[quote=MN3]That doesnt look like a stock H18 jib. that clew plate is not needed (with all those adjuster holes) since you have a 4 way adjuster on H18's... but you are correct they are used to change the shape of the sail (much more useful on a H16 that can only move the jib blocks in and outboard on the front beam)
those lines are leech lines and foot lines (they look like huge lines for that purpose) .. add more or less cup / curve to your sail. many jibs come with leech lines. Useful when the sail is blown out and flaps while sailing. foot lines are less common.
[quote]What are they tied to or pulled against to tension the sail?[/quote]
attached to the head of the sail (for the leech line) and typically have a little plastic cleat near the clew plate to fasten it.[/quote]
No HTML tags allowed (except inside [code][/code] tags)