Tuesday, July 29, 2014

Time to sign up for the Cape Cod ABK clinic

The ABK clinic is coming to Hyannis in 5 weeks - time to sign up! Waiting until a few days before the clinic starts to see if it will be windy is not going to work! Many tried this the last two years, only to discover that the clinic filled up one or two weeks before. I am sure this will happen again this year - many regulars I talked to plan on attending, and I have seen many new faces at Kalmus this year. So sign up now! Yes, Marty and Steve, I am talking to you (and many others!)
Andy Brandt teaching Nina the duck jibe at Kalmus
Do you need reasons to sign up? Well... do you want to improve your windsurfing? Plane through your jibes? Learn to water start? Get into the harness? Finally get into the footstraps? Learn to duck jibe, heli tack, loop, or vulcan? Then grab the opportunity and learn from some of the best windsurf instructors in the world! They are coming to Cape Cod to teach you on September 5-7.

What about the wind, you say? I have attended the ABK clinic in Hyannis since 2009. Every year, we had at least one day, and often two days, of planing conditions. There's still plenty to learn on the light wind days. Nina actually learned to get into the back footstrap on a light wind day at the ABK camp Cape Cod a few years back. She had spend the windy day before with really learning the water start - well enough to go to Maui and the Gorge the next year. She also learned the heli tack during the same camp. I don't learn as quickly, but there's always a lot to be learned in these three days.

You still need more reasons to sign up? How about making new friends who are at least as crazy about windsurfing as you are? How about the opportunity to hear a guest lecture from Caesar Finies, a PWA sailor and one of the best light wind freestylers on this planet? He will be on Cape Cod during the clinic days. He'll be also giving a demonstration of his crazy tricks during the clinic. Many windsurfers who have not seen his "Hail Mary" in real life think that the videos on YouTube where he takes the rig off the board, throws it 20 feet into the air, and then catches it again after it flipped a few times, must be photoshopped. Come see for yourself!

Besides making sure that you get a spot in the clinic, another reason to sign up now is that it may allow Andy Brandt to expand the clinic by getting additional instructors to come. There are quite a few highly qualified ABK instructors around who can help out - but chances to get them to help out are better the more advance notice they have. I have been to more than a dozen ABK camps, and the bigger, the better: larger camps mean that skills within any group are closely matched, which makes teaching and learning easier.

So - sign up now! Don't tell me (again) "I should have listened to you"! Don't wait until you see "6 spaces left" - for the Cape Cod camp, the last 6 spaces may fill up in less than a day! I hope to see you all at the beautiful Kalmus beaches in September.

For those who want to learn windsurfing before then, or take lessons to improve their skills, here is a list of other places that offer windsurfing instructions on or near Cape Cod:

Another option for windsurfing lessons at Kalmus Beach in Hyannis is to support our "Help Us Bring Caesar to Cape Cod" campaign. Anyone who donates at least $100 to the campaign can get a 2 hour windsurf lesson. There are only 4 of these $100 "perks" left, though, so you may need to act fast.

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.
Please note that the GP102 is not waterproof! Several users (myself included) had units break after minimal water exposure. This can happen even inside a water-proof bag if just a little bit of water gets inside the bag. I strongly recommend to double-bag the GP102: put it inside a zip lock bag, and then inside a waterproof armband.

4. Install the Canmore GPS software
Update 8-31-2014: 
Steps 4-7 are now optional, since ka72.com has recently added support to read Canmore GP102+ files directly. The newest version of GPSResults can also read .fit files.
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 and 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, and a friend has also reported the same issue on with a Windows7 computer.

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 data file to ka72.com. The site now supports the Canmore "fit" file format. Simply connect the GP102 to your computer; after a few seconds, a new "Canmore" USB drive should show up. The data files are in the "Activities" folder in this drive, and can be uploaded directly. Alternatively, you can upload files in GPX format created from the Canmore software or with GPSBabel.
After uploading, the ka72.com 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 some GPS analysis software versions cannot read (but ka72.com and GPSResults can!). If you want to use GPS Action Replay to analyze your data, 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.
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.

Friday, July 18, 2014

The 5 GPS Comparison

I received two additional Canmore GP102+ GPS units today. With not much wind in the forecast for the next few days, I decided to drive around a bit to test them. I mounted a total of 5 GPS units right next to each other on the dashboard of my car: two Locosys GT-31s, a FlySight, and the two new GP102+ units.

