Help identifying a part of the rig?

[Gunnadoit]

Heyo, thank goodness for anonymity on here, because I'm sure I'm a dope but I'm going to ask anyway:

Just got back from a week chartering a Saba50... and I'll be goddamed if there wasn't a whole thing on the mainsail that I had no idea what it was for. I'd have asked at the base when I got back, but I forgot. Now I've searched all over the Goog, but can't figure out what the name of this thing is, so can't research what it's for.

So here it is: at the mast, at the top corner of the squaretop mailsail, there was a large metal HOOK with a very small line attached to it which ran all the way to the foot. The hook looked like it was supposed to hook over a little bar in the top sail car, but I couldn't get it on there. So, when we were sailing, the very top of the sail wasn't actually attached to the mast, but was held in place by the halyard. The first attachment point of the sail to the mast was the second car, maybe 18" lower.

Obviously, we survived the ordeal. But just as obviously, this thing has a name and a purpose.

What is it?

[Benz]

Sounds like it was supposed to somehow be the solution to a problem created by having square topped sails, which because of the "gaff batten" (which tries to get the best of a gaff rig, that is, more sail area aloft without having a real gaff with a peak halyard), will not stow easily in a sailcover. The solution is to allow the headboard to break away from the mast as the sail is doused, so the head of the sail can collapse. The problem then is to reattach the headboard to the track when you want to hoist the main. There are some pretty complicated and expensive systems out there (Anomaly makes one), and there are those who simply climb up there each time and put on a lashing every time they want to hoist the main. Your mystery setup might have been an attempt at solving a problem created by not wanting a peak halyard.
Ben
zartmancruising.com

[Gunnadoit]

That sounds about right. I gave it a pretty good shot, trying to hook that thing onto the top car, and I didn't get close. The line leading down seemed like it might have been used to sort of pull open and closed the 'hook'... but I couldn't figure it out.