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What is a Boat Keel? & What Does It Do? – Detailed Explanation

Written by J. Harvey / Fact checked by S. Numbers

Knowing the different parts of a boat is important for any mariner. If you look at your vessel exterior, one of the things that’s noticeable is the keel. But what is a boat keel and what does it do?

The keel is a horizontal structure at the bottom section of the hull, which acts as the boat’s main support. We’ll cover keel definition boat use and other relevant information.

Keep reading to learn more.

Table of Contents

The Boat Keel and What It Does

6. centerboard and swing, frequently asked questions.

The keel of a boat is a beam that acts as structural support for the hull and entire vessel. It has many types, and varying designs lead to differences in appearance, with some being longer and extending deeper into the water.

However, serving as support for the hull is not the only purpose of a keel on a boat. It also counterbalances a vessel, which helps to keep it in place and not be displaced by external factors. It is also partially responsible for moving a boat forward and aids steering.

The keel of a ship functions similarly to the keel on boat, serving as the backbone and ballast. It is often the first thing to be constructed on a ship.

Types of Keels

This type usually covers the entire length of the vessel and is one of the most common types used. This keel offers a high degree of safety, owing to its very stable performance along with the ability to run through sand without breaking off.

This is similar to the full keel but shorter, running less than 50% of the length of a vessel. This difference allows it to contribute to a boat’s ability to turn while also giving improvements to its speed. This type is commonly found in racing models.

This keel boat part is similar to the fin, except for the bulb attachment at the bottom, which resembles a torpedo.

The shape of the bulb also makes it less likely to be damaged by contact with rocks, and this type is excellent for cruising.

This design extends the length of the keel, making it similar in appearance to an airplane wing. This design allows a vessel to turn and maneuver more easily, but it is more susceptible to breaking or digging into the ground.

Instead of just one at the center, the bilge keel has one for each side of the hull. A vessel with this type of keel has less roll, which gives better comfort on the water. It also has a lower draft and allows easier anchoring on shallow waters.

These are two different types of keels but are grouped because of their similarities in design. These can adjust their length, making them usable for both deep and shallow water. However, centerboards only partially retract, while swing types have their entire length fully adjustable.

These have the advantage of adjustability but less performance, and they also have more components that require checking compared to fixed keels.

This is similar to the swing keel in that its entire length is connected to a hinge at the bottom of a sailboat but adjusts from side to side, starboard to port, and vice versa.

It can boost speed and maneuverability by wetted surface reduction and weight shifting. This is often used for racing vessels but is still considered experimental as there is a high rate of failure due to its reliance on hydraulics.

Hull and keel: what is the difference?

The keel hull confusion likely stems from the fact that the keel is often part of the hull. However, they are two entirely different things, since the hull is the main body of the boat while the keel is a beam that is connected to the bottom of the hull and may extend farther down from it.

Do all boats have a keel?

Most boats do, but not all boats, as flat-bottomed ones are the exception. The keel boat Lewis and Clark Expedition used in 1803 is a well-known example. This was a barge, a type of flat-bottom vessel that was a boat without a keel.

How is the keel of the boat different from the keel at the bottom of a ship?

Both ships and boats have keels that function in similar ways, but how they are constructed and even the keel shape are different. While most types of sailboat keel are fin-like in appearance, a keel ship needs to be much wider to be able to support the entire ship’s size.

Knowing what is a boat keel is a very important matter that you should no longer have trouble with. Now, you can move on to learning other major parts of vessels. Just remember to consider the draft and use a boat keel guard to safeguard your vessel.

Which type of keel is best in your opinion? Tell us all about it in the comments section below. We’ll be waiting to hear from you.

Remember to boat safely.

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Sailboat Keel Types Compared: Pros and Cons of 13 Types

There are various keel designs, each with specific advantages and disadvantages. For instance, full keels provide better stability and tracking, making them a popular choice for long-distance cruisers. On the other hand, fin keels enable sharper turns and quicker reactions, which appeal to racers and those seeking a more nimble experience. Choosing the right keel type for your sailboat depends on your sailing preferences, cruising goals, and intended destinations.

A sailboat's keel plays a significant role in its overall stability, performance, and comfort. It helps you maintain balance, steer your boat, and improve your boat's sailing efficiency. Sailboat keel types impact not only the performance and handling of your sailboat but also its suitability for different sailing conditions.

Let's compare 13 different keel types, and discuss their strengths and weaknesses, as well as their practical applications.

• The keel types that are known for their comfort and seaworthiness are full keel, bilge keel, wing keel, Scheel keel, and fixed keel.
• The best keel types for speed are canting keel, bulb keel, and wing keel.
• For improved maneuverability and agility , the best keel types are swing keel, centerboard keel, and daggerboard keel.
• The keel types that provide the most stability are bulb keel, fixed keel, and fin keel.

On this page:

Pros and cons of 13 types of keel, canting keel, centreboard, daggerboard, lifting keel, scheel keel.

If you're curious what these keel types look like, here's our illustrated guide on sailboat keels .

Full-length keel : Full-length keels run the entire length of the boat. They offer excellent stability and are popular among offshore cruisers who require a solid, rugged sailboat. Full keeled boats are better suited for heavy weather, but they may be slower due to their weight and drag.

Fin keel : Fin keels are thinner and generally used for racing, as they provide a good balance between speed and stability. Their reduced drag means faster speeds but might be less stable compared to full-length keels in heavy seas.

Bulb keel : A bulb keel features a heavy, rounded weight at the bottom of the fin keel. This extra weight lowers the boat's center of gravity and provides additional stability without significantly increasing drag.

Canting keel : A canting keel is a high-performance feature that can pivot from side to side, allowing the boat to maintain optimal stability while heeling over on its side to maximize speed in racing scenarios.

Centerboard : This keel type features a retractable board that can be lowered for sailing upwind and raised in shallow waters. Centerboards are often found on smaller boats and dinghies.

Swing keel : Swing keels operate on a hinge, swinging up and down to adjust the boat's draft. They balance the benefits of a larger keel with the convenience of a shallow draft for docking and beaching.

Wing keel : Wing keels are similar to bulb keels but with two small wings on either side of the bulb. These wings increase the effective surface area, offering better stability and shallower draft capabilities, ideal for coastal cruising.

Bilge keel : Bilge keels are found on boats with two smaller keels on either side of the hull rather than a single central keel. This design is most commonly used in tidal waters and on small fishing boats, allowing the boat to sit upright when grounded during low tide.

Daggerboard : Similar to a centerboard, a daggerboard is a non-weighted, removable board that slides vertically through a slot in the hull. This type is also commonly seen on dinghies and smaller sailboats.

Fixed keel : Fixed keel provides good stability and is less prone to damage than other keel types. However, it can limit the boat's ability to sail in shallow waters and may make it more difficult to trailer the boat.

Lifting keel : A lifting keel can be raised or lowered, providing both the benefits of a deep keel for improved stability and performance and a shallow draft for easier access to shallow waters and docking.

T-keel : T-keels provide improved stability and upwind performance, which can be desirable for sailors. However, their larger draft and vulnerability to grounding should be considered when deciding if this keel type is the right choice for your sailing adventures.

Scheel keel : This offers unique benefits, and it could be an excellent choice for your sailboat if you prioritize stability, shallow draft, and efficient upwind sailing. However, you should consider the potential drawbacks, such as decreased speed and increased maintenance, before making a final decision.

