Sailboat Keels Are Made of These 4 Materials (Lead, Iron)
There are two parts to any sailboat keel, and each part is traditionally made of just one of three materials each. But there are large differences between the materials.
Sailboat keels are typically made of reinforced fiberglass layers, steel, or wood, depending on the hull material, boat model, and build year. Keel ballast usually consists of lead or iron.
Ballast can consist of other materials too. Below I'll discuss all materials and the arguments for each one.
What Material Are Sailboat Keels Made Of?
Keel outer materials
There are two parts to any sailboat keel: the shell and the ballast. The shell is generally made of the same material as the hull. This can be wood, laminated fiberglass, or steel. In some cases, the keel is made from a different material than the hull, but this is not very often the case. You mostly see this when the keel is a separate part from the hull, for example with fin keels, which can be bolted on.
Ballast materials
Most ballast is made out of lead or iron. However, there are more materials that can be used, depending on budget or space availability.
Frequently used ballast materials:
- lead
- (cast) iron
- concrete with iron waste
- water
The most popular materials are definitely lead and iron, with lead being the best ballast material.
Why are keels made of lead?
Lead has the highest specific weight of the different sailboat keel materials available, which means it requires the least amount of volume. At 11.3 kg/dm3, it is 56% denser than iron (7.25). This means you'll need 56% less volume to get the same ballast weight, saving you nearly half the space.
Do all sailboats have lead in the keel?
Not all sailboats use lead in their keels. For example, a lot of cheaper boat designs will use cast iron to reduce cost. Some sailboats carry no ballast in the keel at all. Especially inland-water boats with flatter hulls require less ballast or none at all.
Ballast can also consist of multiple materials, and often times boat builders choose a different material for the integral ballast (the ballast in the hull) and the keel ballast (the ballast in the tip of the keel) to keep costs down. In the popular fin keel design, space is very limited, which is why lead is the go-to material for larger cruisers that require high keel ballast. For daysailers, which require lower keel ballasts, iron can be used, or even cement.
Ballast Materials Compared
| Material | Specific weight in kg/dm3 |
|---|---|
| Lead | 11.3 |
| Cast iron | 7.25 |
| Concrete with iron | 4 - 5 |
| Concrete | 2.4 |
| Water | 1 |
Lead
Lead is the densest material, but it also the most expensive. High-end sailboats will use lead as their preferred ballast material, or a combination of lead and iron.
Cast iron
Whenever iron is used in a keel design, it is always cast iron. Cast iron is the second densest material available, and a lot less expensive than lead. Most budget sailboats use cast iron ballast, both in their keel and hull.
Concrete
Sailboats that require less ballast and have a strict build budget can use concrete instead of metals. Concrete is more than four times less dense than lead, which means it is only a viable option if you don't need a lot of ballast to begin with. Whenever concrete is used, iron waste is added into the mixture to roughly double the weight without driving up the cost dramatically.
Water
Some sailboats use water as integral ballast (ballast carried in the hull), but it is very rare. Well-known sailboat models that use water ballast are the Hunter series (over 26 feet).
The use of water is a lot more common on ships like cruisers, motor yachts, and container carriers. The advantage of using water is that you can easily increase or decrease the ballast by adding or dumping water, which is readily available wherever you go.
How Much Does a Lead Keel Weigh?
The weight of a lead keel depends on the desired ballast to displacement ratio. The used weight would be the same for any ballast material, be it lead, iron, or cement. The difference is that lead would take the least amount of volume, since it has the highest specific weight of all typical keel materials.
The average weight of a 35-foot sailboat keel is between 5,000 - 6,000 pounds, but the weight varies between 200 - 12,000 pounds based on the sailboat size, use, and keel design.
How Do Sailboat Keels Work?
In short, a sailboat keel's weight is used to to increase displacement and lower the center of gravity, while its surface is used to increase wetted surface. This helps to stabilize the boat, but also provides directional stability. For a more detailed explanation on how sailboat keels work, I recommend reading this article.
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