International Committee

MINUTES of a Meeting of the International Technical Committee held on 30th January ?

1st February 1999 at the Annapolis Yacht Club, Annapolis, Maryland, USA.

Present:David Pedrick (Chairman)

Andy Claughton

Friedrich Judel

Lex Keuning

David Lyons

Jussi Mannerberg

Alessandro Nazareth

Jim Schmicker

Nicola Sironi (Chief Measurer)

Jim Teeters

Kenneth Weller (ORC Consultant)

Observers:Bill Cook, Keppel Associates

Ian McCurdy, McCurdy & Rhodes

Miguel Rosa, Spain, RFEV

The Committee expresses its appreciation to the Annapolis Yacht Club for its hospitality, arranged through AYC member and past ORC councilor Gaither Scott.

1.Minutes of Meeting during the AGM

 The minutes of the previous ITC meeting, published with the proceedings of the Annual General Meeting in November 1998, were approved as written. A correction was made in the Measurement Committee minutes regarding the “heavy items” gyradius credit for a genoa furler. (See Minute 12.)

2.Post-AGM VPP Revisions

 As noted in the Addendum to the minutes of the 1998 AGM, Council approved by a substantial majority the combination of sail twist effect presented for the AGM and the revision of residuary resistance produced by the ITC following the AGM. Subsequent review and comment by the IMS community has been encouraging about these changes.


3.Presentations at Chesapeake Sailing Yacht Symposium

 This ITC meeting was scheduled to coordinate with the Chesapeake Sailing Yacht Symposium. Committee members Andy Claughton and Lex Keuning presented two VPP-related papers, and David Pedrick and Ken Weller delivered a presentation on the IMS and ORC Club Rule. Papers of present and past symposia may be ordered through the Chesapeake Sailing Yacht Symposium. (CSYS contact: e-mail,; or web site,


4.ORC Club Implementation

 The ORC Club Rule was inaugurated during 1998, and as of the end of the year there were close to 1,000 ORC Club certificates worldwide. This is expected to at least double for the 1999 season, with substantial fleets anticipated in Northern and Southern Europe, and smaller fleets in other countries.


ORC Club uses a combination of existing, measured hulls and a simplified means of entering an unmeasured hull. The IMS standard hull library, listed on the ORC web site, presently has 1700 hulls. All IMS measured hulls are automatically eligible for ORC Club. All participating rating offices can access this combined world library for ORC Club handicapping purposes. IMS99 enables rating offices to directly enter displacement instead of freeboards, and to use an automatic method to assess righting moment when the RM, VCG or true inclining data is not available.


ORC Club also intends to produce data files for unmeasured hulls, which have been called “unidentified sailing objects,” or USO’s. Designer’s lines will be accepted, subject to verification. Alternatively, a database of measured hull files has been selected, representing a broad range of design types. The database is searched for a few closest fits to selected parameters of a USO. Combined with the USO’s principal dimensions, and architect’s plans or photographs taken from ahead, abeam and astern, a surrogate offset file is identified and scaled to the USO’s dimensions. Appendages are then added. Some problematic boats will require more complete design data. This process is being used initially in the conversion of approximately 500 yachts in the NKK fleet of the Netherlands.


Yachts having ORC Club certificates enjoy full scoring compatibility with regular IMS yachts, because they share a common handicap prediction basis. In addition to the simplified scoring alternatives of ORC Club ? two-number performance line system (PLS) and single number time-on-distance (TOD) and time-on-time (TOT) ? the full handicap matrix is available to scorers using performance curve scoring (PCS), as is recommended for racing under full IMS. Therefore, ORC Club yachts can be mixed seamlessly into regular IMS fleets.


5.Single Number Handicaps

 It was the sense of the 1998 AGM to emphasize greater use of the ILC course mix for windward-leeward types of courses, in preference to GPH for this purpose when single-number scoring is used. The committee agreed to placing all three of the IMS single-number options at the top of the certificate ?ILC, its TMF conversion just below it, and GPH.


The composition of GPH remains unchanged, and is furnished to permit an orderly transition toward increased use of the ILC average. The ITC recommends promoting the use of the ILC average when typical day races are scored with a single number, although advises that GPH remains suitable for coastal or offshore races without a predominance of beating or with unpredictable wind direction.


  1. Righting Moment
  2.  When investigating the bias in righting moment effects in 1998, which were considered to be predominantly heeling-moment related and addressed by “twist,” some additional terms directly affecting righting moment were also reviewed. Among the terms dating from the original Pratt Project VPP in 1978 is a dynamic righting moment adjustment, RMV, that is now being studied by the committee for improved accuracy. Other heel-related terms are being studied at the same time. There may be type-forming trends among these terms, and it is intended to keep them in balance. The effects of longitudinal trimming moment on drag were also discussed.