Pros of full keel

A full keel has several advantages that make it an appealing option for many sailors. First and foremost, it offers exceptional stability , which is particularly important when you're out at sea for extended periods. With a full keel, your sailboat can better resist the forces acting on the sails, ensuring a smoother and safer journey.

Another significant benefit is the durability of a full keel. Because of the large surface area and the way it's constructed, full keels tend to be very strong and resilient, making them perfect for long-distance cruising. Additionally, this type of keel provides excellent tracking , helping your sailboat stay on course in various conditions.

Lastly, full keel sailboats are less likely to be damaged when grounding , as the keel's large surface area allows for better weight distribution. This characteristic can be especially useful when navigating shallow waters or exploring uncharted territories.

Cons of full keel

Despite the many advantages of a full keel, it also has some drawbacks. One of the most noticeable disadvantages is its effect on sailboat performance. Full keels tend to be less maneuverable than other keel types, which can be a drawback in tight situations or when you need to make quick adjustments during sailing.

Another downside is the increased wetted surface area, which leads to higher drag and slower speeds when compared to other keel types, such as fin keels. This reduced efficiency can be a concern, especially for those who prioritize performance and speed on their sailing journeys.

Additionally, full keel sailboats may be more challenging to maneuver in tight spaces , such as crowded marinas, due to their reduced maneuverability and larger turning radius. This can make docking and mooring more complex, particularly for inexperienced sailors.

Pros of fin keel

Fin keels hold several advantages for sailors. First, they offer improved performance. A fin keel's streamlined shape cuts through the water more efficiently, allowing sailboats to reach higher speeds with less drag. Moreover, fin keels generally provide better upwind performance than other keel types.

Their maneuverability is another significant benefit. Fin keels allow sailboats to turn more quickly and easily, making them nimble in tight spaces and responsive to the helm. Additionally, they typically have a reduced draft, meaning they can navigate shallow waters more effectively than boats with deeper keels.

Lastly, fin keels are popular for their ease of maintenance . Since they're typically bolted onto the hull, routine inspections and potential repairs are relatively straightforward and accessible.

Cons of fin keel

Despite the benefits, there are a few drawbacks to consider when it comes to fin keels. First, they tend to have less stability than full or bilge keels. Their slender design and reduced weight can make them more prone to sudden heeling, which some sailors may find uncomfortable or disconcerting.

Another potential issue is structural vulnerability . If a fin keel strikes a submerged obstacle, such as a rock or shipping container, it may suffer damage or even become dislodged, which could pose a significant risk to the integrity of the boat. This stands in contrast to more robust full keels, which can better absorb the impact of groundings or collisions.

Lastly, fin keels are sometimes considered less comfortable for cruising sailors. Due to their design, boats with fin keels can experience more motion (both side-to-side and up and down) in rough seas, potentially leading to discomfort or seasickness for the crew.

A bulb keel is a type of sailboat keel that features a streamlined fin with a bulb-shaped weight at the bottom. This design aims to improve the boat's performance, especially in racing conditions. In this section, we will explore the pros and cons of bulb keels.

Pros of bulb keel

Stability : The main advantage of a bulb keel is its ability to provide excellent stability. The bulb's weight is concentrated at its lowest point, which lowers the center of gravity of your sailboat. This design helps keep the boat upright and stable when sailing, especially in strong winds.

Performance : Bulb keels contribute to a sailboat's overall performance by reducing drag. The streamlined shape of the fin and the placement of the bulbous weight make it easier for your boat to glide through the water, increasing your overall speed and agility when sailing.

Upwind sailing : A bulb keel allows your sailboat to sail more effectively upwind. By reducing leeway and maintaining a consistent course, your boat can navigate better through a variety of wind conditions.

Cons of bulb keel

Maintenance : One potential downside of a bulb keel is the increased maintenance required. The bulbs can be more prone to collecting marine growth, which may necessitate regular cleaning and antifouling treatments to maintain peak performance.

Depth : Bulb keels, due to their design, have a deeper draft than other keel types. This means that your sailboat might struggle in shallow waters or require extra diligence while sailing in areas with submerged obstacles or coral reefs.

Pros of canting keel

Canting keels are a popular choice among performance-oriented sailors due to their remarkable benefits in several areas. They offer increased stability and enhanced performance , especially when sailing upwind. This type of keel allows the boat to maintain a more upright position when healing, reducing drag and improving your overall speed and efficiency on the water.

Moreover, canting keels are adjustable , which allows you to alter the keel angle depending on the wind conditions and desired performance. This flexibility can make a significant difference in how your boat performs on the water. Another advantage of canting keels is their improved handling characteristics , which make them easier to maneuver in various conditions.

Cons of canting keel

Despite the many advantages, there are also some notable drawbacks to using a canting keel. One significant downside is their complexity and cost . These keels often require sophisticated engineering and systems, which can drive up the overall price of your boat and may require more maintenance and repairs over time.

Another potential issue with canting keels is their increased vulnerability to grounding . Since the keel can extend deeper beneath the boat, there is a higher risk of hitting obstacles or running aground, especially in shallow waters or unknown territories.

Lastly, canting keels can contribute to changes in the boat's handling characteristics , particularly when sailing downwind. While their adjustability may enhance upwind performance, it may also lead to instability and increased difficulty controlling your boat in heavy downwind conditions.

Pros of the centerboard

A centerboard is a movable keel that can be retracted or lowered to provide stability and balance to your sailboat. Here are some benefits you can enjoy with a centerboard:

• Shallow draft : With a centerboard, you can easily navigate shallow waters and get closer to shore. This is particularly useful for exploring coves, anchorages, and beaching your boat.
• Adjustable performance : By adjusting the position of the centerboard, you can fine-tune your sailboat's performance based on the current sailing conditions.
• Easier transport and storage : Retractable centerboards make it simple to trailer your sailboat and store it in tight spaces without worrying about a fixed keel's height or depth.
• Grounding protection : In case of accidental grounding, a centerboard can help minimize potential damage by absorbing the impact instead of transferring it to your boat's hull.

If you're torn between centerboard, swing, and fixed keels , here's our in-depth article on their pros and cons.

Cons of the centerboard

Despite the advantages, centerboards also come with some drawbacks that you should consider:

• Less stability : When compared to fixed keels, centerboards offer less stability, especially for larger sailboats. This may lead to reduced performance in rough waters or strong winds.
• Maintenance : Centerboards require regular maintenance to ensure they remain functional and efficient. This may include cleaning, lubricating, and inspecting the related components.
• Complexity : The moving parts and additional mechanisms in a centerboard system can be more complex than a fixed keel, potentially increasing the likelihood of mechanical issues.
• Reduced interior space : Depending on your sailboat's design, the presence of a centerboard trunk may limit the available interior space, impacting your comfort and storage options.

The swing keel is a type of sailboat keel that essentially pivots on a hinge or bolt, allowing the keel to swing up or down as needed. This feature grants a sailboat with a swing keel the ability to adjust its performance and stability depending on the sailing conditions or water depth. Let's discuss the pros and cons of swing keels in detail.

Pros of swing keel

Versatility : The swing keel's ability to pivot grants your sailboat the capability to navigate shallow waters and safely beach your boat without getting stuck. This is advantageous for exploring coastal areas and coves.

Adjustability : Swing keels provide the opportunity for better control over your boat's performance. By adjusting the keel angle, you can find the right balance of stability and speed tailored to your sailing experience and conditions.

Trailerable : A sailboat with a swing keel can be easily trailered and transported, as the keel can be retracted, reducing the boat's weight, draft, and overall dimensions.

