Principal VPP Changes for IMS 2004:

·         Heeled Drag model. Implementation of a new formulation to replace the one that has been in place for 10 years.

·         Downwind sail coefficients revised for decreased spinnaker and increased mainsail forces.

·         Fixed forestay credit The hard limit for has been replaced by a sliding scale tied to percentage of jib fractionality.

·         The upwind aero model has been revised with a correction to apparent wind angle with heel.

·         PIPA (propeller installation drag) formulation has been revised based on towing tank tests of struts.

·         DA has been modified from a single value applied uniformly across the VPP to a formulation that more accurately apply the dynamic effects at the appropriate wind directions and varies the value with wind speeds.

·         Hull windage area calculation has been revised with a more robust method that calculates the real area. The drag coefficient for hull windage has been reduced in 5% from the 2003 VPP one. This plugs an exploitation loophole in that exists in the 2003 rule.

·         Jib Luff Length will be used for Foresail Area Calculation (no effect in current fleet). This was done to avoid boats gaining un-rated jib area by building boats with down-sloping bows.

What do these all mean?  The net effect of these changes is a "speeding up" of the entire fleet. The AVERAGE speed-up for a 12-knot windward-leeward course is 7.4 seconds per mile.  For greater IMS Facts please visit www.ORC.org or stay tuned here.

Other Actions.

• Canting Keels. The desire is for IMS to rate them with full certificates - as opposed to provisional or experimental ones. Because the rating process has just been initiated, the actual capability to issue certificates awaits two things:

(1) Finalizing the details of the actual rating functions. These were identified at the ORC's Annual Meeting in Barcelona, but wait coding and debugging.

(2) Establishing stability safety criteria. The ORC has authorized funds for testing and analysis at the Wolfson Facility. The results should be available by late February.

-Allotting time for the ITC to review findings from 1 & 2 in their winter meeting and recommend safety criteria realistically means an April issuance of Canting Keel certificates.

• Masthead Halyard locks for boats greater than 20 meters LOA was approved.

• Relief is granted on Permitted Materials for boats greater than 20 meters LOA
  • Titanium, PBO standing rigging, and all-carbon winches was approved.
  • The exact wording needs to be worked out. The submission wording asked for complete relief on materials restrictions. That would permit use of Tungsten, Tantalum or depleted Uranium in keels. This is not intended.

Summary of IMS VPP and Rule Changes for 2003 –

Principal VPP Changes:

• Windward sail coefficients reduced for fractional rig induced drag per wind tunnel tests

• Downwind sail coefficients revised to decrease spinnaker and increase mainsail forces

• Windward sail coefficients increased for simple, fore-and-aft mainmast stays

• Mainsail battens allowed above MGT and the oversize headboard penalty reduced

• Experimental IMS certificate enabled for water-ballasted yachts

Certificate and Scoring Matters:

• Provide input data fields and certificate space for asymmetric spinnaker data

• Revise wind averaging for short duration race constructs

• Change Inshore Performance Line course to 50%/50% Windward/Leeward

FOR COMPLETE DETAILS OF CHANGES, as approved by the ORC, click here

2003 US Prescriptions to the IMS Regulations. Click here.

Summary of IMS VPP and Rule Changes for 2002 –  

IMS VPP and Rule Changes – The overall effect on the fleet is small. The extremes of the changes are plus or minus one second per mile. Most boat’s rating change is far smaller. A summary of the individual components modified follows.

Asymmetric Spinnakers Tacked on Centerline -
In the 2000 VPP, "asymmetric spinnakers set on-centerline effectiveness when running" was reduced to correct over-estimated performance when compared to symmetric spinnakers on poles. Race experience, primarily in Europe, showed that reduction was too large. Glenn L. Martin Wind Tunnel tests confirmed that observation and in the 2001 VPP running thrust was increased (see The Glenn L. Martin Wind Tunnel results). Last season’s race data showed the correction to be too little. Therefore, in 2002 a small additional increase in thrust has been made.

Rudder Span (draft) Effects on Hydrodynamic Induced Drag
There is evidence that rudders can contribute significantly to increasing the total effective draft of a sailboat. This effective draft serves as an index for the hydrodynamic induced drag of the hull/keel/rudder. Towing tank testing performed at the Institute for Marine Dynamics in Newfoundland to obtained data on this effect. Results have been analyzed and incorporated in the 2002 VPP.

Institute for Marine Dynamics Rudder Span Test Results

Carbon – Three changes are associated with carbon construction.

Carbon hull construction is now approved for all yachts
Previously carbon was approved only for Racing yachts and Cruiser/Racers longer than 17 meters.

Carbon Gyradius effect is reduced by 50 percent
This is primarily a seakeeping term and was shown to unduly impact smaller yachts at its previous value.

Gyradius penalty for carbon (light) booms eliminated
The penalty was typeforming to fragile, lightweight aluminum booms.

Age Allowance and Dynamic Allowance for Racing Yachts
Age allowance will now be applied to racing yachts and be included in the certificate VPP values. Dynamic Allowance will also be applied to racing yachts starting in their fourth year. It will be phased in at 20 percent per year until full value is reached in the eighth year.

A propeller allowance for 3 bladed props was added

Mainsail batten spacing – The requirement for approximately equal batten spacing has been removed.

Regulation 205 – Sail Inventory has been changed from IMS L to GPH as the measure. Classes are usually assigned by GPH. This change minimizes the possibility for boats racing in the same class to have different sail inventory allowances.

2002 US Prescriptions to the IMS Regulations. Click here.

Meeting Minutes:

• Minutes of the OCR Management Commitee, RORC, London
  
• Minutes of the USSA IMS Committee Meeting Minutes, Newport, RI
  
• Minutes of the Combined USSA IMSOC and IMS Committees
  
• Comparison of US SAILING Spinnaker Tests with IMS Aerodynamics Report
  
• Minutes from the November 15, 2001 Offshore Racing Council Annual General Meeting, Lisbon, Portugal