I tried several knots from Reed's to lash the sails to the spars on a Skerry and found they were either too bulky or did not stay tied well on the slick synthetic lines. What seemed to work best for me was just a simple overhand knot, knotting both ends of the line at once. Wish I could draw a picture, but I simply held the two ends together, made a loop with both lines and passed the ends through the loops. This is simple, compact, and seems to be secure so far.
Is there a recommended knot for this purpose that I don't know about?