ASA and PSIA Instructor
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The jib halyard block must be below the forestay. As GT says above, it must be sufficiently below so the halyard pulls the furler swivel at an angle. you should see if you can get a manual for your system, it'll identify what the ideal angle is, probably something like 10-15 degrees. If you use a smaller sail, it needs a lead on the top fo the swivel comes to the same ehight, producing the same angle.
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