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Board » Technical Support » Something weird happened at Sydey TSR

Posted by JakeS Posts 18 Registered at 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 Attachments sidney_TSR_9.10.___1943.jpg (189.4 KB)
Posted by RainbowChaser Posts 2656 Registered at 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 ________________ --- Last Edited by RainbowChaser at 2013-10-09 17:12:16 ---
Posted by JakeS Posts 18 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 Posts 346 Registered at 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 --- Attachments fullrigger_polar_negative_speeds.png (35.2 KB)

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