Ease of maintenance : Swing keels are often easier to maintain and repair, as they can be retracted for inspection or servicing without having to haul out the entire boat.

Cons of swing keel

Reduced performance : A trade-off with the swing keel's versatility is that it generally doesn't offer the same level of performance as a fixed keel sailboat, especially when it comes to upwind ability or pointing.

Additional complexity : The presence of a pivot point and moving parts can make swing keels more prone to wear or damage. This can lead to additional maintenance requirements or repairs if not properly cared for.

Increased weight : Given the swing keel's construction, materials, and additional hardware, it can add extra weight to your boat compared to other keel types. This may affect your boat's overall performance.

Potential leaks : Like any keel with moveable parts, a swing keel can introduce the risk of water ingress if the seals or hull are not properly maintained.

Pros of wing keel

The wing keel is an innovative design that has gained popularity among sailors due to its unique features and benefits. One of the main advantages of this keel type is its shallow draft . The horizontal wing allows the keel to have a larger surface area without going as deep as a fin keel of the same size, making it ideal for sailboats navigating shallow waters.

Another benefit of the wing keel is its relatively good upwind performance . While not as efficient as a fin keel, it still performs well in many sailing conditions, offering a great balance between maneuverability and stability.

The ease of grounding and recovery is another plus for the wing keel. Since it has a relatively shallow draft, you are less likely to hit the seabed when navigating shallow waters. Furthermore, if the boat does become grounded, the wing keel design makes it easier to refloat.

Cons of wing keel

However, the wing keel is not without its drawbacks. The most notable disadvantage of this design is its reduced pointing ability compared to fin keels. The wing keel may struggle to sail as close to the wind as a similarly-sized sailboat with a fin keel, which can be a disadvantage when racing or sailing in tight spaces.

A wing keel sailboat may also be prone to increased leeway due to the lower depth and surface area of the keel. This can make the boat more difficult to control in strong winds or challenging sea conditions.

Another issue to consider is the maintenance and cleaning of the wing keel. Due to the horizontal wings, it may be harder to access and clean the keel properly, leading to increased fouling or potential damage.

Bilge keels are an interesting combination of two smaller keels mounted on either side of the hull, which provide stability and added performance benefits in certain conditions. In this section, we will explore the pros and cons of bilge keels on sailboats.

Pros of bilge keel

• Shallow draft : Bilge keels allow you to access shallow water areas, expanding your cruising options. The dual keel design keeps your boat stable in shallow waters, making it ideal for exploring remote destinations, such as tidal estuaries or hidden coves.
• Low maintenance : Compared to other keel types like fin keels or lifting keels, bilge keels require less maintenance. They are sturdy and simpler to maintain due to their fixed position.
• Self-righting : With bilge keels, your sailboat has a natural ability to self-right after a capsize. Their wide footprint provides additional support and stability, reducing the chances of a full capsize.
• Beaching ability : Bilge keel boats can safely dry out on the beach or tidal flats without tipping, making it easier for you to conduct maintenance or give the hull a thorough clean.

Cons of bilge keel

• Reduced performance : While bilge keels offer stability and shallow draft benefits, they can reduce your sailboat's performance in certain conditions. They create more drag, causing your boat to be slower and less agile than boats with fin keels.
• Heeling angle limitations : Due to their wide footprint, bilge keel sailboats experience a larger heeling angle, which could make sailing at high speeds or in strong winds challenging.
• Less upright stability : Bilge keel boats may be less stable when sailing in extreme conditions, as the dual keel design provides less leverage for the boat to lean on compared to a deep fin keel.

Pros of daggerboard

A daggerboard can enhance your sailing experience in several ways. First and foremost, it provides improved maneuverability . With a daggerboard, you can navigate through shallow waters more easily, making it ideal for exploring coastal areas and inland waterways.

Another advantage is the ease of maintenance . Daggerboards are simpler in design compared to other keel types, making them easier to maintain and repair. Additionally, they are easily retractable, allowing you to adjust the draft of your sailboat depending on the depth of the water, avoiding running aground or hitting underwater obstacles.

Daggerboards are also typically lighter in weight compared to other keel types, which contributes to better sailing performance, particularly in light wind conditions. It is also worth noting that their simple design often results in lower production costs for boat manufacturers, resulting in more affordable options for you, the buyer.

Finally, daggerboards are popular on trailer sailers due to their retractable nature, making it more convenient for you to transport your sailboat on a trailer over land when necessary.

Cons of daggerboard

Despite the various advantages, there are a few downsides to consider when it comes to daggerboards. One notable drawback is their limited righting moment . This means that sailboats with a daggerboard are generally less stable and more prone to heeling or even capsizing in rough conditions. If you frequently sail in choppy waters, this could be a significant concern for your safety.

Another downside is the space occupied by the daggerboard case inside the cabin of the boat. This can reduce the available living space, especially on smaller sailboats. In addition, daggerboards can be noisier than other keel types when sailing due to water noise around the daggerboard case.

Lastly, the lack of keel protection in boats with daggerboards makes them more vulnerable to damage by underwater obstacles. While the retractability feature might mitigate this risk somewhat, it is still essential for you to remain cautious when navigating shallow and uncharted waters.

Pros of fixed keel

A fixed keel offers numerous advantages that can make your sailing experience more enjoyable. First, fixed keels provide better stability as they have a lower center of gravity, resulting in a more comfortable ride. This is particularly beneficial when sailing in rough weather or choppy seas.

Moreover, fixed keels offer improved upwind performance compared to other keel types. The deeper draft allows the boat to generate more lift and point higher into the wind, making it faster and more efficient when sailing upwind. Additionally, these keels are low-maintenance since there are fewer moving parts to wear out or require replacement.

Lastly, fixed keel boats tend to have better handling under power . They can make precise turns and handle well in reverse, allowing for easier maneuvering in tight spaces and marinas.

Cons of fixed keel

Despite their advantages, fixed keels also come with some drawbacks. One of the main concerns is their depth , which limits the boat's ability to access shallow waters. This may restrict your sailing options, especially near shorelines or in tidal areas.

Additionally, fixed keel boats can be less maneuverable at slower speeds compared to boats with swing keels or centerboards. This can make tight turns more challenging, especially in crowded harbors or narrow waterways.

Finally, fixed keel boats are generally heavier and harder to trailer , as they require a higher towing capacity and specially designed trailers to accommodate the boat's deeper draft. This added weight can make transportation more difficult and lead to higher fuel costs for road transportation.

Pros of lifting keel

A lifting keel is a type of keel that can be raised or lowered, allowing you to adjust the depth and balance of your sailboat. When properly utilized, a lifting keel can provide a number of benefits to enhance your sailing experience.

• Versatility : A lifting keel allows you to sail in shallow waters as well as access ports and harbors with limited depth. This is especially useful for exploring coastal areas and navigating tidal waters.
• Improved performance : By adjusting the depth of the keel, you can optimize your boat's performance in various sailing conditions. This can result in better speed, stability, and upwind performance.
• Easier transportation : With the ability to raise the keel, transporting your sailboat on a trailer becomes more manageable as it reduces the overall draft and height of your boat.

If you're choosing between swing or lifting keel , here's our more detailed guide on their pros and cons.

Cons of lifting keel

While a lifting keel offers several advantages, it is essential to be aware of some potential drawbacks before choosing this type of keel for your sailboat.

