Wednesday, July 23, 2014

Perhaps there is hope

Great day at Kalmus today - wind around 20, gusting 25, sunny, warm, and a decent crowd on the water. My back has been acting up, so I decided to not mow the lawn today - too much work. I grabbed the easy freestyle board and the magic 6.5 m sail instead, and had fun. On the water, my back was mostly forgotten - I like seat harnesses!

Nina and Marty were both on the water, setting a good example with 360s, planing push tacks, donkey jibes, and flaka and duck tack tries. Chris and Drew were out on slalom and freerace gear - with my 24 cm fin, I had no chance of keeping up with them. So I imitated Nina and Marty. Of course I played it safe and mostly limited myself to duck jibes, jump jibes,  carve 360 attempts, and body drag attempts. I even threw a little bit of working on my jbes in - I need to get the "independent arms, front arm long" concept from my head into my arms. Just for good measure, I threw in a few pops, in preparation for Grubbys.

As a result, the Clew-View GoPro footage from today was a lot more interesting than usual. The pops looked better in the movies than they had felt - the fin came clearly out of the water, but the height was not too high. I slowly worked up my courage to have the nose of the board touch first. In my last try, I actually managed a proper nose landing:
That was a first. Much to my surprise, I survived! Without any injury! Sailed away without any problems. Maybe it's time to add turning the board and sliding backwards soon...

For my geek and speedsurfing friends: I used two Canmore GP-102+ today, as well as my GT-31. With the GT-31 in "normal" power mode, the tracks looked much nicer, and positional and doppler speeds were very close. Speed results in the GPSTC challenge catefories were almost identical for the 3 units, with most numbers being within 0.1 knots for all three units, and a maximum difference of 0.21 knots for the 2 second value. No surprise, but still nice! Here's a section of the speed tracks for the 3 units that is typical for the entire track:
Hard to even see that these are 3 different tracks!

Tuesday, July 22, 2014

Low Power Is Bad

I like power when windsurfing. Speedsurfing does not work without power. Turns out this is also true for the GT-31 GPS (yes, this is another geeky post about GPS, so feel free to stop reading).

In my recent post about comparing 5 GPS units,  I had described how one of the two GPS units I used had given substantially worse results than the other one. One of the great names in speedsurfing, Andrew Daff (aka Sailquick), pointed out that this could be due to differences in settings - and he was right. I discovered that my "bad" GT-31 still was set to "low power" mode, while the other unit was in "normal" power mode. It appears that the "low power" mode restricts the GT-31 to tracking at most 6 satellites; in normal power mode, the unit can track 8 or more satellites, which gives much better accuracy. I took both GT-31s I had for a drive to see the effect - here are the tracks from "low power" mode:
Low power mode tracks from two GT-31s
For comparison, here are the tracks in normal power mode from the way back:
Normal power mode tracks from two GT-31s
In normal power mode, the positional accuracy is a lot better - both tracks are right on top of each other, and I'm not driving over houses anymore. The differences are most pronounced when driving in circles. Here are enlargements of the top sections of the tracks:
Low power mode circles
Normal power mode circles
In normal power mode, the tracks actually show the circles and ovals I drove; In low power mode, they are all over the place. In low power mode, the GPS units tracked only 4 satellites; I normal power mode, they tracked 7-8.

Here are the speed and doppler speed graphs for the low power mode:
Speed graphs for low power mode
In low power mode, the speed graph shows a lot of spikes (I actually removed the biggest one to get better scaling). The doppler speed graph does not show any spikes, which is a nice illustration why we doppler speeds are preferable for speedsurfing. However, even the doppler speeds are quite different for the two units at many time points.

For comparison, here are the speed graphs in normal power mode:
Speed graphs for normal power mode
With 7-8 (mostly 8) satellites tracked, the positional data are free of spikes, and very close to the doppler data. Differences between the two units are much smaller, and limited to just a few short regions.

Fortunately, the "normal" power mode is the default setting for the GT-31 (I think). So why did I ever switch my GT-31 to "low power"? I did it when I tried to set a personal best for distance within 24 hours. Somewhere, I picked up a suggestion to switch to low power mode to make sure that the battery would last long enough. Neither the suggester nor I had seen Redsurfbus' comment that low power mode creates spikes...

I did not even sail 24 hours that day. I got too tired after sailing about 12 hours in chop, sailing only 270 km. Apparently, I was still too tired the next day to remember to set the power mode back to normal. This affected my jibe analysis using GPS data for the next two years...

