Texel Rating 2010 updatet

Nico Boon: Texel Rating, OMR und Multi 2000 sind etwas mehr harmonisiert in 2010

For multihulls there are three handicap systems using the basic 1984 Texel rating formula. Since 1997 its main formula is used in the Australian OMR rule, for racing with around 170 multihulls, mainly on the East coast of Queensland. In the same year 1997 they started to use the same TR formula in the French Multi 2000 rule. With more than 110 multihulls on their rating list. Technical advisor there is the well-known designer Erik Lerouge. That rule organization now is in the hands of the national sailing Union in France, the FFV.

In both rules, naturally, you find the formula used in 1997. (the updated form of 1993). Both rating committees found no arguments to follow our update in 2002, when the power for RW has been lowered again, from 0.325 to 0.3, in order to lessen the disadvantage for very light and fast multihulls, mainly in the group of trampoline cats.

The rating committees wish to harmonize the rules towards one rule for all multihulls. The Dutch rating committee as step 1, decided to return in 2010 to our formula used before 2002. At the same time we will start using the same constant of 1 as in the OMR and the Multi 2000 rule. This change of the constant factor only determines the level of the rating numbers, not their relative differences.

Our formula then becomes:

 TR = 100 / (rl ^0.3 * rsa ^ 0.4 / rw ^ 0.325). 

The constant 1 could be left out. OMR and Multi2000 prefer to use a TCF, a time correction factor, so their basic formula is even more simple:

 TCF = rl ^0.3 * rsa ^ 0.4 / rw ^ 0.325. 

The value found, will be multiplied, with several factors for elements specific in each rule. Elements considered to influence the performance of the designs. In the Netherlands they are a correction factor K for catamarans generally being thought to be a bit slower than comparable trimarans.

A correction factor P for boats with various kinds of propellers under the waterline. Finally a correction factor Q for designs with NO efficient dagger boards or centre boards, based on the ratio draft / RL (rated length). For details in the Dutch version, see the formulas in the text of the rule on www.texelrating. org, in the section for cabin multihulls.

The consequence of the changes in the basic formula are that heavy, relatively slow multihulls get a TR number, that is relatively higher than the one used before. The maximum difference between the fastest and the slowest designs will be around 10 % more then with the formula used from 2002 – 2009.. Another consequence of the change in the power for RW and the constant factor is, that the formula predicting Vb (boat speed) from Vt (true wind speed) had to be changed too. This formula now becomes

 Vb = 164 * Vt ^ 0.75 / TR.

In the Dutch version of the rule, TR numbers as well as TCF numbers have been published for years on the lists with the rating numbers. In these lists all the data of the boats for which they have been calculated can be studied. The lists can be downloaded as Excel files. See the website for them too. There are lists for measured boats and a longer list for unmeasured designs. The data for these boat have been found in designer brochures, internet etc. Apart from the return to the older basic TR formula, some changes have been made which have to do with the rating of screachers. They can be defined as narrow spinnakers, with ratios of mid girth length (smgscr) divided by the foot length (sfscr) less than 0.75. They tend to be near 0.50 now, or even a bit lower. Following a suggestion of the Norwegian multihull club a gliding scale has been introduced in 2009 to calculate their rated area. In 2010 this scale is slightly softened in two ways. The formula now is:

 Rated sail area screacher (rsascr) = (0.80 – smsgscr / sfscr) * (msascr – rsag).

The constant in 2009 was 0.82. Because of the reduction of msascr in the formula with rsag, the rating % of screachers varies from 17 % to 22 % of their real (measured) area.

In case owners use a spinnaker as well as a screacher in their sail wardrobe, rsascr is reduced to 0.16 * msascr.

After the 2010 season, the effects of all the changes in 2010 naturally will be evaluated.