• Maintenance and complexity : Lifting keels typically require more maintenance due to the moving parts involved. Extra care is needed to inspect and maintain the keel's lifting mechanism, which might include a winch, cable, or hydraulic system.
• Added weight : The lifting mechanism adds weight to your boat, which can have negative effects on performance and fuel efficiency.
• Potential weaknesses : The structural integrity of a boat with a lifting keel can be compromised if it is not designed and engineered properly. This could lead to stress points or even failure in extreme situations.

Pros of T-keel

T-keel is a unique design that has its advantages to consider. First, it offers improved stability . With a heavier weight concentrated at the bottom of the keel, your sailboat will resist heeling, maintaining a more upright position in strong winds. This added stability allows for better control and a smoother ride when sailing.

Another pro of the T-keel is its powerful upwind performance . The shape and design of this keel allow for a low center of gravity while minimizing drag. This combination helps your sailboat efficiently point into the wind, allowing for a quicker upwind speed. This increased performance can make a difference when racing or navigating through tight spaces.

Cons of T-keel

However, T-keels are not without their drawbacks. One potential downside is that T-keel boats tend to have a larger draft than other types of keels, meaning they require deeper water for sailing. This can restrict your ability to sail in shallow waters around bays or near shorelines, limiting your access to certain areas.

Another drawback of T-keels is that they can be more prone to grounding due to their design. If you accidentally run aground or hit an underwater object, the T-keel may be more likely to experience damage or become difficult to dislodge. This can lead to costly repairs or complications when trying to free your sailboat.

The Scheel Keel is a unique keel type that was designed by naval architect Henry Scheel in the 1970s. This keel offers a compromise between performance and stability, making it a popular choice for many sailboat owners. In this section, we'll discuss the pros and cons of the Scheel Keel to help you decide if it's the right choice for your sailing needs.

Pros of Scheel keel

Shallow draft : One of the main advantages of the Scheel Keel is its shallow draft. This allows you to navigate in shallower waters, making it easier to access more anchorage spots and enjoy cruising in coastal areas.

Stability : With its wide, flat bottom, the Scheel Keel provides good stability, making your sailboat feel more secure and comfortable in various conditions. This can be especially beneficial for less experienced sailors or those who prefer a more stable ride.

Efficient upwind performance : The Scheel Keel is designed to improve upwind performance without sacrificing stability. This means you can sail more efficiently and at a better angle to the wind, which can be a noticeable advantage in many sailing situations.

Cons of Scheel keel

Potential for decreased speed : Due to its wide, flat bottom, the Scheel Keel can create more drag, which may decrease your overall speed in comparison to other keel types. While the Scheel Keel offers improved upwind performance, it may not be the best choice for you if maximizing speed is your primary concern.

Maintenance : The unique shape of the Scheel Keel can make it more susceptible to damage, particularly if you frequently sail in shallow waters or near shorelines with rocks and other hazards. As a result, you might need to pay closer attention to the maintenance and repair of your keel.

Limited availability : While many sailors appreciate the benefits of the Scheel Keel, it's not as widely available as some other keel designs. This could make it more difficult for you to find a sailboat with a Scheel Keel or to have one retrofitted to your current boat.

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Practical Boat Owner

• Digital edition

Keel types and how they affect performance

• Peter Poland
• June 19, 2023

Peter Poland looks at the history of keel design and how the different types affect performance

The Twister is a well-proven example of a generation of production yachts with ‘cutaway’ full keels and keel-hung rudders. Credit: Graham Snook/Yachting Monthly

Having been a boatbuilder for around 30 years until the very early ‘noughties’, I’ve already witnessed – and even taken part in – a lot of changes in the world of yacht design and building.

Yacht design originally evolved as traditional workboats developed into leisure craft.

In his History of Yachting , Douglas Phillips-Birt writes that the Dutch, who gave the name ‘yacht’ to the world, were probably the first to use commercial craft for pleasure in the 16th century.

They created the first yacht harbour in Amsterdam in the 17th century.

When the schooner America visited the UK in 1851 and raced around the Isle of Wight, this led to the America’s Cup and the resulting merry-go-round of race-yacht design that continues to this day.

The Jeanneau Sun Odyssey 35 offers three different fin keel configurations with different draughts plus a lifting keel version with a centreplate housed in a shallow winged keel stub. Credit: David Harding

The creation of what is now the Royal Yachting Association ( RYA ) in 1875 led to the introduction of handicap rules, establishing the sport in Britain.

These rating rules – and their numerous successors down the ages – have helped determine the evolution of yacht design and keel shapes.

Many early yachts were closely based on workboats, commercial cargo carriers or even privateers and naval vessels.

Initially, the ballast was carried in a long keel and the bilges .

New racing rules of the day taught designers to seek and tweak performance-enhancing features.

Maybe racing did not always improve the breed, but it certainly kept it moving ahead.

Artwork inspired by Ted Brewer’s illustration of keel types (excluding centreplate or lifting keels)

The late, great designer David Thomas believed that fishing boats, pilot cutters and oyster smacks had a large influence on the sport of sailing.

Each type of workboat was built to fulfil a specific purpose. And many had to be sailed short-handed while carrying heavy cargoes.

So they needed to combine form and function, sail well and be able to cope with heavy weather.

Proof of the versatility of working boat designs was provided by Peter Pye and his wife, Anne.

They bought a 30ft Polperro gaff-rigged fishing boat (built by Ferris of Looe in 1896) for £25 in the 1930s.

Having converted her to a sea-going cutter, and renamed her Moonraker of Fowey , they sailed the world for 20 years.

It proves how the simplest working boat design can cross oceans and fulfil dreams.

Racing influence on keel types and design

Most early yacht designs were schooners, but during the latter half of the 19th century the gaff cutter rig started to dominate the scene.

Many notable yachts were built at that time and the most important racing design was probably the yawl Jullanar (1875).

Designed and built by the agricultural engineer EH Bentall, she had, in his own words, “the longest waterline, the smallest frictional surface, and the shortest keel”.

She proved to be extremely fast and in her first season won every race she entered. Jullanar became the forerunner of such famous designs as GL Watson’s Thistle (1887), Britannia (1893), and Valkyrie II and Valkyrie III , both of which challenged for the America’s Cup during the 1890s.

Compare the She 36’s graceful overhangs with the vertical stems and sterns of most modern cruiser/racers

In the USA, Nat Herreshoff experimented with hull forms for racing yachts and produced the ground-breaking Gloriana in 1890.

She was a small boat for the times, with a waterline length of 46ft. Her hull form was very different to anything yet seen in the USA.

With long overhangs at bow and stern, her forefoot was so cut away that the entry at the bow produced a near-straight line from the stem to the keel.

It was a revolutionary design, and nothing at the time could touch her on the racecourse.

Many French models, such as this Beneteau, have opted for substantial pivoting keels. Credit: Peter Poland

Herreshoff wrote: “Above the waterline everything on Gloriana was pared down in size and weight… and every ounce of this saving in weight was put into the outside lead.”

Early English rating rules produced the ‘plank-on-edge’ yacht, where the beam became narrower and the draught got deeper.

New rating rules were then adopted to discourage this extreme type and eventually the Universal Rule was introduced in the USA and the International Rule – which produced the International Metre Classes – took over in Europe.

Yet again, racing rules proved to be a major influence on design development.

By the start of the 20th century the big, long-keeled racing yachts like the J Class attracted a lot of public attention, but after World War II everything changed. Yachts built to the Universal Rule fell from favour.

