Miles,

   I purchased Annie with 16mm genoa sheets fastened to the sail with a cowhitch/larkshead.   I replaced the sheet shortly after purchase and found the knot was rock solid...no chance it would slip at all.  After an hour with a marlinspike I gave up and cut the knot.  I used a cowhitch/larkshead on the new line and it held fine, no slipage.  I untied the know after a year because I didn't like the way the line looked like it was bending as it left the knot under load.  I cut the line and used two bowlines, which I still have now.  

The bowlines do seem to catch on the forward lower shrouds and if the sail is allowed to flog during a tack the weight of the two knots seems to make things worse.    

Take home message:  cowhitch is smother, does not seem to slip once set, but I am concerned about concentrating force on a small point of the line.  Bowlines seem to spread the stress across a larger area of the rope, won't slip and have the benefit of being two separate sheets in the event of a failure near the knot/sail.  

                    Regards,  John

SV Annie  SM37

Le Marin Martinique