What do we learn? Well, if you have a GT-31, go to "Settings", scroll down to "Power mode", and make sure it is set on "Normal". The other take-home message I took from this is that the number of satellites tracked is a very useful bit of information to have - it is tightly linked to speed accuracy. Although I believe that other factors also come into play when SDoP and HDoP are calculated, the number of satellites could be a good-enough stand-in for recreational (i.e. non-record) windsurfing. With newer GPS chips typically tracking more satellites than the old Sirf3 chip, if should be possible to set the minimum number of satellites higher that the currently suggested cutoff of 5 - at least to 7 or perhaps 8. Why does this matter? Because only very few GPS units can record accuracy values (SDoP and HDoP) directly, but many support the NMEA format that does support satellite information, or similar formats.

I really hope that I'll be done with this geeky stuff for now, and that the promised wind will show up tomorrow and this weekend so that I can spend some time on the water!

Monday, July 21, 2014

Nina at Kalmus

I like my GoPro and my Clew-View. But if I use it, it tends to get boring. How interesting can it be watching someone mow the lawn? So I try to get others to use my camera. It seems, though, that my camera is shy. When I gave it to Marty, it worked for about 2 minutes. A few days ago, I gave it to Nina. It worked for about 20 minutes - not bad, but not the 90+ minutes I usually get. Maybe I should really throw out the old battery.

Anyway, while it was a short session, the camera still captured a few things of interest. Here's a short video:


If you wonder about the music - Vimeo has started to use the same copyright detection system that YouTube has been using for years. I happened 2 months ago, but I just discovered it yesterday, when my initial upload was rejected. I replaced it with something free from the Vimeo music store, but the free selection does seem rather limited. Now the main reason to use Vimeo is history.

Back to windsurfing. Nina has been working on the planing duck tack for a long time now (she can do light wind duck tacks all day long). She has not been able to repeat her success from a few months ago, when both Marty and I witnessed her first dry one. The Clew-View video was helpful: it showed that she is not pulling & throwing the clew to the tail of the board. Something to work on..

You may have noticed that I got to use Nina's sail for a while during the session. It's her new Idol 5.0. I love this sail! It feels extremely light in your hands. I kept wondering "why am I planing without any pressure in the sail?". The feeling reminded me of the TR-7 race sail. Both sails seem to convert wind directly into speed, with minimal sideway drag. On the TR-7, it lets you hold on to a bigger sail and go faster; on the Idol, it lets you use a smaller sail to plane early. Quite amazing that a 4-batten non-cam sail can feel as efficient as an 8-batten, 4-cam sail!

On the day shown in the video, I was just barely powered on the Idol, but I loved it. It rotated so nicely in jibes that I finally managed to step lightly. Surprise (not!) - not stomping around keeps the board flat and fast. Feels good, too!

The next day, it got even windier, so I got to use the Idol again. This time, I ended up being fully powered. Wind averages were in the high 20s, gusts in the 30s (mph). The sail still behaved well, especially after I stopped to add some downhaul and outhaul. It seemed as stable as a good 5- or 6-batten sail; but I think it's real strength is at the low end, when it's just big enough to get you going. Even I, the perpetual lawn mower, felt inspired to try things, and might have done a few pops on downwind runs, trying to get enough courage to dip the nose and really go for a Grubby. Maybe next time.

So far, the summer has gotten off to a windy start. We sailed 10 or 11 days in the last three weeks, Nina often on 4.2 or 4.7, and never above 5.0. Tomorrow evening holds some promise for more, and Wednesday looks like it will be another funtastic day, with sunshine and wind in the mid-20s.

Saturday, July 19, 2014

Getting started with the Canmore GP-102+ GPS

Here is a set of quick instructions to get started with the Canmore G-Porter GP-102+ GPS for speedsurfing, all the way to posting data to the GPS Team Challenge.

1. Read the user manual
Using the GP102 is pretty straightforward. It has two buttons at the button for navigation which allow you to access all the functions. Still, it worth to download the user manual from here, and spending 5 or 10 minutes reading it.

2. Setup the GP-102
The device comes with enough battery charge so that you can use it right away. The first time you switch it on, you'll have to put it outside for a few minutes so that it can see which GPS satellites are in view. Just put it outside where it has a clear view of the sky, and leave it there for 10-15 minutes,

The only other thing you have to do is change the log rate. By default, the GP102 logs every five seconds. You need to change this so that it logs every seconds. The user manual explains how to change settings.

