Performance Curve Scoring

   
 

Performance Curve Scoring is the most powerful engine of the ORC International (ORCi) rating system. It is this unique feature which makes this rule fundamentally different from any other handicap system, as it recognizes that yachts of varied design perform differently when conditions change.

This means that yachts of different designs will have different time allowances in each race depending on the weather conditions and the course configuration for that particular race. For example, heavy under-canvassed boats are slow in light airs but fast in strong winds, boats with deep keels go well to windward, and light boats with small keels will go fast downwind.
 

   
 

Where is it shown on the certificate?

   
 

   
 

An ORCi certificate provides a range of ratings (time allowances expressed in s/NM) for wind conditions in the range of 6 – 20 knots of true wind speed, and at angles varying from an optimum VMG beat to 52, 60, 75, 90, 110, 120, 135, 150 degrees of true wind angle, as well as the optimum VMG run angle.

  Windward/Leeward (up and down) is a conventional course around windward and leeward marks where the race course consists of 50% upwind and 50% downwind legs.
  Circular Random is a hypothetical course type in which the boat circumnavigates a circular island with the true wind direction held constant. 
  Ocean for PCS iis a composite course, the content of which varies from 45% Beat VMG and 55% Run VMG at the 6 knots with decrease of Beat and Run parts and increase of reaching parts with increase of the wind speeds
  Non Spinnaker is a circular random course type (see above) but calculated without the use of a spinnaker.
   
   
 

How is it calculated?

   
 

The use of PCS is not as complicated as it may appear. It requires the Race Committee provide only a little more data in addition to their usual work of setting up the course, following the wind changes, making starts and taking finishing times. There are different varieties of Scoring software that will do all calculations, which enables results to be ready as soon as the elapsed times of the race are entered.

   
   
 

Step 1 - Define the course

   
  Course may be selected from one of 4 Pre-defined types above or simply constructed with following parameters for each leg:
 
  • distance
  • course bearing
  • wind direction
 

Leg Distance Bearing Wind direction
Start - 1 1.83 NM 215 210
1 - 1a 0.06 NM 107 210
1a - Gate (2-2a) 1.78 NM 035 210
Gate (2-2a) - 1 1.78 NM 215 195
1 - 1a 0.06 NM 107 200
1a - Gate (2-2a) 1.77 NM 033 195
Gate (2-2a) - Finish 0.10 NM 330 195
       
Typical course definition. Distance and bearings of each leg are entered, as is the approximate wind direction. Note wind speed is not entered.
Current velocity and direction can also be entered for each leg, if it is known.
   
   
 

Step 2 - Prepare the scratch sheet

   
 

For any of the selected courses described above, the true wind angle is calculated as being the difference between the wind direction and compass bearing of each leg. With this information, a table is made for each boat that describes the theoretical speed of the boat over that course for a variety of wind conditions. With this data a curve can be plotted which represents the predicted optimum performance along a scale of wind speeds. This curve is called the Performance Curve, and for each yacht this curve is different for any different course sailed.

   
 
  6 kt 8 kt 10 kt 12 kt 14 kt 16 kt 20 kt
TP 52 624.0 503.2 437.6 397.9 370.8 350.4 319.0
ILC 40 758.3 614.6 537.6 492.4 463.8 444.3 418.4
Marina 36 Sport 756.1 617.1 543.2 499.9 472.0 452.0 422.1
IMX 45 770.4 621.9 542.1 495.6 466.7 447.7 424.0
Grand Soleil 42R 778.5 626.6 545.1 497.6 468.4 449.2 425.0
JV 42 778.3 629.1 550.4 505.7 478.8 461.2 437.8
Vrolijk 42 787.0 633.9 552.2 505.1 476.4 457.7 434.0
Salona 41 811.9 653.3 567.6 517.3 486.0 465.4 439.6
   
   
 

Step 3 - Calculate Implied Wind

   
 

Performance curves for each boat are presented in figure 1 below:

 

  Figure 1 - Performance Curve
   
 

In a typical Performance Curve plot, the vertical axis represents the speed achieved in the race, expressed in seconds per mile. The horizontal axis represents the wind speed in knots. When the finishing time of Yacht A is known, its elapsed time is divided by the distance of the course to determine the average speed in seconds per mile. This number is represented by point A on the vertical axis. The computer then finds the point on the horizontal axis that corresponds for that course to the average speed obtained.

This results in point Aw, the so-called “Implied Wind.” This means that the yacht has completed the course “as if” it has encountered that wind speed. The faster the boat has sailed, the higher the Implied Wind, which is the primary index used for scoring: the yacht with the highest Implied Wind wins the race.

The Implied Wind is intended as an interpolation between time allowances, not an extrapolation. This means that when the Implied Wind drops below 6 knots or raises above 20 knots, the time allowances used for calculating the corrected times will be those of 6 knots and 20 knots respectively. This does not mean that ORC races need to be stopped (or not started) with wind below 6 knots or above 20. When the “implied wind” results calculate to be less than 6 knots or more than 20, the corrected time values at these wind speeds are then used.

The highest “Implied Wind” of the best boat in the race is then used as the wind speed for corrected times calculations. For that wind on the horizontal axis, the appropriate time allowances are determined on each boat’s curve on the vertical axis. Such a time allowance is then used as a single number Time on Distance coefficient

“Implied Wind” for the winning boat normally approximates the predominant wind strength for the race. However, in cases where the “Implied Wind” does not represent fairly the real wind strength during a race, the wind strength may be determined by the Race Committee.
 

   
 


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