  3. Heeled Drag Increment
  4.  The change in drag due to heel is being reviewed as part of the committee’s 1999 agenda. There is now greater insight into factors that affect this component of drag, including viscous effects. A review of Delft model test data is planned. Tank tests scheduled for this year through US Sailing at the Institute for Marine Dynamics (IMD) in Newfoundland will also contribute to the data for improving the heeled drag increment and RMV.


  5. Induced Drag of Combined Keel Plus Rudder
  6.  Model tests of a rudder series is planned to predict the effect on performance of span and aspect ratio, and not just wetted area as is now the case. Previous studies using a biplane computational approach to combine the effects of keels and rudders showed inadequate correlation to model test data. A discussion of an appropriate rudder series concluded to build three separate rudder models, each having a chord length appropriate to the rudder’s span. Spans are to be 50%, 75% and 100% of an aggressive contemporary rudder design. It was proposed to perform the tests at the University of Athens and to fund model construction costs through the new research program. The hull will be the parent model of the US Sailing/IMD series. Andy Claughton said that the results might be compared to runs of a relevant, inviscid CFD code at the University of Southampton.


  7. Dynamic Length

 The committee discussed a new investigation of effective sailing length variation for different hull forms over the range of Froude numbers used by IMS. The Delft Series models require increased density of stations through the stem knuckle area for this study. A committee member will liaise with Delft about developing offset files with a suitable station grid. The method of allowing for hydrodynamic effect beyond the transom also should be reviewed.


10.Tank Test Models

 Two Delft Series models planned for testing in 1998 are now scheduled for this year. They produce a systematic series consisting of a typical IMS type-formed bow, the parent bow of Delft Series IV and an intermediate bow. These models can be integrated into the existing regression database. As noted above, the US Sailing/IMD tests scheduled for this year will assist in improving the treatment of dynamic righting moment and non-lifting heeled drag increment.


11.Sail Force Coefficients

 11.1Mainsail Checkstay Assessment

 The assessment of mainsail force coefficients for a “simple rig” having no checkstays below the hounds of a fractional rig was reconsidered. Prior to the 1998 season, the common practice in counting running backstays, originally meant in IMS 810.2c as checkstays below the hounds, mistakenly included the runners opposing the headstay of a fractional rig. Therefore, to obtain the “simple mainsail” credit given for not having running backstays, a fractional rig could not have runners opposing the headstay. This was not the intent when IMS 810.2c was written, which was to provide a reduction in lift and an increase drag for the mainsail of a fractional rig with runners opposing the headstay, but not having any checkstays or inner forestays that would permit mast bend control. The change recommended by the ITC and recorded in the Measurement Committee minutes of the 1998 AGM was to restore this intent. It was realized only afterward that removing the checkstay(s) from a normal, existing, runners-plus-checkstays fractional rig might be excessively typeforming. Therefore, the Management Committee, with the recommendation of the ITC, rescinded the announced change in the VPP’s assessment of running backstays. No change was necessary in the individual National Authorities’ databases. A more equitable treatment for crediting mainsails that do not have the advantage of mast bend control by checkstays will be developed as part of this year’s agenda.


11.2Headsail/Spinnaker Transition

 It was felt that the crossover from jib to spinnaker occurs in the VPP at an unrealistically small apparent wind angle. The coefficients affecting the tails of the respective curves will be examined to produce a more realistic transition. Consideration is also to be given to a perceived tendency for predicted speeds to increase too much for larger than rule minimum spinnakers, especially in lighter winds. Additionally, it appears that not enough advantage is given to short LPG jibs with the wind farther aft.


    1.  Other Sail Force Considerations

 The committee discussed potential improvement in the effect of heel angle on windward sail force coefficients. Some progress is likely to be attainable through the committee’s volunteer activities, although further wind tunnel tests and research activities would be useful. This will be considered as part of the new, funded research program (see Minute 19). Genoa overlap and mainsail roach that exceeds rule limits are additional candidates for refinement of existing methods.


It was also suggested to credit extra drag for jibs not opposed by a backstay; and to permit an adjustable headstay if there is no backstay, although without receiving sail force credits for the jib in that case.


  1. Dynamic Allowance Heavy Items

    Various details of the new Appendix 9 describing the Cruiser/Racer Heavy Items pitch gyradius allowance scheme were refined. The genoa furler credit does not include a staysail furler, and credit is given regardless of whether the genoa furler’s weight is included in the mast weight. The committee confirmed the automatic gyradius allowance of .006*Lcanoe for a Cruiser/Racer, which accounts for the typical weight distribution difference between a minimum IMS C/R and a sistership meeting only Racing Division requirements. The allowance of .004*Lcanoe for forward accommodations also remains.


