Unofficially Handicapping the IMSYC Challenge 2010

11 02 2010

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 110Ā° reaching at 6, 10 and 20 knots. Lower numbers are faster.

TMF

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.

PLT-?

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 Ratings (Click to enlarge)

Discussion-Boatspeed

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 šŸ˜›

We’ll gather for beers and griping about ratings post race. It’s traditional.





Cape Horn 50-50

5 01 2010

The run from 50 degrees South around Cape Horn and back to the starting latitude is one of the most spectacular tests of offshore sailing. It was one of the benchmarks against which the fastest Clippers were raced and remains one of the greatest sailing rites of passage. Join us as we commission SOL’s new Clipper and race “wrong-way” around the Horn!

SOL’s Clipper is modeled after the three masted “extreme clippers” built in the US, with an overall length of two hundred forty feet. These ships owned the majority of offshore sailing records for more than one hundred thirty years, only being displaced by modern purpose-designed sporting boats in the last two decades.

The polar we’re using should be pretty close, and gives virtual clipper sailors a shot at some of the old records. Performance originally fell off as the wind increased further, but this feature was eliminated to avoid confusion. In a real clipper, you didn’t expect to make way to windward in strong gale to storm conditions, and reaching was to be avoided at all costs.





Lake Superior Lights Tour

18 12 2009

Will be back to routing strategy in a bit, but for now we’d like to offer a photo-tour of Aetheria on SOL’s “Lake Superior Lights” race. This 600nm race uses some of the great lighthouses as turning marks. In order of appearance:

Wisconsin Point

Micipicoten

http://freepages.genealogy.rootsweb.ancestry.com/~pcaddict/Carpentier-Leask/Carpentier/Carpentier-Pictures/Brassar/Michipicoten_Island_Lighthouse.jpg

Caribou Island

http://marinas.com/view/lighthouse/917_Caribou_Island_Lighthouse_Wawa_ON

Stannard Rock

http://lighthouse.boatnerd.com/gallery/Superior/StannardRock.htm

Passage Island

https://www.msu.edu/user/kilpela/ir0504.jpg

Outer Island

http://picasaweb.google.com/lh/photo/ZmNieWM1THNb-qhOzFHPMA

Chequamegon Point

http://www.lighthousefriends.com/light.asp?ID=695

Ashland Breakwater

http://lighthouse.boatnerd.com/gallery/Superior/Ashland%20Breakwater.htm

All mages sourced from public domain





Arrr

31 10 2009

heen





Using the VMC polars

27 10 2009

So far we’ve only hinted at ways to use the VMC polars while starting to try to explain the concepts. The printed polars give you a couple of advantages, and there are two main ways to use them for “no math” navigation. Advantages for normal use are that they are bigger, and that there are more windlines to help with planning.

VMCexample1rotated

I suggest two ways that they can be best used to find the best VMC angles for a given target. The first is to lay the polar over the boat (or over your position on a paper chart in rl) and align it to the wind, as in the previous VMC examples. The VMCmax is the point on the polar that is furthest toward your target – TWA 50Ā° in the example we’ve been using, for a target of 30Ā° off the wind.

I find that I can see through the polar well enough even printed on regular paper, so long as the room lights are dim, but printing on thin paper or better yet transparencies would work better. Another option might be to wax the polar… rub with candle wax and iron (don’t use the “good” iron if you know what is good for you). Rubbing in a very dry coat of salad oil works too.

SO76TP-90mono

The other method makes use of those radial “spokes” that are a prominent feature of the polars posted here. The spokes trace lines of maximum VMC for given target angles relative to the wind. The heavy lines are for targets of 0-90-180Ā°, while the solid and dashed lines mark of 30Ā° and 10Ā° intervals respectively. We’re used to finding VMG, so you can see pretty quickly that the 0Ā° spoke just traces those points (remember that VMG is just a special case of VMC). If you rotate the polar, you can see that the spokes always point to the point furthest “up”… max VMC!

