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Board » Technical Support » qtVlm thread

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Posted by
Zorba777


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2020-06-06 08:22:54
2020-10-02 08:55:45 - Re: qtVlm thread
Hi Satori. I liked your Rum Run report. Figuring out how to squeeze a little bit more out of QtVlm routing is part of the fun for some of us. I think you are on the right track with your experiments. I am still learning too, but some of the things I try are:
1) Using barriers is a good way to force the routing to go around a buoy, or to close off possible paths that lead nowhere (like dead end fjords) and thus made the routing faster.
2) Another way to optimize/simplify faster is by using the "Selection" tool (blue square icon) and only optimize/simplify on that selected part. Much faster, especially on multi-day routings.
3) Watching the isochrones unfold during a routing is important to spot tactical alternatives. I mark them with waypoints and then do separate routings from boat to those waypoints to see how much they differ in time and to see which routes are improving (or getting worse) on subsequent WX updates.
4) As you pointed out in your report, with tallship polars QtVlm can sometimes struggle with the polar hops. You can then see the isochrones behave strangely and may even fall apart completely. Then you have a very unreliable routing. In that case try to route again with longer steps.
5) Varying the step can also give you routes that optimize better. 30 minutes or even 1 hour steps will sometimes give you quicker routes that a routing with 5 minute steps didn't find. Experiment.
6) It's also important to verify. Your boat position after 4 or 5 hours should be very close to where your used routing indicates it should be. If not you may be on wrong polar or be using an out of date grib. Both have happened many times to me. Checking where my boat is helps me to spot those problems.
7) When the routing tackes/gybes a lot it is often useful to adjust the route manually, before simply/optimize. Reduce the number of tacks/gybes can give you a faster ETA.

Good luck.
Posted by
dtayls


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2014-06-23 03:34:16
2020-10-03 04:41:53 - Re: qtVlm thread
Interesting. I wasn't aware of the 'selection tool'. I'll have to give it a go.
Posted by
Zorba777


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2020-10-26 15:07:51 - Re: qtVlm thread
@Satori Another great race report for the recent Hatteras Sprint. I have had a busy week, so here are my belated comments to some of the points you raise about Qt routing.

It's important to experiment with some settings and find what works for you. This may vary depending on the boat polar and on the type of race.
I always set my crank duration to 1 minute for max accuracy. Simplify/optimize the route will reduce the number of DCs anyway.

In the boat settings for "tacks and gybes" is where many SOLers probably use very different values. This is the part where Qt is the least accurate because the PL loss formula in SOL differs from what Qt does. I prefer to set both tacks and gybes to 97% of polar speed for only 1 crank. In reality, depending on the wind speeds, my PL penalty will be more than that. But I will take that into account when I clean up my route. With those settings I know it will tack and gybe more often than needed. I manually improve my route when it has lots of tacks, as was the case in first part of the race here.
I just tacked manually going on max VMG, and I didn't use the intermediate tack to try to limit PL. In this case the boat speed was mostly around 7 kts. My PL always recovered to 100% within 1 or 2 server updates. Then I don't believe you can gain much by going on a lower speed for 10-20 seconds. That's like giving yourself a 30% performance penalty for 1 or 2 server updates. That doesn't pay off.
At boat speeds of >12kts it becomes another matter.

Where the router was very helpful (and will usually beat sotp navigation) is in the curved passages we had just before and after Hatteras inlet. I believe that's where I gained some time on most of the other boats. This are the type of passages where you can let the wind steer your boat without getting any PL. That's what I did here. I kept switching between COG and TWA to turn my boat to the wanted COG directions.
At Cape Hatteras turn it was of course straightforward, no router needed. Being only 0.01 NM behind I knew there was a chance to win by taking a bit more risk.
What I do there is set a DC that will turn about 10-12 seconds after the Cape. But at the same time I am ready to turn my boat a little bit earlier with a direct command. In this case I probably pushed the command about 8 seconds before the DC would have fired, when I eyeballed my boat to be right at the corner. That put me on inside with a slightly better angle.

It is really small differences that decide this kind of races. You have to squeeze out every inch you can, because many others are doing the same.

For short races like this one I route with 5 minute step. In longer ocean races I usually do 15 or even 30 minute steps. But it is important to test and compare with other step sizes. In some case you get better results with longer steps. Testing = knowing.




Posted by
Zorba777


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2020-06-06 08:22:54
2020-10-28 10:01:56 - Re: qtVlm thread
@Satori On the topic of NMEA failing to connect. I have had it a few times, but not nearly as often as you report.
Up to know I have always fixed it by closing both AGL and qtVLM. Then first restart AGL and wait until it has properly connected. You can see when it has connected to server. Can take as much as 30 seconds.

Then I restart qtVLM and it always connects to NMEA very quickly.

One thing you may want to check. Click on the boat in top-right in qtVLM to open a bunch of tabs. There is a tab for NMEA and there you can change the "update interval". Mine is set to 3 seconds. You may test and see if other values solve your problems. May too often can cause a bottleneck. Or too infrequent may cause connection loss. Just try.
Posted by
Dingo


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2013-03-09 04:23:58
2020-12-10 09:59:40 - A QtVlm beginners tutorial
Attached is the gist of the email I sent to Satori who has indicated he will tidy it up and post it somewhere when he has the chance. Meanwhile, this might help get a few more SOLers into QtVlm and routing in a fairly simple way with instructions which follow the normal sequence of routing using QtVlm for SOLing.

I'll monitor for queries and suggestions and try to incorporate what I can into the tutorial as time permits.

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Posted by
Dingo


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2013-03-09 04:23:58
2020-12-10 11:08:45 - Re: qtVlm thread
One configuration setting which is useful to adjust is under the advanced tab. There you can adjust the amount of detail shown in coastlines. For more detailed routes near land it could be useful to raise the level of detail.
Posted by
RainbowChaser


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2009-06-14 09:44:50
2020-12-18 17:56:44 - Re: qtVlm thread
Dingo - would you be happy for me to include that as a QtVLM Quick Guide under the Links tab?
Posted by
Henrys


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2010-03-07 13:33:35
2020-12-21 11:39:24 - Re: qtVlm thread
Hi Dingo or anyone for that matter. Question...How do you copy a Location from qt to enter into aGages Optimum Angles Tool to work out the best VMC?
Posted by
Jawz


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2009-07-21 09:51:19
2021-01-02 13:48:06 - Re: qtVlm thread
I have worked it out. The coords must be decimal and without the degrees symbols. Set this up in settings. Otherwise its the same almost. Alt and click then there is a box that opens up. Copy the coords into Agages tool and remove the symbols and off you go!
Posted by
Silvarius


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2020-05-09 13:50:09
2021-01-25 21:24:01 - Re: qtVlm thread
Hello,

I'm new to SOL and I am trying to connect the game to qtVlm ... with some difficulties :-)

I am using the brainaid proxy server to export NMEA data to qtVlm. The server is properly running and qtVlm receives now a NMEA feed (NMEA raw data window shows it).

The brainaid server receives data from a boat that is sailing in the "Shetland race 2021".

The problem is that nothing happens on the screen. The race WP are not shown, my boat is not positioned and all instrument are inactive.

Once qtVlm receives properly the NMEA feed, is there any other setting that is to be activated so that the feed can be processed concretly? Or maybe the feed itself doesn't contain the proper data?

Has anyone of you already had this kind of problem in the past?
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