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Board » Technical Support » Something weird happened at Sydey TSR

Posted by
JakeS


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2012-09-25 16:23:40
2013-10-09 17:02:40 - Something weird happened at Sydey TSR
I try to set my boat to cog 262.2... (to get to pr start) and that kind of predictor line came up (see pic). I try twice, same both times . . . and as you can see my bs is -0,03 and twa is 51.65 :)
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Posted by
RainbowChaser


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2009-06-14 09:44:50
2013-10-09 17:11:37 - Re: Something weird happened at Sydey TSR
As discussed in race chat - there is nothing weird (fortunately)... its just how tall ships are. Best VMG is around + / - 72d :-)
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--- Last Edited by RainbowChaser at 2013-10-09 17:12:16 ---
Posted by
JakeS


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Posts
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Registered at
2012-09-25 16:23:40
2013-10-09 17:19:34 - Re: Something weird happened at Sydey TSR
Sorry my mistake. Was just thinking that twa +50 usually move you boat forward not backward. Did not remember that we sail by TSR boats :)
Posted by
kroppyer


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2010-02-05 15:25:55
2013-10-09 18:08:00 - Re: Something weird happened at Sydey TSR
The square rigger polar contains negative speeds. This was, as far as I can tell, not intended. I think it's a result of the spline calculation that was used to create the polar. The designer probably set some values like
twa -> sog
0 -> 0
20 -> 0
40 -> 0
55 -> 0
60 -> 0.3
65 -> 2.3
70 -> 4.3

And then the computer was used to make a smooth line through these points to determine the values in between. The algorithm that did the smoothing was not told it could not use negative values to make the line smooth.

Tall Ships are probably the only polars that have this, as no other boat would have a SOG of 0 when TWA != 0

.. ok, that was a poor explanation... but I added a nice colourful picture to make you all happy again :)
It's the polar, zoomed in to the centre, you can see the loops that were the result of the spline calculation.

--- Last Edited by kroppyer at 2013-10-10 05:10:39 ---
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