I suggest:
THIS IS A REEF HOOK - It is where you hook the "reef cringle" (of the tack corner) of the mainsail when your are reefing the mainsail.
Mac's did not come from factory with a special cunningham hook on the gooseneck, or a special cunningham cringle in the standard mainsail.
This may stir up a hornets nest of conversation - but ...
- a cunningham is:
a line that goes from the gooseneck area (where this reef hook is situated in the photo) to a special cringle just above the regular tack cringle. The control end of this line can also be led aft for easy operation.
- a cunningham is used to:
pull down on the mainsails lower luff, used together with the main halyard tension to adjust the "draft position" of the sail fore and aft (but does have a small affect on the "draft depth", while the outhaul mostly adjusts "draft depth" but also has an affect on the "draft position" slightly).
* on many boats it's easier to adjust a cunningham "on the fly" than adjusting halyard tension - to change draft postion.
ps;
I have a cunningham line on our Mac from this reef hook to a sail slug cringle - it works ok, but very small amount of gain in sail shape. Mostly for MacTweekers
