As I'm also involved in this; indeed the formula is changed this year.
The differences are not big but we try to get closer to reality.
The document can be found on
http://www.texelrating.org/ (open cats)
The text on the website is:
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Update for 2010
New method of rating sails
Since 1982 the aspect ratio has been used to calculate the efficiency of sails.. Modern square top mainsails are more efficient than triangular mainsails. The aspect ratio approach is not correct for ‘modern’ sails. In Australia a new system already has been introduced in 2008. In the OMR, (offshore multihull rule), for around 140 cabin multihulls of the multihull yacht club of Queensland. In 2008 comparable new formulas have been tested in Holland which will be introduced in the Netherlands, Germany and Norway and other countries.
The new formula for the mainsail is a combination of two values. One is the measure of rectangularity of the main. That is sail area main divided by the rectangle p times e. (p being the height of the sail (vlm), the length of the luff, e being the dimension e, the length of the foot of the main). The other ratio is the ratio (p/e). A higher and narrower mainsail is more efficient. The product of both values gives: msam_ex_mast / (p * e) * (p / e) = msam_ ex_mast / e ^ 2.
The formula to find the right efficiency factor is:
Efficiency factor main = c 1 * (msam_ex_mast / e^2) ^ p 1. For beach multihulls
The constant c 1 = 0.67, the power p 1 = 0.3
The efficiency of jibs is based on the ratio: msag / lpg^2.
Lpg is the perpendicular from tack to luff. The formula being used is:
Efficiency factor jib = c 2 * (msag/ lpg^2). ^ p 1
The constant c 2 =0.72, the power p 1 = 0.3
For cabin multihulls the formulas are the same as the one for the beach multihulls., The rated areas will be:
rsam = eff. factor main * msam_ex_mast + area mast (if a swivelling mast). For open cats msam always includes the area of a swivelling mast if that is the case. No separate adding of the mast area.
rsag = eff. factor jib * msag.
Basic TR formula
To harmonize the basic Texel Rating formula with the ones used since 1997 in Australia for a group of around 170 cabin multihulls and in France for a group of around 120 multihulls, the decision is made to return for the open cats to the formula used here before 2002, resulting in TR = 100 / (1.15 * RL ^ 0.3* RSA ^ 0.4 / RW ^ 0.325). For all cabin multihulls the constant 1.15 is lowered to 1, like in both foreign countries. That changes the absolute values of the rating numbers, but not their relative positions..
Correction for no dagger board(s) or centre board(s)
The correction factor for designs without efficient dagger board or centre board is changed from 1.03 in 1.04
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Geert
