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OFFSHORE MULTIHULL RATING (OMR) PREAMBLE – JULY 2016

Multihull Yacht Club Queensland Inc

Northern End of Manly Boat Harbour,
22 Trafalgar Street, Manly

P.O. Box 178,
Wynnum Qld. 4178

ABN: 97 324 509 351
Website: www.mycq.org.au

The Offshore Multihull Rule by the Multihull Yacht Club Queensland (Inc)

First issued February 1997

Source Filename: OMR PREAMBLE 2016.docx

1. Acknowledgement

1.1 This rule is a development of the Texel Rule, developed in Holland.

The MYCQ gratefully acknowledges the development work of Nico Boon and the KNWV.

(Royal Dutch Watersport Association)

2. Administration

Authority: The authority for the administration and development of this rule is the MYCQ

(Multihull Yacht Club Queensland Inc). Only electronic ratings issued by the MYCQ and appearing on its website register, or ready for uploading by the OMR rating officer, will be accepted in MYCQ events.

Development: This is a development rule. The MYCQ reserves the right to alter or amend the rules, formulae or interpretations as it sees fit, without notice.

Interpretation: The MYCQ Sailing Committee shall appoint an OMR officer, who shall be the impartial arbiter of these rules. The OMR officer shall interpret any part of the text, or sailing innovation in accordance with the spirit of the rule, to ensure fair sailing for all race competitors.

Owner’s responsibilities: It remains the owner’s responsibility:

  1. To prepare the boat, sails and equipment for measuring
  2. To ensure that he/she is the holder of a current rating
  3. To ensure that the vessels measurements agree with the published online rating
  4. To ensure that, during races the yacht is equipped in accordance with the prescriptions of the rating

A failure to do so shall require the vessel to be disqualified from any race in which the vessel is not properly equipped.

Ratings: A Rating shall be issued by the rating officer and shall remain current for four years from the date of measurement unless a change is made to any parameter applicable to the rating. A full reweighing and measuring is mandatory should any changes be made to the structure of the vessel or its rig.

Re-measurement: If re-measurement is requested at any time, a fee decided by the committee, may be incurred.

Valid Rating: A yacht shall have only one current valid rating.

Notification: A current rating must be available before a yacht’s entry in an OMR event will be accepted. When a regatta includes races of different safety categories, only one rating will be valid for the duration of the regatta. (See also Para 6.9)

MYCQ Measurement Fees: The following fees may be charged by MYCQ. (Any extra costs incurred by the measurer such as traveling, accommodation etc. will be charged additionally.)

1: Weighing Equipment Maintenance Levy: This fee covers cost of weighing equipment and recalibration. For Brisbane-based boats, MYCQ Club members shall have the Weighing Equipment Levy waived in the first instance.

2: Sail Re-measurement: This a processing fee charged for re-measurement of any new sail configuration and subsequent rating recalculation and website listing. The measurer may also charge a further fee.

3: Annual Listing Fee: This annual fee is payable by the owner of each boat, and covers website re-listing of ratings annually.

3. Abbreviations and units of measurement

3.1 Units of Measurement.

All dimensions are given and recorded in meters to two decimal places, square meters and kilograms.

3.2 Abbreviations

The following abbreviations are used.

AOC Aft overhang component
ARG Aspect ratio genoa
ARM Aspect ratio mainsail
FOC Forward overhang component
LF Factor applied to Rated Length
LOA Length overall, hull
LOAA Length overall, ama
LPG Perpendicular from clew to luff of Genoa
LPM Perpendicular from tack to longest side of triangle contained by the head, tack and clew of the main
MAM Measured area of rotating mast
MSAD Measured sail area drifter
MSAG Measured sail area genoa
MSAM Measured sail area mainsail
MSAS Measured sail area staysail
MSASc Measured sail area screecher
MSASp Measured sail area spinnaker
NC Number of Crew
OMR Offshore Multihull Rating
RL Rated length
RSA Total rated sail area
RSAD Rated sail area drifter
RSAG Rated sail area genoa
RSAM Rated sail area mainsail
RSAMz Rated sail area mizzen
RSAS Rated sail area staysail
RSASc Rated sail area screecher
RSASp Rated sail area spinnaker
RW Rated Weight
VLM Vertical length overall of the mainsail
WC Total weight of crew in normal fair weather clothing
WCD Declared weight of crew
WE Weight of movable equipment declared
WM Weight of boat and all equipment
WS Weight of boat with racing equipment

For measurements and abbreviations for sails see relevant paragraphs.

