Re: New sail Dacron characteristics
Actually if the dacron luff or foot is boltroped, the sail's 'edge' dimensions will 'shrink' as the boltrope is subject becoming 'fatter' and 'shorter' with constant cyclical strain. That's why a dacron sail should have its boltrope adjusted or 'eased' after about 200 - 300 hours (about every season) of 'hard' sailing if the sail is 'cross cut', longer adjustment interval if 'radial' cut and high modulus and aligned material.
A loose footed sail if over-stressed repeatedly will/may increase by 0.5 to 1% along the foot ... but thats from a lot of overstressing with the outhaul. Where this 0.5 -1% stretch on an old dacron sail is noticeable with age is along the leech (a blown 'open' leech)