The Progress of the ORC Weather Routing Scoring by Andy Claughton

February 6, 2025 - ORC has now spent one year on the development of a new paradigm in offshore race scoring: Weather Routing Scoring. After analyzing >50 races in 2024, and some current races being sailed now in the winter season, ITC Chairman Andy Claughton summarizes the progress of this innovative approach in the new March issue of Seahorse Magazine.

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TCF tombola

Back in the day with Team New Zealand, we were treated to a motivational session hosted by the head coach of the Auckland Blues Rugby League team. He told us he viewed the versatility, and skill sets of his players like the contents of a golf bag. The muscle-bound second row had only a couple of clubs in their bag, perhaps a driver (tackling) and a 3 wood (pushing). The wingers perhaps carried a couple of extra clubs, a 3 iron and 7 iron, because they had to be more versatile, whilst the scrum half and fly half needed to add a putter and a pitching wedge to do what they needed to do. The coach didn’t regard the lack of clubs in a player’s bag as necessarily a bad thing. He just needed the players to remember what clubs they had in their bag, so that in the heat of battle they did not try playing a delicate chip shot when the club they had in their hand was a driver. I was minded of this story when I read the RORC handbook for this year:

‘Why use a complex rating system when you can achieve the same results with a simple, single number system? Easy for clubs, event organisers and sailors to understand and use. Focus on the racing with straightforward calculated corrected time while on the water, no waiting for complex and unnecessary scoring calculations.’

It’s a fair question, offshore races that have been dual scored using a single number IRC time correction factor (TCF) and the ORC All Purpose Handicap (APH) produce similar results. A well sailed boat wins and the places shuffle a bit in the mid fleet.

It is possible to complete a round of golf using only a 6 iron, both IRC and ORC have a very serviceable 6 iron in their bag, but the ORC handicap system needs many more clubs in its bag to deliver our product:

• a VPP that predicts boat speed on all points of sailing in winds of four to 24 knots, not just a calculation based on length weight and sail area
• an aerodynamic force model that handicaps based on the boats available sail wardrobe, or sail chart,
• a definition of hull and keel shape to separate the drag due to wetted area and wave making,
• an allowance for the pitch inertia differences
• an accurate position for the boats vertical centre of gravity and righting moment.

The ORC fleets around the world understand the rationale of ‘Polar Curve Scoring’ (PCS) which scores races based on the polar speed curves and the wind speed and direction.

In 2024, the development of Weather Routing Scoring (WRS) has added a new club to our golf bag, making Polar Curve Scoring available for offshore racing as an alternative to the All-Purpose Handicap (APH). The methodology of WRS has been extensively described in this column during the last year. Now, having streamlined the process of race simulation with our partners PredictWind, we can quantify the degree to which WRS levels the playing field for a mixed fleet in an offshore race.

As a thought experiment, imagine a race around the English Channel, Cowes, to Weymouth Bay, CH1, and finish at the Nab Tower. If the whole fleet sailed a perfect race, and the single number handicap was an accurate reflection of performance, then all the boats would record the same Corrected Time (CT), a dead heat. In the grey bordered section of Table 1, there are six typical boat types, and their Time Correction Factors (TCF) based on the ORC All-Purpose Handicap. The race was started at midday, and I entered into the scoring program an Elapsed Time (ET) for each boat that would produce the same Corrected Time (CT), (CT=ET*TCF) for every ship, 23h:07m:41s. This is how time-on-time racing works.

Next, I simulated the race the evening before the putative race start. Each boat was raced around the course using ORC Weather Routing. The certificate polar table was input to the PredictWind weather forecast and optimum routing software. This simulation returns, for every boat, the predicted track, the Predicted Elapsed Time (PET), and most importantly, the distribution of True Wind Speed (TWS) and True Wind Angle (TWA) experienced during the race.

Now we can score our simulated race using the tabulated TCF’s. The simulated results are shown in the red part of the table ‘Weather Routing Scoring. Clockwise’. The TP52 had a predicted elapsed time of 00:14:03:44, winning the race with the lowest corrected time of 00:17:35:21 (CT=ET x TCF). The Landmark 43 completed the course in 00:21:50:11. giving a corrected time of 00:21:31:56, for a 3rd place finish. The “Corr. T delta to winner” column shows how far behind the winner each boat was on corrected time. For example, the Landmark 43 was 03:56:35 behind.

Using the APH TCF gave the TP52 nearly a four-hour head start over the Landmark 43. This difference arises from the race conditions that are not under the crew’s control: the wind was dropping as they approached the finish, the TP 52 being able to use its headsail set flying for a long leg of the course, whilst the Landmark 43 was only able to set a jib, the TP52 seeing less adverse current. The difference between the times in the “Corr. T delta to winner” column for any pair of boats shows the help or hindrance handed out by the single number. This is inevitable when the race conditions do not match those inherent in the calculation of the APH.

Taking this thought experiment further, a second race was simulated, same fleet, same start time, only the course was sailed in reverse, start at the Nab and finish in Cowes.

The start time was the same and the entered finish times to give a dead heat must be the same because the course length is the same. The WRS simulation however delivers a different scenario from the clockwise race, shown in the green part of the table ‘Weather Routing Scoring. Anti-Clockwise’. The TP 52 wins again, but the free lunches (Corr. T delta to the winner) have smaller portions and shuffle the mid fleet places.

