Several Sailmakers have intentionally attempted to circumvent IRC rules 2.4 and 2.5 by developing headsail foot shelf profiles that artificially reduce the headsail measurements, reducing the IRC rating without a corresponding reduction in performance. To do this the curve of the foot is exaggerated to create a far larger foot shelf than required. This means that the measured tack point and clew point are not extended, and therefore move up the luff and leech, artificially reducing the sail’s dimensions.
To avoid exploitation of ERS sail measurement rules, if the maximum offset between the edge of the headsail foot and a straight line between the tack point and the clew point is 6% of LP or greater, or if a headsail has a batten or battens adjacent to the foot, then that measurement shall be provided.
IRC Rule Notice 2012/02 Headsail Foot Offset
If foot offset is greater than 7.5% of LP, it will be considered that IRC Rule 2.5 has been infringed. This will result in an increase in Rig Factor to correspond to the artificial reduction in rating, plus a small penalty.
This notice has immediate effect.
It is intended that IRC for 2013 will be drafted with an additional rule to control this development and prevent sailmakers from pursuing this loophole at owners’ expense into the future.
RORC Rating Office website