Saturday, October 20, 2018

Hatteras Videos

As usual, we had a blast at the ABK camp in Hatteras the last 5 days. We had a nice mix of light, medium, and strong wind - here are a few videos, starting with a planing upwind 360:

A bit of light wind freestyle:


On the medium wind days, we got to try the foil demo gear from the ABK van. Fortunately, they had shorter masts that worked well with the water depth at the camp location in Waves. Here's a video where I prove that I can spin out a foil, too:


Nina, of course, did a bit better on the foil:


Plenty of wind in the forecast for tomorrow - mid-30s in the morning, dropping into the 20s after noon. We'll have a skippers meeting at Ocean Air in Avon for the ECWF Hatteras at 10 am - hope to see you there!

Saturday, October 6, 2018

Is 5 Hz enough?

This is a geeky post about GPS speedsurfing. You've been warned.

I am currently trying to get a couple of GPS devices that I have developed approved for the GPS Team Challenge. The units use u-blox 8 GPS chips, which are very accurate and provide speed accuracy estimates that can be used to automatically identify "bad" sections, for example artificially high speeds related to crashes.

One of the issues that came up is: at what rate should the data be recorded? Some popular GPS watches record only every few seconds, which is good enough for some uses, but not for speedsurfing. The venerable Locosys GT-31 recorded once per second; current Locosys units record at 5 Hz, every 200 milliseconds. The u-blox chips can record up to 18 Hz, although that limits the chips to using only two global satellite systems; for the highest accuracy, tracking satellites from 3 systems is desirable, which limits recording speed to 10 Hz.

There are some theoretical arguments that higher rates are better, because they give more accurate data. One big part of that is that random measurement errors tend to cancel each other out, and the more data points you have, the lower the remaining error gets.

But there are also some practical issues with higher data rates. The resulting larger files are usually not much of an issue, unless you're traveling to a spot that has a slow internet connection, and want to upload data for analysis to web sites like ka72.com.

Slow analysis and drawing speeds can be more of a pain. Most of the currently developed analysis software was developed for 1 Hz data, and can get quite slow with large 5 Hz files. Some steps appear to be coded inefficiently, showing N-squared time complexity - they take about 25 times longer for 5 Herz data. With 10 Hz data, add another factor of 4, and now we're talking about 100-fold slower.

A bigger issue is that higher data rates can lead to "dropped" points when the logging hardware can't keep up with the amount of data. I recently ran into this issue with my prototypes, and have seen indications of the same problem in data files from a GPS specifically developed for speedsurfing that's currently coming onto the market. But fortunately, the frequency of dropped points in my prototypes is low enough (roughly one point per hour) that the data can still be useful.

To see how much we actually can gain from increasing data acquisition rates to 10 Hz, I did a little experiment. It started with a windsurfing session were I used two prototypes at 10 Hz (for control, I also used 2 or 3 "approved" GPS units). Comparing the data on these units for the fastest ten 2-second and 10-second runs gives a good idea about the actual accuracy of the devices; the data from the other GPS units I used help to confirm that.

Next, I took one of the 10-Hz data files and split it into two 5 Hz files by simply writing one record to one file, the next one to a second file, the third one to the first file again, and so on. This simulates measuring at 5 Hz, but I get two 5-Hz files from the same device.
In the same way, I created a couple of 1-Hz files from the original file, this time selecting every 10th record for the first file, and every 10th record but starting one record later for the second file.

I analyzed the speeds for all these files in GPSResults, put them in a spreadsheet, and calculated the differences. Here are the results:
Looking at the "Average" lines, the observed differences increased from 0.041 knots to 0.074 knots for 2 second runs, and from 0.027 knots to 0.036 knots for 10 second runs. Going down to just one sample per second increased the observed differences more than 2-fold for both 2 and 10 seconds.

The observed differences are close to what would be expected by sampling theory, which predicts that the error is proportional to the square root of the number of samples taken. The expected numbers are shown in the "Theoretical error" line above.

