20171031 Clipper Leg 3. Caution: Discrepancy between polar diagram and actual boat speed
Post by iconPost by Alexandria | 2017-10-31 | 12:58:49

Recently, Cvetan said VR is using the proper Clipper polars for Leg 3.

So, today I took a bit of time to check the polar diagram available here against the actual boat speed.

I had in mind a polar hump that was characteristic of the boat in the previous edition.

Well, it is there.

At a TWS of 10.6 knots, the boat speed stops increasing when the TWA reaches 50-55 degrees, and even decreases as TWA increases to 70 degrees (already Code Zero region).

The relevant screen captures are at https://1drv.ms/f/s!AqbPXGCYaCXN6DchJleupJc3dOYO.

My guess is that they are using the Clipper 2015 polar diagram, which I happened to find ar http://gwranking.forumactif.org/h10-outils-pour-vrtool.

If this is correct, the routing suggested may be significantly affected, to the point of becoming useless.

I am sending this to Cvetan, so that he can see what's happening and fix it if necessary.

2017-10-31 1058 UTC

commenticon 4 Comments
Post by iconPost by zezo | 2017-10-31 | 13:14:47
Oh, I fixed it yesterday, but forgot to touch the parameter that would expire the browser cache (many files are heavily cached for 24 hours to save traffic and loading time)

Control-Shift-R or similar would do the trick, now simple reload should suffice. The router itself used the proper polars for the past 20 hours or so.
Post by iconPost by zezo | 2017-10-31 | 13:20:15
I also posted an update here http://sail.zezo.org/forum.pl?tid=6082, dated 2017-10-30 | 16:24:11 (EET) bit it got lost in the noise ;-)
Post by iconPost by zezo | 2017-10-31 | 13:28:18
BTW there is a simple check if the router and polars match - the track tool uses the same files as the polar chart, so if the projected track matches the isochrones and the polars look fine then everything is OK.

But you may have to clear the browser cache first to be sure.
Post by iconPost by Alexandria | 2017-10-31 | 14:48:51
Thanks!
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