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During boat shows, several boaters came to ask us for information on the differences between a reefing furler and a flying furler.


The oldest boaters or those who sail on small units or traditional units know this : the reefing furler or the flying furler remains an optional accessory. The traditional method of setting up a headsail is to attach it to the forestay with snap shackles and then hoist it all up. Disadvantage : The sail must be stowed after each navigation and cannot be easily trimmed (reduce its surface).
The reefing furler or the furler allows above all to avoid this chore by a clever furling system.
The reefing furler has been installed as standard on all sailboats for many years now, with the exception of certain racing sailboats. The furler remains an accessory offered only as an option and is often offered in a pack with an additional sail. Often a gennaker.
We are going to go into the details but to make it very simple, the 2 systems allow the furling of sails. The furler manages the furling of the main sail which remains in place all the time while the furler manages the furling of the additional sails which are generally stowed after their use. Now let’s take a closer look at all of this.


The easiest point to understand is that a reefing furler integrates the main stay of your sailboat (the cable that holds the mast towards the front of the sailboat)
If you accidentally remove the top or bottom pin of your reefing furler, your mast will soon fall backwards !
Regarding the flying furler, it has no structural vocation and you can therefore remove it or replace it without worrying about the hold of your mast.
The reefing furler being perpetually in place, the main headsail is therefore also perpetually stationed there. It is possible to lower this sail for repair or wintering, but it does require a little time and effort. The generic name of this sail is the genoa. If you’re interested, another article discusses the different types of headsails.
Whatever the brand of your reefing furler, you will always find the same elements :
  • A drum where the rope is stored which activates the system.
  • Trough aluminum profiles in which the main forestay passes with a system to connect these profiles to each other.
  • A swivel sliding along the profiles to hoist / lower the sail.
  • 1 upper fixing for the mast and one low fixing for the deck (universal joints)
The furler is only made up of a drum and a swivel, but without an aluminum profile. The connecting piece is a rope or an anti torsion cable integrated into the luff of the sail and installed by your sailmaker.
On a reefing furler, one turn of the turret (bottom) always involves one turn of the swivel (top). Whatever the conditions, aluminum profiles will systematically transmit an applied force from the
down to the top. This is what allows a uniform furling of the sail.
For a furler, the force transmission element is the anti-torsion cable. As efficient as it is, this rope or textile cable will never be as efficient as an aluminum profile (stainless steel, titanium or carbon). This is the main reason which explains why it is possible to take a reef in your genoa with a reefing furler and that it is impossible to do it with a furler.
A furling sail can therefore only be used fully extended.
Another particularity of the furler : the furling system is mainly a continuous line wheel fitted with a looped rope instead of a single line.
Several reasons for this :
1- The furler must remain light and compact equipment for
taking advantage of a maximum sail area and be easy to install (weight and bulk are 2 choice criteria).
2- It sometimes happens on a reefing furler that you miss a few turns of the rope to finish furling your sail, which requires you to intervene quickly on the foredeck. This phenomenon will recur even more frequently when a single line is used on a furler.
Some deck plans require this configuration. This is not a major problem, but it does require a bit of monitoring and anticipation.


Some sailing racing boats or some high-performance boats are looking for the lightest possible systems to avoid unnecessary weights in the upper parts of the mast.
The Tuff Luff is a one-piece plastic profile on which is installed a sail with a bolt rope. The forestay passes through one of the chutes. Be careful ! This system does not allow furling a sail.
The structural furler (or stocker) is an improved and secure furler that integrates the forestay but does not use aluminum profiles. This system makes possible to have a set extremely
light and allows the sail to be furled. Disadvantage : it is still not possible to partially use it.


All new production sailboats are usually delivered with a mainsail and a furling genoa. These sails are intended to be in place for long periods and are also protected by anti UV fabrics.
Since the reefing furler genoa is by definition always in place, a furler can be used to furl an additional sail.
A furling sail is usually stowed after each use. It is for this reason that we sometimes speak of flying sails. In practice, the sail can remain in place for several hours or several days.


