The measurement I remember for the Tornado spi setup, is 9100mm from the block at the mast to the bearing surface on the pole. If the spi is buildt to 9150mm, you have 50mm of 'surplus', but I doubt that the sailmakers dont take a small amount of stretch into the equation and buildt the luff a tad shorter (can try measuring the luff on my Gran Segel spi tonight as I already have it in the basement).


BUT, from looking at pictures of current designs in the F-16 and F-18 class, it looks like they are sailing with a luff set up or designed looser than in the Tornado class. 2.5% might be right for those.