Code zero furling and gennaker furling

Code Zero furling, which is a quick and effective way to douse this big sail, is a bottom up furling system. Due to its instant success and broad appeal people started experimenting with furling gennakers and asymmetric spinnakers in the same way. This is where top down furling originated. Asymmetric sails furling offers the same major handling benefits as code zero furlers. It often means that cruising sailors get far more use out of their downwind sail inventory compared to traditional spinnakers.

What is the difference between a Code zero and gennaker furler?

A dedicated top-down furler has an independent swivel situated on/above the furling drum which allows the tack of the asymmetric / Gennaker to fly freely whilst the torque of the furling drum is transmitted along the length of the torsional cable. However, more and more manufacturers are switching to top-down adapters rather than dedicated top down drums. The benefit is that the same code zero furling drum can be used with multiple sails. Each asymmetric sail has its own Top down adapter which lives with the sail in the sail bag when not in use. 

Top-down vs Bottom-up furling and how are they different from a genoa furler

Bottom up furling came first, this is “generally” the method used for furling code zero sails. This is a straight luff sail used for reaching and light, upwind sailing. A torsional cable is encased in a pocket which runs up the luff of the sail. The tack of the sail is lashed to the cable thimble which sits in the jaw of the furling drum. When the drum turns the tack of the sail immediately starts to furl around the cable. The furl makes its way up the luff of the sail.

Top down furling has developed in recent years and is “generally” used to furl asymmetric spinnakers and gennakers. The luff of these downwind sails flies free of the torsional cable to allow the luff to project forward. The tack of the sail is attached using a strop to an independent swivel, either on the top of the drum or mounted between the drum and the cable. This swivel allows the tack of the sail to remain free-flying while the drum turns the torsional cable. The cable transmits the torque from the furling drum along the full length of the cable to the head of the sail. The sail is directly lashed to the top of the torsional cable and so the furl starts at the head and works its way down the length of the cable.

Some modern racing code zero’s, which are designed deeper, for light airs and deeper angles, are changing to top-down furling. They are still straight luff sails with the cable contained in a luff pocket, but the tack of the sail floats free from the cable and the furl starts at the head of the sail. This prevents an air bubble being trapped ¾ of the way up the furl, which can sometimes be a problem with bottom up furling of deeper sail shapes.

The traditional jib/genoa furler is a fixed installation on the main structural forestay. They normally use aluminium foils along the luff with the jib/genoa luff tape running up a groove in the aluminium foil. Jib/genoa furlers are designed for large cruising genoas which are designed to be used partially furled. Code zero and asymmetric furlers use a composite torsional cable and the sail furls directly around the cable. Code zero and asymmetric furlers cannot be used on a partially furled / reefed sail sail – the sail is either all-out or furled all-in!

Can I add a code zero / gennaker furler to my boat?

Adding a code zero or asymmetric is generally considered to offer major handling improvements to older boats. However, there are a couple of things which must be considered before looking at investing in a furling system.

Do you have a masthead rig?

This is the biggest potential show-stopper in retro-fitting a code zero or asymmetric furling system to your boat. To allow the head of the sail to furl, free from interference from the main forestay, you need to create at least 250-300mm of separation between the halyard exit and the top of the forestay. ON a true masthead rig – this can be a problem. The common solution is to build a forward mast crane which projects a spinnaker halyard block forward of the masthead. Unfortunately there are NO standard retrofit solutions and you will need to talk to a local rigger, or refit yard, about your options to achieve this separation.

Bowsprit

In the same way, you need to make sure you have 300-400mm distance between your furler and the forestay to allow the sails to furl freely. This is normally easier to achieve than the forward masthead crane. It is often possible to use/create an attachment point on top of your anchor/bow rollers. Otherwise, there are several retrofit bowsprit solutions available for monohulls and trimarans. It can be harder for catamaran owner as there are no standard retrofit products available. This is due to the complexity of interfacing with the main structural forward cross-beam. However, a good refit yard should be able to help you with this

If you can create this separation between forestay and furling system at the top and bottom, then retrofitting a code zero or asymmetric furling system is a feasible option.

What furling equipment do I need for a complete code zero furling system?

There are several key components to a basic furling system:

• Furling drum – usually a continuous loop line drum but suingle line drums are also available
• A Top swivel which is the link between the halyard shackle to the torsional cable
• A torsional furling cable – around which the sail furls
• A furling line for the drum (generally NOT included with the drum)
• Double fairleads – which guide the furling line back to the cockpit and keep the side decks clean. These are no essential and race boats will often lead the furling line directly back to the cockpit

Can I use the same furling drum for code zero and asymmetric furling

Yes – with the use of a top-down adapter on your asymmetric spinnaker or gennaker, a code zero / bottom up furling drum can be used for your code and multiple asymmetric sails.