  3. ILC Classes
  4.  The performance matrices of the ILC 25, 30 and Maxi classes have been updated for IMS99. The Level 50 class is developing enthusiastically. An ILC rating band of 585-595 has been set initially. The Offshore Classes Committee will monitor the class’s activity and owners’ wishes during the year. The ILC 40 class is inactive, although there is interest in reorganizing the class around a rating band.


  5. Hull and Appendage Measurement
  6.  It is desired to implement separate measurement and input of appendages in regular IMS offset files. The lines processing software requires modification to do this, which the committee recommends. Separate input of simple appendages has been provided in surrogate offset files for USO’s under ORC Club. Improvement is also recommended in the treatment of the lower 20% of the keel.


    The US project on improving hull measurement tolerances has progressed. Prototype validity gauges, called “pogo sticks,” have been made and will be tested in early spring.


  7. Construction Materials

    A request to consider PBO as a hull construction material has been made to the ITC. As an unproven and potentially costly material, the committee recommends that PBO not be permitted in any aspect of construction other than for sails, for which it was approved in early 1998.

  9. Sail Materials and Measurement

    PBO as a sail material has made a significant appearance in the racecourse. Experience seems to be mixed. Sails have been heavier than originally anticipated, cost is somewhat higher than sails made of Kevlar, and concerns have been expressed about short useful life. PBO’s performance record and free-market acceptance will be reviewed later in the year.


    A question about the rated area of asymmetric spinnakers relative to symmetrics is being researched by the US IMS Committee. A concern was raised about the “code 0” type of asymmetric, characterized by narrow girths and a substantial boltrope to allow them to be flown as jibs. It was noted that the Rule requires sails to be measured as they are flown, and measurers are to be alerted to measure any headsail with a substantial boltrope as a jib.


  11. Scoring Program

    The ORC Windows scoring program is maintained through the Race Management Committee. The ITC emphasized the importance of its ease of use. It was noted that downloaded scoring data will now identify whether a certificate is regular IMS or ORC Club.


  13. VPP/LPP Program Documentation

    The considerable task of documenting the VPP is now committed through the new, funded ORC research program. Code documentation will evolve with the identification of a new ORC programmer for the VPP and other technical matters. Attention is drawn to the paper by committee member Andy Claughton for the recent Chesapeake Sailing Yacht Symposium in which all of the principal, conceptual changes of the IMS VPP of the last few years are documented.


  15. ORC Funded Research Program


The new research program will permit several important areas of research to proceed. Specific projects planned so far include:


  • Support for USO offset file development
  • Model costs for rudder tests
  • VPP/LPP documentation


A new area of research is the validation of computational fluid dynamics (CFD) methods for hydrodynamic modeling. Another is the development of improved data and modeling for aerodynamic forces and moments.


Hydrodynamic CFD validation will begin by comparing SPLASH code runs of the first three, large US Sailing/IMD models to their tank test data. A proprietary test series of different after overhangs has also been offered to evaluate and refine overhang assessment using CFD.


Research into more accurate modeling of sail aerodynamics will include study of the limited work available in this field and investigation of new methods. For example, improvements in lifting line codes and computer processing power now enable interactive optimization of vertical lift distribution for a particular sail plan within the VPP equilibrium solution.


20.Other Matters

 The Chief Measurer had received correspondence about a proposed carbon fiber mast that was engineered to induce twist of the spar tube, as well as a wing mast production boat with a rotating mast. The committee confirmed prohibiting such rigs in IMS, including any whose rotation is produced by intentionally induced twist of the mast tube. For ORC Club purposes only, the committee supported the Chief Measurer’s proposal to add the chord length of such masts to the mainsail girths and to eliminate credit for mast windage. This will permit such masts within ORC Club without making them advantageous.


The popularity of sportboats that do not comply with IMS headroom and certain other regulations has generated a desire to produce a category of modified regulations for sportboats. The US IMS Committee is working on a submission for this.


There have been requests for permitting water ballast. It was noted that water ballast might be added as crew weight for righting moment purposes only, without adding to sailing displacement. This would be allowed for ORC Club only. The Committee encouraged the ORC Club working group to experiment with adaptive interpretations that will be inclusive as to unusual, existing yachts.


  1. Next Meetings

 The next meeting of the committee will be a “virtual meeting” by e-mail in the first half of May. The summer meeting has been planned for Friday-Sunday, August 27-29 at Delft University in the Netherlands. The ITC will meet Sunday-Tuesday, November 8-10, 1999, during the ORC Annual General Meeting in Sydney, Australia.