The story of a reefing furler I never planned to design
By Marin Clausin, founder, president, and head of the engineering department at Karver
In 2021, Karver launched the first KRS reefing furlers. Five years later, more than 1,000 units are sailing all over the world on monohulls, catamarans, and trimarans—both cruising and racing vessels.
However, when I founded Karver, developing a genoa reefing furler was absolutely not part of the plans.
To understand the origins of our KRS reefing furler, we have to go back well before Karver was founded.
A family story, first and foremost
My father, Pierre Clausin, founded Profurl in the late 1970s. I grew up on boats equipped with his products, watching him work as an engineer and observing his high standards.
I realized very early on that, at sea, a good idea isn’t enough. Equipment must function under heavy use, withstand salt, impacts, the test of time, and sometimes particularly harsh conditions.
I then joined Profurl as head of the design department. There, I learned a great deal about reefing furlers, but above all about how to design a product: observing users, understanding mechanical stresses, and prioritizing reliability above all else.
When my father retired and Profurl was acquired by Wichard, I decided to strike out on my own by founding Karver. My goal was to develop products that were more innovative, more high-performance, and more geared toward offshore racing.
But I wasn’t starting from scratch. I wanted to carry with me everything my father had passed on to me over the years: his technical rigor, of course, but also his vision of the business, his respect for users, and his conviction that safe equipment carries with it the responsibility of those who design it.
Karver was born out of a desire to build something new without losing sight of its roots.
Why did you wait so long to develop a reefing furler?
For more than fifteen years, Karver never considered developing a product to compete with traditional reefing furlers. We were focused on furlers and equipment for IMOCA, Ultim, Class40, cruising multihulls, and superyachts.
Then several factors gradually made this project a foregone conclusion.
First, Karver had grown large enough to finance such an ambitious project. Developing a complete line of reefing furlers represents a considerable investment: research, testing, tooling, inventory, and spare parts for many years to come.
Then, during the COVID-19 pandemic, we had just finished developing the third generation of our KF furlers. My team and I had some free time to take on a new project.
Finally, the purchase and subsequent refit of my sailboat, the Grande Vadrouille (an Océanis 473), was a real eye-opener. While sailing extensively on a cruising boat, I realized how outdated much of the equipment installed as standard on modern sailboats really is.
We then decided that the next twenty years would be largely devoted to cruising and simplifying onboard maneuvers.
The first obvious product in this new 100% cruising line was the genoa and staysail reefing furler.
When we started the project, we simply put ourselves in the sailors’ shoes. Very quickly, several goals became clear.
Essentially, our specifications boiled down to five words:
• Durability
• Lightweight
• Compactness
• Aesthetics
• Full options
We definitely didn’t want to make “just another reefing furler.” We wanted to develop a product that offers real benefits to sailboat owners.
Four years of development
The first prototype was installed on my own sailboat. For two years, it sailed in a wide variety of conditions.
Then my entire family unwittingly took part in the testing program.
Our sailboat, the Grande Vadrouille, travelled more than 10,000 nautical miles with several prototypes on board.
My brother Quentin then outfitted his Dufour 35 before setting off on a trans-Pacific voyage and spending two years in Polynesia.
Finally, our baptism by fire came when Philippe Poupon decided to install our KRS reefing furler on Florence Arthaud’s historic trimaran for the Route du Rhum. The mechanical stresses were extreme, and this test allowed us to definitively validate our design.
In total, the development process took nearly four years of research, numerical simulations, prototyping, and real-world sea trials.
Since then, the KRS yachts have crossed the Atlantic and the Pacific and are now sailing in a wide variety of conditions, from family cruises to demanding offshore programs.
Technical Choices That Make a Difference
The profile of a reefing furler is often viewed solely as a structural component that connects the drum to the swivel. However, it is located directly in the airflow, along the entire height of the stay, just in front of the leading edge of the sail. Therefore, its shape affects the aerodynamics of the entire system.
We compared several geometries before settling on an elliptical cross-section, which is more conducive to airflow than a circular profile while maintaining excellent mechanical strength in all directions.
Choosing this shape required finding a precise balance. The more we refine the profile to improve aerodynamics, the greater the risk of losing stiffness in certain directions.
We therefore conducted numerous numerical simulations—particularly focusing on torsion—to achieve the best balance between aerodynamic efficiency and stiffness.
The sleeves are ultimately made of 6061 aluminum, with a double groove that allows for sail changes, among other things.
A profile is only as good as the quality of its joints.
The KRS splice plates are particularly long and thick to ensure proper force transfer between the various ducts. The screws press the splice plates against the profiles and hold the assembly in place without any gradual loosening.