In our 30Ā° example, you pick the 30 line (first solid line counting clockwise) and read off the TWA where it intersects your wind line. Like magic! You get the same 50Ā° answer as the overlay method.

Using the VMC spokes is a particularily good way to work out a set of delayed commands for those awkward times when you have to sleep. It is easy to pick a TWA to about a degree of accuracy just by eyeballing the polar. Believe it or not this is better than most routing software will give!





VMC Sailing in shifts

21 10 2009

So what is this VMC business? We’ll stick to a simple upwind case for now, but remember that VMC is just a way to measure your speed toward a certain goal. A relatively common question on SOL is to ask why some boats are sailing “upwind” Ā a little bit below the proper tacking angles as indicated by VMG. The explanation usually offered is that the boats that are footing aren’t trying to get to windward, but are sailing as fast as possible toward their goal, which is usually the next shift. VMC might enter the discussion.Ā Occasionally, someone with years of race experience chips in to explain that there’s no such thing as VMC on “pure upwind” legs, or that you never see the pro boats footing. It is easy to understand the following:

VMCsteady

Black is sailing VMG and has no trouble pulling away from Red, who is footing, or Green pinching. Upwind on most boats, you steer to your telltales and tack on headers, and at first glance this is what isĀ guaranteedĀ fastest. You can see the loss in distance that either boat not on the proper tacking angle is incurring just by looking at the polar. Max VMG is the furthest point forward… anything else is slow to windward. Though the footing boat might feel fast, it’s common knowledge that he’ll lose out in the end.

The problem is that “pure upwind” sailing doesn’t exist in the real world and rarely online. Once you introduce any variation in the wind the decision is no longer as simple as VMG. Why don’t we see the big boats footing? Well… you do if you know what to look for. Often the difference between VMG and VMC angles is a degree or so. That’s sheets cracked a quarter inch, or letting the tails of the leeward ticklers lift just a bit on a puff… Where it really comes into play is offshore, over long time periods. Boats with wide polars like those of a typical multihull benefit more.

VMCshifts

Here is the same diagram we used for VMG, but with VMC relative to a 0Ā° target indicated. The target is not usually going to be the mark. This scenario is set up to show a really clear-cut case.

The red track is our VMG boat, tacking on the same TWA 37Ā° as in the no-shift example. Black is sailing angles of 50Ā° TWA, a pretty healthy ways below Red’s track. Black is clearly sailing faster, but he’s losing ground to windward, just like Red did in the first example. How can he get away with it?

Fast forward to the all-important shift. Not only is black going to get to it first, but look at what happens to the “distance to windward” measurement once both boats are in the new wind. Black is instantly both further upwind (dramatically so, in this example) but also further up-course. He happily tacks over onto port and can lay the mark on the same fast 50Ā° angle while Red can just barely lay it at all. Red is going to get rolled to windward – Black seemingly came out of nowhere.

The red target lines and “ladder rung” maximum VMC lines allow you to visualise what is happening. In these 30 degree shifts, maximum VMC Ā is around a knot faster toward the average wind than VMG. The boat more than makes up for the extra distance sailed by sailing with almost two knots more boatspeed. Sailing VMC upwind usually, but not always takes the form of footing on the favoured tack, but if you were stuck Ā for some reason, you can see from the polars that best VMC for the bad tack is a (some would say crazy) 27Ā° or so – sailing slowly but not getting swept further off track…





Transat VMC example

21 10 2009

SOL Mini6.5 Exmeromotu coasting home with a huge lead! At this point in the race, boats are starting to get worried about whether to sail for maximum boatspeed or best VMG. When the screencap was made Brazil was keeping the decision easy enough, but once the fleet is around the corner we’ll see some scattering.

exmer

The blue line is Exmeromotu’s polar curve for this windspeed, and the the polar diagram has been rotated to align with the on-screen wind arrows. You can see that he is neither sailing his fastest TWA (around 110Ā°) or VMG (170Ā°) – he is working his way down the coast on a middle angle that gives him max VMC along the red arrow, which not coincidently is pointing right where he wants to go.