Zezo forum:

Post by Gab | 2018-11-08 | 12:17:11

Hello everyone,

I'm quite a new user of zezo (I started my first race a week ago) so I'm still trying to understang how that router works exactly.

For instance, today zezo suggest me to follow a way that has some variations between 120� and 130� TWA. And thoses variations make kind of a zigzag on the map. Do they are really the fastest way ? Or maybe the fastest way would be a constant TWA around 125� but Zezo is maybe only able to calculate with 5� gap ?

How does Zezo works when it calculates the way ?

Thanks in advance, and thanks to the developpers for the work that has already been done.

4 Comments

Post by zezo | 2018-11-09 | 11:15:17

The router works in 5 degree increments indeed, with the exception of optimum angles which can have any value.

You should consult the boat polars to see what's the case. Sometimes it does not matter and the 120-125-130 is just a noise (flat spot in the polars), but there are points where 120-130 is faster than 125 (the line is actually concave)

With what boat, wind speed and present sails did you observe that behavior?

Post by Gab | 2018-11-09 | 12:29:49

I have done only 2 regatta so far. The first was Odyssey 3 (with class 40) and the second is the RDR withe ULTIME. On both regatta zezo gave me that kaind of route.

I would even say that it always give that kinf variations.

For instance, right now with my ULTIME (which is equipped with foils only) I'm currently at thoses coordinates :
28� N 48'35"
41� W 06'02"

The points coming are nearly in a straight line but not perfectly. I have to follow :
1) 142 TWA for 10min
2) 140 TWA for 60min
3) 135 TWA for 20min
4) 140 TWA for 10min
5) 130 TWA for 10min
6) 135 TWA for 30min
7) 130 TWA for 10min
8) 135 TWA for 10min
9) 130 TWA for 10min
10) 135 TWA for 10min

So, first I notices that the time increments must be 10min right ?
Then if I use the green toggle I can see that it crosses the route I discribed on the 10th point but the toggle is equivalent to 137 TWA for 2h50min.

My question is : will I go faster if I follow the 10 points route or is it the same with the "average" route that the green toggle gives to me ?

Average routes are way easier to use because they don't need me to be available steering so often, but are they as much fast ?

Post by Gab | 2018-11-09 | 12:44:20

I juste had a look on my polar and I can see that with 13.1 knots of wind, the polar is perfectly constant between 130� and 125� TWA. Si if zezo tells me to do zigzag by alternating 125 and 130 I can follow an average route with 127.5 TWA and I will even go further because I won't be doing zigzag.

Then if the polar is concave between 125 and 130, I would (most probably) prefer to alternate 125 and 130.

And if the polar is convex between 125 and 130, I would prefer to go 127.5.

Right ?

Post by zezo | 2018-11-09 | 13:34:47

Yep. Exactly. Only it's unlikely that there is a dip between 125 and 130 because the original polars come in 5 degree increments and the data between is result of linear interpolation.

Look at the Ultime, 13 knots, Jib for example of a dip at TWA 85. Alternating between 80 and 90 would probably get you slightly better result there.

BTW I was doing exactly the same thing yesterday - sailing at TWA 127-128 for a while.