Texel rating rule for multihulls, 2015
Preface
The purpose of this rating is to enable multihulls of various classes to race together. To give all room for research and development by designers. These rating regulations are applicable at all races where various designs or classes partake together, but one racing result is desired.
Rule administration
The rule is published under authority of the CTC, the Catamaran and Trimaran Club of the Netherlands. The CTC has the right to amend the regulations if necessary. In case of doubt about any part of the text of the rules, the spirit of the rule counts, not the letter.
TR numbers
The TRnumbers as used in the Netherlands are available for measured as well as unmeasured boats.
Easy calculator
On this website you find an easy calculator to test with your own boat or to experiment with a new design. Only use the tab key to go to all cells that may need your input. Starting with the name of your boat to the last one, asking a true wind value Vt. In the example given on the file, the value of the heeling force is made equal to the righting force by adapting Vt. This is done by using the function goal seeking in the cell heeling. Make the value in that cell = righting, by changing the value for Vt. That value for Vt is the stability limit. Above that value, reefing is recommended, even may be required.
Rating
Ratings will be determined for all types of multihulls on measurable data, guaranteed by the class organisation, the builder, the owner, using formulas, verifiable by anyone. A Texel Rating (TR) is calculated, with the formula given at the end of the ruletext, using normal rules of rounding.
Abbreviations, formulas and calculations used (Drawings and formulas)
Hulls
AOC  aft overhang component 
FOC  forward overhang component 
LOA  length overall 
RL  rated length (LOA  AOC  FOC) 
Weight
RW  rated weight (WC + WS) 
WC  weight crew 
WE  weight declared equipment 
WM  weight boat without equipment 
WS  weight complete boat (WE + WM) 
Sails
MSAG  measured area jib (genoa) 
MSAM  measured area mainsail 
MSAS  measured area spinnaker 
MSAScr  measured area screacher 
MSAST  measured area staysail 
RSA  RSAM + RSAG + RSAST + RSAS + if(RSAS>0;0.8*RSAScr;RSAScr) 
RSAG  EG * MSAG 
RSAM  EM * MSAM 
RSAST  EST * MSAST 
RSAS  rated sail area spinnaker 
RSAScr  rated sail area screecher 
VLM  vertical projection of luff of main : That is the distance measured alongside the mast from the highest point of a normally hoisted sail towards the lowest point reached when the downhaul is used. ( P ). 
VLG  vertical projection of the luff or leech of the jib/genoa. That is the distance between the horizontals on the mast taken from the highest point of the jib/genoa towards the lowest point of luff or leech whatever is the case.. It will be measured alongside the mast. ( I ). In practice: VLG = luff * 0.94 
SF(scr)  length foot of the spinnaker (screacher) 
SMG(scr)  distance between middle of luff and leech spinnaker (screacher) 
SL1(scr)  length luff of the spinnaker (screacher) 
SL2(scr)  length leech of the spinnaker (screacher) 
Various
P  correction factor for propellers