4. Preparation for measurement

4.1. The owner or his representative shall be present when measurements are taken, and shall check and sign off on all forms supplied by the measurer.

4.2. All equipment shall be stowed in the location where it is normally kept while racing.

4.3. An inventory shall be made of all moveable equipment and its location and provided to the measurer at the time of measurement. Inventory forms are available from MYCQ measurers.

4.4. The owner may elect to carry whatever equipment or fittings he desires, (unless otherwise prescribed in the Preamble) so long as all equipment is inventoried and remains on the vessel while racing.

4.5. A copy of the inventory list, signed by the measurer, shall be carried aboard at all times and shall be produced to the race committee on demand.

4.6. The boat shall be dry and bilges free from water. Water tanks and fuel tanks shall be empty or pressed up. If pressed up, the calculated weight of their contents shall be subtracted from WM. Portable toilets, or waste holding tanks where carried, shall be empty.

4.7. Sails shall be laid out flat ready for measurement.

4.8. The measurer shall mark each measured sail near the tack with his name and the date of Measurement.

4.9. Measurement shall be undertaken upon appointment only.

4.10. The vessel must be ready in all respects. If not ready another appointment will be necessary.

4.11. Payment of all fees is the responsibility of the owner.

4.12. Ratings will not be issued until fees are paid. Discounts may apply to MYCQ members.

(See also Appendix 1. Preparing your boat for measurement)

5. Hull measurement

Measurements are taken from the hull or deck surface at the fore and aft extremities whether these fall above or below waterline. Bulb bows shall be included. Extensions or fittings such as prodders, anchor rollers, rub rails, rudders etc. are not included. . All equipment shall be in its normal position as when racing. No persons shall be aboard.

  1. Measure the length overall of the longest hull. (LOA)
  2.  With the vessel in racing trim in preparation for weighing: if the forward extremity of the LOA overhangs the true waterline mark a position on the stem 2.5% of LOA above the true waterline. (HCE)
  3. If the stern extremity of LOA overhangs the true waterline mark a position on the stern 2.5% of LOA above the true waterline. (HCE)
  4. Measure the distance from the forward extremity of LOA to the forward extremity of the hull at or below HCE. (FOC)
  5. Measure the distance from the aft extremity of LOA to the aft extremity of the hull at or below HCE. (AOC)
  6. Rated length RL = LOA – (FOC +AOC)
  7. If the LOA of the Ama of a trimaran is equal to, or greater than the central hull, RL = LOA of the Ama.

6. Weight

Weight of the vessel shall be measured with all fixed equipment and accessories which will be carried during racing as documented in the inventory but without crew, crew personal kit, or consumables including water and fuel. The vessel must be dry and all bilges and lockers open for inspection.

6.1 Weighing equipment must be capable of measuring to an accuracy of + or – 0.5%. {WM}

6.2 Only weighing techniques as approved in the appendix hereto shall be used.

6.3 Equipment which may be added for certain race categories shall not be aboard. These items shall be listed and weighed separately and individually. (WE)

6.4 Crew number (NC) and total weight in normal fair weather sailing clothing shall be declared. (WC)

6.6 The WCD shall not fall by more than 2.5% without change to the rating. Extra crew numbers and weight may be carried without change to the rating.

6.7 A Race Committee at its discretion may require the weighing of the crew immediately prior to particular races or regattas for the purpose of rating those specific events only.

6.9 Rated weight RW = WM + WCD + (WE when applicable)

7. Sail Measurement

7.1. The true area of each sail is to be measured as accurately as practicable.

Although parameters and formulas for measurement are given for conventional sails, these procedures shall not restrict the measurer from using alternative means to obtain an accurate area for any sail which is an unusual shape and is deemed to require a different measuring technique. The measurer shall record the method and parameters used together with the actual measurements of such sails. Any doubts shall be referred to the OMR officer for a final decision.

