LS: Class 40

Class40 polar graph for LiveSkipperThe set of sails on LiveSkipper’s 40ft class boat consists of a jib, a genoa, a code 0, a reacher and a runner. A composite of the full set results in the graph shown here.


As with the other polars, a little tweaking is required if the polar is to be used in Bluewater Racing. After converting it, with the conversion tool for example, replace twa2/bs2 and twa9/bs9 column with the optimum upwind/downwind VMG values listed below.

twa2    bs2      twa9	bs9
41      5.4      140	5.8
35      7.2      152	8.4
35      7.6      152	10.2
35      7.8      150	12.3
35      7.6      152	14.5
37      7.5      156	16.5
35      8.1      160	18.1
35      5.7      161	14.8

TWA/TWS	0	6	12.0	16.0	19.0	23.0	27.0	31.0	39.0
0	0	0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
45	0	5.7	8.0	8.3	8.5	8.5	8.3	8.9	6.3
60	0	6.5	8.6	9.1	9.4	9.6	9.8	10.2	7.2
75	0	6.9	9.2	9.8	10.2	10.8	11.3	11.8	8.5
90	0	7.1	9.6	10.5	11.3	12.1	13.0	13.8	10.2
110	0	7.2	9.9	11.2	12.5	13.6	14.9	16.0	11.8
120	0	7.0	10.1	11.6	12.7	14.1	15.5	16.9	12.6
135	0	6.2	9.6	11.7	13.5	15.2	16.7	17.9	13.6
150	0	5.0	8.6	10.4	12.3	14.8	17.2	19.1	14.7
180	0	3.66	7.1	8.8	10.0	12.1	14.4	16.3	13.5

Update: The full Class40 polar suitable for use with Bluewater Racing can be downloaded from here.

4 thoughts on “LS: Class 40

  1. Have you done any tests between polars optimized for BWR and non-optimized?
    TBH I cant say I saw much difference the one polar I tried it for, hence havent bothered since. Also, thinking about how the route time is computed, the optimizer knowing explicitly which are best UW/DW VMG angles shouldnt really make a difference ?? Unless you are routing an olympic course ;-)
    This aspect of BWR has had me scratching my head for a while now…

    • Well, I didn’t really test this thorougly but I did notice differences between the optimized and the non-optimized polars, especially when the optimum VMG angle is way off like it is with this one, sometimes off by 10°. In those cases, if you check the estimated average speed, it is not even close to what is possible. I was planning to do some testing and when I get the time I’ll post about it then.

  2. Well, I now have a tool to output optimised BWR polars [http://wp.me/P1pn1p-3G], and they sure shouldn’t produce SLOWER routes, so as its about 6 seconds to make a polar with the correct VMG angles (a little longer if it downloads the data from SOL) – we may as well use polars how BWR likes them ;-)
    I actually thought after that prev comment that perhaps the optimization algorithm may take some shortcuts/make assumptions about TWA when it gets close to up/downwind ?
    TBH though I often did very well with non-optimised polars in BWR (very close to winning IMOCA L5 on SOL – stupid DC error that lost it for me with 300nm to go!! :( )

    • Well, I may have to reconsider what I said about the polars. I did a quick comparison and there was very little difference between the two. Mind you, only small sample size. I was using weather gribs from the LiveSkipper site, but I now am using the ones from zyGrib and it gives far better result. LS uses a 0.5 x 0.5 grid size and BWR would crash if I used a grid size of 2 or smaller. With zyGrib’s gribs, I can even set BWR to 0.5 without any problems at all. Just takes longer to compute.

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