Recently, there’s been much discussion and experimentation with the ORC and IRC ratings at the club, with comparative testing at the Fling Regatta and Mykonos Offshore showing very positive results. Many sailors may not know too much about ratings, so what follows is an attempt to explain some similarities and key differences, without getting too technical.
Both IRC and ORC are measurement-based rating systems, and both are endorsed by the World Sailing (formerly ISAF – the International Sailing Federation) for offshore keelboat handicap racing. Both are used successfully and effectively around the world.
For the purpose of this explanation, let’s presume that the measurement methods are equally sound (in fact, many of the measurements are exactly the same), such that the inputs and the rating formula used to derive a single-number rating would result in closely comparable handicap results on both systems. What would be factors to consider in choosing between ORC or IRC?
I’d argue that the decision would be based on ease of measurement, cost of certification, ongoing technical service and support received, and possibly the popularity of the rating in the broader context, to ensure the “currency” of the rating in other waters, near or far. So far, so good. We can objectively compare these items head to head to make an informed decision.
But there’s a fundamental difference between the two ratings: IRC has a single-number time-correction coefficient, based on a secret ratings formula. ORC has a number of different rating options to suit different course types and wind strengths. ORC also offers time-on-distance allowances, which offer advantages on certain course types where you race on distance, not the clock.
ORC uses an ever-evolving Velocity Prediction Programme (VPP), using inputs of the yacht’s measurements, and publishes both the time allowances and target speed predictions, across a variety of wind speeds and points of sail, on the certificate. From these numbers, one can directly formulate the ratings on this system, using open and published formulae for the various options. (I will illustrate these later in the article.) But to start, let’s compare the two different approaches to ratings by using an analogy South Africans will relate to…
Imagine a good rugby team comprising of 15 players who are all suited specialists in their given position. One gets a pretty clear image of what your tighthead front-ranker might look like. Similarly, you can imagine the physical stereotype for you scrumhalf, wing, lock, and so on. You can even imagine differences between similar positions, like the props (loosehead vs tighthead), or the locks (enforcer vs athletic lineout specialist), or the flanks (open-side fetcher vs blindside carrier) or the centres (inside defender vs outside attacker). Now imagine you could only field a team with 15 clones of a single position type or player from the specialist team above to fi ll every position in the team. I’d imagine the best-suited single player type in terms of skill, versatility and physicality would probably be a flank, an eighth-man or a centre. So pick one position, and clone it to make a full team. Now imagine the specialist team plays against the cloned team. What do you think the outcome would, or should, be? Is it a fair contest?
I think this is probably the easiest way to make a comparison between the IRC and ORC rating systems for normal racing – that is, excluding the special rating allowances for non-spinnaker or double-handed racing.
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IRC uses one single number time on time-coefficient general-purpose rating for all racing, regardless of wind strength, direction or course type. ORC offers several specialist rating options, from general to specific, to suit the wind strengths and course types, yet there’s an overall general-purpose option if there’s insufficient race-management expertise to decide the conditions. A single-number rating solution can’t compare to a “horses for courses” multiple-number system. To illustrate this, follow along as we get more technical…
If you look at the supplied VPP data on an ORC club-rating certificate, you’ll see a table for time allowances across different winds and points of sail. These numbers are predictions of how long, in seconds elapsed, a boat will take to complete one mile. This is called Time on Distance (ToD). Here’s an example from a yacht in our fleet.
The ORC ratings for inshore windward-leeward courses use only the pure beat-and-run Velocity Made Good (VMG) time allowances generated through the VPP. They don’t include any data for any other points of sail, as those are irrelevant in windward-leeward racing. The ToD allowance for the windward-leeward selected course type row below these numbers is the mean of the beat-and-run VMG in each wind band. If you’ve followed this so far, you’ll understand that this is powerful information, and it’s openly available on your certificate.
Here are the rating options for the same yacht above.
The rating options allow some margin here, and the Inshore ToD number is a weighted averaged of the selected course windward-leeward ToD numbers at eight knots (25%), 12 knots (40%) and 16 knots (35%). To convert this to a Time on Time coefficient for inshore windward-leeward sailing, the simple formula, using a base number of 675 seconds per mile, is used. The Inshore Single Number coefficient = 675/Inshore ToD number. The even more accurate Inshore Triple Number scoring options are derived similarly, using the more focused Low, Medium and High wind bands. The proportions and wind bands for each are published, so you can work this out from your certificate. Ratings for offshore circular random course types can also be derived from the VPP data on the certificate. There you have it.
Article by Luke Scott
