On Wed, 29 Aug 2007 07:02:29 -0400, "Roger Long"
wrote:

Must have been snap hooks; not snap shackles.

Yes, I agree. Snap shackles do have a nasty habit of shaking
themselves open when flogged. I've seen it happen several times on
spinnaker halyards.

There is a type of shackle suitable for jibsheets but they are pricey
and there is no real need for them on cruising boats where sail
changes are rare.