Q  correction factor for NO (dagger) board(s) Q = 0.94 / (draft / RL)^{0.037} 

K  Variable for catamarans, 1 for all trimarans. 1 / (0.19 * RSA^{0.4} / RW^{0.36} + 0.91), for cats, if > 1 
Determination of the rated length
The length overall is the horizontal distance from the most forward point of the hull to the farthest point at the stern of the hull. Lines through these points have to be measured both from vertical positions. Rudders and rudder equipment not to be included in LOA.
 FOC, Forward Overhang Component
That is the difference at the bow between the most forward point and the forward end of the rated length. If the bow is vertical or hanging backward than FOC = 0  AOC, After Overhang Component
That is the difference at the stern between the most afterward point of the stern and the aft end of the rated length. If the stern is vertical or leaning forward than AOC = 0  RL, Rated Length. The rated length is the horizontal distance measured at 2% of LOA above the waterline of the boat, without the crew on board. To calculate FOC. the freeboard VL at the stem and the angle α at the top of the stem have to be measured.
 FOC = VL * tangent α  (2% of LOA) * tangent α
The same must be done to determine AOC, for designs with a genuine stern overhang.
Generally AOC = 0
RL = LOA  AOC  FOC
Determination of the sail areas of main and foresails
The real sailarea is determined by one of the usual methods. For cabin multihulls the area of the mainsail is measured, using the Simpson rule. Applying the methods given on sheet 2, results in the real areas of mainsail, jib, drifter, staysail, as well as the spinnaker (screacher). From these data, the effective areas, will be calculated by using an efficiency percentage. That requires the determination of some ratios, specified below.
If a mast is used which is swivelling, with a section which is not a circle, (a wing mast), then the area of the mast (defined as follows) is added to RSAM calculated from MSAM, as shown below, which results in the final RSAM, to use in RSA.
Area mast  =  0.5 * maximum circumference * (VLM 1 + VLM 2) 
EM  =  0.67 * (MSAM / E^{2})^{0.3} 
EG  =  0.72 * (MSAG / lpg^{2})^{0.3} 
EG 2  =  0.72 * (MSAG 2 / lpst^{2})^{0.3} 
RSAM  =  EM * MSAM + area mast (if applicable) 
RSAG  =  EG * MSAG 
RSAG 2  =  EG 2 * MSAG 2 
Determination of the spinnaker or screacher area
For open cats provided with a spinnaker, RSAS = MSAS * 0.15, if the spinnaker area satisfies the following conditions. Spinnaker areas as given in class regulations. Otherwise use maximum allowed spinnaker areas, as given below.
crew


one man

two men


Boats up to 16 ft < 4.87 m: 
14 m^{2}

17 m^{2}

from 16 up to 19 ft > 4.87 m <= 5.80 m: 
17 m^{2}

21 m^{2}

from 19 up to 22 ft > 5.80 m <= 6.71 m: 
20 m^{2}

25 m^{2}

For boats with a length of more than 22 ft (6.71 m) depending on the spinnaker area, a rated area will be calculated. Spinnakers have to be measured as illustrated on the drawing.
The following dimensions have to be measured along the sides, stretched normally.
SF  =  foot 
SL 1  =  luff 
SL 2  =  leech 
SMG  =  straight line connecting the middle of luff and leech. 
The area is calculated as follows :
MSAS(cr)  =  SF * (SL1 + SL2) / 4 + (SMG  SF/2) * (SL1 + SL2) / 3 
SMG  >  75% of SF (For a screacher SMG < = 75% of SF) 
RSAS  =  max value of (0.03 * MSAS) and (12 / (SMG / SF)^{1.1} * MSAS * 0.01 – 0.3 * RSAG) 
RSAScr  =  max value of (0.06 * MSASCR) and (12 / (SMGSCR / SFSCR)^{1.1} * MSASCR * 0.01 – 0.3 * RSAG) 
All spinnakers have to be measured by a measurer and have to be stamped by the measurer with the following information:
• date of measuring
• spinnaker area
• name and/or nr. of the measurer
• paraph of the measurer
Determination of the weight of the crew
For calculation purposes 
weight each crew

LOA boat <= 4.00 m 
65 kg

LOA boat <= 4.80 m 
70 kg

LOA boat > 4.80 m 
75 kg

If the total sailarea >= 11 m^{2}, than for crew oneman boats always take 75 kg.
For cabin multihulls the crew weight in kg. is calculated as follows:
WC = 70 * RL^{0.78}  60
Centreboards
The rating for open catamarans not having an efficient centreboard is calculated by raising the not rounded ratingnumber with 4%.
For cabin multihulls the correction factor Q for not using a centreboard or daggerboard,
using RL and the draft as input, is calculated as follows:
Q = 0.94 / (draft/RL)^{0.037}
Rating formula
TR rating = 100 / (RL^{0.3} * RSA^{0.4 }/ RW^{0.325}) * K * P * Q
The rating number is rounded to an integer of two or three digits, using the normal rules for rounding.
A TCF number, if preferred, is calculated as follows: 100 / TR number (with 3 decimal numbers).
Inspection during races
During the season, the CTC rating committee may inspect boats on the measurements and weights used in the formulas. To keep the rating system as simple as possible (the KISS principle), no penalties are included yet, for instance for excess bowsprit (spinnaker boom) length, or for less than minimum headroom etc. It is easy to include extra multiplying factors, if users want to.