The age of the racing dinghy arrived and the ocean racer became the performance yacht of the future.

To new extremes

A 300-mile race from New York to Marblehead saw the start of offshore racing and the first Bermuda race was run in 1906.

The British were slower to compete offshore, but in 1925 seven yachts took up the challenge to race round the Fastnet Rock, starting from the Isle of Wight and finishing at Plymouth.

EG Martin’s French gaff-rigged pilot cutter Jolie Brise won the race and the Ocean Racing Club was formed.

In 1931 this became the Royal Ocean Racing Club (RORC), which remains the governing body of offshore racing in Britain.

The ‘cutaway’ modified full keel was famously used by Olin Stevens on his mighty Dorade. Credit: Christopher Ison/Alamy

The early competitors in RORC races were long-keeled cruising boats, many of them gaff rigged and designed for comfort and speed.

But everything changed in 1931 when the young American Olin Stephens designed and then sailed his family’s 52ft yawl Dorade across the Atlantic to compete in that year’s Fastnet race.

She won with ease. Then she did it again in 1933, having first won the Transatlantic ‘feeder’ race.

At 52ft LOA, with sharp ends and 10ft 3in beam, some said Dorade looked like an overgrown yawl rigged 6-metre. But her triple-spreader main mast was revolutionary. As were her cutaway forefoot, lightweight construction, deep ballast and 7ft 7in draught.

Dorade took the long keel format to new extremes.

In the USA, the Cruising Club of America (CCA), founded in 1922, played much the same role as the RORC did in Britain.

It introduced its own rating rule which influenced the evolution of yacht design in the USA.

The Elan 333. Both the deep (1.9m) and shallow (1.5m) draught models feature an elegantly faired bulb keel and spade rudder. Credit: Peter Poland

Beam was treated more leniently under the CCA rule, so wider American designs later offered more space for accommodation and a bit more inherent form stability than RORC-rule inspired yachts.

Many famous designers of long-keel racing yachts at this time developed their skills at the yachtbuilding firms they ran, such as William Fife II (1821–1902), his son William III (1857–1944), Charles E Nicholson (1868–1954) of Camper & Nicholsons and Nat Herreshoff of Bristol, Rhode Island.

Around the same time several British yacht designers made their names, including George L Watson (1851–1904) who set up one of the earliest Design Offices and Alfred Mylne (1872–1951), who designed several successful International Metre Class yachts.

Norwegian designers Colin Archer (1832–1921) and Johan Anker (1871–1940) also joined the party.

Continues below…

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Sailing in the 1970s was characterised by innovation, enthusiasm, mass participation and home boatbuilding. Rupert Holmes reports

In 1873 Archer designed the first long keel Norwegian yacht, but his real interest was work boats – pilot boats, fishing craft, and sailing lifeboats – some of which were later converted into cruising yachts.

Erling Tambs’s Teddy was a classic Colin Archer long keel canoe-stern design in which he wandered the globe with his young wife and family.

He proved the seaworthiness of Archer’s yachts, as well as their speed, by winning the 1932 Trans-Tasman yacht race.

Fellow Norwegian Johan Anker – a one-time pupil of Nat Herreshoff – became equally famous, thanks to his Dragon-class design that still races today.

As a new generation of designers arrived on the scene in the 1930s, hull tank testing became more sophisticated.

Long keel designs became as much a science as an art.

The leader of this new wave of designers, Olin J Stephens, had been a junior assistant to Starling Burgess who designed race-winning J Class yachts, including the iconic Ranger .

Tank testing was then in its infancy but the USA was ahead of the game and Stephens stored away everything that he learned. He enjoyed a head start over his contemporaries.

Keel types: Fin keels

Between the 1930s and the 1980s more fin keel designs began to arrive on the scene and his firm Sparkman & Stephens produced many of the world’s top ocean racers.

He also designed America’s Cup 12-Metres that defended the cup up to 1983 until Ben Lexcen’s winged keel shook the sailing world.

Many S&S fin keel and skeg production boats – such as the Swan 36 (1967), 37, 40, 43, 48, 53 and 65, She 31 (1969) and 36 and S&S 34 (1968) – still win yacht races and are much sought after as classics.

The S&S 34 has several circumnavigations to its name. Stephens, of course, had his rivals.

Among these was the Englishman Jack Laurent Giles, whose light displacement race-winner Myth of Malham had one of the shortest ‘long keels’ of all time.

(L-R) A Sigma 38 designed by David Thomas and Gulvain (1949) by Jack Giles as a development of his Fastnet-winning Myth of Malham have very different keel types. Credit: Peter Poland

The Dutchman EG Van de Stadt designed the Pioneer 9 (1959) which was one of the first GRP fin keel and spade rudder racers.

Towards the end of his career, Olin Stephens also came up against Dick Carter, Doug Peterson, German Frers and the Kiwis Ron Holland and Bruce Farr.

The development of new shaped keels went hand in hand with this rapid evolution in yacht design.

The full keel, as still found on motor-sailers such as the Fisher range, gave way to the ‘cutaway’ modified full keel as famously used by Olin Stephens on his mighty Dorade , designed back in the late 1920s.

She still wins ‘classic’ yacht races in the USA. American designer Ted Brewer wrote in ‘ GoodOldBoat ’ that Dorade’s offshore racing successes proved that the full keel is not essential for seaworthiness.

The Nicholson 32’s modified ‘cutaway’ long keel results in excellent performance and handling. Credit: Genevieve Leaper

As a result of its improved performance and handling, the modified ‘cutaway’ long keel caught on quickly and became the standard for around 35 years.

This keel type is found on numerous popular designs such as the Nicholson 32 , 26 and 36, Twister 28 and many Nordic Folkboat derivations.

The modified full keel format had a cutaway profile, giving good handling and directional stability while having less wetted surface than the full keel designs.

These yachts can perform well in all conditions and have a comfortable motion.

Even though they are generally of heavier displacement than fin keelers, they are not much slower in light airs , despite their added wetted surface area.

Their main drawback is a wide turning circle ahead and reluctance to steer astern when under motor.

Keel types: Increased stability

The modified full keel was subsequently cut away more and more for bluewater and inshore racers in an attempt to reduce wetted area until, finally, some designers took it to extremes.

As a result, much-reduced directional stability produced craft that were difficult to steer in breezy conditions, broaching regularly.

Whereupon the fin keel and skeg-hung rudder took over, reinstating increased directional stability, improving windward ability, reducing drag and restoring – when under power – control astern and on slow turns.

This fin and skeg format was later followed by the NACA sectioned fin keel with a separate spade rudder .

Soon, many performance cruisers followed this race-boat trend.

The Hanse 430 has a spade rudder and bulbed keel (draught 2.16m or 1.79m shoal draught. Credit: Peter Poland

Many builders now also offer shoal draught fin keel options and shallower twin rudders.

Some, such as Hanse, incorporate L- or even T-shaped bulbs on some Hanses and Dehlers at the base of finely shaped cast iron fins.

A new international competition had encouraged the initial development of modern fin keel yacht designs.

The revamped One Ton Cup was launched in 1965 for yachts on fixed handicap ratings (typically around 37ft long).

This spawned later fixed-rating championships for Quarter Tonners (around 24ft), Half Tonners (around 30 ft), Three-Quarter Tonners (around 33ft), and finally Mini-Tonners (around 21ft).

All these yachts were eventually handicapped under the International Offshore Rule (IOR) that replaced the old RORC and CCA rules.