3. Gather some data
To make sure we have something to play with in the next step, switch the unit on, turn logging on (I usually use the biking or running mode, but I don't think it makes a difference what you choose), and walk, bike, or drive around for a few minutes. Then, switch the unit back off.

4. Install the Canmore GPS software
There are several ways to get the data off the device and ready to be analyzed, but the easiest way is to use the Canmore software. It's Windows-only, but in my tests, it worked perfectly fine on OS X with Parallels and Windows 7.
Download the installer from the "Datalogger software" installer from the download section on the Canmore web site, and run it. When asked, install the USB driver, too. When you run the "CanWay" software the first time, it will ask you your name, birthday, weight, etc. Enter it, or just use whatever the defaults are, it does not matter.

5. Download the GPS tracks onto the computer
Start the "CanWay" software you just installed. Connect the GP-102 to the computer with a standard USB cable (included in the box the unit comes in), and switch the GP102 on. After a few seconds, it should show a cable icon on the display, and Windows should mount the data logger as a regular USB disk.
In the CanWay software, go to the "Logger" menu, and select "Download Trip" (or choose the "Download Trip" icon in the toolbar). That will open a dialog that shows you the trips on the GP102 (every time you turn the unit on nd start logging, it starts a new trip). Select the trip(s) you want, and download them.
The Canmore software seems to have a bug which sometimes causes the import to fail. I have seen this problem on Windows 98, but had no problems on Windows 7 and 8.1. A friend has also reported the same issue on his computer, but I do not know which Windows version he is using.

6. Check your trips in the CanWay software
The CanWay software lets you look at an overlay of your tracks onto Google maps, see your speed over time, and gives you a basic summary (top speed, average speed, total time and distance). It's nice to get a first glance at your data, but it does not give you all the information you need for posting to the GPS web sites. For, that, you need to..

7. Export your trip as a GPX file
Select the trip you want to analyze further, go to the "File" menu, and choose "Export" => "GPX" (or use the "Export to GPS" icon in the toolbar). Save the file to a location where you will find it again, for example your desktop.

8. Upload your trip to ka72.com
The simplest way to get the speeds you need for posting to the GPS Team Challenge site is by uploading the GPX file that you just create to ka72.com. After uploading, the site will automatically analyze the data, and show you your top speed, 5x10 second average, 1 hour, alpha 500, etc. speeds - everything you need to enter your trip on the GPS Team Challenge Site. 

9. Post your data to the GPS Team Challenge
Near the bottom of the results page from the previous step, there should be a button "Post to the GPSTC website". Click it, and the data will be automatically entered on the GPS Team Challenge web site. You may need to log in first, however, and you'll have to press the "Post" button on the GPSTC web page. You may want to enter some information about the session in the "Comments" section first, though - it's always nice to be able to see what gear others were sailing, and what the conditions were.

That's it. You're done. Next time, you can start at step 5, so things will go faster. The instructions above are just one way of doing this, but it's the easiest way. If you want to have a closer look at your data, you can use software like GPS Action Replay Pro or GPSResults.  I like GPS Action Replay a lot, for example to analyze jibes. But I'm a geek. Both programs run on Windows and OS X (GPS Action Replay is Java-based, so it should run on Linux, too).

If you are a Mac user without access to Windows, you will need to do a couple of things differently. You can connect the GP102 to your Mac with a USB cable, and the device will show up as an external drive, making it easy to copy the data files from the unit. However, the files are in ".fit" format, which the GPS analysis software cannot read (neither can ka72.com). So you'll have to get the current version of GPSBabel, and use it to convert the .fit file to a file format that can be read. As the format of the input file, you'll need to choose "Flexible and Interoperable Data Transfer (FIT) Activity file". For the output file, I suggest that you use "GPS XML" as the format - that seems to work well.
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If you are German and therefore (or for other reasons) feel obligated to play strictly by the rules, you'll have to omit step 9. That's because right now (July 19, 2014), the GP-102+ is not in the list of "valid" GPS devices for the GPS Team Challenge. However, I have demonstrated in previous posts that the GP-102+ appears to be at least as accurate as the official "best" GPS, the GT-31 (which has been discontinued by the manufacturer). The GP-102+ is clearly more accurate than many of the older GPS units that are still on the "approved" list. I hope that he GPS Team Challenge Technical Advisors will soon add the GP-102+ to the list of "approved" GPS units.