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Board » Technical Support » False TWA = 0

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Posted by
A2


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2009-10-26 00:39:42
2010-12-03 17:50:37 - False TWA = 0
This is more in the nature of a report than an actual, perhaps, technical issue.

During this finishing portion of the Barentsz Run I experienced 2 instances where my boat "flipped" to TWA = 0, without any apparent obstacles.

On approach to the Kappe Linne mark there are two long sections of coastline. Having made a nominal turn at approx. 14.5E/77.2N I made a course adjustment to the far end of the first coastal section & pointed my boat using the Wheel icon to clear the next apex in my path. According to my predictor line this would take about 4 hours time to clear.

My constant bearing was 341.75 and at max zoom I had at least 6 boat widths clearance from the landform. This was a gradual near parallel course. I was surprised to notice not long afterwards, when I returned to check my progress, that my boat was head into wind.

My first instinct was to get underway immediately without understanding what had caused my predicament. My boat was put underway with a bearing 341.50 and while close to land I was not as tight as many other occasions during SOL events where I have skirted the coast without incident. I reset the bearing to 341.75 which was still a near parallel course.

The second incident occurred in near proximity to where Garganey also reported a like anomaly at approx. 14.365E/77.225N. You will notice a distinct veer in his course away from the coast at that point as a result.

Now, as this was a long race with several episodes of interrupted sleep I considered the possibility of having been tripped up by a delinquent DC left unintentionally in the buffer. After the second occurrence I changed my password.

Then other boats began to mention having similar experiences in the chat. The most notable of these was Nacrr who was dueling with the redoubtable Jepson for a high finishing position.

Now, of course, one could speculate that there was some overlay discrepancy between where the land was shown and where the server expected it to actually exist. Further speculation might suggest that the high latitudes for the race caused a loss of precision for the alignment that normally exists in other venues.

This is the report that RC asked me to provide, others may recount their own experiences here should they so choose.
None so blind
Posted by
nacrr


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2010-01-01 15:57:17
2010-12-03 19:01:51 - Re: False TWA = 0
Same happened to me! I was on 10th place and looking for a good position in the end. Instead I got 42nd!
nacrr
Posted by
76Trombones


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2009-08-03 18:04:56
2010-12-04 23:42:30 - Re: False TWA = 0
I saw the aftermath of the shore-run the other night and it looks like the boats "crashed" into the beach... There have been several times that we've noticed boats "jumping" sideways by one server refresh on otherwise straight courses. They don't show up as kinks in the track - SOL seems to shift the whole track.

I don't remember which race it was but fairly recently there was an occurrence of a boat having rounded (and correctly scored "rounded") where sometime after the fact his track was shifted by one refresh-jump to stb so that the displayed route no longer appeared to pass properly.

It seems like *maybe* sometimes the boats move from one update cycle to another, and somehow the position is recalculated to compensate. Most places you'd never notice, but on a long run up the beach...

Pure speculation, but what I saw didn't look like phantom commands. Only the tech crew knows.

In the meantime, staying one "jump" offshore might make sense.

---Just realised that the tracks pre-collision still showed properly offshore... who knows?
Posted by
captjack1942


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2008-01-18 03:24:03
2010-12-06 06:25:55 - Re: False TWA = 0
A2, are you sure that you were entering a CC course. A TWA course will change over an update.
Also, I have noticed in the last couple of months the predictor line cannot be totally trusted, especially on TWA courses.
The other thing is that lack of sleep can cause lots of things...like forgetting DCs that should have been canceled. At least those type of things happen to me.
A couple of years ago we did have the dreaded TWA-0 bug that seemed to strike randomly. But that was on the old Open GL client. The flash client seems to be a lot more stable. (We used to think that Jakob put it in on purpose because he claimed not to believe it existed. ;-) ). It just became one of those things that we lived with, like IRL sailing stuff happens...masts break, spinnys blow up, rudder shafts give out, etc.
Not saying that what happened wasn't some glitch in the server. After all it did show show bright daylight above 70 N when everyone knows that the sun won't come up in Longyearbyen till Feb 16, 2011.
Posted by
A2


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2009-10-26 00:39:42
2010-12-06 09:58:36 - Re: False TWA = 0
Re: Jack

I am absolutely Positive that I was navigating with a Constant Course Bearing which is why I included that wording in my description.

In my judgment there was something amiss from personal observation and from comments posted in the chat during the race.

My mention of the predictor line was in reference to the time involved to emphasize the gradual nature of my course relative to the coast.

I was reticent to bring this topic to the forum as my placement in this race was not critical (Near 80-90 at the time of these incidents) nor am I involved in the member rankings overall.

I am well aware of all the usual circumstances in which a sailor erroneously claims that the "System ate my boat" & cries Wolf, only to later sheepishly admit to some operator error as the true culprit.

I therefore did not dash off some hastily written J'accuse diatribe in the heat of the moment but rather waited until the race had run its course for me as well as others and then and only then at the behest of RainbowChaser to place these observations here so that they might attract the attention of those who in this particular race had any similar problem.

The purpose of this thread is for those who were so affected to briefly affirm the existence of a general condition rather than a mere isolated incident.

--- Last Edited by Hubert Bonisseur at 2010-12-06 10:07:27 ---
None so blind
Posted by
nacrr


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2010-01-01 15:57:17
2010-12-06 10:25:07 - Re: False TWA = 0
The boat I was sailing was "nacrr" and I was sailing in "cc". I am also sure that I had no forgotten "dc" programmed.
My distance to shore was close but on a clear parallel.
I was in 10th just behind jepsom and it was a clear disappointment to see this happening.
nacrr
Posted by
kalle


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2007-06-01 09:58:04
2010-12-06 12:09:20 - Re: False TWA = 0
Just wanted you guys to know that we keep an eye on this. One question, were you sailing *very* close to land? On some maps SOL allows zooming into centimeter-precision which makes it possible that the precision at which the calculations are made (even though correct) can come into play. I'm not saying this happened here, I simply have no data to support that, but it could be one reasonable explanation.
Posted by
Schakel


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2008-12-19 09:19:00
2010-12-06 12:45:32 - Re: False TWA = 0
Some were. I mentioned to someone that he was closer to land than I ever dared to and that I thought that perhaps that caused it.

HTH, HAND,
Philip
Posted by
A2


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2009-10-26 00:39:42
2010-12-06 13:11:09 - Re: False TWA = 0
Yes I understand your concerns regarding how close is too close.

In my normal experience I was not pushing against the shore to be as close as possible, instead I had made a reasonable turn and then pointed to the end of a perfectly straight coastline. I had indicated where this occurred and you may review the tracks of those boats already mentioned or even bring back back that coastal stretch for further testing if there are any concerns as to whether this was in part due to the higher latitudes at which this race was conducted.

I also recall that Yorkshire Pudding was stymied in like fashion in near vicinity to where these events occurred.

In the recent Norrtelje archipelago. race I indeed came as close as possible, much closer than the race we are discussing, and never once had any unintended interuptions to my voyage.
None so blind
Posted by
nacrr


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2010-01-01 15:57:17
2010-12-06 15:36:36 - Re: False TWA = 0
I was navigating quite close to land, but I still could see a reasonable gap between land and the boat when fully zoomed in.
nacrr

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