Sail Design Terms




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Headsail Size by Percentage: Headsail size is generally described as a percentage of your boats foretriangle area (the triangle made by the deck, mast, and headstay). A 100% sail fills the entire triangle, but does not extend past the mast, anything more than 100% extends past the mast. The higher the percentage, the larger the sail is. While there are some other variables due to changes in design as the sail gets larger, a 150% sail has about 50% more sail area than a 100% sail.

Headsail Size by Sail Number: Sometimes headsails are described by their number within the sail inventory, especially on race boats. This system avoids confusion by eliminating the percentage description of the sail altogether. The #1 is the biggest headsail, the #2 next, then the #3 and so on. As a general rule a #1 would be a 150% to 153% Genoa, a #2 would be a 130% to 135% Genoa, a #3 would be a 100 to 105% Jib, a #4 would be about 85%, and a #5 would be a storm jib. The #3 is also sometimes referred to as a "Blade" because it is designed for upwind work in fairly heavy wind and is cut very flat. The 100% Jibs we sell are not cut as flat as a blade because they are designed to work well in a much larger wind range, giving a more all purpose sail.

Crosscut: A sail with the seams running horizontally across the sail. The most simple and basic (and least expensive) construction, still used on most woven Dacron sails.

Radial (or Tri-Radial): A sail with the panels cut so that they radiate out like slices of a pie from each corner of the sail. Radial cut sails allow the sailcloth to be placed so that the loads on the sail are better aligned with the strength of the cloth, this allows lighter cloth to be used while maintaining performance and durability. Radial cut designs are much more common when using laminate cloth as the design gains are bigger, and the added cost is more easily justified in a more premium sail.

Mainsail Slides (or Slugs): Small plastic slides that are attached to the mainsail with webbing or plastic shackles. Slides can be fed into the mast track when you rig the boat and then kept in place with a sail stop or mast gate cover. Slides make raising and lowering the sail quicker, safer, and easier, and allow the option of running your main halyard aft to the cockpit so you can raise the sail without leaving the cockpit.

Bolt Rope: The rope sewn into the edge of many mainsails to allow them to be fed directly into the mast or boom. All Mac mainsails come from the factory with a bolt rope and no slides. These sails need to be manually fed into the mast every time the sail is raised and dump out of the mast onto the deck when they are lowered. While there is a very small performance gain to a bolt rope sail, most non racers (and some racers) find the convenience and safety of sail slides to be well worth it.

Loose Footed: A mainsail that is attached to the boom at the corners only (no bolt rope on the bottom of the sail), this lets the sail have a better airfoil shape all the way to the bottom and makes the outhaul easer to adjust, All BWY exclusive mainsails have this upgrade.

Shelf Foot: A feature on some mainsails that allows the sail to hold it's shape all the way to the bottom almost as well as a loose footed sail. These sails have a section of lightweight cloth that matches the airfoil shape of the sail sewn to the bottom edge so that the sail is not pulled flat to the boom.

Ropeless Foot and Luff: Historically most sails have been built with a rope sewn into both the luff and foot of the sail to allow it to be fed directly into the mast and boom. Unfortunately the rope adds weight and bulk to the sail and worst of all, they shrink up over time and reek havoc with sail shape. With sail slides and a loose footed design, this rope is no longer needed. All BWY Exclusive mainsails use reinforced Dacron edge tapes that eliminate the troublesome rope.

Cunningham: A ring pressed into the luff edge of a mainsail just above the tack. This allows a block and tackle to be used to pull down on the sail to flatten it as wind builds.

Jackline: A system that allows the sail to be easily reefed without having to remove the lower slides from the mast.

Power Head: A mainsail that is wider at the top than a standard sail. These sails have more “roach” area outside of the triangle formed by the mast and boom. On boats with fixed backstays the difficulty of tacking the sail past the backstay limits the amount of roach that is practical. On the 26M you can add as much sail area as you want since there is no backstay, all our 26M sails have more roach than a conventional sail, we also offer a flat top sail for the 26M

Flat Top (or Square Top) Mainsail: These sails can be used only on boats without a fixed backstay. Flat top sails have more sail area than standard sails, but more importantly they have much more chord, or width, at the top. On a traditional triangular sail the top several feet are largely useless because the sail gets so narrow that it produces nearly no power in that area, by making the top of the sail much wider it produces lift all the way to the top. Square top sails work like adding several feet to the mast height without adding nearly that much sail area.

Full Battened: A mainsail with battens that run horizontally all the way across the sail rather than being just a couple of feet long at the back edge of the sail. Some designs use two full battens at the top to support the roach of the sail (especially on power head and flat top sails) and partial battens lower in the sail. Full battened sails can be easier to stack on the boom and are quieter when tacking in heavy wind, but are somewhat heavier.

UV Cover: A strip of UV stabilized Dacron or Acrylic fabric sewn to the edge of a roller furling jib or genoa to allow it to be left on the furler without a pull up sock to protect it. Sewn on UV covers make life very simple (no sock to put on after you get back to the dock), but add to the weight of the sail which hurts light wind performance, shorten it’s life somewhat, and do not provide dirt and abrasion protection while trailering like a sock type cover does. We recommend White UV Dacron for the sewn on cover as it adds less weight to the sail than acrylic and has much less detrimental effect on sail shape and performance as the sail ages.