Fig 2
Fig 1
Psychologically for the crew it’s challenging because their handicap versus their rivals’ will change from race to race; as it should if last week’s race was a drifter and this week there is a good breeze. We made (at least) one mistake; ‘Weather Routing Scoring’ is
the wrong name. And is also offputting. The output of the process that is most closely scrutinised is the predicted tracks, and these obviously vary depending on the forecast used (GFS, Arome etc). Now the discussion starts about what is the right forecast to use. In fact, the handicapping doesn’t take any notice of the predicted track, it just needs to know how long you sailed in each wind speed on each point of sail. The ORC also generates a single-number All Purpose Handicap
(APH) by simulating a race around a circular island, an equal time at each true wind angle, in a range of true wind speeds. (This is the closest ORC offer to the single-number time-on-time IRC TCC- based system). The distribution of the wind speeds is most heavily weighted around 12kt, as shown above. This gives us the percentage of the race time each boat spends
sailing in each ‘bin’ of true wind speed and angle. Each bin is a range of wind speed and angle. This is shown in Figure 1 (above) with the size of the bubble in each bin proportional to the percentage time spent sailing in that bin. The APH assumes that in every race you see a bit of everything.
This of course never happens in a real race. As an example, a few days ago I laid a course around the Isle
of Wight and raced a small fleet around it. The simulated tracks are shown in the upper part of Figure 2 (top right). Then this morning I raced the same race again but with a different forecast and the simulated tracks for the two races looked a little different. The output of the race simulations was analysed to show how
long each boat spent sailing in each ‘bin’ of true wind speed and angle. The bubble plots (Figure 3) for two of the competitors show what wind speeds and true wind angles were sailed in each race. It doesn’t matter if you tacked and gybed in exactly the predicted
place, the scorer needs the distribution of TWS and TWA so he can replace the less appropriate distribution assumed by the APH. With Weather Routing Scoring the complexities of post-hoc scoring are removed, competitors get a single TCF for the race before the start. The early trials with the system have proved interesting. Suddenly
crews who have raced with the same TCF for years are concerned that their handicap advantage over their rivals in certain conditions has been eroded. ‘We would have won today with our APH!’ But APH is a blunt instrument. On another day WRS will give you a better chance to win in conditions where you previously struggled. Weather Routing Scoring sets out to offer a more equitable scoring outcome. But it also gives every competitor their own science project
46 SEAHORSE
Fig 3
to work out why it didn’t quite get it right for their boat in this particular race. ‘Yes, it was fairer than a single number, but today it wasn’t quite fair enough for us…’ In practice corrected time differences are so great that changes
in the race positions from using WRS instead of APH (or IRC TCF) are usually small. The winner usually sails such a good race that he would win under any rational scoring system. But for ORC three things sustain our belief that WRS has its place in mixed fleets. 1. It makes best use of the VPP predictions, which is where this all began 40 years ago. 2. No owner need feel that today is not his day because the conditions are wrong for his boat. 3. In marquee, one-off races, which attract good crews, sailing well- prepared boats of very diverse types, a scoring system that is sensitive to the conditions does level the playing field. For example, using a single-number rating, a TP52 will always struggle against a Volvo 70 on a reaching course in a breeze, for example the 2024 Gotland Runt. Thanks to our partnership with PredictWind the process for running
the simulations is quick, two or three minutes for a 50-boat fleet around a Channel course. The ORC Scorer software interacts directly with the PW engine to run the simulations. It (really) is simple to use, set the course, download the handicap polars for the competitors, run the simulation, publish the TCFs. At this stage of development ORC rely on PredictWind to give us
the most appropriate forecast for the race area and duration, this is after all their stock-in-trade. To retrospectively worry whether a different forecast would
produce a better result is intellectually attractive, but there is no agreed metric as to what constitutes a better result. The option of using different weather models that may be more accurate for some regional areas may be for future development. Meanwhile, the whole point of WRS is to get handicaps before the race that are better than the simple APH. There is a danger that the perfect (which we can’t define) becomes the enemy of the good. As I finish writing this the latest issue of Seahorse has arrived.
The excellent piece from Judel-Vrolijk, about race simulations using historical weather data to design for the next Admiral’s Cup, is pertinent to this discussion. The designers and analysts have gone to great lengths to optimise the rating for the anticipated race con- ditions in 2025. But if the weather doesn’t play ball you will have to take your lumps, as usual. In an ORC regatta with Weather Routing Scoring you can sail your boat, without optimisation, and be rated for the conditions forecast hours, not years before the start. Not that I anticipate the Admiral’s Cup will shift to ORC any time soon. Andy Claughton, ITC Chair
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