Integration with QtVlm - Data files and Import/Export

[maitai]

FYI you can display the polar in a similar way in qtVlm. Just press "L". You can also ask it to follow the interpolation point of a particular route if you move the grib's date.

[jonasaberg]

Good.

I still think it could be valuable as a part of OpenCPN proper. My thinking is that even if i don't do a full routing it can still be valuable to use as a what-if tool to play around with.

Example: In my waters it is quite common with fluctuating weather patterns. A low or high that blows past some distance away. When it passes the wind direction and speed will vary heaps.

Since prediction of the speed of the centre of the low can vary, this gives a "time fault" in the prdiction. The prediction might be quite correct, but the timing off. So, by considering this and the use of the polar, you can play with the timing of the grib and the position of your boat and check how this might affect your possible options.

[sinbad7]

Jonas and rgleason..

Could not agree more,but how would you react to Thomas´s ´quote´ ?

All forecasts are just forecasts; they are not statements of fact. It is my view that if you do not understand these simple facts and are not prepared to put some of your own thought into forecast interpretation, then you are probably better sticking to rowing boats on the Serpentine - in settled weather, of course!

Sorry,but I am not one for ´turning the other cheek´ you get what you give,and if that is too much for you,rethink your postings before you make them.

I got a bit tired telling Thomas all the time that this was for PLANNING purposes.
If you do´nt take anything seriously why introduce qtVlm at all?

As I concluded in my last email:
"I suggest we all take a deep breath and stop this inane and futile banter."

Tore

[maitai]

Originally Posted by jonasaberg

Good.

Since prediction of the speed of the centre of the low can vary, this gives a "time fault" in the prdiction. The prediction might be quite correct, but the timing off. So, by considering this and the use of the polar, you can play with the timing of the grib and the position of your boat and check how this might affect your possible options.

In qtVlm in the routing module you can choose "what-if" scenario. For instance what-if the wind is stronger than predicted by the grib, or what-if the weather moves faster/slower than the grib. Analysing the inversed-iso shape is helpful too to make a decision.

[rgleason]

Gribs are about wind (and increasingly current) predictions, one component of Weather. Yes we are best served developing our own understanding of weather. Gribs are one way to help visualize, but should not be accepted verbatim as they change as fast as time.

[sinbad7]

Thanks to maitai,here is a sample of the route PLANNING information
you will have access to in the next release. The suffix in the DNM should
be ´nm´

I like the compass rose in qtVlm and I have created a moveable POI
for the purpose..

Tore

[wdkester]

1. I try to do a "routing" POI1 to POI2.
2. I get a message "No Polar loaded".
3. I go to boat>Polar analysis, and I get the attached screen
4. "Reload Polar" doesn't do anything useful.

I've tried to deleting the qtvim folder and going back to the compressed files but the problem remains. I need to trick qtvim into thinking that the boat has no polar diagram at all.

[maitai]

You cannot create a routing (and many other things) if your boat as no polar. Go to Boat->Boat settings and choose an existing polar (or you can create your own)

[wdkester]

Originally Posted by maitai

You cannot create a routing (and many other things) if your boat as no polar. Go to Boat->Boat settings and choose an existing polar (or you can create your own)

OOPS! I had loaded a polar sometime in the distant past, but it seems to have gone missing. sorry.

However, I do have another question on the polar files.

Looking at the csv files I see
1. a header that contains a string of wind speeds delimited by ";"
2. followed by lines containing a wind angle and boat speeds for the wind speeds,also delimited by ";"

I have found a polar for a boat similar to mine, that looks like this:
WindVelocity 6 kt 8 kt 10 kt 12 kt 14 kt 16 kt 20 kt
BeatAngles 45.0° 44.7° 43.6° 41.2° 40.1° 39.4° 39.2°
BeatVMG 2.58 3.18 3.69 4.01 4.19 4.29 4.38
52° 4.03 4.97 5.54 5.85 6.09 6.21 6.32
60° 4.32 5.28 5.73 6.04 6.28 6.46 6.59
75° 4.62 5.55 6.01 6.32 6.45 6.66 7.00
90° 4.89 5.72 6.17 6.52 6.80 6.94 7.15
110° 4.81 5.69 6.15 6.51 6.83 7.14 7.71
120° 4.57 5.55 6.03 6.39 6.72 7.02 7.62
135° 4.02 5.09 5.73 6.13 6.46 6.77 7.36
150° 3.41 4.39 5.27 5.79 6.17 6.49 7.07
RunVMG 2.96 3.80 4.61 5.28 5.75 6.11 6.70
GybeAngles 147.7° 153.1° 157.0° 169.6° 174.4° 175.8° 176.3°

My question is this, can I just map this data into your format and save as a csv file in the polar folder?? Should I delete the BeatAngles and GybeAngles lines? Should I change BeatVMG to 45 deg and RunVMG to 180 deg?

Thanks for your help

[maitai]

You can do that safely. Don't put the beatAngles, the gybesAngles lines etc, qtVlm will compute that on its own.

