About ORC WRS by Andy Claughton, ORC ITC Chair in Seahorse Magazine March 2024 issue

Weather Routing Scoring (WRS) promises to be the most accurate and objective scoring method available today. It merges modern weather routing from PredictWind and rated polar performance from ORC to achieve results that help filter out the luck factor from offshore racing.

The details are described in the following Q & A and should help guide race organizers and sailors to how and when it should be used in coastal and offshore races.

The following description outlines the procedure and explains the terms used in the Weather Routing Scoring system.

The ORC certificate shows the Polar Speed Curves in winds from 6-24 knots on all points of sail. The speeds are shown as knots and seconds/mile.

The WRS system calculates a Predicted ElapsedTime (PET) for each boat to sail the course.

For example, the fastest boat (Boat-F) has a PET of 10 hours, and the slowest boat (Boat-S) has a PET of 15 hours. A boat between them (Boat-M) is predicted to take 12 hours to complete the course.

How does the Organising Authority (OA) handicap Boat-M against Boat-F and Boat-S?

The WRS calculates a PET for each boat to sail the course. 
Using the PETs, we calculate a Time on Time (ToT) correction factor (TCF) for each boat. The Corrected Time (CT) is calculated by multiplying the actual Elapsed Time (ET) with TCF.

The OA chooses a Scratch Boat in the fleet, say Boat-M. We fix her TCF at 1.000.
Corrected Time = PET x TCF; therefore, Boat-M’s corrected time is 12 x 1.000 = 12 hours.
Boat-M’s corrected time is exactly equal to her Predicted Elapsed Time.

Then, we calculate the TCF for Boat-F and Boat-S.
For all 3 boats to be ranked equal (a dead heat), their Corrected Times should be the same, therefore:

PET = 10 hours. The CT to be equal with Boat-M must be 12 hours. Therefore TCF = 12/10 = 1.200

PET = 15 hours. The CT to be equal with Boat-M must be 12 hours. Therefore TCF = 12/15 = 0.800

Our simulated Timing sheet looks like this


PET hours


CT (PETxTCF) hours













When the race is sailed, the boats are not automatons, the crew will make mistakes, and the wind may not exactly match the forecast. The actual timing sheet could therefore look something like this.


Start Time

Finish Time

ET hours


CT (ETxTCF) hours























ORC - Weather Routing Scoring (WRS) Q&A

Q: When should Weather Routing Scoring be considered for use?

A: WRS is best used for coastal or long distance races where the course length is sufficiently long to have predictable changes in the weather forecast that may affect the race.


WRS is considered when there is a variety of boat types in the fleet and/or variable weather conditions. Conversely, short distance races held in steady weather conditions, or when the course is being set or changed with marks according to the wind direction (such as windward/leeward races), may be better scored with constructed course/performance curve scoring.

Q: Can use of Weather Routing Scoring be better than existing scoring methods?

A: WRS is an addition to the existing scoring options (All Purpose Handicap and predefined course matrices, such as country-specific scoring options).

ORC VPP polar tables give the possibility to handicap every boat against another in wind speeds between 6 and 24 knots on all points of sail. To date, distance race scoring methods have primarily used three scoring methods:

(1) the All Purpose Handicap (APH)

(2) pre-constructed course models (country-specific scoring options found on Page 2 of ORC certificates)

(3) pre-calculated wind and point of sail matrices based on typical conditions from previous races or local knowledge.

While (2) and (3) are often better than (1), with WRS not only is each boat’s handicap calculated from her polar diagrams following the predicted wind conditions, but each boat is routed according to her best performance so that the ratings will address situations when a faster boat is not sailing the same in the same wind conditions as a slower boat.

For example, in any rating system that single number rating is calculated the same way for all boats, the race may start in a steady breeze. Faster boats may sail the course and finish, yet when the wind drops slower boats will be at a disadvantage. Conversely, faster-rated boats may be disadvantaged when the wind speed increases after they finish. With WRS each boat is routed separately and the slow boat can still win over the fast boat, even if wind drops after the fast boat has already finished the race.

Q: Is the system too complicated for reliable use?

A: Google Maps is a complex system, but it’s not complicated for the driver. It predicts an optimum route and elapsed time by combining maps, vehicle type, traffic conditions, road closures etc.

The WRS process is similarly complex, but it can deliver a simple and fair way to provide Time Correction Factors based on the boats polars. And it can insulate race managers from making difficult decisions on which scoring model to apply.

The process works as follows:

- Gather the entries and start times in his usual system.

