Funny, I'm just considering going from the two-shackle system to the single-shackle one (only lower hole).
I have the two shackle setup now but find that my trapeze wires don't really sit well along the lower shackle. Of course I had to replace the lower shackle by a much larger one. The one we put on it at the DCC was bend during the DCC and completely bend after the Rem-race that was 2 weeks later. Now I have more than enough room on the lower shackle to group them with the stays.
I always wondered why many boats have the two shackle system ? Does anybody know ? From a load perspective it does't seem to matter much what system is used.
So if anybody knows the answer than please tell
Wouter