In a single race, across this very mixed fleet the ‘horses for courses’ effect is of the order of hours. Reversing the course direction distributes these not insignificant gifts quite differently. Table 2 shows how TCF’s (using the Landmark 43 as the scratch boat) should change to give very boat an even chance in our two races, around the same course, at the same time, but in different directions.

Finally, forty plus years after the IMS project began, we see the degree to which a single number handicap, which is blind to the prevailing race conditions, gifts or steals the time allowances amongst the fleet. Don’t for a second think these simulations are a worst case, every race simulation produces a variation on this theme.

It’s hard to unsee this analysis. I’m glad I wasn’t aware of the hidden single number TCF tombola going on as I bounced around the English Channel in my youth

The ORC fleets now use a range of well-defined scoring options implement Polar Curve Scoring.

• For the cruiser racers using ORCi at championship level, the inshore races use Polar Curve Scoring. The ‘scoring wind’ is derived after the finish and the results are calculated as the last boat finishes. The offshore races are scored using WRS.
• The ORC multihulls and the J Class, which race a mixture of windward leeward and round the buoy day races demand to use PCS with a constructed course.
• The Superyachts use handicaps that are based on the anticipated wind speed range, and course geometry. For ease of use these are pre-calculated and shown on the certificate.
• In the USA local fleets have adopted a similar approach that offers a TCF for 25 constructed courses and wind band ranges.

The apparent complexity of ORC scoring, and some missteps along the way, have handed our detractors a heavy stick to beat us with. Whist most of the ORC sailors have got the hang of things work, some common misconceptions persist, for example:

‘Under ORC, ratings in each class are now calculated relative to the 'scratch' boat in the class and this can change on a daily basis depending upon the conditions. Thus, it is not possible to back calculate this, nor fully understand the calculation of the daily rating This therefore makes comparisons of deltas impossible across a wider fleet.’

This makes comparisons very difficult and makes combining fleet results from the same course less meaningful, as the ratings are in effect based on a different scratch boat.’

Every handicap system that uses a Time Correction Factor (TCF) has a scratch boat, it is the boat with a TCF of 1.000. The ORC Certificate shows an All-Purpose Handicap which is the equivalent of the IRC TCF. The APH and polar speed curves are fixed for the life of the certificate. The choice of scratch boat makes no difference, except that its helpful to normalize the TCF’s based on the speed of the fleet. For example, some multihull fleets would have an average TCF as high as 2.0, this makes the corrected time deltas twice as big as the actual time on the stopwatch.

‘Reviewing corrected times is also meaningless, as IRC TCCs are based on the worldwide fleet, whereas a comparable PCS base line is only set from boats in that class at that time.’

The presence or absence of a ‘worldwide fleet’ is of no consequence for evaluating individual races. Every ORC certificate is created using the same VPP. If a fleet of 10 boats race, and use say Polar Curve Scoring, the handicap of every other boat in the ORC database for that specific race can be calculated if a comparison is needed.

A further short-coming of this is the accuracy of measurements from the racecourse, especially wind speeds at different heights above the water, knowing that wind shear seen up the 30-50m height of a maxi yacht rig will not be comparable to that seen and used by the scorer on the race committee boat.

The speeds published on an ORC certificate are for 10m above the water. The VPP assumes a vertical wind speed distribution (shear) to account for the wind getting stronger as the height above water increases. This is a fixed formulation based on typical conditions.

Race scoring is never based just on the committee boat anemometer or masthead data. The exam question for the scoring software is ‘what was the wind speed and direction on each leg of the course?’ There are several answers depending on the type of race:

Where wind speed is set to a particular band before the start, or a WRS based scratch sheet is calculated, observations are unnecessary to score the race.

For Windward Leeward or triangular courses aligned to the True Wind axis Polar Curve Scoring gives results at the end of the race based on the calculated ‘scoring wind’. No observations are needed to complete the scoring, but on-board observations are compared to the published wind speed.

For round the cans day racing the options are to pick a wind band and pre-constructed course type, or use the course geometry and observed wind direction and speed, from mark boats etc.

Competitors will not know their rating, and therefore their results, until after the scorer has completed their calculations.

True, if the Race Organiser has chosen to use Polar Curve Scoring. Results are available a few minutes after the last boat has finished.

Even after this is complete, understanding this, and the full data used, is not going to be available.

The scoring wind conditions and associated TCF for the race are published in the results. For WRS the simulated tracks together with the boat speed and heading as well as the wind speed and direction are available for scrutiny.

Under ORCi Onboard, individual weather data may be used, leading a competitor who, for example, sees their light air performance to be better than the predictions, to hunt for holes in the wind rather than avoid them.

No ORC races are scored using an individual competitor’s wind data. Naturally in a system where the wind speed and direction affect the scoring, there is always a lively discussion as to whether this value is appropriate. Given properly worded SI’s and competent race management, this is a discussion for the bar rather than the jury room. Finally, good luck to any competitor who seeks out wind holes to improve their chance of winning.

ORC #TheEqualChanceToWin, well a bit more equal.

Andy Claughton, ORC ITC Chair