Understanding how the system works

As a dominant internationalo rating service, ORC relies on science to handicap dissimilar boats. In this report by Thomas Nilsson and Matt Gallagher, they describe how the system functions, how data is used, how ORC responds when designs move into new territory, and how the rule is updated over time:

Handicap racing relies on a simple idea: boats of different shapes and sizes should be able to compete fairly. Achieving that fairness, however, requires a sophisticated scientific model behind the scenes. In ORC, that model is the Velocity Prediction Program (VPP). Over the past year, discussions in the sailing community have highlighted how important it is to understand what the VPP is—and what it is not.

This article offers an explanation of how the ORC system works, how it uses data to generate fair handicaps, why design limits sometimes become necessary, and how ORC continually updates the rule to stay aligned with modern yacht design.

1. What the ORC VPP Actually Is

The VPP can be thought of as a very large technical reference book for a given yacht. For every possible combination of wind angle and wind speed, the VPP calculates the forces acting on the boat and predicts its speed.

To do this, it uses:
• Physical models of hydrodynamic and aerodynamic forces
• Empirical data
• Trained mathematical models (including Artificial Neural Networks, or ANN) where direct physical modelling is not feasible

The VPP is not a single formula. It is more than 100,000 lines of computer code and over 100 pages of documentation, carefully calibrated each year by the International Technical Committee (ITC).

2. How the VPP Makes a Prediction

When a boat is measured, a long list of numerical parameters is generated: hull shape descriptors, sail dimensions, stability characteristics, appendage shapes, and more. Imagine the VPP as a huge library where each “page” describes how boats with certain characteristics behave.

For example:
If a boat with parameter set X is sailing upwind in 12 knots of wind, the VPP goes to the appropriate “page,” reads the instructions for that type of boat, and returns a speed prediction—say, 6.49 knots.

When the system has solid data behind those instructions, the prediction is robust. But like any scientific model, the reliability falls if a design pushes into a region where data is scarce.

3. When Designs Go Outside the Known Data

Modern yacht designers constantly explore new ideas. Sometimes those innovations bring a boat into an area of design space where the VPP has little or no data to base its calculations on.

When that happens, the model is forced to extrapolate—essentially making an educated guess based on the nearest information it does have. This can lead to unreliable predictions of drag.

These cases are rare, but when they occur, ORC is obliged to take corrective action to maintain fairness for the whole fleet. This corrective action is always supported by research and an appraisal of the physics. It is never a subjective one size fits all penalty.

4. Why Parameter Limits Exist

In scientific modelling, it is normal to set limits around areas where the data is strong. Outside those limits, the model becomes less reliable. If a design parameter lies well beyond the known data range, ORC normally fences the calculation by capping the parameters used in the calculations to prevent the VPP from producing unverified outputs.

This kind of safeguard:
• Prevents accidental rating distortions
• Stabilizes the system for all users
• Buys time while the ITC performs additional research

Such limits are not political tools — they are standard scientific practice.

5. How ORC Responds When Such Situations Occur

When ORC identifies that part of the VPP needs updating, a structured process begins:

A. Technical investigation
The ITC analyses:
• Hull and stability parameters
• VPP outcomes across the fleet
• Behavior of relevant mathematical models

B. External research
This may include:
• Additional CFD simulations
• Analysis of logged performance data
• Collaboration with external experts

C. Limited adjustments for the coming season
These time-limited adjustments are used only when needed to stabilize the rule while long-term solutions are developed. This is necessary because the VPP is updated on an annual basis so as to provide stable ratings for a given calendar year.

D. Full scientific update
A complete, validated change enters the rule the following year, once the evidence base is complete. This process is deliberate and transparent, ensuring that changes are driven by data—not by emotion, pressure, or isolated regatta results.

6. What This Means for Sailors

For the vast majority of boats in the fleet, the VPP operates entirely within well-mapped design space, and the predictions are reliable and stable from year to year.

For new designs that push into new territory, ORC must sometimes gather new data before the model can catch up. That is a normal and healthy part of evolving any rating rule.

With the rapid rise of modern hull forms—including fuller bows, lifting foils, and shapes inspired by the restricted classes—it is natural that the rule must expand its parameter ranges. ORC is actively working on this, and a broader, more flexible formulation is already planned for 2027.

7. The Goal: A Stable, Scientific, Fair System

At its core, the ORC VPP is built on one principle: Science is not negotiable. The system will always be updated when evidence shows that improvements are needed.

Whilst the impetus for change can come from the analysis of performance data, this is not observed performance handicapping. Currently for the bulk of the fleet the actual performance of the boats correlates with the VPP prediction within a few percent. This is a very satisfactory situation given that the process is entirely driven by the physical dimensions of the boat.

The VPP is not a simulator, it is a tool for handicapping racing yachts. Fairness for the entire international fleet, based on sound analysis, remains the guiding priority.

Closing Thoughts

Understanding the VPP is key to understanding why rating systems occasionally need adjustment, and why ORC continuously invests in research, CFD, and performance analysis. Innovation in yacht design is welcome—and the rule must evolve with it—but handicapping will remain grounded in verified physics.

As the technical work currently underway is completed, ORC will publish clear explanations of the findings and their implications for future VPP versions. Transparency is fundamental, and sailors deserve to know not only what changes are made, but why they are made.

For more information: http://orc.org/