CRF MkII Background, Formulae, and Factors
The primary goals for CRF MkII are better handicapping, continuity with previous versions of CRF, and transparency. The expectation is that CRF MkII ratings will better reflect real world performance potential via the following improvements over earlier versions of CRF:
- Assessing effective sailing length at its full linear value rather than at its square root, resulting in ratings that are similar to LWL, and thus better suited to the Herreshoff TA tables typically used in scoring Classic races.
- Assessing effective sailing length by weighting LWL more heavily than LOA, since length at deck level is seldom immersed or fully effective in generating sailing length.
- Assessing the primary performance parameters draft (including ‘board down’ draft for centerboarders) and displacement directly in its new formulae, rather than by applying ‘Adjustments to Base Rating’ (ABR’s) and/or ‘Cruising Adjustments’.
- Retaining a length/beam term in calculating rating, but basing it on a smooth curve and an assumed ‘base length/beam ratio’ that varies with length, rather than on a step function.
- Assessing genoa overlap in calculating ‘with spinnaker’ ratings.
CRF MkII is careful to maintain continuity with CRF’s previous versions in several ways, as it is fully recognized that without the decades of hard work by Chris Wick and others in the development and administration of CRF, there would be no Classic racing as we enjoy it today. This continuity is maintained first by the fact that both versions share ‘development DNA” with the Cruising Club of America (CCA) rating rule. In original CRF the CCA connection is quite direct, and in MkII it is maintained through the CCA rule’s contributions to the IOR rule, on which CRF MkII is loosely based. Continuity is further maintained by the fact that CRF MkII requires only the following data input declarations beyond those that have been required in earlier versions of CRF.
- Centerboard extension beyond fixed keel draft. (CRF’16 does not account for ‘board down’ draft)
- Distance from the mast to the tack point of an asymmetrical spinnaker, if one is carried while racing
- A ‘closest match to sample sketches’ declaration for a range of keel and rudder configurations.
- A ‘square head’ mainsail type declaration (only allowed on Spirit of Tradition yachts)
- An off center exposed propeller option
- A ‘trim tab’ (adjustable flap on a keel trailing edge) option
CRF MkII intends to make its development and administration as transparent as possible. This will be done most simply by avoiding the application of undocumented ABR’s and Cruiser Adjustments to MkII ratings, and more fundamentally by calculating ratings via published formulae and factors, (see below) rather than via an unpublished ‘black box’. For those without the time or inclination to wade through the formulae shown, a short text summery of how they are constructed follows:
- A ‘base rating’ is calculated first. Its most important initial term carries the performance contributors length ‘L’ and the square root of rated sail area ‘S’ in the numerator, and the performance limiter displacement ‘DSPS’ in the denominator, much as in Nathaniel Herreshoff’s Universal Rule and later in IOR. This first term is then adjusted by a Draft Correction ‘DC’ and a Length/Beam Correction ‘LBRC’.
- The final CRF MkII rating is calculated by applying Propeller, Displacement/Length, Sail Area/Displacement, Keel, Spar, and Moveable Appendage factors to the base rating. MkII retains the general approach of the earlier version of CRF in the Rig and Propeller Factors, but the other factors are new in CRF MkII.