place of iron. By the mid-20th century aluminum began to be used for hull construction. Fiberglass took over in the 1960s as the standard pleasure boat material.

Modern Sailboat Construction

Sailboat manufacturers use similar yet different methods when constructing vessels.  

While wood, steel, and aluminum continue to be used, fiberglass is the predominant material of sailboat construction.  

What Is Fiberglass?

Fiberglass, also known as glass reinforced plastic (GRP) is a material made from glass fibers.  To create the fibers, glass is heated to a molten state and then forced through very fine holes. This causes the glass to form 3-20 micron thick filaments which can then be woven into sheets.

When a resin is applied to fiberglass sheets it becomes a super strong material that can mold into virtually any shape. Fiberglass is noncombustible, unaffected by sunlight, and has the strength of steel but without the added weight.

Designing A Sailboat

Sailboat design has come a long way with advances in technology. By utilizing design software, sailboat designers are able to create highly detailed and innovative plans.

Creating plans by computer allows the manufacturer to utilize robotics in the construction of hulls and decking. The precision and consistency of robotics eliminates issues related to human error. Every port opening and screw hole is drilled in exactly the correct place.

Hull Molds

The second step in building a sailboat is creating or tooling the molds for the hull and deck. When constructing a boat out of fiberglass, a mold is used to create its shape.

There are two types of molds: male and female. Fiberglass layers are applied to the outside of the male mold and the inside of the female mold.

A mold is created using a plug. A plug is like a replica of the hull or deck. A wooden framework is created and covered in planks. The planks are sanded and filled until they are smooth and level. A layer of primer and wax is added last.

Once the plug is built, the mold is created around it. This begins with a layer of gelcoat followed by layers of fiberglass and core material. Finally, the exterior of the mold will have stringers applied to add strength to the mold. The mold is then separated from the plug.

A properly cared for mold can be used repeatedly for years. It's said that when a boat is built, it's really like building three boats: the plug, the mold, and the final hull.

Building The Hull

After the mold is completed, hull construction begins. Fiberglass is laid sheet by sheet into the hull mold. After every sheet of fiberglass, a layer of resin is applied. The resin hardens as it cures.  By repeating this pattern, a very strong but light material is created.

Once at least a dozen layers of fiberglass have been applied, a core layer is laid. The core can be constructed from foam or balsa wood. The core is pre-cut and laid by hand.

There is some debate whether foam or balsa is superior. Balsa is more rigid and requires fewer layers of fiberglass than the more flexible foam. The end result is that balsa hulls may be lighter than foam hulls. I think it all comes down to personal preference. The core is there to help absorb vibration and strengthen the hull. Both foam and balsa fulfill that job well and are currently used by luxury yacht builders worldwide.

Hull Sandwich

A fiberglass and core sandwich sounds like a difficult thing to choke down, but it's a delicious combo in a boat hull. Sandwiching core material between fiberglass layers allows for a super strong, relatively light structure that lasts for decades.  This sandwich also helps to insulate the vessel, keeping it cool in hot weather and warm in cold weather.

To create the sandwich, an additional layer of fiberglass sheets and resin is applied throughout the entire hull on top of the core. Some manufacturers use a vacuum system to ensure that every inch of the core has been filled with resin.  After the last layer of fiberglass and resin has cured, the internal construction of the boat begins.

Deck Construction

The deck of the boat is created in much the same way as the hull. A plug is built and a mold is created from that. The mold then has a fiberglass sandwich applied within.

Some boats are designed with upper and lower layers of deck construction. The upper layer is seen from deck level while the lower layer is the cabin ceiling. Lights and wiring are installed between the layers prior to their joining.

My sailboat is constructed with only the upper deck layer. The underside of this layer was then covered with a headliner to hide the imperfections in the fiberglass. I'm sure it looked lovely when it was new, but after almost 40 years of use, the headliner was far from appealing.

One of my criteria for our next boat is to have both the upper and lower level deck construction.  It's easier to keep clean and free from mildew. As I said earlier, I removed the headliner and painted the fiberglass. It's miles ahead of what it was, but it certainly doesn't have the finished look of a fabricated fiberglass ceiling.  The weave of the fiberglass is huge. Most of my boat's interior looks like it's made like a basket as evidenced by the ceiling pic below.


Internal Anatomy Of A Sailboat

A structural grid made from either wood or steel is installed in the bottom of the hull. This stable floor section takes the force of wave action against the hull. It also holds the weight of the tanks (water, fuel, holding), engine, mast, and internal walls of the sailboat.

At this point, automation generally begins to find its place in the fabrication process. Some manufacturers use machines to cut the fiberglass sheets to precise specifications, or use machines to evenly spray resin onto the fiberglass sheets. But almost all major boat manufacturers have begun using robots to cut the necessary holes into the hull.

By using an automated robotic machine arm to cut the ports, screw holes and thru hull openings, human error is eliminated. This provides for perfect placement of fittings every time.

Once the openings in the hull have been cut, the internal structure begins to be installed. Some hulls have slots in their form which the wall sections slide into. Other manufacturers fiberglass the walls and bulkheads in place.

The electrical wiring and plumbing lines are installed in such a way that they are hidden from view. This can be a time consuming process as cables and tubing gets threaded through cupboards and compartments, under flooring and above ceilings. The end result is that all the unsightly aspects of the electronics and plumbing are out of sight and out of mind. Having all those system components hidden can make it difficult to repair and replace them down the road. However, it's a fair compromise for a clean, neat cabin interior.