But what error is "good enough"? Let's look at the top 10 teams in monthly ranking for the GPS Team Challenge for September to get an idea:
In the 2-second rankings, teams #7 and 8 are just 0.06 knots apart; in the 5x10 second average, the difference is 0.07 knots. The smallest difference in the 5x10 second category is 0.6 knots between teams ranking 8th and 9th.

Looking back at the observed differences at 5 Hz, we see that the average was just 0.036 knots (note that this is actually the average of the absolute differences).  For a 5x10 ranking, the expected error would be roughly two-fold smaller, or less than 0.02 knots. This seems quite adequate, it would have given the correct ranking in the 5 x 10 second category. Note that errors go down even more for the "longer" categories like nautical mile, 1 hour, and distance. Only in the 2-second category were two teams so close together that the observed average error is similar to the difference in posted speeds. Note, however, that many speedsurfers still use GT-31 devices that record at 1 Hz, and that even the 5-Hz Locosys units tend to have 2- to 3-fold higher errors than the u-blox prototypes I used in this test. It is quite well known that the 2-second category is the most likely to be subject to errors; however, it is still a lot better than the "maximum speed" category that is used in some other GPS competitions. For 5 Hz data, the expected error for single point "maxima" is about 3-fold higher than for 2 seconds!

So, to answer the question in the title: yes, it is!

Tuesday, September 25, 2018

ECWF Cape Cod: GPS Racing

It's been a couple of days since we completed the sixth annual East Coast Windsurfing Festival Cape Cod, and it's just beginning to appear possible that we might have it again next year. A longer report of the event will follow, but for now, let me talk about the GPS Racing.

The best wind of the weekend was last Friday, so I decided to hand out GPS units to anyone who was registered for the event and would take one. That included several Kalmus regulars (mostly non-speedsurfers), as well as PWA slalom pro Marco Lang. Since we all wanted to go to the event party at Inland Sea in the evening, we all had to stop early, just before the wind picked up, so most of the results were from 19 mph or lower wind averages. Here are the results:
Speeds are in miles per hour.  Everyone went faster than the average wind speed of 19 mph. Marco beat everyone by at least 4.5 mph (4 knots). Check out this picture of Marco flying on the fin:

The next group of three (PR, AR, and CE) all reached about 31.5 mph. Two of them (PR and CE) sailed exactly the same equipment as Marco; one (AR) was on slalom gear with a larger sail. Weight also plays a role in speed, but two of the three weighed in roughly the same as Marco - so the 4 knot speed difference is entirely due to skill.

The next sailor, NS in 5th place, stands our in a group of her own with 28.4 mph. She was also on full slalom gear, sailing happily along with Marco:
The last group of three sailors with speeds around 24-25 mph was on freeride or freestyle gear. Going just a bit of the wind is usually faster, as JSh's speed shows. All of them looked quite fast, and were going about 5 mph faster than the average wind speed.

All the speeds were from the Friday before the event. Since we never got enough wind during the event to run a GPS race, we used to top speeds from Friday for the GPS ranking at the event. Congrats to the winners, and many thanks to all who competed - and to Marco for showing what real speed looks like!

ECWF Cape Cod 2018

We had the 6th East Coast Windsurfing Festival Cape Cod last weekend. 21 windsurfers competed over the course of 2 days in racing, freestyle, SUP racing, and SUP relays. A big "thank you" to all that helped make this event a success, especially:
  • Marco Lang for traveling from Austria to participate at the event, answer many questions at the event party and on the beach, explaining the gear, and many helpful tips
  • Phil Mann from InlandSea for hosting a great party on Friday evening, organizing demo foils from Naish, and being at the beach both days to set up the demo gear and help anyone wanting to try it
  • Jason Meunier from VoilOka for driving the huge trailer with demo gear down from Canada, and setting up the demo gear
  • Bruno Robida from 2 Rad Windsurfing for financial support and raffle items
  • Vincent Lindauer for his efforts to get demo gear to the event, and for asking Marco to come to the event
  • Chris Eldridge, a local windsurfer and Fanatic/Duotone team rider, for help with the demo gear 
  • Peter Kimball from AP Kimball Construction for financial support and setting up a canopy for the event 
  • Jerry Evans from Chatham Wind and Time for making the trophies and financial support
  • Tom Ben-Eliyahu for help with the demo gear and driving the boat during the tow-in foiling
  • Barbara Baldwin for helping with registration and running the event
  • Joanie Scudder for arranging the sponsorship from Hy-Line cruises
  • Everyone who contributed to the Gofundme campaign to pay for Marco's travel expenses

Many of the people listed above had helped similarly in the past, and participated in the races during the event.

