Texel rating rule for multihulls, 2015

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 TR-numbers as used in the Netherlands are available for measured as well as un-measured 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.

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)


AOC aft overhang component
FOC forward overhang component
LOA length overall
RL rated length (LOA - AOC - FOC)


RW rated weight (WC + WS)
WC weight crew
WE weight declared equipment
WM weight boat without equipment
WS weight complete boat (WE + WM)


MSAG measured area jib (genoa)
MSAM measured area mainsail
MSAS measured area spinnaker
MSAScr measured area screacher
MSAST measured area staysail
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)


P correction factor for propellers
one folding propeller: 1.02
one fixed propeller: 1.025
two folding propellers: 1.03
two fixed propellers: 1.0375
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 * RSA0.4 / RW0.36 + 0.91), for cats, if > 1


Determination of the rated length
The length over-all 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


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 / E2)0.3
EG  = 0.72 * (MSAG / lpg2)0.3
EG 2  = 0.72 * (MSAG 2 / lpst2)0.3
RSAM  = EM * MSAM  + area mast (if applicable)
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.

one man
two men
Boats up to 16 ft    < 4.87 m:
14 m2
17 m2
from 16 up to 19 ft > 4.87 m <= 5.80 m:
17 m2
21 m2
from 19 up to 22 ft > 5.80 m <= 6.71 m:
20 m2
25 m2

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 m2, than for crew one-man boats always take 75 kg.

For cabin multihulls the crew weight in kg. is calculated as follows:
WC = 70 * RL0.78 - 60

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 / (RL0.3 * RSA0.4 / RW0.325) * 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.