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» Online Classroom   » Marine Weather   » Public Discussion of Marine Weather   » TWA with qtVlm

Author Topic: TWA with qtVlm

 - posted July 20, 2021 06:10 PM      Profile for vserbin           Edit/Delete Post 
Is there an easy way to set up constraints on TWA when calculating the optimal routing with qtVlm? I am evaluating against OpenCPN and I find qtVlms's routing to be easier to use and less error-prone. On the other hand, it is quite simple to set up limits on TWA in OpenCPN, and I have not found an equivalent in qtVlm.
David Burch

 - posted July 20, 2021 08:51 PM      Profile for David Burch           Edit/Delete Post 
Let me look into this and get back to you.
From: Starpath, Seattle, WA
David Burch

 - posted July 28, 2021 12:36 PM      Profile for David Burch           Edit/Delete Post 
Sorry for the delay. I wrote this out the next day, but seems i did not post it.

In the base system the routing will not cross over from green to red in the TWA seen in the polars (menu Boat/Polars/Wind polar analysis). That demarcation is determined by the shape of the polar. But if you want to override that, you can Force these limits to be what you want.

Do this in menu Boat/Boat Settings/Polar

I believe that is the action you are asking about.

Then run a route with and without the forcing and then look at the logbook (record of TWAs in use) to see that it is behaving as you desire.

From: Starpath, Seattle, WA

 - posted July 29, 2021 05:50 PM      Profile for vserbin           Edit/Delete Post 
Thank you David! Seems like you are talking about
Boat -> Boat Settings -> Polar -> Set Best Angle
Or maybe not? I did set the best angle limits to 50 and 160, and indeed that's where I see the demarcation line between green and red when I do Boat -> Polars -> WindPolar Analysis. However, after computing a routing/route, I still see TWA angles of 170 or so. What I am doing wrong?

David Burch

 - posted July 29, 2021 06:24 PM      Profile for David Burch           Edit/Delete Post 
Please send me the polar, the grib file, the start and end points and the starting time and we will have a look.
From: Starpath, Seattle, WA

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