Hi Ian:

I have had the same thing happen, i.e. the main sail furling bolts loosening while under sail and the furling gearbox dropping down.  I suppose, having been advised by Olivier Beaute when he gave us the new boat owners indoctrination as we purchased our new boat, to "not over tighten" those bolts I had been less than diligent in assuring they were tight enough.  There is probably a happy medium between too tight and risking stripping the threads and not tight enough to prevent the furling gearbox from falling down.  When the boat was delivered to us, Amel did supply s specialty piece of line with a loop in the end of it that was designed to loop over the furling handle and be taken on cleat to one of the main mast cleats to hold the furling handle in this exact scenario. I would estimate it is about 1/4th to 3/8th inch diameter white line about 3 feet long with a loop.    I still have mine and keep it with the other emergency bits of kit in the cockpit locker.  Your improvisation worked no doubt.  It is now part of my scan of rigging to assure the bolts are tight enough and I also scan the gearbox from time to time while on long passages to assure that there is adequate engagement of the gearbox with the pins on the bottom of the mail sail furling foil.  

On another subject, at one point due to slipping of the outhaul line I had to manually cleat the outhaul to the main boom cleat that is cut into the aft end of the boom.  I looped my line incorrectly and when it came under load it pinched itself such that I had a terrible time getting it undone when the time came to furl the main.  So careful attention to routing that bit of kit is called for if you manually cleat the outhaul.

All the best, 

Gary Silver

s/v Liahona  SM 335   Jolly Harbor, Antigua

only three weeks until I am aboard again!!!!