The revamped One Ton Cup helped encourage the developed of modern fin keel designs. Credit: Getty

Countless production fin keel cruisers designed and built in the 1970’s to 1990’s boom years were loosely based on successful IOR racers that shone in the ‘Ton Cup’ classes.

The IOR handicap system’s major drawback was its Centre of Gravity Factor (CGF) that discouraged stiff yachts.

Once the international IRC rule replaced the IOR, more thought was given to increasing stability by putting extra weight in a bulb at the base of the keel.

GRP production boats followed suit. The keel foil’s chord needed to be wide enough to give good lateral resistance (to stop leeway), yet not be so wide as to add unnecessary drag.

Exaggeratedly thin foils are not suited to cruising yachts because they can be tricky upwind.

Tracking is not their forte and they can stall out. A bonus was an easier ride downwind thanks to wider sterns.

Keel Types: Lead or iron?

And then there is lead. Almost every production cruiser has a cast iron keel for one simple reason; it is much cheaper than lead. But it’s not as good.

Not only does it rust; it is ‘bigger’ for the same given weight. A cubic metre of iron weighs around 7,000kg, while the same cubic metre of lead weighs around 11,300kg.

An iron keel displaces far more water (so has more drag) than the same lead weight. We had always put iron keels under our Hunters – as did our competitors.

But when we came to build the Van de Stadt HB31 cruiser-racer, designer Cees van Tongeren said “No. We use lead.” “Why?” I asked. Cees replied: “If we use iron, the keel displaces more, so the boat sails worse.”

Rustler 36 long keel’s cutaway forefoot delivers responsiveness and manoeuvrability – a reason the design is so popular in the Golden Globe Race. Credit: Beniot Stichelbaut/GGR/PPL

Which explains why top-flight race boats have lead keels – or at the very least composite keels with a lead bulb or base bolted to an iron upper foil, thus lowering the centre of gravity (CG).

Some modern production cruiser-racers offer high-performance lead or lead/iron composite keels – but at a price.

Many Danish X-Yacht and Elan race-boat models, for example, have a lead bulb on the base of an iron NACA section fin.

Rob Humphreys, current designer of the popular Elan and Oyster ranges, said: “The T-keel is good if you have sufficient draught available. If not, the fin element has too short a span to do its job. This is because the T-bulb doesn’t contribute as usefully to side force as a ‘filleted L-bulb.’

“I developed and tested this shape (a blended-in projection off the back of the main fin) for the maxi race boat Rothmans in 1988/9, and have since used it on the Oysters and Elan Impressions. The ‘filleted’ keel we tested for Rothmans had slightly more drag dead downwind (more wetted area) but was significantly better when any side-force occurred; and side-force goes hand-in-hand with heel angle – which is most of the time! When the model spec allows for reasonable draught, the keel option with the lowest centre of gravity will invariably be a T-keel, with a longer bulb giving the greatest scope for a slender ballast package. An L-keel is a compromise and doesn’t suffer from the risk of snagging lines, mooring warps, and nets. [many modern production cruisers have 100% cast iron L- or T-shaped keels]. A lead bulb is preferable to a cast iron keel in terms of volume and density, but it costs more. However, a lead T-keel in a production environment will almost certainly use a cast iron or SG Iron fin, which may rust.”

The Mystery 35, designed by Stephen Jones and built by Cornish Crabbers, has a lead fin keel. Photo: Michael Austen/Alamy

Rustler Yachts also uses lead instead of iron for their keels.

The Rustler 36 long keel (designed by Holman and Pye and winner of the 2018 Golden Globe Race) has a cutaway forefoot to improve responsiveness and manoeuvrability.

The long keel creates more drag but, as with the Rustler 24, the cutaway forefoot makes the 36 more nimble than a full long keel boat, which are more difficult to manoeuvre in reverse under power.

The rest of Rustler’s offshore range – the Rustler 37, 42, 44 and 57 – designed by Stephen Jones – have lead fin keels.

As does his Mystery 35 built by Cornish Crabbers.

These offer an excellent combination of directional stability, performance and lateral stability. The yachts track well, are comfortable in choppy seas, and have good manoeuvrability, all without the flightiness of shorter chord fin keels found on many production family cruisers.

A digital future

Influential designer David Thomas said: “When I started designing, I integrated sharp leading edges to the keel; until someone told me a radius was better. Then we were all taught that an elliptical shape was better still. With the advent of computers, designers could better visualise the end-product; and clever ‘faring programs’ speeded this up.”

So where next? A combination of lighter and stronger materials, rapidly developing computer programs, a desire for maximum interior volume and low costs has led us to today’s production yacht.

Twin rudders improve the handling of broad-sterned yachts when heeled.

The IRC rating rule permits low CG keels, wider beam and near-vertical bows and sterns.

And designers now have an array of new computer tools at their disposal. But maybe there’s still that element of black magic?

As David Thomas so succinctly said: “You can design a yacht 95% right, but the last 5% can be down to luck.”

Keel types : the pros and cons

Full length keel

The Fisher 31 and many motor-sailers have long keels. Credit: Peter Poland

Pros: Directional stability. Heavy displacement leading to comfort at sea.

Cons: Poor windward performance. Large wetted surface leads to drag. When under power at low speeds, the turning circle is wide unless fitted with thrusters. The same applies to manoeuvring astern.

Cutaway modified long keel form with keel-hung rudder

Pros: Reduced wetted surface area leading to increased boat speed. Better windward performance and handling than full length keel. Rudder on the aft end of the keel improves self-steering ability on some designs.

Cons: Under engine, this keel form has a large turning circle ahead and poor control astern. Since the rudder is not ‘balanced’, the helm on some designs can feel quite heavy.

Fin keel with skeg-hung rudder

The skeg gives protection to the rudder. Credit: Graham Snook/Yachting Monthly

Pros: The further reduction in wetted surface area leads to more boat speed. Directional stability and close-windedness are also improved. If full depth, the skeg can protect the rudder against collision damage.

Cons: When combined with a narrow stern, this keel format can induce rolling when sailing dead downwind in heavy winds.

Fin keel with separate spade rudder

Fin keel with spade: Low wetted surface and aerofoil shapes enhance performance. Credit: Graham Snook/Yachting Monthly

Pros: The fin and spade rudder mix reduces wetted surface and gives a more sensitive helm – especially if the blade has ‘balance’ incorporated in its leading edge. Handling under power in astern is precise and the turning circle is small.

Cons: The rudder is fully exposed to collisions. There are no fittings connecting the rudder to a keel or skeg, so the rudder stock and bearings need to be very robust.

Shallow stub keel with internal centreplate.

Pros: When lowered, the plate gives good windward performance. The plate can act as an echo sounder in protected shallow water. There is normally no internal centreplate box to disrupt accommodation. With the plate raised, off-wind performance is good.

Cons: The plate lifting wire needs regular inspection and occasional replacement. Windward performance with the plate raised is poor.

Lifting or swing keel

Boats with lifting keels tend to surf earlier downwind. Credit: Graham Snook/Yachting Monthly

Pros: Shallowest draught so more cruising options; can also be moored on cheaper moorings. Surfs early downwind. Small wetted surface so can be fast.

Cons: Reduced living space due to internal keel box. With a raised keel, poor directional control. Susceptible to hull damage if grounding on hard material.

