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post #6 of Old 11-20-2011
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Drawing to determine location of pedestal and length of jib-boom for a trackless, semi-self-tending jib. You need to know the jib's chord length at your tightest sheeting angle and the chord length at the widest sheeting angle that you intend to tack through. The clew is located at C1 when sailing deeper and the sail is trimmed as full as as the design allows, with the chord at the minimum designed length. The clew is located at C2 when close hauled, and the draft is shallow, with the chord at its maximum designed length. To determine dimensions for deck layout: Draw a line connecting C1 and C2, and find the midpoint, B1. Draw a line perpendicular to C1-C2 thru the midpoint, B1. The pedestal should be located where this line intersects the centerline of the boat(B2). The length of the jib boom is the distance between B2 and C2, which is the same distance as B2 to C1. When you change course from a deep reach to a close haul, trim the boom tighter with the jib sheets on both sides. The chord will increase, and the draft will get shallower. Thereafter, as long as your tacks are symmetrical, the jib will self-tack and be well trimmed. (You need a block outboard about 2/3 of the way back from the front of the club for leading the jib sheet. You trim the jib with the UPWIND sheet.) A more complete discussion of the sheeting can be found in Brion Toss' book _The Rigger's Apprentice_.
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