Trying to use Zezo to select best combination of sails to select
Post by iconPost by Pierre | 2021-02-08 | 22:29:56

Hi,
Another question from a beginner (less beginner after Vendee Globe, and still enjoying it. Thanks a lot!) As I don't buy full packs, I'm trying to use Zezo to guess which sails I should select for the race.
For Tara 3 for example, I ran zezo without additional sails, look at the ETA, and then I tried different combinations of sails to see which one gives the best ETA.
I find results that I do not understand:
-The ETA is always the same whatever the combination of sails I select. Only when I select full pack I see an improvement. Does that mean that taking one or two extra sails is useless for this race if I do not buy them all ?
- On parts of the route, I noticed that when I do not add sails, the Jib is used. If I select light sails, it get used on the same part of the route, but the speed is less than with the jib on the first test. So why is the light sail used in that case as the jib would bring a better speed ?
I had similar results for Sydney - Auckland

commenticon 6 Comments
Post by iconPost by Hardtack | 2021-02-09 | 13:40:15
In my experience ETAs do vary with the set of sails, but the difference depends on the weather, duration and the course itself. If you're using 'pro' sails, you should always enable the 'winch' option because the speed bonus can easily be nullified by the additional sail change penalties. Selecting 'Full Pack' automatically enables 'winch'.

Regarding your second observation - the router cannot use an inferior sail by definition, but the router will trade speed for distance as required to find the best route. The resulting route can be very different for a faster boat.


Post by iconPost by Pierre | 2021-02-09 | 16:00:11
Thanks Hardtack for your details answers as always!

Post by iconPost by Pierre | 2021-02-10 | 13:38:12
Just did more investigation. Indeed, selecting Winch Pro really makes a difference. I did not think it was so efficient!
Post by iconPost by SummerIsles | 2021-02-18 | 16:05:30
Anomaly? How come this ship is notably faster at TWA 48 degrees in 17.5 kts wind than in 18.5 kts wind? The difference is at least half a knot faster at the lower wind speed! (8.54 kts boat speed at the lower wimd speed vs 7.83 kts at the higher wind speed). Polar diagram confirms this, but why!?
Post by iconPost by BooBill | 2021-02-18 | 16:30:52
If you are talking about the Maxi Tri, that's where the cross over occurs between the Light Jib and the Staysail. That's a pretty realistic aspect of the polars. You've often dips in the polar where you have gaps in your sail inventory.

Little related tip. If the router oddly wants you to alternate back and forth between 2 TWAs that are 10 degrees apart, that's probably because the angle in the middle corresponds to one of those dips. That's always a signal to check the polar chart.
Post by iconPost by SummerIsles | 2021-02-19 | 20:49:06
Hi BooBill,
I had mean the Tara Ocean boats, but thanks anyway. Interesting info. I wondered if it was windage on the big hull and also maybe the sea state increasing and slowing you down.

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