I drove around for about 20 minutes at speed similar to typical windsurfing speeds - 30-50 mph. Here's a Google Earth overlay of all 5 tracks:
I uploaded all tracks to ka72.com, so you can download the tracks or look at the Google overlays there (filter by track type "Driving", and look for "Osterville, MA, USA" tracks from July 18, 2014).

Most GPS units do well when you sail or drive in a straight line at constant speed, but some have accuracy problems during turns, for example in jibes. I drove around in circles in a parking lot to check for problems - here's a blowup of this section:
Tracks from the two GT-31 units are in yellow; from the Canmore GP102+ units in green; and from the FlySight in purple. All tracks are reasonably close, except for one of the GT-31 tracks. This track happens to be from the unit I have been using for a couple of years (the other GT-31 track is from my wife's unit, which has been used a lot less). A look at the speed graph also shows big differences between these two units:
For the better unit, speed and doppler speed tracks are smooth and close to each other. For the other unit (light green tracks), the speed tracks have lots of spikes. The doppler speed tracks look better, but still show some minor spikes.

In comparison, the speed tracks for the GP-102 units are more similar:
In this case, the speed calculated from position data and the doppler speed are very close, but the doppler data show fewer artifact peaks. This illustrates why we definitely want to use doppler speeds for higher accuracy.

To see what caused the differences between the two GT-31 units, I looked at the trackpoints. The better unit tracked anywhere between 8 and 10 satellites; the "spikey" unit tracked only 5-6 satellites. Both units had a virtually identical view of the sky. The differences also existed when I checked the satellite screen on both units in my backyard.

No surprise here - the more satellites a GPS device can track, the more accurately it can triangulate the position. Five satellites is the bare minimum (according to the settings suggested by GPS-speedsurfing.com). However, even the "bad" unit always tracked at least 5 satellites, and the error estimate (HDoP) was 2.2 or less for all points (GPS-speedsurfing.com suggests to remove points with HDoP above 5.0).

I do not know why one of the GT-31 units was able to track 8-10 satellites, while the other was only able to track 5-6 satellites. But whatever the cause, the difference in accuracy was quite pronounced. This is quite visible when we compare the speed results that ka72.com gives for the tracks:
The first GT-31 units has substantially higher top speeds than the other units tested (I suggest to ignore the "alpha 500" values, since I did not simulate a alpha run while driving - this value includes multiple full circles from the blowup image above). Taking the values from all 5 units in the test to calculate a standard deviation allows us to see which units give results that fall within one standard deviation of the average. Both Canmore GP-102 units do for all values, but the GT-31_1 unit consistently outside this range.

In this test of two GT-31 units and two GP102+ units, the GP102-units gave overall more accurate results. This is by no means surprising, since the GP-102 units use a newer GPS chip (the Sirf IV), which contains multiple improvements over the Sirf III chip used in the ancient GT-31. One of these improvements is the number of "channels" for tracking satellites: the Sirf III in the GT-31 has only 20 channels, the Sirf IV in the GP102+ has 48 (more about this here). This alone means that the GP102+ should generally be able to track more satellites, resulting in more accurate data.

The results I describe above creates an interesting dilemma: should I keep using my old GT-31, which I know to be less accurate, or should I start using the GP102+? The GPS Team Challenge currently lists the GT-31 as a device "valid for the purposes of the challenge", along with a number of Garmin GPS devices that are known to be less accurate than the GT-31. But no new devices have been approved since the GT-31 was released many years ago (the "GT-35" that is listed was never commercially available).

If I play by the rules, I have to post results from the GT-31. I cannot post results from the FlySight, which is clearly much more accurate than the GT-31, or from the GP102+, which is at least as accurate as a "good" GT-31. From the results I have shown here and in previous blog posts, I will be "rewarded" with higher speeds, since the lower accuracy of the GT-31 tends to result in higher speeds.

Or I could ignore the rules, and post results from one of the more accurate GPS units I have. Sure, these units are not perfect - we'd ideally want more raw data, including number of satellites tracked and error estimates. However, it does appear that the newer units always will track more than the number of required satellites, and provide more accurate data that a GT-31 unit that still gives data points within the limits specified on GPS-speedsurfing.com.

I know two local racers and slalom sailors who are looking for a GPS so that they can be part of our team. I'd really love it if they'd post their speeds - it would be a sure way keeps our team from fighting for the second-to-last place in the monthly rankings. Who knows, maybe we can even dream of making it into the top half in a lucky month! Both of them would buy a GT-31, but they are not available in the US anymore. Should they really pay 2x or 5x as much for an approved Garmin unit, instead of buying a more accurate Canmore G-Porter GP102+? Maybe it is time to change the rules!

