UK Sailmakers' Encyclopedia of Sails
4.2 -Genoas and Other Jibs
You'll notice that some of the jibs on certain price lists include a percentage figure in their name and some do not. Examples are "150% No. 1 Genoa" and "Working Jib." The percentage figure is a measure of overlap, some times called an LP percentage. "LP" is another term from the rating rules, like "I" and "J." It is the acronym of Luff Perpendicular and designates the shortest, or perpendicular, distance from the clew to the LP or Luff Perpendicular Shortest distance between clew and luff. luff of the sail.
If the luff of the sail is considered to be the base of a triangle, then LP is the height, and the area is the base times the height divided by two, or one half of LP times the luff length. LP is often expressed as a per-centage of the base of the foretriangle (the J measurement) and that is the percentage figure which appears in a price list. For example, if J is 10 feet, a 150% genoa will have an LP equal to 150% of 10, or 15 feet. Its area in square feet will equal 15 times its luff length divided by two.
The luff length is not specifically shown on price lists although we do show the area of every sail. To calculate these areas, the computer uses a "maximum available luff length" equivalent to the hypotenuse of the foretriangle (the length of the headstay) less an allowance for the space devoted to the shackles, splices and other hardware needed to secure the head and tack of the sail.
In the case of jibs with less than full-length luffs, time tested rules of thumb are used to compute the areas shown. Where appropriate, these areas are chosen to comply with the regulations of the Offshore Racing Council. The working jib, for example, is comfortably below the maximum specified for a "Heavy Weather Jib". The storm jib also falls below the maximum area specified for that sail. These regulations were promulgated for a racing environment, but they nevertheless define a good, conservative standard for anyone on the water in a sailboat. As we mentioned at the outset, none of these areas are carved in stone; changes can always be made in any case to fit particular situations.
Occasionally a price list may show a choice of areas for the No. 1 genoa, a circumstance which possibly can cause confusion. It should be understood that the term "No. 1 genoa" is nonspecific as to size. It denotes the largest genoa on the boat, whatever size that may be. (The next step down in size becomes the No. 2 and so forth.) The size of the No. 1 is based on factors such as the weather conditions in which the boat is to be sailed, the size of her rig, the applicable rating rule, if any, the owner's requirements, etc. Obviously, the size of the No. 1 is one of the factors involved in picking the size of the No. 2. For instance, if the chosen No. 1 has an LP of 150%, an appropriate No. 2 might well be 135%. On the other hand, some older boats are short rigged by today's standards and would do better with a 170% No. 1. In that case a more appropriate size for the No. 2 would be about 150%.
At the level of the No. 3 genoa, the variations in size tend to become minimal. In almost all cases, a good No. 3 is a full length luff sail with an LP in the 100% range. This sail is a real work horse in the inventory and is usually added before a No. 2.
The Passagemaker Genoas are cruising genoas with all the options for roller reefing. UK Sailmakers offers this popular sail in three different constructions. All three are designed to retain their aerodynamic shape when reefed by using a foam luff pad. The most common size Passagemaker has an LP of 135%, but they can be made to any size. All three Passagemakers come with reefing reinforcements so that they can be partially furled without unduly stressing or distorting the fabric. In short, they are reasonably priced, durable, easily handled, multipur-pose cruising genoas.
The Passagemaker I is a Dacron sail and the Passagemaker II is lighter-weight alternative. The Passagemaker II is made with UK's Tape-Drive® construction system.
The Passagemaker II is the ultimate sail for the cruising sailor who wants a sail designed to reef and keep its shape over a great range of wind conditions and sail configurations. Its lighter-weight construction makes a sail that is light enough to set well in light air, while strong enough to hold together in heavy air.