After a year of using the method of jib sheet connecting that is described here under "Tod's Method" http://www.msog.org/how-to/sails/kelch_jibclew.cfm I've noticed a phenomenon: The loop has been very gradually slipping back into the whipping and this last time out I almost couldn't fit the knotted line through the loop. Clearly, just whipping isn't a positive enough attachment. Probably need to sew through the sheet too. Tod