Twin or bilge keel

Bilge- or twin-keelers can take the ground on the level. Credit: Graham Snook/Yachting Monthly

Pros: Can take the ground in a level position. Modern twin-keel designs with around 15º splay, around 2º toe-in and bulbed bases perform well upwind. Good directional stability due to the fins. Modern twin keels with bulbed bases lower the centre of gravity.

Cons: Older designs do not point upwind well. Slapping sound under windward keel when at a steep angle of heel on older designs. Antifouling between the keels can be tricky. Can be more expensive than fin keels.

Wing keel: A low centre of gravity gives a good righting moment. Credit: Graham Snook/Yachting Monthly

Pros: Low centre of gravity means good righting moment. Shallow draught. Sharper windward performance.

Cons: Larger surface area means it is more likely to pick up fishing gear, like lobster pots. Difficult to move once it is grounded. And difficult to scrub keel base when dried out alongside a wall.

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• Mastering the Depths: The Sailboat Keel Guide

The keel of a sailboat is more than just an architectural feature; it's the foundational element that ensures stability, performance, and the directional integrity of the vessel. Acting as the backbone of the boat, it runs longitudinally along the bottom, playing a crucial role in preventing the boat from being blown sideways by the wind. But the keel is not just about stability; it's intricately linked to how a sailboat interacts with the water and wind, affecting everything from speed to maneuverability. Diving deeper into the specifics, the variety in keel designs is vast, each tailored to suit different sailing needs and environments. From the slender and deep fin keel, known for its speed and agility, to the bulb keel with its characteristic bulb at the bottom for enhanced stability, the design choices are many. There's also the wing keel, designed for shallow waters, reducing the draft without losing stability, and the full keel, which is excellent for long-distance cruising due to its exceptional directional stability. Not to forget the twin keel, which allows a sailboat to stand upright on low tides and offers remarkable stability in heavy weather conditions.

The Balancing Act: Keel Types and Sailboat Performance

The keel's influence on a sailboat's performance cannot be overstated. It's a balancing act, quite literally, where the keel's design directly impacts the boat's stability, speed, and maneuverability. The choice between a deep keel and a shallow keel, for instance, is a decision that touches upon the very nature of one's sailing. Deep keels excel in open waters, offering unmatched upwind performance, while shallow keels are better suited for navigating coastal areas and shallower bodies of water.

But how does one choose the right keel? It's a combination of understanding the specific sailing environment, the performance expectations, and personal sailing style. Whether it’s for competitive racing or leisurely cruising, the keel must align with the sailor's aspirations and the challenges of the waters they intend to navigate.

Navigating Choices: Selecting the Right Keel and Ensuring Its Care

Selecting the right keel for your sailboat involves a detailed analysis of various factors, including the type of sailing you're interested in and the conditions you expect to face. Each keel type brings its own set of advantages and challenges. The maintenance and care for sailboat keels are equally important. Regular checks, cleaning, and upkeep are essential practices that extend the longevity and preserve the performance of the keel, preventing long-term issues that could hamper your sailing experience.

Read our top notch articles on topics such as sailing, sailing tips and destinations in our Magazine .

Check out our latest sailing content:

The voyage of evolution: from simple structures to sophisticated designs.

The history of sailboat keels is a fascinating journey of evolution, showcasing human ingenuity and the relentless pursuit of better, more efficient designs. This evolution is not just about improving performance but also about adapting to the changing environmental conditions and the growing demands of the sailing community. Innovations in sailboat keel designs continue to emerge, driven by a desire to enhance efficiency, reduce environmental impact, and push the boundaries of what's possible on the water.

Charting the Future: Innovations and Trends in Sailboat Keel Design

The future of sailboat keel design is as promising as it is exciting, with new advancements focusing on optimizing performance, eco-friendliness, and adaptability to diverse sailing conditions. These innovations are not just about pushing the limits of speed and agility but also about ensuring that sailing remains a sustainable and accessible sport for generations to come.

The keel is a testament to the intricate dance between form and function, a crucial component that defines a sailboat's relationship with the sea. Understanding the various types of keels, their functions, and how they impact sailboat performance is essential for every sailor. As we look to the horizon, the continuous innovation in keel design promises a future where sailing is not only about embracing the wind and waves but doing so with an eye towards efficiency, sustainability, and harmony with the marine environment.

So what are you waiting for? Take a look at our range of charter boats and head to some of our favourite  sailing destinations.

I am ready to help you with booking a boat for your dream vacation. Contact me.

Denisa Nguyenová

What is a Sailboat Keel?

Last Updated by

Daniel Wade

June 15, 2022

The keel protrudes from the bottom of the sailboat hull. Sailboats utilize a long keel, skeg, or blade to keep a straight course under sail.

The keel is one of the most important parts of the sailboat structure, and it's often the first major piece to be laid down during construction. The keel is the backbone of the boat and often contains a significant amount of ballast to keep the boat stable. There are several types of sailboat keels.

Table of contents

How Sailboat Keels Work

In simple terms, the keel of a sailboat acts as a water foil to keep the boat on a straight course. The protruding keel of a sailboat serves the same function as a centerboard or a leeboard with additional structural integrity.

But why do sailboats need a long keel when powerboats use a flat keel? Sailboats don't always navigate with the wind directly behind them. If they did, there would be no need for an extended keel. In other words, sailboats can sail in almost any direction to the wind because the keel helps convert angled force into forward motion. Without the keel, strong side winds would simply push the boat sideways or flip it over.

Keels also provide additional stability and allow the boat to heel over without capsizing. Long, heavy keels reduce rolling in rough weather, and thin, sporty keels reduce friction and increase speed in lighter winds. Next, we'll cover the most common types of sailboat keels and their uses.

Sailboat Keel Types

Designers and engineers have perfected the design of sailboat keels over the years. Keel types vary between boats based on size and the intended purpose of the boat. Fixed keels, which are used on medium and large sailboats, include full keels, modified full keels, fin keels, bilge keels, wing keels, and bulb keels .

Traditional sailboats often utilize a full (or 'deep') keel. This long and heavy keel flows with the shape of the vessel and extends far below the bilge level of the hull. Full keels run the length of the boat, and they're typically deepest at the stern of the vessel. The rudder often runs deep and matches the length of the keel.

Deep keel sailboats are often heavier and displace more water than other boats of similar length. They often have a very deep draft as well, making shallow-water cruising off-limits in many cases. That said, deep keels offer an enormous amount of stability and seaworthiness. Full keels offer the most comfort in rough weather.

Deep displacement hulls are excellent in heavy weather. They're also quite stable at extreme angles, as the added weight and depth of the hull make knockdowns less likely. However, some full keel designs have a tendency to heel violently to a certain angle, which makes some sailors uncomfortable. The 'sweet spot' angle of a full-keel boat is often a bit more dramatic than some would prefer.

Modified Full Keel

The modified full keel is a slightly modernized version of the old-fashioned displacement hull. It runs long and deep like a standard full keel but stops short of the bow and stern. Modified full keels are common, and they likely produce less drag than traditional deep keels.

One benefit of the modified full keel is a reduction in heeling. These vessels offer good all-around performance, but they're not designed for shallow water. Like the full keel, the rudder runs deep along the length of the modified keel. Modified keelboats are quite comfortable at sea, but nothing beats a full keel.

Fin keels are quite common on modern boats, and they range in size in depth dramatically. Fin keels are generally mounted from the center of a round-bottom sailboat and extend several feet below the base of the hull. At their base, fin keels are usually no longer than 1/3 of the vessel's waterline length.

