Does an alternative sail have to fit within the profile of the 'largest' measured sail?
The 2002 class rules C.8.1 Limitations stated: "The profile of each alternative sail shall fall within the profile of the sails recorded on the certificate."
Is this no longer a requirement in the 2016 class rules?
No. Under the 2002 class rules it is required that 'alternative' sails shall fall within the profile of the sails recorded on the certificate. The 2016 class rules do not require this.
Sail makers will be aware that sails are 3D objects and small changes to the inbuilt shape at the seams will have an effect on the profile of the sail. Although apparently simple in its requirements, the 2002 class rule creates several problems. Unless the sailmaker knows the leech length of a sail he is replacing he is unable to make a sail of the same profile (even if it is a purely 2D object). Even 1 mm more, or 1 mm less, leech length or luff curve results in the profile of the replacement sail not matching the original. It is not smart to have a class rule that does not allow the owner to replace his equipment and easily meet the class rules. Further, unless the sails measured and recorded on the certificate are retained by the owner when he has replacement sails they, and the other 'alternative' sails cannot be checked according to the class rules.
The 2016 class rules no longer require alternative sails to fall within the profile of the sails recorded on the certificate but treat the issue in a slightly different way that solves the problems mentioned above and gives other benefits. How?
The way in which the 'largest' sail is placed on the measurement grid has been revised marginally - the head and tack are placed on a line perpendicular to the transverse grid lines with the clew placed on a grid line. At and above the clew the cross widths are taken as usual (but at 200 mm intervals instead). Below the clew the depths are taken at 50 mm intervals. The dimensions are recorded on the certificate.
'Alternative' sails are checked by placing them on the grid in the same way and checking that their dimensions (measured in the same way) are equal to or less than the certificate dimensions.
There is no requirement for these 'alternative' sails to fall within the profile of the 'largest'. This introduces freedom to have sails made with different luff curves (or fullness/camber for example) but which comply with the certificate. Any width added at the luff needs to be removed at the leech. Provided the cross widths measured at all grid lines remain less than or equal to the certifiate values, the sail complies. See the diagram above.
The sail maker has all the information he needs to make sails that comply with the class rules as extended by the boat's certificate without asking for more. At equipment inspection there need be no difficulty in establishing a sail's compliance under the 2016 class rules.
This freedom exists for boats with certificates to the 2016 class rules only. Boats measured to the 2002 class rules and any new sails made for them shall continue to comply with those class rules.