[quote=Wolfman]If you have the original rig then the only purpose of the downhaul is to tension the sail and remove wrinkles. This allows it to form a solid wing shape while sailing instead of tending to collapse and allowing the draft to move randomly.
A high purchase downhaul is meant so you can bend the mast backward along its major (thick) axis. What this does is take shape out of the sail flattening it and depowering it. Basically the luff of a sail is curved so that when it is put on a straight mast it bows out to the side forming an aerodynamic wing shape. When you put bend in the mast that conforms to the luff curve, the 3D shape of the sail is reduced. It is actually more complicated than this but that is the easiest way to picture it.
On a modern cat (post 1999) the normal downhaul is about 8:1, some have as much as 16:1. In order to be able to take advantage of this your boat has to be equiped with several things.
- a modern sail (i.e. one with a large reinforced bolt rope) designed for high downhaul, old sails will likely rip
- swept back spreaders to allow you to put rearward tension (prebend) into the mast, otherwise the mast will bend sideways
- a ring lock halyard connectin at the top casting, a wire with bullet and fork arrangement will slip when you haul on it.
If you don't already have all these things, just stick with the 4:1 downhaul. The upgrades are very pricey and to be honest unless you are racing they probably aren't worth it. With that downhaul and loose diamond wires (i.e. tensioned to the manual specs so you can just press them to the mast about 12" above the turnbuckles - not really loose) the sideways bend in the mast and mainsheet can provide adequate flattening for most conditions.
Regards,
Dave[/quote]
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