©Karver Upffront.com Structural Furling Forestays The use of continuous line furlers and torsional cables for main structural forestays 1 www.upffront.com Contents: Page No. 1. Introduction 3 2. What is a “Structural Furling Forestay”? 3 a. Description 3 b. Advantages 5 c. Perceived disadvantages 8 3. Wire vs composite furling forestay 10 4. Deck and mast interfaces a. Fixed forestay length 11 b. Toggles or strops 11 12 5. Sail interfaces 13 a. Luff 13 b. Hoist 14 6. Specifying considerations 15 7. Conclusion 14 2 www.upffront.com 1. Introduction In this document you will be introduced to the use of continuous line furlers, together with torsional cables, as an alternative furling system for the main structural forestay. This is NOT a “traditional” genoa furling solution i.e. with an aluminium foil over the existing wire forestay, however, it is an increasingly popular, lightweight alternative for both offshore racing and cruising sailors alike. Traditional Genoa furler / foil system (©Facnor) We will be describing the key components, advantages and disadvantages of the system, discussing the appropriate use of wire vs composite fibre stays, setup methods and various sail interfaces and investigating the implications for the boat’s sail plan. Finally, we’ll be offering some guidance on correct specification. 2. What is a “Structural Furling Forestay”? a) Description The main forestay on a sailing yacht is a crucial part of its “standing rigging” i.e. primary mast support, without which the mast will fall down! It is a permanent installation, normally with a fixed length and an essential element for maintaining the correct rig tension and tune. Traditionally, we have accepted the forestay as a “given” and then added appropriate sail handling systems to it, depending on your sailing style. For example, old school headsails are hanked on to the 3 www.upffront.com wire stay with piston hanks, racers clip on lightweight plastic twin-groove foils for seamless upwind headsail changes and cruisers add aluminium foils and furling drums onto the fixed stay to allow genoa furling and reefing. Soft Hank (©Equiplite) Tuff Luff Headfoil A structural furling forestay is different in as much as the forestay itself is an integral part of the furling system. Instead of being attached directly to the mast tang and deck chainplate, the forestay attaches to the furling drum at deck level and a swivel sits between the stay and the mast tang and the sail furls directly around the revolving forestay. Both Drum and swivel are therefore permanent, structural elements in the system and take the full rig load. Structural furler (©Karver) 4 www.upffront.com Old style furler / foil systems have evolved to fit on / around the existing wire forestay. However, continuous line furlers were developed for independent code zero and asymmetric furling systems where the drum, swivel, cable and sail all form part of an integrated system. Continuous line furler manufacturers have now evolved their product ranges to take in this new, niche, structural furling forestay system application to offer some significant benefits. b) Advantages Weight The primary advantage over traditional furling systems is weight reduction. The forestay itself is the longest, heaviest individual element of your standing rigging. Saving 1 kg of weight in the mast and rigging package is equivalent to adding 4 kg to the bottom of the bulb of your keel and is regarded as one of the most cost-effective methods of improving boat performance. Reduced weight aloft will increase stability, reduce pitching and heel angle, improve acceleration and even reduce rolling at anchor. The best way to demonstrate the weight benefits of a structural furling forestay system is to run a simple case study example: A 56 ft cruising boat with a 17 m long, 12 mm wire forestay: Traditional furler / foil setup: • Wire forestay: 12 mm wire = 0.7 kg/m x 17 m = 11.9 kg • Aluminium foils: at this size, average foils are approx. 1 kg/m x 16 m = 16 kg • Furling drum and swivel: We are not aware of a single traditional furling unit manufacturer which publishes furling unit/swivel weights, but at this size, a conservative estimate would be approx. 6 kg • Total system weight: 33.9 kg Structural furling forestay setup: • 17 m Composite K49 forestay (see reference cable here) = 4.2 kg. o This is a robust cruising option…….. a race cable would be approx. 