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Chicago Mac Adds Third Custom Rating for Upwind Races

May 25, 2019 11:53 AM

For the first time in recent years, there is a significant change in the way the ORR rating will be applied to boats racing in the Chicago Yacht Club Race to Mackinac. Based on conditions over the past few years, a new Custom Rating has been developed to better handicap the race in conditions such as the fleet faced in 2017 and 2018 with a significant portion of upwind sailing.  


As you know, the Race to Mackinac is a handicap race. The elapsed time for each boat is adjusted by a correction factor designed to level the playing field between the wide range of designs that participate in each summer’s race. It is adjusted time, not the actual finish order, that governs leaderboards for Divisions and for handicap sections.


Our handicap system of choice is the Offshore Racing Rule (ORR). ORR is a "Velocity Prediction Program (VPP)" -based rule. A VPP uses as inputs many detailed measurements of your boat. These measurements are plugged into the VPP, which then simulates the speed of your boat under specific conditions and points of sail. Boats are then handicapped by the VPP via assigning a rating (in the case of the Mac, this is a time-on-time rating—so that the rating expresses how much time is added to/subtracted from each boat’s elapsed time) so that all boats are put on a level playing field.

One of many benefits of a VPP-based rule is that the ratings used to handicap the fleet can be tailored to a specific course mix and wind mix appropriate for the conditions of the individual race.  The "course mix" refers to the mix of points of sail used to derive the rating.  The "wind mix" is the combination of wind speeds.  These have to be considered because boats go faster/slower relative to one another on different points of sail and at different windspeeds. The choice of course and wind mix is most easily done on a short buoy race where all competitors are limited to a relatively small racing area and the course is highly restricted. For example, a windward/leeward course with an equal number of windward and leeward legs would include a mix of 50% optimum beat and 50% optimum run at a given windspeed.   When the VPP simulates a course/wind mix using a scenario like this, the result is a "Custom Rating"


As race distance lengthens and competitors are dispersed over a wider area developing a Custom Rating becomes more challenging. The Chicago Mac is — unlike many other offshore races — highly variable year to year in the weather conditions experienced. Whereas the Newport to Ensenada and Transpac, for example, are almost always reaches/offwind, the Mac throws a wide range of conditions at our sailors, often radically different from year to year. We have therefore developed multiple ORR Custom Ratings that account for this variation. We are adding a new one in 2019.


Traditionally, we have had two options to choose from when handicapping the Mac: Chicago Mac All Purpose (a roughly-equal combination of upwind and downwind) and Chicago Mac Offwind (a reach/more downwind-focused Custom Rating). After two races (2017 and 2018) with large upwind components, the Mackinac Committee has decided to broaden the selection of Custom Ratings available by adding "Chicago Mac Upwind" to the options available to handicap the race.  You will see this new Custom Rating on your 2019 ORR certificate.


So, how does this new Custom Rating differ from the old ones? For each of the 3 (previously 2) rating choices, we first start with a wind mix tailored to the Mac Race. Our wind mix is a weighted-average wind speed of approximately 11.5 knots, broken down as follows:


            6 kts = 5%

            8 kts = 15%

            10 kts = 30%

            12 kts = 30%

            16 kts = 15%

            20 kts = 5%



Next, we combine the wind speed percentages with a range of True Wind Angles (TWA).  This is the course mix referenced above) to produce a composite time-on-time rating under each of the three wind/course mix options. The following tables show the actual course mixes used for each of the Mac ratings.  You can see from the percentages that the new Chicago Mac Upwind Custom Rating has a much larger portion of its course mix as upwind sailing than the legacy ratings do:




Custom Rating


Chicago Mac Upwind

Chicago Mac All-Purpose

Chicago-Mac Offwind

Optimum Beat




52 deg Reach




90 deg Reach




135 deg Reach




Optimum Run










So how is the specific rating to be used selected at race time?  Fortunately, with expert advice from race meteorologist Chris Bedford of Sailing Weather Service and routing tools such as Expedition, this task is straightforward. Routing is run for several boats in each Division representing fast, medium and slow entrants in the Division.  The routing results are based on the latest of several forecast models and provide numerous data points including percentage of time upwind, reaching and downwind. 


After reviewing the available data and consulting with Chris Bedford, the best fit from our three Custom Ratings (AP, Offwind, or Upwind) is selected. While all boats in a single Division will use the same Custom Rating, it is possible that two different Divisions could be scored based on different ratings (for example, cruisers could be scored AP when forecast to spend a long Friday night beating to windward, while the other Divisions could be scored offwind when the outlook for Saturday and Sunday brings a steady spinnaker reach from the Southeast). 


Both the 2017 and 2018 races were decidedly upwind, but we didn’t have the new upwind rating available to handicap the fleet. Now that the menu has been expanded to include an upwind option we have probably guaranteed that we’ll never see those conditions again … or, maybe not! Either way we have all earned a break so here’s to a beautiful, reachy Mac in 2019!


Ron White

Chief Measurer




Chicago Yacht Club




Pentastar Aviation

Team One

Barton and Gray






West marine





US Sailing

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