Tuesday, July 15, 2014

A smaller, better, cheaper GPS?

For many years, the only recommended GPS for speedsurfing was the Locosys GT-31. It relied on technology that can only be called ancient - so ancient that the company had to stop producing them because they could not get the parts anymore. During the last couple of months, it has been impossible to get a GT-31 in the USA.

This created a problem for new speedsurfers. Several asked me recently what they should buy, and I could not give them a recommendation. The speedsurfing sites officially allow some Garmin watch-type GPS units, but label them clearly as inferior to the GT-31. But when I recently checked their prices on Amazon, I noticed a promising GPS unit: the Canmore G-Porter GP-102+.

On promising detail about the GP-102+ (I'll call it the "GP102" from now on) is that is uses the Sirf4 GPS chip. That's the successor to the Sirf3 chip that the GT-31 uses, and it has a number of improvements. The other thing I liked was that the unit only costs about $50, compare to about $150 for the GT-31. I went ahead and bought one to test it.

Two days ago, I had a chance to use it while windsurfing. I did two sessions, a freestyle session in 15-18 knots in the morning and a speed session in 20+ knots in the evening. For comparison, I wore my GT-31. In the morning, I also wore my FlySight GPS, which I previously reported as being more accurate than the GT-31. However, the FlySight does not have a display, is not waterproof, and costs $250.

I plan to post a more detailed report later, but here are some initial results. I'll start with the tracks from the first session:
GT-31(blue) vs. GP102 (red) tracks
Very similar tracks, very similar speeds. A different view shows some artifacts in the GT-31 tracks:
The artifacts are from wet jibes. The GT-31 tends to loose the GPS signal when you're swimming, and the positions jump around a bit. Here's a blowup from one wet jibe:
Tracks and speeds from one wet jibe, showing artifacts in the GT-31 data (blue) that are absent in the GP-102 data (red).

Here are the tracks from the second session (with reversed colors):
GT-31(red) vs. GP102 (blue) tracks from session 2
Here's how the speed results compared in the GPSTC disciplines:
In general, the results are almost identical, with differences typically being around 1% or less. The one exception is the best alpha 500 from session 1, where the GP-102+ was 3.5% lower. Here's this part of the GPS tracks:
The blue GT-31 tracks shows a very sharp turn, which did not happen (I sometimes do jibe with a hook like this, but not without loosing all speed). This is often seen in GT-31 data during low radius jibes: the track continues forward for too long, then turns too sharply. The effect is that the distance covers appears larger than it really was (the difference is about 2 meters). In other words, the GT-31 speed for the best alpha was artificially high. I have seen the same issue many times when comparing GT-31 and FlySight data.

One of the good things about the GT-31 is that is also records accuracy estimates of the data. In sharp turns like the one above, the GT-31 "knows" that it is not accurate, and many data points have SDoP and HDoP values above the commonly used threshold. But from what I can tell, these data points are still used in GPSResults to calculate alphas.

The GP-102+ produces files in Garmin .fit format, which (as far as I can tell) do not contain any precision data. This might seem as a big drawback - but look at the next table first:

The table shows the difference in speed calculate using Doppler data and positional data. For the GT-31, this difference is large: 28.3% for max speed (2 s), and 10.5% for alpha 500. This is no surprise, and the reason behind the request to always use doppler data when posting to GPS web sites.

But for the GP-102+, the differences are much lower: just 1.4% for max speed, and 1% or less for everything else. In other words, the relative positional accuracy is much higher than for the GT-31. Here's a section of the tracks which show spikes in the GT-31 positional speed data:
Positional vs. doppler speed for GT-31 (red) and GP-102+ (blue)
Why is this relevant if we only use doppler values for speedsurfing? Simply because positional and doppler data are not fully independent. In the example above, the artifact spikes are missing in the doppler data, but the data near spikes often have substantially lower accuracy values. In one GPS unit from a different manufacturer that I tested, spikes in position speed went up to more than 1000 knots! 

I'm a software guy, not a hardware guy, but I know that there is a lot of computation going on to convert the raw GPS signals to positions and speeds. To my eye, the spikes in the GT-31 data simply look like the results of a bug. In later chips and GPS units like the GP-102+ and the FlySight, this bug seems to simply not be there.

This is it for today. The results from using the Canmore GP-102+ for speedsurfing are very encouraging, so I just had to share some of this right away. Stay tuned for more details and tests...

