LUFF SHAPE !!!!!!
"Recreational Sails / Cruising cut" sails have an 'entry' or leading edge shape at the luff that is 'rounded' (by increased 'broadseaming' or curvature cut into the panel seams) to accommodate inattention or lack of experience of the helmsman. A cruising cut is a 'forgiving' shape so that the sail's luff will be 'more stable' (less luffing and less flow separation) for an extra approx. 5-8 degrees of improper 'attack angle'. You can be a sloppy inattentive helmsman and still have the sail 'draw' well.
A 'racing cut' has a relatively 'flat' entry shape which requires PRECISION steering to avoid luffing/separation ... a very narrow 'groove' or angle of attack range for the helmsman to steer. With a well made 'racing cut' the helmsman has to be 'watching the luff' (tell tales) constantly to hold the *very narrow range* of 'attack angle'; a cruising cut can have the helmsman almost asleep.
Cross cut sails can have either shape, racing or 'forgiving', depending on the selection of the amount of 'broadseaming' (curvature shape of the sail due to the amount of 'seam overlap'). Cross cut DACRON sails are 'adjustable' due to the small amount of stretch available in the in fabric; you can change the flatness of the luff entry by halyard (or cunningham) tension. Dacron 'radial cut' are less adjustable and are more or less 'shape stable'; but, not nearly as 'shape stable' as a laminate sail.
Radial cut laminated sails typically have little shape adjustability, the shape you buy is the shape you get, as laminated sails have very little 'stretch'. When choosing a radial laminate sail, the sail designer must take into account 1. the expertise/precision of the helmsman, 2. the narrow wind-range in which the sail is to be used, 3. the typical wave forms encountered (flat or chop, etc.) so that the sail's design shape is 'matched' exactly to the venue sailed. ..... a single purpose sail. Ditto, a radial racing cut dacron sail made of extremely stable materials; although, the fabric will still be a little stretchy thus more 'adjustable'.
So, if you want to be *very* competitive over varying sailing conditions, you need MANY sets/suits of laminated sails to meet those different conditions ... or choose a cut/shape for the 'average' if that is all you can 'afford'. Dacron racing sails, although more 'shape adjustable' will have a 'poorer average' than laminated sails; but, you can 'get away' with a single suit - just dont expect the performance output average to be equivalent to of a 'full set' of laminated sails.
If you want a 'precision' sail for good performance you really need to have the sailmaker KNOW your sailing expertise, your (honest) precision as a helmsman, and the exact venue conditions expected, ... and the historical performance of your boat (or boat class) so those factors can be addressed within the (computer) cutting/lofting program software.
Mail order, plain vanilla cross cut dacron sails will typically be a 'recreational/forgiving' shape, designed for sailing in 15 kts with 2-3 ft. of chop ... therefore a bit 'powered-up' and 'a bit slow' for sailing in 'flat' water ... and minor shape 'faults' are usually 'left alone' or uncorrected in the design execution and actual lofting of the sail. With precision laminates from a 'high quality' loft, sometimes whole sections will be re-assembled many times ... until the shape is absolutely correct.
hope this helps.