Some tricks though:

The first cell must contain "TWA/TWS"
The first line should be 0 TWA and the first column should be 0 TWS (this is already useless in the next version, but as of now you must have these 2)
You can put whatever value in TWA/TWS headers (for instance 15 degrees step, wind by 0.5 kts), even not regular (i.e. 0kts, 10kts, 12kts, 23.5kts, etc), but then all cells must have a value. No hole allowed.
Beware of openOffice that will probably generate " characters that won't be accepted by qtVlm (this is fixed in next version already)

Now to come to your particular polar, you should first add TWA 0 and TWS 0 (with 0 values, easy). Remove all the fancy lines concerning best VMGs and such. Remove the degree character, and add TWA/TWS in the first cell.

There is no values above 20 kts TWS so qtVlm will assume 60kts wind is the same as 20kts... You should do something about that

[Zoef]

I was in the same situation. By putting my data in the "standard" format, including the colum and row of zero's I got a working polar.
This is it for me:
TWA\TWS;0;6;8;10;12;14;16;20
0;0;0;0;0;0;0;0;0
45;0;3.20;4.00;4.50;5.00;5.60;5.70;5.80
49;0;3.50;4.30;5.00;5.50;5.65;5.80;6.00
52;0;3.70;4.57;5.29;5.79;6.05;6.21;6.40
60;0;4.09;5.00;5.75;6.12;6.39;6.58;6.75
75;0;4.42;5.44;6.03;6.39;6.67;6.89;7.21
90;0;4.38;5.40;6.09;6.52;6.85;7.09;7.33
110;0;4.37;5.49;6.16;6.60;6.94;7.24;7.78
120;0;4.20;5.29;6.04;6.49;6.84;7.15;7.70
135;0;3.72;4.74;5.66;6.19;6.58;6.90;7.48
150;0;3.18;4.13;5.00;5.76;6.22;6.59;7.18
160;0;3.10;4.10;5.00;5.64;6.20;6.57;7.19
172;0;3.10;4.00;5.00;5.52;6.10;6.55;7.20
177;0;3.00;4.00;5.00;5.40;5.90;6.35;7.03

[maitai]

Same remark as above, you miss data after 20 TWS. At least add a column with 70TWS full of 0's, so qtVlm understands your speed decreases after 20kts. Also a good idea would be to systematically have something for 180 TWA, otherwise it might trick the best VMG downwind (in your case with 177 it should be OK, but don't end the serie with 160, that's not enough). Knowing the speed at 180 TWA is important to calculate best-vmgs downwind, and this time we cannot guess them (upwind a 0 TWA we know the boat's speed is 0)

[wdkester]

Hi Maitai,
My polar is now:

TWA\TWS;6;8;10;12;14;16;20;60
0;0;0;0;0;0;0;0;0
10;0;0;0;0;0;0;0;0
20;0;0;0;0;0;0;0;0
30;0;0;0;0;0;0;0;0
40;2.1;2.5;3.0;3.5;3.6;3.7;3.8;1.0
45;2.58;3.18;3.69;4.01;4.19;4.29;4.38;1.0
52;4.03;4.97;5.54;5.85;6.09;6.21;6.32;1.0
60;4.32;5.28;5.73;6.04;6.28;6.46;6.59;1.0
75;4.62;5.55;6.01;6.32;6.45;6.66;7.00;1.0
90;4.89;5.72;6.17;6.52;6.80;6.94;7.15;1.0
110;4.81;5.69;6.15;6.51;6.83;7.14;7.71;1.0
120;4.57;5.55;6.03;6.39;6.72;7.02;7.62;1.0
135;4.02;5.09;5.73;6.13;6.46;6.77;7.36;1.0
150;3.41;4.39;5.27;5.79;6.17;6.49;7.07;1.0
180;2.96;3.80;4.61;5.28;5.75;6.11;6.70;1.0

Engine is off at 0.0 knots

The plot I get doesn't make sense to me. It starts off directly into the wind for 6 hours. I would expect to see some big tacks to get to the turning point. I 've looked at he grib and the wind changes very little over the time it takes to get to the big turn. The course is fine for the next 12 hours to the destination.

[maitai]

David,

Your polar is not correct.

First of all you need to add the 0 TWS column. This will not be needed in the next release but as of now it is compulsory.

Then even with that, the numbers are not realistics. Your VMGs are jumping from 165 to 120 very quickly, I doubt a boat can behave like that

You can use boat->polar analysis to see the problems. You can at the same time edit your polar file for instance in excel, and each time you make a change save the file and click "reload polar" in qtVlm, which will display your updated data. Also note that you can click-drag the mouse in the diagram to see more data.

[wdkester]

Maitai,

Thanks for the help. When I added the zero column, the plot looks a lot better. Upwind optimum vmg is 52 deg which seems to me to be reasonable; downwind is 172 which seems too high.

The boat is new to me and I have only taken 1 longer trip. I don't race. Like a lot of folks, when I need toget somewhere before dark, I motorsail. The two key useablilty features, for me, are the "motor allowance" and the "route simplify". Nice job!

If anyone knows where there are a set of polars for a Columbia 8.7, let me know.