Massive Spoiler Warning
What follows is a quick analysis of the fleet for the 2010 edition of the IMSYC Challenge fleet race on http://www.sailonline.org. IF you want to figure out what boat will be fastest 100% on your own – PLEASE stop reading now. The info presented doesn’t identify one guaranteed winner this year, but it helps narrow the choices, and gives some extra insight on the boats and different ways to interpret the polars. The calculated handicaps give you a pretty good idea of which boats will be fast in what conditions, and how they are likely to compete with each other during the race. They also highlight some of the design decisions chosen by Jakob’s students, which are discussed in the reports available along with the polars at http://www.sailonline.org/static/imsyc_2010 .
The ratings shown are based on ORC-Club, which is described in considerable detail at http://www.orc.org. This implementation suffers somewhat in that I have not applied wind-speed smoothing, and the IMSYC rule produces slightly strange boats. Combined, this tends to lead to”rule-beater” ratings for boats designed for extremes of low or high wind. Overall though, the ratings seem to work out pretty well when software-routed finishing times are compared.
A quick breakdown of the different ratings:
GPH: General-purpose Handicap
This is a “single number” time-on-distance handicap that is probably the most familiar type. The ratings are given as seconds/mile, and time owed can be quickly figured out by subtracting your rating from another boat’s. The allowance is multiplied by the length of the course to give corrected time. In ORC, GPH is calculated using the time required for a boat to sail a circular course in 8 and 12knots of wind, giving a good general reference for overall performance. ILCGA is a TOD handicap that can be used for inshore/windward-leeward racing. It’s based on a matrix of up/downwind VMG and 110° reaching at 6, 10 and 20 knots. Lower numbers are faster.
TMF is a time-on-time representation of GPH/ILCGA. Your finishing time is multiplied by the rating to give a corrected time. Why do this? Basically, the time on distance schemes give the same time allowed for every course, so boat A needs to beat boat B by 30 minutes over a 50nm course, regardless of how long it takes to complete the course. If there is lots of wind, big fast boats get beaten on time by the little guys, and the opposite is usually the case for long slow races. Time-on-time scoring is supposed to compensate for this somewhat by including the time to finish instead of the race distance in the formula. Whether it’s *really*any better is one of the great debates of simple-system handicapping. Higher numbers are faster.
Club scoring rules for ORC races can use “Performance Line” scoring to try to deal with the limitations of single-number systems. The correction is based on both race distance and time, and boat performance in high or low winds is included. In theory this evens things out a bit, and makes racing more fair. It seems to work out ok in SOL, though you definitely need a calculator to figure out where you stand during the race. IMSYC-rule polars produce slightly funny looking numbers. The formula for corrected time is (PLT*Elapsed_time)-(PLD*Distance). Offshore ratings reflect boat performance over a mix biased toward windward-leeward work at low windspeed and reaching in higher speed, which seems to reflect the makeup of many courses. The inshore ratings are based on an Olympic triangle at 8 and 16 knots TWS.
OTNLOW-MED-HIG: Off(in)shore Triple Number
These are time-on-time ratings that compensate better for boat performance in different wind strength. The LOW ratings are for windspeeds below up to 9 knots and HIG(h) is above 14. You still get the same advantages to the fast/slow boats but now the spread is over a narrower wind range. This makes the rating “more accurate” but is really intended to give racers a common enemy in the guy who drew the short straw and has to choose the wind range to apply. If true wind is close to the transition, the choice of which set of ratings to apply can turn the corrected order upside-down.
The IMSYC race this year is about 1100nm and will probably take about 7 days to finish, so we can use those numbers as a basis of comparison.
The boats are listed ranked by GPH, which is a reasonable “All-around” number. Windigo is rated fastest, with Uprising and Innsbruck not too far off the pace. Windigo owes Uprising ~6.7 seconds per mile, or just over two hours at the finish. That seems like a big gap, but well inside the margin for the top dozen boats on a race of this length.
Uprising has a significantly faster rating using the inshore numbers though, and is rated basically even with Innsbruck. Why the difference? Look at the polars (and read the reports) for these boats and you’ll see that they are using very similar optimisation strategies, but have chosen different wind ranges based on their research. Windigo is fast in light wind but runs out of righting moment much above 10 knots. Uprising stays on her feet a little longer. ILCGA includes 20knots windspeed in the calculation, which is enough to drop Windigo’s rating to 12th.
The “Triple Number” ratings show the story of the top boats. Windigo rates out fastest in light winds under both offshore and inshore schemes, while Uprising wins the 9-14 knot range and Innsbruck takes it in heavy winds.
The middle of the fleet is pretty even. Normandy and Andren stand out in approach a little and will benefit with light wind, while SnAILBOAT is hoping for a hurricane.
Software routing starting at no particular time gives the top five as Uprising, Innsbruck, Sunny-go, Windigo, NumberOne in around 13knots average wind.
It’s important to point out that the ratings are NOT a measure of what boat is fastest. They are an excellent indicator of how a boat will sail over the course and wind range used to produce the rating. GPH accurately predicts race outcome around a circle in 8-12knot winds, but says little to nothing about how fast a boat will get from Bodoe to Gdansk. The boats all sail fast in certain winds. You can work that out from the polars by overlaying the graphs, or you can try to work out something using the VPP. The handicap numbers are NOT software routing or anything too complex – they are basically just average speeds produced by summing one or more columns (windspeeds) or even just looking at only windward-leeward numbers from the text polars. An “in-depth” no-router approach to choosing a boat might be to pick 2 or 3 TWA and TWS that look good for the race date and do a simple comparison that way. This is the same process that many of the students used in their analysis. The ORC-Club “recipes” are just average conditions.
To illustrate the above, and reinforce the true meaning of the ratings, in a simulated rerun a few minutes ago the finish order is completely reordered: NumberOne, Innsbruck, Optimist, Sunny_go, LoveBoat… all home within 18 minutes of 1st in 15 knots wind. Windigo (fastest GPH) is nowhere close. 1 knot more wind and it’s a new game all over again!
What About Corrected-Time Results?
I’m hoping to post corrected-time rankings for this race as it progresses, using the Performance-Line (Offshore) type scoring. In simulated racing, there is a 130 hour difference between first and last, but they correct out within 10 hours of each other. The majority of the fleet is much closer – throw out the stragglers and the standard deviation is about an hour.
Which boat do you choose if you want to try for a Corrected-Time win instead of line-honours? Funny thing about handicap racing… The fastest boats don’t win that often. They destroy the fleet under the right conditions, and by the same token J-24’s can beat everyone on a good day. In SOL, where boats race true to their polars, any boat _can_ win, but the middle of the pack tends to be pretty safe. The fringes have to take their lumps with their glory. This is why everyone loves handicap racing 😛
We’ll gather for beers and griping about ratings post race. It’s traditional.