8. Mainsails

8.1. All mainsails are presumed to be full battened mainsails. For sails without full length battens, the MSAM is reduced by 6%. A sail shall not be considered full battened if the Sum of the lengths of the battens does not exceed E and the length of the top batten does not exceed 30% of E.

For vessels with a mizzen or more than one mainsail in fore and aft configuration, the MSAM shall be the area of the largest of the mizzen or mainsail plus 50% of the area of each additional mizzen or mainsail.

For vessels carrying two mains in parallel, the second main shall be rated at 0.8*RSA.

8.2 The measurer shall record,

8.3 Measured sail area Mainsail,

       MSAM =0.5(ML1*LPM)+0.5(ML1*HB)+0.66(P*Pr)+0.66(ML2*RDM)+0.66(E*Er)

8.4. Rated sail area mainsail RSAM = MSAM

8.5 Rated sail area mainsail with rotating mast is calculated by rating the main and mast area as a unit.

RSAM = (Windward rating) 0.65 * (MSAM + MAM) + (Offwind rating) 0.35 * (MSAM+MAM)

8.6 ARM = MSAM/E^2 or (MSAM +MAM)/(E+0.375*MC)^2 for rotating rigs.

9. Jibs and Genoas

9.1 The largest sail not otherwise defined set forward of the foremast shall be measured as a genoa

9.2 The measurer shall record,

9.3 Measured sail area genoa

MSAG = 0.5(LL*LPG)+0.5(LG1*HG)+0.66(LL*LLrg)+0.66*(LG2*Lrg)+0.66*(FG*Frg)

9.4 Rated sail area genoa

RSAG = MSAG

9.5 ARG = MSAG/LPG^2

10. Staysails

A staysail is a headsail used in addition to a genoa or other headsail, which is flown between that Genoa or other headsail and the main mast.

A staysail, its area and rated sail area shall be calculated in the same manner as a genoa. Where any sail with a mid-girth of less than 50% of the foot is carried on either a spinnaker pole or a bow pole or any position forward of the forestay, then that sail shall be measured as a genoa, and any additional sail which may be carried between it and the mainsail shall be measured as a staysail.

11. Drifters

A drifter is a lightweight headsail constructed of nylon sailcloth of not more than 1.5 US ounces per square yard (64 gm/m2). It shall be measured (MSAD) in the same manner as a genoa.

Lightweight headsails of other materials shall be measured as genoas.

Rated sail area drifter

RSAD = 0.3((MSAD)-RSAG)

A drifter may not be carried in conjunction with another headsail without rating adjustment

See staysail (10).

12. Spinnakers

12.1 A spinnaker shall be a lightweight sail whose mid-girth equals or exceeds 75%  of its foot measured at the mid-point of luff and leech.

12.2 Additionally, the measured area of the spinnaker shall not be less than:

12.3 The measurer shall record,

12.4 Measured sail area spinnaker,

MSASp = SF*(SL1+SL2)/4 + (SMG-SF/2)*(SL1+SL2)/3

12.5 Downwind rated sail area with Spinnaker component only = 0.3(MSASp-RSAG)

Downwind rated sail area of Spinnaker component with Screecher = 0.295(MSASp - RSAG)

13. Screechers

13.1 A screecher is a lightweight sail without battens not attached to a stay whose mid girth measured at the mid point of luff and leech exceeds 50% of the foot but is less than 75% of the foot. It shall be measured, MSASc, in the same manner as a spinnaker.

13.3 The measured area of the screecher shall not be less than the measured area of the genoa.

13.4 If the screecher is the largest downwind sail it shall be rated in the same manner as a spinnaker with a 0.35 downwind rated sail area component.

The Downwind rated sail area = 0.35*(“Z” constant * MSASc - RSAG)

And the rating of the screecher shall not be less than 0.36*RSAM

13.5 If otherwise satisfying the conditions of a screecher, but having a smaller measured area than the largest downwind spinnaker, the screecher shall attract the following rating:

Rated sail area Screecher, (RSASc) = 0.055*MSASc – RSAG

14. Centerboards

14.1. All yachts are presumed to have an effective centreboard or fixed keel system.

Yachts deemed not to have such an effective centreboard or keel system by the rating officer shall have their OMR decreased by a factor of 0.98

14.2. Yachts that are fitted with a keel or fin which cannot be retracted when sailing shall have their OMR decreased by a factor of 0.995

14.3. A yacht with a pivoting centerboard where the underwater case opening remains open when the centerboard is deployed and has no means of improving water flow such as flaps shall have their OMR decreased by a factor of 0.99

The measurer shall decide whether such an allowance is applicable and shall record same on the measurement form. Any doubt shall be referred to the OMR officer for a final decision.