Please note that the GP102 is not waterproof! Several users (myself included) had units break after minimal water exposure. This can happen even inside a water-proof bag if just a little bit of water gets inside the bag. I strongly recommend to double-bag the GP102: put it inside a zip lock bag, and then inside a waterproof armband.

Tuesday, July 8, 2014

Summer winds

The wind will stop tomorrow (or maybe the day after), and I am glad. Can you believe that? I can't. But it is true. I sailed 6 out of the last 9 days - full power every time, often long sessions, sometimes two sessions a day.

Yesterday's high wind and low tide called for some slalom/speed practice, so the XFire 90 got some use again. I got up to almost 30 knots on water that was definitely not perfectly flat. Not bad (for me, that is). I sailed 95 km overall. Marty sailed 115 km. Marty tried loops, did upwind 360s while overpowered on 4.7, and more. Marty is an animal. I love sailing with Marty (and with Jon, who made a rare guest appearance).

Today called for freestyle. I tried the Kono with the 360 entry. It helped to be nicely overpowered on 6.5 (Marty was on 4.7). Made some progress - I go the board to jump twice. On another try, I got around to backwinded while still planing. Did not matter that I could not do both in the same try - falling backwards into the warm water was lots of fun. Maybe I'll get the Kono one of these days on perfectly flat water. Or with a helping pushy wave. Or maybe I'll just get a slightly wet 360 in the straps with a board flare. At least I can use a big fin! And I'm not too scared to try. Maybe big fins make me brave. Until I end up sliding backwards, the big fin stays in!

Thursday, July 3, 2014

Splash, splash, splash

I'm tired. It was windy 3 days in a row. I got 4 session in, sailed probably about 200 km (the GPS refused to cooperate one day). That would not be so much, except that I copied Nina and Marty. They are both better windsurfers than I am. I think their trick is that they fall a lot. So I tried to fall a lot, too. When you fall, you need to waterstart. Waterstarting makes you tired! So there. That's the story. Told in pictures:
Jump jibes are fun. You are supposed to fall! Poking the sun with the nose of the board gets extra style points.

You're not supposed to fall in duck jibes. But plank walks after the mast hits the water are fun, too.
A splash before the fall
Marty duck jibing. Every now and then, he just turns around instead of falling.
I did not want to mess up my jibe completely, so I had to do other things. Jump jibes are my favorite - you are supposed to fall - what can go wrong? Well, you are also supposed to get right back up with a clew-first waterstart, flip the sail, and sail away. Needs more practice.

Duck jibes are easier. They are my "look, I can do tricks, too" thing. If I sail long enough, I re-discover the ways to mess up duck jibes. Having the mast hit the water so that the board stops, but you keep going at full speed, is my favorite. Then, Nina told me she simply pulled the mast back up after it hit the water, and completed the duck jibe. I had to try that, too, and it worked.

Nina and Marty fall all the time, not just when they are tired. So I needed to try other things, too. Going switch before jibing seemed like a good idea. That worked, but the jibes ended up a bit boring, and I did not fall all the time. Then I saw Marty try a duck tack. Nina tries them, too, and now catches the sail again most of the time. So I figured I just had to try my first planing duck tack. Took some convincing, though - I'm not sure I was really still planing when I finally threw the sail. Success! No, I did not make a planing duck tack on the first try, silly! I managed to fall!

All the falling was wonderful, since the water was just perfect, and I probably would have gotten hot if I had stuck to my usual lawn-mowing ways. But I was not sure if I was getting any better. So on the third day, I decided to spy on Marty: I made him use my GoPro with the Clew-View mount. He proceeded with his usual up- and downwind 360s, heli tacks, push tacks, duck jibes, donkey jibes, and who-knows-what-else. Oh the things I could have learned from the video! When I saw him do a beautiful early-throw switch duck jibe, I waved him over to make sure the camera was still recording. It was not :-{. The stupid extra battery that I had put in apparently had been almost empty, and recorded exactly 90 seconds. In these 90 seconds, Marty did an upwind 360 and a duck jibe. Makes me wonder - what would we have seen in an hour of video? Maybe we will find out soon - the next stretch of 3-4 windy days is coming up this weekend.
On a different topic: many thanks to all the windsurfers who have donated to our campaign to bring Caesar Finies to the ECWF Cape Cod on September 13-14. We were able to reach our fundraising goal of $1200 to pay for Caesar's airline tickets in 6 days. Fantastic!