CRF MkII Objectives, Formulae and Factors
The goal of CRF MkII is to provide an objective, accurate and transparent rating system that provides fair racing across wide range of yacht sizes and types. To that end, it is anticipated that adjustments to the factors and formulae used to calculate CRF MkII ratings will be made from year to year, based on an in-depth analysis of the sailing conditions experienced and race results recorded during previous seasons.
CRF MkII ratings are based on input data that is declared by the yacht owner, and reviewed by the CRF rating office. The essentials of the CRF formulae and factors can be summarized as follows:
- Effective sailing length ‘L’: A primary performance parameter that for most boats is based on a weighted average of LOA and LWL. (For boats designed after January 1, 1990 only, an increment based on beam aft is added to ‘L’ to account for the effects of unusually broad, powerful afterbodies).
- Sail Area; Upwind and downwind sail areas are calculated separately for a wide variety of rig configurations: Sloops, yawls, ketches, schooners, with mainsails that are either jib or gaff headed. The differences in efficiency among these different rig types are addressed via assigned ‘Rig Factors’.
- Displacement; The rating of each boat varies with a declared displacement that should reflect the condition in which she is presented for racing. For boats that are primarily daysailors, this is typically similar to a ‘light ship’ condition. For boats that race while fully equipped and provisioned for cruising, this might be similar to a ‘half load’ condition. Whatever the declared displacement, it is critical that it be consistent with the declared draft and LWL.
- Draft; the declared draft must be consistent with the declared displacement. Rated Draft is either the depth of a fixed keel at that displacement, or the draft of a fixed keel plus a portion of the centerboard extension below that fixed keel. A Base Draft that reflects the fleet norm is calculated as a function of length, and a Draft Correction is function of the difference between the Rated and Base drafts.
- Beam; A Length/Beam Correction is based on the difference between the rated L/BMax and a base L/BMax that is a function of length.
- Stability: A Stability Correction was added in 2019 to address the effect of stability on upwind and reaching performance. The righting moment from both the hull (at the declared displacement) and a calculated crew weight (that varies with boat size) are assessed, and compared to a calculated Base Righting Moment that reflects the fleet norm.
- Displacement/Length Ratio: Boats with less displacement for their length have a higher speed potential at high speed/length ratios. A Disp/Length Factor is a function of the difference between a rated DLF and a Base DLF.
- Sail Area/Disp Ratio: Boats with more sail area for their displacement accelerate more quickly. A SA/Disp Factor is a function of the difference between a rated SA/Disp ratio and a Base SA/Disp ratio.
- Prop Factors: These are assigned to reflect the differences in drag between different prop types (solid, folding, feathering) as well as between different prop installations (in aperture, exposed shaft, strut drive, etc).
- Spar Factors: These are assigned to address the effects of spar material (carbon, aluminum and wood) on performance via both righting moment and rig efficiency.
The formulae and factors used in calculating CRF MkII ratings can be viewed in their entirety by clicking these links: