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How a Roller Furling Sail Differs from Its Hanked On Cousin

How a Roller Furling Sail Differs from Its Hanked On Cousin


There are two fundamentally different styles of furling. They can be looked upon as dinghy systems and keel boat systems. Dinghy systems are simple two piece systems, having a drum assembly at the bottom, and a swivel at the top. Nothing connects the two components except for the sail itself. Sails used with this system typically have rigging wire installed in the luff. This wire acts as the boat's forestay. When the mast is stepped the rig is supported by the wire luff. An additional forestay is not used as it would have less tension than the wire luff and tangle in the sail when the sail is furled. A two piece, dinghy style system is not intended to be a  reefing system. It is only a storage device to eliminate the heads'l while docking or when a spinnaker is hoisted.

In this article, we are discussing sails for the larger keel boat furling systems. These furlers utilize a "foil" extrusion that connects directly to the drum at the bottom. The forestay passes through the foil and supports the mast as usual. The furler simply rotates around the forestay. Typically the load from the rig is born by the forestay not by the furler. The sail is independant of the furler and can be removed from the boat without unstepping the mast.

There are numerous differences between a sail for a roller furler and the same sail built as a hank-on sail. These two sails have substantial differences arising from the unique capabilities inherent in a modern roller furling heads'l system. Converting from hank-on to furling requires at least one of these modifications, and at least a plan on how to deal with the others. 



The first essential difference is the absence of bronze hanks on the luff of the furling sail in favor of a "luff tape". While bronze hanks are used to attach the luff of a traditional heads'l directly to the forestay, the foil of a roller furler completely covers the forestay which prevents you from attaching a hank on sail after a furler is installed. A roller furling heads'l is equipped with a luff tape that includes a bolt rope on the leading edge of the sail. This luff tape, properly sized for the particular brand of roller furler, slides into a grove in the foil via a feeder slot located just above the drum. The groove is shaped to allow the foil to hold the luff tape captive. See the photo at left for an example of a rigid aluminum foil section which has two grooves to allow for easier heads'l changes, or to fly twin heads'ls.



The second difference is the need for protection against ultraviolet light. As most furlers rollup counter-clockwise, this cover is installed on the starboard side of the sail. Hank-on sails spend most of their lives in a sail bag, only seeing the sun when they come out for a day of sailing. Their exposure to damaging UV rays is in small enough doses that it takes years of use for UV exposure to have an effect on the sail. Roller furling heads'ls spend more time on the furler than in a bag and so require a means to protect them from UV exposure. 

UV resistant panels sewn on to the leech and foot are the most common, though certainly not the only way to provide this protection. They are typically on the starboard side of the sail. Since most furlers are rigged to rotate counter-clockwise (when looking down at the drum) the furled sail is automatically covered. Alternatively, some people choose to omit the sewn on cover in favor of a "sock" that they can hoist over the furled heads'l using a spare halyard. This keeps the sail as light as possible for better shape, though at the expense of convenience.

The boat pictured at the right has a cover made of Sunbrella or other acrylic fabric. Sunbrella is an excellent fabric that will last for years in the sun. Weight is its disadvantage. It is substantially heavier than most sail cloth. On smaller boat sails (up to 30 feet) it is so heavy that it changes the shape of the sail. When used on a genoa it takes more wind to fill the sail from the shear weight of the cover. This is why we use a UV treated white sail cloth for the cover on smaller boat sails. This cloth is more closely matched to the sail’s weight and improves performance compared to a heavy acrylic cover. 



The third difference is the presence of strips of foam (or alternatively rope) sewn between layers of sailcloth running next to and parallel to the luff of the sail. This feature is known as a foam luff. This enhances the shape of the sail when you are using the roller furler as a reefing system. In order for the sail to create the lift that moves the boat forward, the sailmaker designs an airfoil shape into it. By cutting a subtle curve in the sides of adjacent panels, the sail becomes an airfoil shape when the panels are sewn together. A challenge arises when you reef the sail by partially furling it. Since there are more layers of cloth at the leach and foot, the draft increases as the sail is furled. This increase in draft creates more power, exactly the opposite of what you want when you are reefing. By adding thickness to the sail at the middle of the hoist, the draft is reduced as you furl, thus de-powering the sail. It is only practical to have foam extending into the body of the sail so far, so that means you can typically reef down about one size class and still have a sail with proper shape.

In the photo left, the more opaque cloth at the left is the foam luff. Note how it tapers toward the top. The same taper occurs at the bottom as well.



The last notable difference is the overall shape of the sail. Hank-on sails will usually have a very low cut clew to maximize available sail area. A furling heads'l will usually have the clew cut higher so that it will stack more evenly on the foil as it's rolled up. There are two nice side effects of the higher clew: it's easier to look beneath the sail and have a clearer view of what lies ahead, and it helps the sail get over the lifelines when changing tacks.



How does the furling system does its job? Bigger boat systems possess a foil that contains the boat's forestay. There is a drum at the bottom, and (sometimes) a swivel that can travel up and down the foil. This swivel allows for the use of the boat's jib halyard and provieds quick adjustment from moment to moment in response to wind speed or point of sail.

A notable exception is CDI's flexible furler system. To save cost, they use a halyard that is integral with the furler, thus eliminating an expensive swivel assembly. This does, indeed, save cost, but at the expense of adjustability. Luff tension is only adjustable from the bow pulpit and is best left for variations due to the season. But do you frequently adjust halyard tension and sail shape?

Deploying a roller furling heads'l is safe and simple. Simply uncleat the furling line and haul in the leeward sheet. This will cause the sail to unfurl. Control the speed that the heads'l unwinds by slowly paying out the furling line while pulling out the leeward sheet. This will prevent excessive mechanical shock to the rig and cause the furling line to wind onto the drum neatly. Some manufacturers reccomend the use of a ratcheting furling line block at the most rearward position to help accomplish this.

To furl the heads'l, head the boat toward the wind to luff the sail a bit and remove load from the furler. Haul in the furling line until the sail is rolled up. You should not use a winch to do this. It can put more strain on the bearings and drum assembly than is good for them. If you have applied halyard tension with a winch, you may also need to slacken the halyard just a little. The sail should be wound snug, so periodically haul the working sheet back in to snug the sail around the furler. If the sail isn't going to be unrolled again for any significant period of time, it's a good idea to continue to pull on the furling line until you have two or three wraps of sheet around the sail. This will prevent it from unrolling by itself in heavy winds. The sheets (both) should be cleated off, as should the furling line.

There will be a certain amount of work involved in installing a roller furler system. Some of the finer points to consider are where and how the furling lines should be lead, and through what sort of hardware. The furling line can be lead through any of the following, including combinations of the following: Stanchion mounted furling blocks (expensive, but very low friction and the line stays off of the deck), stanchion mounted fairleads (fairly low friction, and line stays off of the deck), or deck mounted fairleads (lowest cost, relatively low friction, but line will pass over the deck, a potential tripping hazard depending upon how it's run). All Catalina Direct Furling Gear Kits include blocks and fairleads that are appropriate for the size of boat. When you purchase a furling system from Catalina Direct, all of the hardware needed for a typical installation is included, so you don't have to make multiple trips to your local hardware store and chandlrey.

Happy sailing from the crew at Catalina Direct!