15. Propeller corrections.

15.1. All yachts are presumed to have either no propellers, or retractable leg systems. Yachts with propellers remaining in the water while racing shall have their OMR decreased in accordance with the following table.

The rating officer may apply an appropriate factor for propellers which are considered to be intended to or apparently provide a rating advantage.

15.2. Any yacht having more than one special adjustment, propellers or centerboards shall have the product of each individual adjustment applied to the OMR. For example a trimaran with a fixed propeller and no effective centreboard, the factor would be 0.975 * 0.98.

16. Rating Calculation

Rated Sail Area, RSA = “Configuration RSA” + RSAS + RSAD + RSAMz

The four major sail configurations covering the majority of the current multihull racing fleet are as follows:

16.1. Mainsail and Genoa / Jib only

A vessel carrying no downwind sails will attract a downwind premium on its rated sail area in the RSA algorithm equal to 120% of the rated working sail area. This is a ‘base rating’ which adds the equivalent of 36% of the rated area of the main as a de facto spinnaker, to correct mathematical anomalies in the rating of boats at the lower extreme of sail area relative to their size.

The relevant changes to the RSA formula are as follows:

Rated sail area of Main + Rated sail area of Genoa/Jib + Offwind correction factor

New RSA 6b = (RSAM + RSAG) + 1.2*(Rating of Working Sail Area [= RSAM+RSAG] where RSAM +RSAG is rated in the same manner as a defacto spinnaker)

This equals - (RSAM + RSAG) + 1.2*(0.3* (RSAM+RSAG-RSAG)

This simplifies to: If no valid screecher or valid spinnaker, then

(RSAM + RSAG) + 0.36*RSAM

(The committee will monitor the premium applied to vessels in ‘cruise’ mode without any rated downwind sails and reserves the right to change this correction factor if deemed necessary.)

16.2. Mainsail, Genoa / Jib and Spinnaker only

If no screecher but valid spinnaker, then (RSAM + RSAG) + (0.3*(RSASp – RSAG)

Where RSASp = MASp

16.3. Mainsail, Genoa / Jib and Screecher only

If a valid screecher but not valid spinnaker, then (RSAM + RSAG) + (0.35* (RSASc Screecher – RSAG))

Where RSASc = MASc

16.4. Mainsail, Genoa / Jib, Spinnaker and Screecher

If valid screecher & valid spinnaker, then (RSAM + RSAG) + (0.295*(RSASp – RSAG)) + (0.055*MSASc - RSAG)

(+ RSA Staysail, RSA Drifter, RSA Mizzen, RSA Second Main) if applicable

16.5. The Final OMR Algorithm

OMR = (Drag/Lift Factors) * 0.93 * RL^LF * RSA^0.4 / (RW ^0.325)

Where 0.93 is a constant. This constant has been modified from 1.0 to 0.93 in the 2016 OMR review to correct for the overall shift upwards in ratings with the removal of sail efficiency factors.

17. Data from other clubs

17.1 Each club providing OMR rating measurements or data for on-line listing must ensure clear identification the origin of the data, measurement form and inventory listings, complete with owners and Measurer’s signatures.

17.2 Before accepting a copy of a rating certificate issued by another club, the race committee must validate the copy by contacting the relevant official of the issuing club.

18. Weighing and measuring techniques

Acceptable techniques and paradigms are noted in the appendix. The MYCQ committee shall decide on changes or additions to allowable paradigms and techniques as may be required from time to time.

19. Time Correction Factor

19.1 The OMR Time Correction factor is provided to three decimal places

19.2 Corrected time = Elapsed time * OMR

Appendix (see website menu: OMR | OMR Guidelines)

Preparations for measurement (including weighing procedures)

Sail Measurement (Diagrams)