Special countersinks absorb axial forces and prevent the various components from shifting relative to one another.
This work on the splice plates improves not only the overall rigidity of the profile but also its long-term performance. This detail is hardly visible once the reefing furler is installed, but it is essential for maintaining smooth operation after several years of sailing.
A reefing furler turns easily when it is new and tested without a load. The real challenge is maintaining that smooth operation when the rig is under tension, the halyard is loaded, and the sail is pulling strongly backward.
KRS mechanisms use high-strength 100C6 steel bearings. They operate in a grease bath and are protected by custom-designed seals that combine stainless steel and rubber resistant to the marine environment.
The bearings are double-sealed in both the swivels and the turrets.
This design helps distribute the loads created by the halyard tension and the force pulling the sail backward more effectively.
We also selected high-quality materials and oversized the main components. The goal was not only to ensure smooth operation from the very first use, but also to maintain reliable mechanics under load and over time.
The drum diameter directly affects the force required at the winding point: the larger the radius, the greater the available torque.
We therefore sought to use the maximum diameter compatible with a realistic installation. It would have been easy to increase the drum size even further to achieve a lower force requirement, but that would have created integration challenges with the forward balconies, anchors, or certain deck surfaces.
The final design specifications are therefore the result of a very practical balance between the winding torque, the capacity of the drum, compactness, and the installation constraints encountered on boats.
Compactness is one of the KRS’s most noticeable features.
The turret and swivel have been designed to take up as little vertical space as possible. Depending on the size of the boat and the product being compared, the space saved can amount to several tens of centimeters.
These extra centimeters aren’t just for looks. They increase the available luff length—and thus, potentially, the sail area—while bringing the tack closer to the deck.
The reefing furler is also equipped with a removable drum. It takes about thirty minutes to switch to a configuration suitable for regattas.
We have chosen not to offer a wide variety of versions and options.
The same level of mechanical quality, finish, and equipment is offered to both recreational sailors and competitive sailors. High-end materials, double bearings, hard anodizing, a removable drum, a stainless steel luff guide, and various mounting options are not reserved for a higher-end version.
The principle is simple: features that improve reliability, performance, or ease of use must be incorporated from the very beginning.
We sought to make the operation as smooth as possible.
To achieve this, we developed large-diameter drums that naturally increase the available torque. Combined with double-row heavy-duty bearings in the spool and swivel, they ensure exceptionally smooth winding, even under heavy loads.
Our goal is for a KRS reefing furler to last for twenty years on a boat.
We must, however, remain cautious about this claim: the product line is still too new to claim a proven 20-year lifespan at this time.
This is a design goal, supported by the component sizing, bearing protection, the tests conducted, and the ability to replace certain components.
Routine maintenance is minimal. We primarily recommend rinsing with fresh water, especially before winter storage.
Certain trim components, such as the carbon fiber veneer, can also be replaced without affecting the entire mechanism.
Environmental impact is an important issue for many sailors, and it is for me as well.
We have chosen to approach this issue in a pragmatic way. At Karver, we do not view eco-design as merely a marketing ploy or as simply adding “green” materials to an existing product. We believe it begins with the very first design decisions.
When we seek to design a product that is more compact, lighter, and more reliable, we are directly addressing several key aspects of eco-design.
Compact design reduces the amount of material used. Lightweight construction limits the consumption of resources required for manufacturing and transportation. Durability reduces the frequency of replacements and, therefore, the number of products manufactured over the course of a boat’s lifetime.
We have also made sure that certain wear-and-tear parts and trim components are replaceable so that the entire system does not have to be replaced when a single part reaches the end of its service life.
Boating equipment is designed to remain on board for a long time. Extending its lifespan is undoubtedly one of the most effective steps we can take to reduce its environmental impact.
Ultimately, the pursuit of reliability, compactness, and durability that guided the development of the KRS naturally aligns with the fundamental principles of eco-design. We didn’t develop a sustainable product simply because we needed to be more environmentally friendly; we sought to develop a better product. And the two often go hand in hand.
Reliability and Aesthetics
KRS grew out of a family history, but it wasn’t created out of nostalgia.
It is the result of the experience gained at Profurl, followed by more than twenty years of product development at Karver for offshore racing, multihulls, IMOCA yachts, and long-distance cruising.
We wanted to combine durability, compactness, lightness, performance, and aesthetics in a single product.
If a boat owner were to take away just two things after discovering the KRS, I’d like them to be these: reliability and aesthetics.
Because a beautiful object can be a true work of engineering. And because equipment designed to remain at the bow of a boat for twenty years must inspire confidence whenever conditions take a turn for the worse.
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