In the old days I used to buy a Danish boat magazine, called Bådnyt (Boatnews). In it there were frequently shown tests of new boat designs. The tests always included a heel-to-righting- arm curve and a polar diagram. The polar diagram mostly showed the results in two wind-strengths, and with and without spinnaker.

What the polar diagrams all had in common was that the speed dropped rapidly when the true pointing angle approached 45°. Sometimes the best VMG to windward was achieved when pointing 1-3° lower than 45°, and on a few of the best boats, the best VMG was achieved  at 43-44° from the wind. There was no way they would sail at 30° from the true wind.

Now I had another look in Tony Marchaj’s “Sailing Theory And Practice”. ‘Fully close-hauled’ in his diagrams is 30° to the apparent wind direction.

Those I have spoken to about this, have been happy to sail at 30° to the apparent wind. My own wind indicator on my Marieholm IF is set to 32° and I am happy enough when I sail within that angle. In practice, that means that I tack just a bit inside 90° on the compass.

I therefore have to say that I am sceptical to some of the shown results for the Smoothed STW (speed through water). On Poppy the results look half-realistic (..but alarmingly good...), with the VMG t.w. culminating some 45-35° from true wind. However, I find it hard to buy the results of Calisto, which appears to improve the VMG all the way up to 30° from the true wind.

Another thing:
The way the VMG is shown is confusing. Unless I am totally wrong, the VMG is the horizontal component (in these diagrams) of the STW, either straight upwind or straight downwind, so it makes no sense to draw it as a polar diagram, or in fact draw it at all. If we have the STW at a true angle to the wind, then the VMG will show itself automatically (if one knows what to look for).

Conclusion:
In case the numbers are right, and I am wrong, these boats (in particular Calisto) must be real world beaters.

Arne

Anonymous wrote:

Robert,

that was very impressive numbers. I have never seen polar diagrams where the boats sail 30 deg. from the true wind direction before. 

Could this be apparent wind angle? In that case, the  VMG to windward will not make sense.

Arne

Your question is really for those who collected the data. The apparent angles that translate to the true wind "30 deg"  bin, i.e. angles between 25-34.9 degrees is in the data.....and often lots of them....see plot for Calisto below...lots of msmts around the 30 deg mark.

In # 6902791 Slieve reasoned that whoever was steering Poppy during the test runs was using the installed electronic devices. If you step down in time through the Poppy csv enclosed you'll see what looks to me like pinching up to lower apparents/trues then falling off. That's the only explanation that I can come up with. Each blue data point is 1 second of time...so my inclusion minimum of 100-or-so points is only 3 minutes of data spread out over hours.

I'm wondering what the polars would look like if measurements were on Ketil G.'s fjord flyer. Hasn't he wrote in the racing forum going 20-something degrees apparent? I wonder if the builder of the X-99 yacht has published its polars for comparison? 

rself 

Here are some results for Calisto (bermudan) and Miranda (aerojunk) below.

Now that I've seen results for all the boats; for comparisons, I'll stick to true wind speeds where most of the boats had good sample sizes which means: 6 knts,8,10,12,7,9,11.

In prep are pdfs showing polars for 1) all boats, all even wind speeds, 2) all boats , all odd wind speeds, 3) scaled stw's (Alan's factors) all boats, max upwind vmg's, max downwind vmg's and beam reach (90 deg) stw's.

The rescaling, i.e. multiply STW's by Alan's factors, I think attempts to isolate the effects of the rig type by correcting for the boat's characteristics ...length, displacement, sail area, etc.

rself

I've put the vmg's onto the polar plots. See examples, formulas and vector plots. The vector angles and magnitudes from CAD match the formula results. Point scatter of vmg's not shown...not visually different from stw's. 

All completed plots here:https://drive.google.com/drive/folders/1d5lF1XT4DlbX9-ie7WZpWFcVDLl9FPbm

or https://drive.google.com/drive/folders/12SnnPouRegorGlzFRwViCk-fRIQeMHgq

Plot interpretation--the red square is the median boat speed (STW knts) in the direction shown (TWA deg). The aligned green circle is the boat speed (VMG knts) straight up- or down-wind. So if traveling 90 deg to the wind direction your vmg approaches zero. Plots make sense.

rself

Anonymous wrote:

Anonymous wrote:

Ideally, we should write our own software for the recording programme as the prospects of getting the authors of NavMonPC to update theirs seem slim.

Hi Alan--Question about the processing steps:

1. All the data collected by the electronics is in the .txt files (??).

2. .txt files read by NavMonPc --- user sets some parameters---then outputs a .csv file.

So date, time, aws, awa and port/stbd information are all in the .txt file?

Found a Matlab nmea decoder in the Mathworks file exchange but none of $G--strings in your files match the strings in the prog. Do you have a source for the sentence definitions?

I'll post first half of Poppy results pretty soon.

rself

I think David has answered some of these questions, but the sequence is not quite as you describe, in that the .txt and .csv files appear to be recorded simultaneously with NavMonPC adding the time stamp to the .csv file and recording only pre-selected data, but the selection does not seem to be under user control. We have to start and stop the recording of each file manually on the laptop at the start and finish of each run.

I did play a bit with trying to set up filters in NavMonPC (to eliminate the non-existent GPS data) but it seems they only work if we send the output elsewhere. They did not seem to affect the .csv file recorded by NavMonPC.

I can't recheck that as I have sent all the electronics to David so he can try out and calibrate the water sensor in his new float.

I had to search around on the web to find definitions of the NMEA sentences, and I have created a little summary of what I discovered which I will send to you, and I have put on this page on the JRA website. http://junkrigassociation.org/page-1858647 which you can also find under Junk Information/Sailing Performance/Interpreting NMEA Data.