SORC 1998

 

All of these formulas conform to the same basic equation of: speed promoting variables divided by the speed restricting variable or waterline x sail area / weight. Yes there are many other variables contributing to a boats performance and many of these are included in the way sail area is calculated etceteras, but a basic simplicity is very important if comprehension and sanity are to remain.

Please note there are differences, generally minor, between the systems that are not noted here. For example: how sails are weighted before adding into the total rated sail area, whether rated weight includes crew, efficiency factors for rotating and wing masts, and various other items.

The purpose for listing this data is again to find ways to improve the MASF formula. We will attempt to apply these weightings to existing race data to see what kind of affect it has.

How to read the table: with the exception of the factor these numbers are all exponential powers that are applied in the formula. The factor has only the effect of scaling the results and has thus no effect in the rating itself. The other numbers which are used as exponents in the formula control the balance between the three variables of waterline, sail area and weight.
Rating system Factor Rated Length (RL) Rated sail area (RSA) Rated weight (RW) Formula

Bruce

1.0000

0.000

0.50

0.3333

F*RL*SA/RW

MOCRA

0.5000

0.500

0.50

0.5000

F*RL*SA/RW

Texel

0.4024

0.300

0.40

0.3250

F*RL*SA/RW

IOMR

0.3275

0.311

0.42

0.3180

F*RL*SA/RW

MASF

0.1595

0.500

0.33

0.2500

F*RL*SA/RW

Average of above

0.4779

0.322

0.43

0.3453

The following is an additional formula and explanation from John Shuttleworth taken from the Ronin multihull mail list:

So here is a quick way to determine performance for all multihulls.

KSP Number = 0.5 x Sq Root of (SA x DWL / Displ.)

SA = Sail Area in Sq. ft.
DWL = waterline lenght in ft.
Displ = Displacement in lbs.
KSP = Kelsall Shuttleworth performance number.

 

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