Deck installation

After all the internal structures of the sailboat have been installed (engine, tanks, plumbing, cabinetry, walls, and bulkheads) the deck is put in place on top of the hull section.

The deck on a sailboat is generally connected to the hull with an inner flange. This means that the hull has an inward facing lip that the deck rests on. An adhesive sealant is placed between the deck and the hull. Screws or bolts are also used to secure the deck to the hull.  The toe rail is installed on top of the bolts in most applications.

Below The Waterline Construction

Keel Construction

There are two types of keels: bolted on and encapsulated.

A bolted on keel is made of cast lead and bolted onto a keel stub at the bottom of the hull.  Bolted on keels tend to make a boat faster than an encapsulated keel while also allowing for easier repairs, when necessary.  A bolted on keel can be unbolted and repaired at a different location which is not possible with an encapsulated keel.

An encapsulated keel is structurally part of the hull itself. The keel cavity is filled with cement or resin and lead or iron for ballast. The encapsulated keel allows for greater bilge capacity, lower maintenance as there are no bolts requiring maintenance, and are less expensive.

Propeller Shaft Installation

Once the engine has been installed, the propeller shaft is inserted through the shaft tube which is attached to the hull, and into the shaft seal. The shaft then passes through the stuffing box and into the shaft coupling at the engine.

The propeller shaft is generally installed prior to the rudder due to their alignment.

Rudder Design

The rudder is installed after all the hull openings have been cut. Rudders are generally made using a fiberglass shell filled with a metal frame work welded onto the steel rudder shaft. Foam fills the remainder of the rudder interior. The rudder shaft enters through the hull at the stern and connects up with the vessel's steerage system.

The rudder shaft is designed to bend should a grounding occur in order to save the hull. If the shaft were made too strongly, it could rip a hole in the hull during a rudder grounding.

Above Deck Installations

Before the deck is secured to the hull, much of the hardware is installed. Winches, cleats, windlass, steering column, and ports are all already in place when the deck is fitted to the hull. Cleats are generally backed with a stainless steel reinforcing plate within the cabin. This ensures that the cleat will not rip through the fiberglass when strain is put upon it. If an anchor chain windless is installed, it too is backed with a stainless steel plate.

Mast construction

Masts were originally made out of wood and some vessels still have wooden masts to this day. Wooden masts were constructed using the trunk of a conifer tree. Larger ships required multiple tree trunks lashed together to create a single mast.

Today, the vast majority of sailboats have masts made of aluminum. The mast is hollow which causes the structure to be light while retaining its strength.

Some racing sailboats have masts made from carbon fiber. These masts weight half as much as aluminum masts but cost 3-4 times as much. The decreased weight increases the racing boats speed.

The wiring from the equipment at the top of the mast, or masthead, is run down through the mast to the cabin below. The typical mast head equipment includes: anchor light, wind speed indicator, and wind direction indicator. Modern vessels also have a steaming light half way down the mast on the front side and deck lights on the spreaders.

Some vessels have mast wiring installed in the cabin ceiling while others have the wires running under the floor and back to the electrical panel.

My vessel has its masthead wiring running down the deck stepped mast, through its support pole, and under the floor in the cabin. It's very difficult to see, much less access, for maintenance.

Mast Installation

The rigging and mast are installed once the boat is in the water. Depending on the height of the mast, a crane may be necessary to install, or step, the mast.

Masts are either deck stepped or keel stepped. A deck stepped mast stops at the deck and a support pole runs from the cabin roof down to the keel. A keel stepped mast runs through the cabin top directly down to the keel.

The standing rigging is all the steel cables that run from the deck to the mast. The cables are secured to stainless steel fittings at the deck and run up to the spreaders or upper mast. Some vessels have an adjustable backstay to modify the boat's performance under sail.

From Wikipedia:

Standing rigging on a fore-and-aft rigged sailboat.

Key: 1. Forestay 2. Shroud 3. (Spreaders) 4. Backstay 5. Inner forestay 6. Sidestay 7. (Boom) 8. Running backstays

Running rigging is the lines, or ropes, which connect to the sailboats sails and boom. Halyards, vangs, braces and sheets comprise sailboats running rigging.

One summer when I was about 15, my family was crossing Lake Michigan in our Chris Craft sailboat when it was dismasted. Our vessel had a deck stepped mast and its support pole failed. The mast came crashing through the cabin top before being ripped back out again by the sails. It was a nightmare of a situation with the mast eventually ending up in the bottom of the lake. I was wary of deck stepped masts after that experience. My current boat is deck stepped with a much beefier pole than that Chris Craft had, thank goodness.

Painting The Boat

The raw fiberglass on a boat is painted with gelcoat which is a thick, durable modified resin. It generally has a thickness of. 02 to .03 inches. Gelcoat is resistant to damage from the sun and water.

Some boat manufacturers apply gelcoat to the mold prior to the first layer of fiberglass. This method creates a beautifully finished hull right out of the mold. Another method is to apply the gelcoat and striping to the hull after it has been removed from the mold.

The same techniques are used for the deck. Some companies apply gelcoat to the mold while others wait until the deck is out of the mold. This is also true of non-skid decking. When a boat has teak decking it is applied after the deck has been removed from the mold and it generally undergoes a vacuum resin process to attach the teak to the deck material.

How Are Sailboats Made?
Beth York

Beth York

Beth lives on board her 1983 30ft S2 sailboat with her husband, 6 year-old son, and her two fur babies. She has been sailing and boating for most of her life. Beth has been blessed to experience cruising in the Great Lakes, the Bahamas, and in Alaska. She loves to travel and adores living on her tiny boat with her family.

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