Second Wind (a reprise article from 2008)

by Vin Mariani

[Note: This article was originally posted February 18, 2008
by Vin Mariani on SLSailing.com. Although it is five years old,
the information in the article (and in the preceding “Part I“)
still applies to many SL boats that have wind algorithms
based on Kanker Greenacre’s original Tako scripts. /JFos]

Ready to hear more about how race wind works? This time I’ll answer more of the questions I posed in my first article. So you don’t have to jump back and forth, I’ll repeat each question in bold before I give an answer. And for those who suffered flashbacks of high school math classes during my first article, let me reassure you that there will be no equations or computer code this time. But there will be dangerous experiments.

Before I continue with the wind, I’d like to respond briefly to some of the gratifying comments on the first article. Bea Woodget and Liv Leigh expressed concerns that this information could make sailing more artificial, less like real sailing. After all, we are out there to sail, not to do math. I agree. I had the same “Frankenstein moment” myself as I was studying the wind. Maybe we would all be better off not knowing about these things. Or should I just use the knowledge privately for my own gain? Or perhaps it would be wrong to make any use of it at all?

The problem is, if only a few of us search out the (cue spooky music here) “secrets of the wind”, those few may have an advantage. It would be really unfortunate if a mathematical inclination gave a few people an edge in SL sailing. Let me be blunt: I think that would suck. It involved some soul-searching and several discussions with my fellow sailors to decide what to do about this. Here is what I decided upon: 1) present the results openly and completely, so that no one is left behind. 2) Make it easy for everybody to use the wind variation, if they want to. (Or of course, we can always turn it off or reduce it.) And last, 3) I decided not to use this information in competition before it is available to everyone. That’s what these articles are for.

So let’s continue.

Q2) Jane Fossett’s original question: in a race, do all boats of a type feel the exact same wind variation at the same time? Are they lifted and headed together? Yes, all boats in a race carry the same two wind functions with the same parameter values. So if two boats independently “ask” the wind speed and direction at the same time, they will get the same answer. If their HUDs display wind data numerically, all HUDs would show the same values at the same times. This has been experimentally verified a number of times using various boats in various places, as you’ll soon see.

In this way, all boats in a race “can feel the same wind”, even though the specific times at which they actually “check” that wind may not be identical. Since they check often and the wind functions vary slowly, they are essentially subject to identical wind. And once a boat has gotten the brief message from the windsetter before the race, all of the rest is done without any more messaging. Kanker was clever. And what a relief; all of us are racing in the same wind. So winning is due to differences in skills, not differences in wind.

Q3) Even if they are in different sims? Yes. Because the wind functions are set up with the same parameters in all boats in a race, boats in different sims will feel the same wind variation at the same time, no matter how far apart they get. ASSUMING that the value of the “time” is the same in all sims. Oddly enough, this is not exactly so in all cases. What do we find when we actually compare wind variations across sim boundaries? The experimental results are interesting.

Recently, an international team of hardy explorers braved terrible conditions to test this theory in the remote southern ocean of United Sailing Sims, far from any windsetter. M1sha Dallin, JeanCarlo Kepler (with crew Scout Catteneo), and Pensive Mission volunteered to join me in the hazardous, yet tedious task. We rezzed our four Beach Cats at the NYC race line in Bismarck Sea and made sure we all had race wind, which varies there by dir+- 15, spd+- 3, and rate 1. Then we set sail for our objective, a remote patch of water where four sims meet. This would normally be a picnic, but the “weather” was so bad that many boats were lost before we even arrived at the site.

After many misadventures, we managed to arrange ourselves, one in each sim, but all within chat range. You can see it was a dreadful night, with St. Elmo’s fire glowing all over my boat and a bolt of red lightning striking the water in our very midst.

Moments later, JeanCarlo and Scout had their anchor warp part suddenly, were blown off-station and never heard from again. (Well, actually they showed up the next day with some tale of crashing and relogging problems, but where’s the drama in that?) Undeterred by our loss, the remaining marine mathematicians gathered the essential data. Here is what we found.

When Pensive chatted the wind speed that he saw on his HUD every few seconds, M1sha always saw the same speed also appear on her HUD, perhaps a second later. I saw the same speed appear on my HUD, but always 3-4 seconds later than when Pensive said it. Could this somehow be due to lag between us? But, when I chatted the wind speed that I saw on my HUD, Pensive and M1sha had already seen that speed a few seconds earlier on their HUDs. So it wasn’t lag, since it is a delay in one direction and an advance in the other direction. The only conclusion is that the clock in my sim was a few seconds behind the clock in the other two sims, and M1sha’s sim must be just a tiny bit behind Pensive’s. But if we neglect these small clock differences, the three sims showed the very same wind speed variations together over a long period of several minutes. This is what you would expect if all our boats used the same wind functions, but listened to separate, not-exactly-synchronized clocks.

How does this happen? Well, the Tako v2.1 wind functions find out the time by calling llGetTimeOfDay, and the documentation for that command indicates several ways that it can vary from sim to sim. The biggest way is if the day/night cycle in a sim is different from usual. Some sailors may be old enough to remember that, when crossing into what is now Ortega Channel from the north (on SYC’s Oscar course for example), day would suddenly become night and the wind would shift radically. Now we know why. That sim had a totally different TimeOfDay, so the wind jumped as we crossed in or out of the sim. In the general case, the effects are much smaller. Since TimeOfDay is counted by each sim itself, and these clocks are on different computers, even in the normal course of events they can be different by a few seconds. This is why we often feel the wind change a little bit when we cross a boundary. Interestingly, there is one sailboat that doesn’t suffer from this effect at all. Do you know which one? But that’s another story, for another article.

You might think there will be three or more installments coming, but most of the remaining questions have brief answers, now that we have covered the key issues. And I remind the readers that the goal at the end is to provide everyone with a very simple way to take as much or as little advantage of wind variations as they would like. Stay tuned for more wind.

Vin

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