VMG and zezo are not good friends?
Post by iconPost by wakeup | 2020-05-31 | 21:43:17

I am surprised that zezo very rarely propose the VMG as the good route?
Of course sometimes you have to luff up or bear away because of Wind rotation but sometimes you just have to make VMG route and zezo very rarely propose it?
Is it a silly question?

commenticon 4 Comments
Post by iconPost by BooBill | 2020-05-31 | 23:18:47
If you are close to the front in the Tahiti race, there's going to be a gybing duel for the next few days. Sail max VMG on each tack and see how your gap to the leaders is.

Difference in VMG between max and sheeted in 5 deg is tiny. Difference in boatspeed is huge. There are often times that you want to make it to stronger wind faster. Since zezo knows where all the puffs are with certainty till the next update, it's often steering towards wind at the expense of max VMG. IRL you could never do that, since you never know with precision where the puffs are going to be.
Post by iconPost by wakeup | 2020-05-31 | 23:37:03
OK got it. In fact I am close to the front in Tahiti race and I am really hesitating between VMG and following more accurately zezo's routing ;) .
I'll try to manage it the best way I think it could be (and probably loose compare to follow zezo :-D ).
It is now time to program for the night.
TY.

Post by iconPost by YC6211 | 2020-05-31 | 23:39:53
You need to try to figure out why zezo is routing you where it is. Is it sending you into more breeze? Is there a subtle shift it's positioning you for? Zezo will tell you to sail VMG if it's the best route, if it's telling you to do something else it has it's reasons.
Post by iconPost by zezo | 2020-06-01 | 07:46:44
The router knows the VMG angles, but does not have a preference for them, and as noted above, sometimes the polars are quite flat around that spot, VMG-wise.

That's is why the red and green line of the projected track exist - they let you compare a fixed TWA/HDG course against the isochrones and decide yourself where to point the boat.

My usual process is to check the projected track then check the polars for the VMG and possible sail changes, also for sail crossover points.

Sometimes polars have dips that make it faster to sail TWA 65 and 75 alternatively instead of straight 70 - See the Maxi polars at 16 knots TWS (also at TWA 130 there). The router usually gets that, but still may not propose the exact optimum route, or may suggest a change more often than needed.
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