We are beginning to see evidence that sailmakers are attempting to gain unrated advantage under IRC by increasing mainsail widths in the top quarter of the sail, ie above MTW.
We do not wish to increase the complexity of IRC measurement for typical owners and are therefore reluctant to introduce additional rules to directly address this issue.
Noting however IRC Rules 2.5 and 26.2.2:
2.5 The spirit of IRC requires that owners and designers shall not seek means of artificially reducing the rating of a boat, e.g. increasing performance without a corresponding increase in rating.
26.2.2 RF above unity may be applied for: fractional, racing and lightweight rigs, high aspect ratio and efficient plan forms, wing and double luff sails, specialised sail stiffening, large headboards/cranes, permanently bent or highly controllable spars, hi-tech rigging, exotic rig materials, advanced winch and deck gear arrangements, flush/efficient deck design, and any other feature which increases sailing efficiency that is not already rated through the rated dimensions.
The Rating Office reserves the right to increase rig factor for any boat with mainsail upper roach considered to be excessive. Specifically any boat which has:
Mainsail Upper Width (the seven eighth width of the mainsail, measured as the shortest distance between the seven eighth leech point and the luff, bridging any leech hollows) in excess of 0.26*E,
or: Any full length battens intersecting the leech above the nine tenth leech point,
shall declare full details to the Rating Office and will have Rig Factor increased appropriately.
The Rating Office reserves the right to amend the above at any time.
RORC Rating Office Technical Director
28 January 2004