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More information on mylar sails, from Frank Bethwaite Re Jib At Concord I arranged a three to one purchase through a clam cleat for the 2mm spectra jib halyard, but the 2mm spectra did not bite properly in the bottom of the cleat, and slipped during the race. Nicholas tied it off as well as he could during the race, but the jib luff was sagging about two inches from the forestay between several of the lower hanks at the end of the race. This would not be fast. At Northbridge the next day I found I had inadvertently left the cleat and tail at Concord, so we arranged a truckies’ hitch around the forward end of the centrecase. The tie-off knot in the 2mm line was much too awkward to be adjusted during the race, so again there was jib luff sag in the puffs. A point needs to be made about jib luff tension (ie halyard tension) with battened mylar jibs which are hanked to the forestay. The hanks allow about two inches of movement fore and aft with respect to the stay. If the tension is set too tight, the battened jib luff moves forward of the forestay in light air, which makes the jib flat, which is slow. If it is not tightened in the breeze, the luff sags (as above) which again is slow. I have now put together an arrangement in which a strong plastic
ring lies on the foredeck by the mast and is tied by a tail to
the centrecase. A
short 4mm
adjuster line connects ring and a trapeze cleat with a 2-1 Re Mainsail At Concord, to show what was possible I had slackened the diamonds to the point where they could be pinched to touch the mast eight inches above the whisker pole fitting, then tied them together at the WP fitting which left them still quite loose. I suggested to Brad that he fiddle the tie if he wanted to experiment. The rotation handle bolt loosened as it always does on its first day out, so the handle drooped and Nicholas had trouble with rotation. The end result was that the mast rotated a long way, bent forward further than normal because of the slack diamonds, and this abnormal bend made the sail very flat as he reports. At Northbridge the next day I tightened the diamonds until they could be pinched to touch the mast 4 inches above the WP fitting - ie still very slack, and this is how they sailed, so the mainsail would have been flatter than when Shane sailed it on his stiffer mast. The rotation bolt had been tightened, so rotation was not an issue. Overview The ability of the combination of slack diamonds and degree of rotation to control mainsail fullness so easily is something I had not anticipated. This is an exciting advance. I will trial a system by which I can set rotation to the degree desired and see what happens to the speed when this is used intelligently. Frank Bethwaite Posted 2005/04/01 |
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