Rating Rules Changes for 2007

Changes to the MOCRA Rating Rule in 2007.

The 'mast rotating factor' and the 'carbon mast factor' were both modified in this year's version of the MOCRA rating rule to more accurately portray the performance gains of different types of masts. Here are a few words to explain the theory behind the modifications.

Previously the rule stated that if the mast was rotating, a fixed proportion of its area would contribute towards the rated sail area. However this did not take into account the change of aerodynamic efficiency for different mast sections. A modification has now been included that calculates the rated mast area as a function of the mast sections 'thickness to chord ratio.' So, a slender mast section with a low thickness to chord ratio will have a higher proportion of the mast area included in the rated area, compared to a circular mast section. It must be noted that even if a boat had a circular rotating mast, a small proportion of the masts area would still account for the rated sail area. This is as the mast is still able to angle the luff of the mainsail to windward to increase the aerodynamic efficiency of the mainsail.

The 'carbon mast factor' (CMF) has now been modified to rate the effectiveness of a carbon mast as a function of the boats 'rated length to displacement ratio' and 'mast height to rated length ratio.' The theory being that a carbon rig will reduce weight aloft and hence increase stability, and a boat with a high 'rated length to displacement ratio' and a high 'mast height to rated length ratio' will benefit more from the reduced weight aloft than a boat with a lower 'rated length to displacement ratio' and a lower 'mast height to rated length ratio.' Overall it was felt that carbon masts were being rated too highly, so even boats with a high 'rated length to displacement ratio' and a high 'mast length to rated length' will find that they are paying less in their rating as they previously did.