Fin keels generally offer superior windward performance compared to full keels. They can be designed to reduce heeling, which can improve occupant comfort in some weather conditions. Fin keels are often made of steel, filled with lead, or weighted down in some way. This additional ballast improves stability and balances the boat.

Speed is another major advantage of the fin keel design. Fin keel sailboats achieve incredible speeds thanks to reduced drag. Racing boats often employ fin keels, but the benefits aren't limited to competition craft. Adding a few knots of speed on a long voyage can shave days off your arrival time, which is why fin keel sailboats are popular for ocean crossings.

Fin keels often run as deep or deeper than full and modified full keels. Sailors need to keep this in mind, as running aground with a fin keel can damage more than just the bottom of the boat. Fin keels are designed for coastal and bluewater cruising. And while fin keels are suitable for bluewater sailing, they can be less comfortable than full keels in inclement weather.

Skeg Rudder Fin Keel

Some fin keels feature a skeg rudder. This type of rudder runs deep and often matches the depth of the keel. But unlike a full keel, a skeg rudder is often separated from the keel itself by a gap. Sometimes, the keel re-emerges right before the rudder. This offers additional protection for the rudder.

Spade Rudder Fin Keel

The fastest fin keel design utilizes a spade rudder and a long, thin knife-like keel. A fin keel with a spade rudder has the least amount of drag and therefore outpaces all other keel designs virtually. However, speed comes at a cost. Windward performance suffers, and so does rough water comfort.

Additionally, sailboats with these types of fin keel have no extra rudder protection. Any contact with the bottom can shear the rudder clean off. Rough water and debris are also quite unwelcome and sometimes pose a serious threat. That said, these boats are superior for racing and traveling on the clock.

A bulb keel can be considered a type of fin keel, but this design deserves its own category. Bulb keels are excellent for shoal-draft boats, as they reduce draft without sacrificing a significant amount of performance.

Bulb keels are shortened fin keels with a torpedo-shaped bulb at the base. The bulb increases the surface area of the fin without significantly increasing its depth and also stores the required lead ballast to maintain stability.

Additionally, bulb keels are less vulnerable to grounding than traditional fin keels. For one, they're shallower and less likely to touch the bottom in the first place. But unlike fin keels and full keels, they're blunt—that means they won't cut into the seafloor like a blade, and they're easy to free from the muck.

The concept behind the wing keel is the same as the bulb keel, but the execution is a little bit different. Wing keels are short fin keels with horizontal outcroppings at the base. From the front or rear, wing keels look like an upside-down 'T' mounted to the base of the boat. They're great for shallow water, and they offer reasonable stability and windward performance.

Bilge keels are indeed multiple keels. The bilge keel is perhaps the most brilliant shoal draft adaptation for fixed-keel designs. Instead of a single long keel in the center, bilge keel sailboats feature two short keel fins on either side of the hull. They're mounted at opposite angles, reducing draft and coming into vertical alignment when the boat heels.

Twin-keel boat performance varies widely, but these vessels can be impressively seaworthy. Grounding isn't the end of the world, as bilge keels allow the boat to rest flat on the mud without digging in. With twin bilge keels, there's no need to sweat it when the tide goes out.

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I've personally had thousands of questions about sailing and sailboats over the years. As I learn and experience sailing, and the community, I share the answers that work and make sense to me, here on Life of Sailing.

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Yachting Monthly

• Digital edition

How keel type affects performance

• Chris Beeson
• December 2, 2016

James Jermain looks at the main keel types, their typical performance and the pros and cons of each

A fin keel and spade rudder configuration gives high pointing but can be sensitive on the helm Credit: Graham Snook/YM

James Jermain has tested hundreds of yachts in his 30 years as Yachting Monthly’s chief boat tester

The performance and handling of a yacht depends on many things, but perhaps the most important single feature is the shape of the hull and the profile of the keel. Over the years hulls have become shallower and keels narrower, but for many types of sailing this progression is not necessarily progress. Of the various shapes that have evolved, each has its own advantages in different circumstances. Here is a run-down of how they may fit your sort of sailing.

FIN KEEL WITH SPADE RUDDER

A low wetted surface area and aerofoil shape means speed and agility

The most common modern option, usually combined with light but beamy hulls with high freeboard.

GENERAL AND TO WINDWARD

• Low wetted surface and good aerofoil shape means good speed, high pointing and quick tacking
• Light steering
• Best designs can slice through heavy seas in reasonable comfort
• High volume, light-weight designs can be lively and tiring in heavy weather
• Flat sections can cause slamming
• Less steady on the helm, requiring more work and concentration
• Strong tendency to round-up when hard pressed
• Generally require earlier reefing
• Can be unstable when hove to
• Quick to surf and may even plane
• Can broach easily and suddenly
• Can be directionally unstable and hard to control in heavy conditions

UNDER POWER

• Handling is precise and turns tight and quick
• Some handle almost as well astern as ahead
• Limited lateral area so susceptible to beam winds at low speeds
• An unattended helm can slam over suddenly

FIN KEEL WITH SKEG RUDDER

The skeg running aft protects the rudder and improves tracking under sail and power

Similar to above but with some key differences.

• Skeg provides better support for the rudder
• Tracking under sail or power is improved
• There is less chance of damage
• More wetted surface so potentially slower
• Objects can get stuck between rudder and skeg
• Limited balancing can make helm heavier

The mass of a long keel is often more seakindly and will carry way well.

The traditional option, usually found on pre-1970s designs.

• Good tracking
• Slow, soft, comfortable motion
• Drive powerfully through short seas but can be wet
• Carry way through tacks
• Resist rounding-up
• Heave-to well
• High wetted surface area and a poor aerofoil shape, so speed reduced, tacking slow, leeway increased and pointing ability reduced
• Long ends can cause hobby-horsing
• An unbalanced hull or rig can cause heavy helm
• Track well and very resistant to broaching
• Very stable in heavy conditions
• Reluctant to surf (a mixed blessing)
• Carry way well
• Track straight
• Heavy construction can reduce vibration and noise
• Large turning circle ahead
• Unpredictable and hard to control astern

LIFTING OR SWING KEEL

A lifting keel enables beaching, but beware of stones jamming the plate

The ultimate shallow-draught option.

• A fully retracting keel offers shallowest draught
• A well-designed lifting keel can be very efficient and fast
• Grounding on anything other than soft mud or sand can damage an unprotected hull
• Stub keels offer better protection but are less efficient and prevent level drying out, except in soft mud
• Stones and dried mud can jam the lifting plate
• Internal keel boxes reduce accommodation space
• Directional stability is poor
• Early surfing and planing
• Control can easily be lost in strong winds
• Good performance and handling with keel down
• Directional control increasingly poor as the keel is raised

TWIN OR BILGE KEEL

A bilge-keeler will dry out upright on a flat bottom

A popular shoal-draught option in Britain, less so abroad.

• Shallower draught
• Dry out upright on a flat bottom
• Good protection when grounding
• Good designs are better to windward than long keels, almost as good as fins
• Pointing and speed to windward is reduced, considerably so in older designs
• When well heeled, waves can slap under the windward keel
• Can topple over if one keel finds a hole or soft ground

Modified water flow over the wing keel foot can give the motion of a longer, heavier boat

Once popular, now largely replaced with various types of bulb.

• Reduced draught
• Low CoG means good righting moment
• Modified water flow over keel foot means greater efficiency and gives the motion of a longer, heavier boat
• More likely to pick up lobster pots, etc
• Risky drying out
• Weed and barnacle growth under wings difficult to remove

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