Furling Genoas- What you need to know
by Andrew Dove, Area Manager for North Sails Caraibes on 10 Oct 2008
Today, a majority of boats have furling Genoas, hence as a sailmaker I am daily asked about these. I would like to give some broad basic tips on this subject to give thought about this basic ‘work horse’ that often we furl away and forget about.
Furling headsails - furl them away and forget about them? .. .
This sail by definition has to work in varied conditions; the design shape is necessarily a compromise and the cloth choice conservative. In a previous article in these pages I discussed cloth choice through a notion of adjusted modulus, relating cloth resistance to load. With furling genoas the sail has a variable geometry and hence a more complex load to apparent wind curve. As the wind builds in strength the load increases until the point where the sail is furled, the adjusted modulus value then stabilises as an increase in wind basically corresponds to a similar decrease in surface.
Naturally loads are concentrated in the corners of the sails and most importantly in the head of the genoas. Head loads are a factor of the angle between the luff and leech amongst other things. There is often a lot to be said for a Yankee cut for a cruising foresail where head loads are shared over a great surface, the sheeting angle is less critical and the helmsman gains visibility.
Head and tack patches have to be flexible for furling purposes but extend down the leech and along the foot to maintain some corner reinforcement when furled. A number of customers ask for reef patches. These are logical though I feel that well designed tack and head patches make these almost redundant. I am never really happy with the extra weight on the leech and the inertia of the patch, the wear this creates and the distortion in sail shape.
Clew patches however must be large in dimension, close to 12% of the sails length in any direction. We are making more and more sails with soft clews rather than pressed rings. I think that these are safer, they avoid unnecessary damage to masts; spinnaker poles stocked up the mast and crews heads! A soft clew is either a webbing or rope loop spread throughout and sewn into the clew. This makes for a well supported smooth patch. On a similar note the head and tack of the sail should be finished with webbing as a flexible attachment. If possible the sail should be lashed to the furling gear with a spectra line removing the shackle, which is often a cause for corrosion and extrusion damage.
Most furling genoas now have some form of device to maintain sail shape when furled. Obviously as the sail is not flat when furled the volume in the sail is not absorbed and the sail becomes fuller with each turn of the drum. Rope or foam luff’s are tapered generally well studied shapes that increase the furling diameter at the height of the extra material. This rolls in more cloth with each furl. If the material is placed in proportion to the sails draft, sail shape should be maintained with furling. The choice of which system is an open question, I quiet often find that it’s somewhat cultural with the Anglo-Saxons preferring a rope luff.
The dimension of your sail is dictated to by the rig. The sail should obviously set well when unfurled. One should avoid that the leech does not sit on a spreader tip. As sailcloth basically shrinks unless seriously under built or of poor quality the luff length can be close to the maximum unless there is a need to lower the head to avoid the leech hitting the upper spreader or to open the head angle. If a shorter luff is chosen it is wise to use a rope or webbing head strop to avoid halyard rap.
To ensure a correct sheeting angle when furled one should remember when ordering a sail that the clew basically rolls up along a line perpendicular to the luff. An approximate car position is on a line extended through the clew from a point roughly 60 up the luff. Do make sure that the sail geometry fits when furled.
One issue when the sail is furled is how to adjust the leech line. With a Yankee type sail the leech line can be run back down the luff. Of course halyard tension has a major affect on leech line tension whether brought back down the luff or not. Good halyards on any boat are not a luxury. Some genoas have the leech lines ran along the foot of the sail to a spot low enough to get to and away from the luff so that the adjustment system is not furled around the furler when sailing. This works to a certain degree though generally the foot tension is inadequate to support a tensioned line.
I have avoided discussion on cloth choice as I feel that this is a subject non specific to a furling Genoas and was treated recently in these pages.( See Sail-World story ) Sail shape is determined by material, cut depends upon it as do longevity and shape retention. Furling a Genoa or folding one into a bag both can damage a sail though not in the same way. Many laminates are more damaged in a sail bag than anywhere else. Sailcloth will however be the key to your sails functionality, so buy in relation to your desires, needs and budget.
UV degradation however is predominantly a problem for furling genoas. An acrylic cover protects the sail well. A sock can be excellent if you can take the time to use it. Otherwise an acrylic UV cover on the sails foot and leech has good UV protection qualities though should also cover the tapes and webbings. There is a lot of skill involved in placing a UV cover on a Genoa. It should stay smooth and not bellow. It should not deform the leech of the sail, though the very weight of the acrylic cloth will always affect sail shape, and more so on smaller boats. Lighter clothes exist, they often give lesser UV protection and tear more readily. Sticky back clothes or glued UV covers often deform the sail with time when the glues shrink in the heat. Changing a glued UV cover can be a nightmare. Some heavy laminates have successfully integrated a Tedlar film. This protects the cloth though not the stitches, tapes or webbings. On a few larger sails we have recently developed a painted UV cover. This idea has been considered by Northsails Nevada and laboratory tests ran. This can be initially the best protect and still very good even if the paint flakes. With Northsails CapeTown we have worked on additives to an acrylic UV paint continuing the earlier work done within our group and we and our customers that have wanted to try this idea are delighted with the results. We continue to work on this project.
We have another exciting project that will be in full use sometime this year during the Mediterranean Big boat regattas. The basic plan is to use America’s Cup type inflatable battens on a full girth blade with a pressure valve ran to the clew and within reach of an air line. The sail will then be unfurled and the battens blown up. Current test models can accept up to 120psi. Obviously once an air source is available nothing stops us from building an inflatable luff system as well.
Furling Genoas have made sailing more accessible and probably safer. Though simple or often even ‘push button’, a number of important decisions need to be made so that your furling Genoa is efficient and long lasting.
Andrew Dove is Area Manager for North Sails, based in Guadeloupe.
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