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Board » Technical Support » Extrapolating boat performance

Posted by thorenj Posts 3 Registered at 2008-02-26 15:37:52	2013-03-08 14:24:16 - Extrapolating boat performance
	Hi all - SOL developers in particular! As you may have noticed, in the current NYC-SFO race we have had stronger winds than those represented in the boat polar. When I took a closer look at what performance I got in winds of 40 knots or above, it seemed to me that the race server does not extrapolate boat speeds above what can be plotted in the graph in the client. Has anyone else experienced this? If this is an accurate observation, can it be rectified? best regards, thorenj
Posted by Schakel Posts 183 Registered at 2008-12-19 09:19:00	2013-03-08 23:05:56 - Re: Extrapolating boat performance
	Stronger winds don't always translate into higher boat speeds. In 40 knot winds you might want to lower your sails a notch or two. -- Cheers, Philip
Posted by thorenj Posts 3 Registered at 2008-02-26 15:37:52	2013-03-10 13:24:42 - Re: Extrapolating boat performance
	Yes, obviously reefing will be important, but: a) As far as i know, reefing is already incorporated in the (nature of) polars, the boat speeds on beating wind angles seems to indicate this. b) The boat speed gets "stuck" to the maximum speed of the polar plot graph. Coincidence? Since we obviously can't have polars for infinite wind speeds, I believe that extrapolating the highest plotted wind speed will be the most accurate simulation. To improve realism, maybe the extrapolation could in fact be interpolation, but "above" the highest comparing value, to incorporate said reefing and wind angle-dependent factors. best regards, thorenj --- Last Edited by thorenj at 2013-03-10 13:31:57 ---
Posted by 76Trombones Posts 362 Registered at 2009-08-03 18:04:56	2013-03-10 16:20:08 - Re: Extrapolating boat performance
	Many of SOL's more recent polars extend the wind speed range where appropriate, while some of the originals only went to 20 knots. The majority do use 30 knots as the upper limit, beyond which performance is fixed. Most of the publicly available data that we base polars on stops at 20 knots, so that's definitely a factor. Practically, for most of our boats the 30 knot curve is already survival conditions. Our best polars do reflect more limited pointing ability/leeway under storm sail, though I'm always a bit surprised at how capable the offshore boats are, and there is less change than you might expect. Downwind is similar. By the time sea states, rigging loads, safe sailing are taken into account very few boats don't "plateau". 30 knots sustained is a whole lot of wind!
Posted by 76Trombones Posts 362 Registered at 2009-08-03 18:04:56	2013-03-10 16:27:50 - Re: Extrapolating boat performance
	Three more considerations SOL's polar display used to only go to 30 knots, regardless of how much data was in the polar. Aaron fixed this. We've made limited use of polar curves that "cross" (as reduced speed higher wind curves would) as there has been concern expressed that the result is confusing. SOL's interpolation has trouble at extremely wide tacking angles (can work around, but extra care needs to be taken when crafting the polar). Any effort to "accurise" existing or new polars can count on my full support though! All ears.
Posted by Sebensa Posts 70 Registered at 2010-10-06 14:50:36	2013-03-10 16:59:29 - Re: Extrapolating boat performance
	I, for one, am so pleased to see that one of the "guru's" of this sailing club, is still watching/alive/interested! Thanks "76" R
Posted by thorenj Posts 3 Registered at 2008-02-26 15:37:52	2013-03-13 12:06:30 - Re: Extrapolating boat performance
	I only have some limited experience working with polars, mainly from my bachelor's thesis in hydrodynamics, but i would suggest something along the lines of: BS(TWS)=BS(max polar TWS)+(TWS/(max polar TWS))x((max polar TWS)-(2nd max polar TWS)) Hope I got that right... /thorenj --- Last Edited by thorenj at 2013-03-13 12:06:55 ---

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