- Define the race course.

- Submit this data to the ORC, who generates a Time Correction Factors for each entry

- Distribute the TCF ratings to the Fleet.


The detailed steps in the process are:

(1) Collect entrants and start times

(2) Extract polars from the certificates

(3) Load the fleet polars on weather routing calculator software

(4) Set up the course

(5) Choose the Grib files and load on weather routing calculator software. Choice of files may be made in consultation with race managers

(6) Run weather routing software

(7) Plot the predicted tracks and check for errors

(8) Extract the elapsed times

(9) Calculate the scratch sheet

(10) Load scratch sheet into the scoring software with each boat’s TCF

For 2024:

1 - 4 are done in the ORC Scorer software

5 - 7 are done by Expedition

8 - 9 are determined by ORC staff and processed with ORC Scorer

10 is done by the OA’s scoring software (ORC Scorer or any other)

Q: When before the start should ratings be determined?

A: 2-4 hours before the race, depending on the optimum schedule of weather forecasts.


The organizer should specify in the NoR and SI when the TCF ratings will be published. The closer to the start of the race the more accurate the forecast can be, so approximately 3 hours before the start of the race is recommended. This will still give time for sailors to get the rating information and prepare for the race, but also to get the most recent forecast. This decision will be related to when updated forecasts are available.

Q: How are TCF ratings determined from the PET’s?

A: The ORC (or the OA) may choose a scratch boat in the fleet and assign its TCF = 1.0000. Then other boat’s TCF’s will be calculated relative to the PET of that boat. The process is described above in more detail.

Q: How will grib files be provided to run the routing software?

A: The routing is done with Expedition for 2024 and choice of grib files will be determined by ORC staff in consultation with the OA. To reduce the processing time described above, it is intended to use PredictWind software in 2025 that will utilize their suite of forecast providers.


There is no need to have a PredictWind account. The ORC WRS process will rely on the PredictWind engine to select the most appropriate weather forecasts for the routing. At the Race Organizer’s discretion current may also be included in the routing process.

Q: Will WRS work when boats may stop on the race course due no wind, either predicted or encountered?

A: ORC has developed a methodology to prevent areas of predicted calms distorting the predicted elapsed times.


Areas of no wind are a feature of many offshore races, they happen on the race course and they appear in the forecasts. It’s been a problem for race scoring since handicap racing began. Experience suggests that even when there is no wind, sailors can keep the boat moving somehow. If weather forecasts were to be believed, boats might never escape the Doldrums, but they do.

The WRS will make sure that boats keep moving slowly through zones of very light winds. This will ensure that the predicted elapsed times are not distorted by a few boats making very large deviations to avoid calm patches.

Q: What happens if a race is shortened?

A: The TCF’s posted pre-race should be used.


WRS is primarily designed to generate the handicaps for the specific race. If the race is shortened, the handicaps shall remain the same. Once the ratings are published they shall not be changed after the start of the race (except as permitted by ORC rules in case of a measurement protest and/or correction of an error in the certificate).

A predicted elapsed time (PET) for each boat is determined by the routing process based on the predicted weather of the race. If the race course is shortened but the TCF’s are not adjusted then this assumes that the boats experienced the same mix of conditions for the shortened race as for the original course.

Q: Can an OA use the grib files after the race or after the start for recalculating the scratch sheet?

A: This is not recommended.

Q: What if, when the polar submission deadline is reached, the PRO does not know the exact location of the start line or needs to use an additional mark for the first leg of the course. Could this affect the distance and scoring of the race?

A: There may be very few occasions where adjustments to the start line position or windward mark positions would require the pre-race scratch sheets to be adjusted. The predicted TCF’s will change by a very small amount for minor discrepancies between the submitted and actual course, especially for races of long duration.

Q: In which format will WRS ToT ratings be available to the organizers? Will it be in a format that can be imported to Manage2Sail, Yacht Scoring or other scoring software programs, or will it need to be done manually?

A: The ToT ratings (scratch sheet) will be available in JSON and CSV format.

Q: Will this option be available in the ORC Scorer software?

A: For 2024 the WRS TCF’s will be calculated by the ORC staff using ORC Scorer.

Q: Will WRS be available for offshore races that my Club organizes? What if the OA wants to test WRS without committing to its official use? How do we contact ORC for this service and what specific information is needed?

A: Yes, during 2024 this will require cooperation with the ORC staff for both official and shadow-scoring purposes. This is described on the application available at this link: https://data.orc.org/public/wr....

The Weather Routing Scoring request form