The measurement formula ORC

For outsiders it is difficult to understand which position is advantageous and who will already have disadvantages from the start. However, for many spectators on the shore it is already difficult to understand who is sailing against whom and how the different yachts can be compared with each other at all. This is one of the questions that has preoccupied the sailors, the organizers and the developers of the ORCi scoring system for many years. Is it even possible to compete fairly with a 29 foot cruising yacht against a 52 foot racing yacht?

Unified Surveying System
In 1969, the Offshore Racing Congress came together to establish a uniform measurement system worldwide. The goal of such a measurement system should be to allow different yachts to sail against each other and still be able to determine at the finish line which crew has performed the best in terms of sailing. In many events, the field will be divided into classes first, if there is a sufficient number of participants and the yachts are relatively different.

The background of this class division is that it is very difficult for a small yacht to be as fast as it would be according to its rating if it has to fight its way through the wind cover of the large yachts. So, while it is possible to offset a 29 foot yacht against a much larger one, this often leads to unfair results when both yachts have to cross the same starting line.

Refinement of the measurement formula
Over the past decades, the rating system has been gradually adapted to technical knowledge and more modern yachts. Gliding yachts are now considered according to ORC as well as classic displacement yachts. In the past years, the formula has been refined more and more in order to prevent owners from obtaining a more advantageous race value by making structural changes.

What is an advantageous race value?
An advantageous race value occurs when a vessel is theoretically allowed to be slow because this would be expected based on the survey, but in practice it is not. Ideally, the survey should balance the advantages and disadvantages of the different yachts and ensure that the sailing performance of the crews is comparable. To achieve this, the yacht is completely surveyed and a value for the performance of a yacht is determined for each wind force between 6 and 20 knots of wind.

A complete survey for ORC-I takes up to 14 hours and includes information from the hull, hull material, hull appendages - keel and rudder blade, righting moment, stability of the yacht, rigging and of course the various sails. Details such as the material of the shrouds are also covered here, as modern rigging made of PBO or carbon fiber are much stiffer than 1x19 wire or rod rigging. The weight advantage of carbon fiber masts or modern rigging is reflected in the stiffness or rankness (= lower righting moment) of a yacht, which is of course also included in the calculation.

The velocity prediction
A rating according to ORC-I is based on a velocity prediction program (VPP). This program should calculate the actual performance of a yacht as accurately as possible. In the local rating office, which now exists in 37 nations, the values of the yacht must be entered. In addition, accompanying circumstances that played a role in the measurement are also taken into account. For example, even the density of the water in which the yacht was measured is determined, as this has an influence on the buoyancy values and displacement.

Disadvantage of transparency
The scientifically based ORC-VPP is constantly being developed and can be accessed by anyone. This has the advantage that the values given by the system can be checked by any owner - so there is almost complete transparency. Unfortunately, this is also linked to the disadvantage that yachts are "optimized" into the formula. It can be a decisive advantage that, for example, the sail area is reduced and the yacht becomes slower, if this "disadvantage" is overcompensated in the calculation and the race value offers advantages as a result.

In past years, preference was given to yachts that got their stability almost exclusively from the hull shape. The resulting U-shaped hulls had good initial stability, but if they tilted beyond a certain point, they became very rank. Seaworthiness was severely limited. This development has been counteracted in the last few years, so that today stiffer and much more seaworthy yachts are "worthwhile" again.

The pure mathematical values are partly influenced for "political" reasons if safety-relevant aspects are affected. Values are weighted more heavily so that the yacht designers and owners push the development in the desired direction because they expect an advantageous rating as a result. However, conversions made to racing yachts to construct an advantageous rating should be taken with a grain of salt.

Out of control
A North German owner once had the folding propeller of his old Admirals Cup yacht welded so that it would no longer fold in. A fixed propeller is of course taken into account in the ORC rating so that the yacht is rated slower. However, the turbulence created by this fixed propeller had such a negative effect on the rudder blade that the yacht permanently ran out of control and into the wind when there was a little more wind. So the small advantage the owner had promised himself in the rating was far outweighed by actual disadvantages.

Conclusion
The formula is very mature and the surveyors do an excellent job. Nevertheless, even the ORC calculation cannot provide one hundred percent equality of opportunity. There will always be conditions where a yacht has advantages or disadvantages due to its specific characteristics. Because of the complexity of wave conditions, which depend on the current wind, wind of previous days, water depth, shape of the seabed and the actual performance of a yacht in a real sea state cannot be reliably predicted by any computer program at present. The real sea state simply cannot be calculated. Even the comprehensive speed prediction according to ORC with the widely developed VPP cannot yet perfectly capture the full complexity of sailing. But the ladies and gentlemen of the Offshore Racing Congress are working on it!
 

Author: Michael Walther