2kg • Furling drum and swivel: a 7-8 t Safe Working Load (SWL) unit would be appropriate and averaging across various suppliers gives an approx. weight of 2.3 kg for drum and swivel • Total system weight: 6.5 kg 5 www.upffront.com Therefore, the structural furling forestay system provides an overall weight saving of 27.4 kg which is a colossal 81% saving over the traditional furler / foil configuration. This rig weight saving would be equivalent to adding 110 kg to the bottom of the keel and make a significant difference to upwind sailing performance in a seaway. N.B. Lighter not only means faster, but also safer. Reduced rig weight means lower loads, less wear / fatigue and more comfortable sailing……….. Lighter, faster, safer and more fun, equals a real win-win scenario! Offshore sail plan A structural forestay furler lends itself to an offshore sail plan. Continuous line furlers are not designed to sail with the headsail reefed, so the genoa is either all-out or all-in (see Perceived disadvantages section below) which means it works well for a smaller high clew jib / yankee used in combination with an inner staysail. This Cutter style rig configuration has been a popular choice with offshore cruisers for centuries and increasingly for offshore race boats as well. 6 www.upffront.com Take a look at the latest IMOCA Open 60 and Volvo Ocean Race fleets and they will often be seen with three reaching headsails, all on continuous line furlers: the inner staysail, Solent genoa (a structural furling forestay) and Code Zero. Three-sail reaching (©Volvo Ocean Race) Windage Not a major factor for most cruising sailors, but like weight, anything that can be done to reduce overall windage will improve your sailing performance and comfort. A continuous line furler is a much lower profile unit and generally closer to the deck than traditional furling drums set on, or above, forestay turnbuckles. However, the main windage gain is the removal of the aluminium foil which sits over the forestay. Using our 56 ft cruising boat example: average aluminium foil section diameters for this size boat would be 50 mm. Multiplied by the length (16 m) gives us a cross sectional area of 0.8 m2 or 800,000mm2. Compare this to the cross-sectional area of 246,400 mm2 (0.25m2) for the recommended 15.4 mm diameter torsional cable in a structural furling forestay setup, and you have 70% lower windage. Maintenance The main maintenance advantage with a continuous line furler on a torsional cable is the removal of the aluminium foil. The traditional furler / foil system sits on, and rotates around, the fixed forestay beneath, which creates plenty of opportunity for interface issues, abrasion and damaged foil sections. Add to that the possibility for external impact damage or getting the sail luff tape caught on the 6-8 joins along the luff length groove…….. 7 www.upffront.com Just the fact that there are so many more individual parts in a traditional system makes them more prone to damage. This parts list diagram for Harken’s MKIV Furling system is representative of the numerous elements that make up a traditional furling system. Conversely with a structural furling forestay – there is one drum, one cable and one swivel – with simple interfaces, which provides a basic, effective and low maintenance system. The cable also has a soft, abrasion resistant outer cover which is kinder to your sail. c) Perceived disadvantages All-in OR All-out This is the main question to be answered when considering a switch from a traditional furler / foil to a structural forestay furling system. Many production cruising boats have a single 140-150% furling genoa which has been designed to be reefed in order to cope with the full range of sailing conditions. A continuous line furler and torsional cable however, are not designed to be used with the sail reefed and therefore the compromise is that the sail is either used at full size or furled completely away. As discussed above, this is not necessarily a problem but a decision to switch to a structural furling forestay cannot be taken in isolation and needs to be seen in context with your foresail wardrobe. Your old 150% furling genoa would need to be cut down or replaced, you would need to be considering the use of a staysail (for heavy airs) and, if you haven’t already got one, a Code zero to give you more power in lighter airs, both upwind and reaching. 8 www.upffront.com Bearing the load The traditional furler / foil is set up on a fixed forestay. The forestay takes all the tensile rig load and the furler and foil, effectively “rest” on the deck chainplate / turnbuckle. The bearings in the drum are just taking the weight of the foil and sail above it, while the upper swivel takes the halyard load and both are allowed to rotate freely with little resistance. On the other hand, with the structural forestay furler setup, the furling drum and upper swivel take the full tensile load of the forestay which is holding the mast up. Whilst the bearings are designed to take these loads, require very little maintenance and can give years of trouble free use, there is the risk that if the bearings seize it will mean that the sail cannot be unfurled, or furled.