Here's the deal....
Hey guys-
Here is the deal:
1). MANY smaller boats still use jib cumminghams-we use it all the time on the T-10, and many One Design boats still do.
2). While it is true that halyard and cunningham affect luff tension all along the luff of the headsail in question, it is also true that as you tension the halyard only you will see the biggest impact in the top half of the sail, and if you add cunningham you will see most of the impact in the bottom half of the sail. The comment about twist is close, but not exact. Adding luff tension will adjust the fore and aft location of the max draft (chord depth). Adding tension on the luff pulls the draft forward, and easing it moves it aft. This is the primary purpose of changing luff tension on a sail. Wrinkles are irrelevant by themselves. If in order to have the draft in the right place for the conditions you have wrinkles, so be it. Adding tension to remove wrinkles in many conditions will result in the draft being pulled too far forward.
When you pull the draft forward you relieve some of the leech load, and the result of this will be an increase in leech twist (or the reverse if you reduce luff tension). So, we use the cunnigham to adjust draft location in the lower half of the sail, and halyard to adjust it in the top portion of the sail.
3). Backstay tension has no impact on sail luff tension. Adding or removing backstay tension will affect headstay tension (sag), but not halyard tension/luff tension.
4).The ring you see on the sail may have been a cunningham, but I suspect it was a changing ring. Did this sail orginally have luff tape and was converted to hanks? It is fairly common on headsails with luff tape to have this cunningham-looking thingy installed, whose function is to allow a new (larger or smaller) headsail to be hoisted in the free groove. When doing an "outside set", a sail tie or line is attached to this ring on the sail being changed, so that the tack on the old sail can be released and the old sail taken down underneath the new one.
Clear as mud?
Cheers!
S