In absolute terms, we could go around the world with a simple reefing furler genoa but in many cases, this one cannot be perfectly adapted.
  • Not enough wind on the wind ! A larger and lighter flat sail would avoid starting the engine. The solution = Code 0, Code 1, Code 2, …
  • Not enough wind before the wind (running) ! A larger sail and much more rounded than a genoa would make possible to go faster and to avoid a particularly unpleasant roll. Solution = Gennaker, Asymmetric Spinnaker, Symmetrical Spinnaker, …
  • Too much wind ! It is then necessary to reduce by rolling up the genoa but the genoa will work badly, faseyera and will deteriorate quickly. A smaller sail would be better suited. The solution = Staysail, Code J, tormentin, …
It is to respond to these problems that both boaters and runners use additional sails. In all cases, it is either a search for speed, or a wish not to use a partially rolled sail and in all cases to always favor
the use of a sail rather than a motor in order to go faster from point A to point B.


For sailing racing boats, all sails (or almost) are on furler and there can be a lot of them ! However, there is no need to have several furlers. Only one can be used for several sails if it is sufficiently sized to be used with the most powerful sail (staysail or code 0 usually).
For a cruising sailboat, the most frequently used sails with a furler are (in order) :
  • The gennaker : It is a particularly easy to use sail (no pole) between the crosswind and the downwind. There are more or less rounded gennakers depending on the wishes and navigation programs. Discuss it with your sailmaker.
  • The spinnaker : The nightmare of many boaters and yet it is the most efficient sail when the wind comes from behind ! The spinnaker can be installed on the fly, with a sock or with… a furler ! Different systems exist but the most common is the “Top Down” spinnaker which is only suitable for asymmetric spinnaker. This is undoubtedly the best way to come to terms with this very efficient sail. A spinnaker furler is different from a furler for other types of sail. A spinnaker furler must be equipped with a swivel system on the lower part of the
    the furler which will allow the spinnaker to be rolled up first on the upper part. This has the effect of smothering the spinnaker without effort whatever the weather conditions and the speed of your sailboat
  • Code 0 : It is neither more nor less than a large genoa made with a light fabric. To be used on the wind, beat or beam. This sail is subjected to significant forces and consequently the fabrics used are often technical (sandwiches, laminates, etc, …)
  • The staysail : The staysail is the only sail that is installed between the genoa and the mast. All other sails set forward and work best with a bowsprit, bowsprit, or rigging point at the end of the bow. Usually used on a releasable forestay (not used 99% of the time and which hits against the mast). Good news ! This sail can perfectly be used with a furling system and solutions exist to replace the releasable stainless steel forestay by an anti torsion textile cable much lighter and above all removable.
As we explained before, a furler is used with an anti torsion cable. Each end of the line must be fitted with a thimble suitable for its furler. It is these thimbles which are fixed in the furler and the swivel.
All sails can be furled as long as your sail is equipped with an anti torsion in its luff.
The spinnaker is the only sail that does not include an anti-torsion cable. For a spinnaker furler, the cable is necessary but it only serves as a furling support. It is therefore external to the spinnaker.


Karver is a world reference for fittings for racing, cruising and Super Yachts. All our products are designed to remain faithful to our DNA: Performance, Innovation, Design.
KF flying furlers have been a flagship product since our inception. The majority of Imocas use Karver furlers. The latest version, known as KF V3, is particularly innovative with a toothed wheel in carbon kevlar and a recent development in flax fibers (Eco Concept version). All models can receive a KTS adapter which allows to store an asymmetrical spinnaker.
Karver has revolutionized the market by offering many innovations: captive fast pins, the quick furling line installation system, patented high load bearings, an automatic locking system that allows the furler to be locked without having to attach the line, drum & swivel protections (KKroks), 2-in-1 lower fitting (KSnap), …
In 2023, Karver markets its first range of KRS reefing furlers. It is characterized by its robustness and ease of installation and use. It is an eco-designed reel that offers all the functionalities usually offered as an option by our competitors: elliptical profiles, black anodization, double throat, removable drum, … All for a particularly competitive price.
Keep visiting our site to find out more…
Do not hesitate to react by sending us your comments through the contact form.
Written by Tanguy de LARMINAT 
Update : September 2023

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