The Rules
The J Class Association was created in 1999-2000 following the Antigua Classic Regatta of 1999. One of the objectives of the association is to deliver J Class racing as they were originally sailed.
2000 - 2017
Initially Dykstra - as they were the principal architects behind the first new replica designs - drew up a VPP based rule which sought to deliver even, equable corrected time racing for all the different Js which actively raced then. As other designs came on stream the Wolfson Unit were progressively brought in to continually update the rule.
Initially all the Js at the time were linked to the Dykstra office and so it made sense that they develop a race performance prediction tool/approach to offer fairer racing between the yachts and use all of the detailed information they had in house on the yachts to support this.
This approach was based on the Wolfson Unit Windesign VPP, but it did have its limitations as the VPP was not explicitly created to evaluate long keel, very large overhang, high displacement yachts. So in 2007, using data going back to towing tank tests carried out in the 1930s on the original Js and other data sources, a new hydrodynamic resistance model was developed to better encapsulate the properties of these hull forms.
This also coincided with Lionheart’s build with the Hoek Design office as the naval architects. With another design office in the mix, it was decided that Gerry Dykstra as Class Technical Officer would transfer the role and VPP development and administration to the Wolfson Unit, as a fully independent body. Since then a number of other new replicas have joined the Class and were rated with this VPP based system.
The Wolfson Unit’s involvement, primarily through Martyn Prince as Technical Officer, continued with the evolution of the VPP, race scoring and general J Class Rules until 2019.
2017 Onwards
After the active, intense season of 2017 which saw two major regattas at the America’s Cup and the inaugural J Class World Championships in Newport the decision was taken to move the rule on to a new level of accuracy, taking into account more measurements – so, trying to include stability, pitch and yaw factors, and better represent the diverse hull and appendage shapes and sizes – and therefore move on to a new all-encompassing VPP which is correspondingly used to predict more segments of the each course.
In 2019 Chris Todter was appointed to develop this VPP Rating System to a new level of accuracy.
Each yacht has been scanned and the digital file has been used to calculate a CFD (Computational Fluid Dynamics) Matrix with sideforce, and roll moment matrix calculated to input into the rating calculation.
This CFD Matrix along with the rig and sail measurements is used to create ratings for each yacht at 5 different leg angles for 1 knot increments of wind speed upwind (less than or equal to 45 degrees), downwind (greater than or equal to 120 degrees), mid angles (TWA of 45 to 60) degrees, reaching between 60-90 degrees TWA, and reaching between 90 degrees and 120 degrees TWA.
Following the completion of a race, all the boats submit the race data that they have logged which is then processed to give the race results.