It was great to have demo gear from Fanatic, Duotone, and Naish at the event. Many of the competitors and a number of non-competitors took advantage of the opportunity to test new windsurfing and foil gear.

Next, a brief day-by-day description of the event.

Friday:
Phil Mann and Naish hosted a party at Inland Sea in West Dennis in the evening, with a Q&A session with PWA pro Marco Lang. It was well attended and fun, although most windsurfers arrived a bit later since we had a nice southerly breeze at Kalmus. The Fanatic and Duotone gear was already available at the beach, so many windsurfers tried new boards, sails, and foils.
To make sure that we would have a ranking in the GPS Racing category, I handed out GPS loaners to everyone I saw who was registered for the event, and had expressed interest in GPS racing. We had about 8 competitors in total. Marco Lang beat everyone else by about 4 knots, reaching a 2-second speed of 31.55 knots (2 second average) on a Duotone Warp 7.7 and a Fanatic Jag 108.

Saturday:
Side-off northwest wind from 10 to 30 mph created interesting conditions for racing, and challenging conditions for the freestyle competition. With a first race start shortly before 11 am, we managed to do five races and a couple of freestyle heats. Many windsurfers again took the opportunity to test race gear.

Sunday:
The wind forecast for the day was extremely light, and unfortunately came true. In the morning, Marco gave a very nice description of the Duotone sail range, followed by a description of the Fanatic boards by Jonathan when he eventually joined us.

After lunch, we ran SUP races and a SUP team relay, which again was tons of fun. We also used out little inflatable for "tow foiling", which created both astonishing rides and spectacular crashes.

Despite the very light wind, we managed to get one freestyle heat and the freestyle final in, where Mike and Henrikas displayed a variety of 360s, Ankle Biters, and more. When Henrikas failed to get his trade-mark Back-to-back in the very light wind, but Mike landed a clean Matrix, the decision when to Mike. Since Henrikas had won the SUP/shortboard class in racing, this set up a tie for the "King of the Cape" title. We had to dig deep into the tie breaker rules to find out who would be the King of the Cape 2018: Henrikas! Congrats to the new King and Jeanne, who is the 2018 Queen of the Cape.  I plan to post the full results of all disciplines in a separate post - for now, a few pictures:
Nina and Marco speeding on Friday
Racing action

Henrikas, King of the Cape 2018

Chris and Marco on the inflatable Fanatic tandem
Towing Tom
"Best Stoke" winner Spencer
Mike mid-Matrix
Freestyle can be exhausting!
Happy winners Ansel and Martin

Overall, it was again a fun event. Many competitors and demo gear users came to us after the event to thank us (which is definitely appreciated!). The stoke was high even on Sunday, when the wind was very light - we know how to have fun even without wind!

You may want to stop reading here.
--
Unfortunately, the light wind also seemed to keep some windsurfers away. The low attendance, despite moving the event by a week to get better wind, and despite demo gear and a PWA pro as the "guest star", makes it questionable whether there will be another ECWF Cape Cod in the future. Organizing the event is quite a bit of work in addition to the event days - just getting the signatures from all necessary town officials can take a day, and that's one of the easier parts. The organization we formed specifically to host events like this, the ECWA, ended up loosing money on this event; unless the ECWF Hatteras in October is a big success, we would need to cut expenses at future events.

Every event will have some unexpected things happen that cause stress for the organizers. Some of these can't be helped, like crashing scoring programs or some random idiot driving over the ladder we use to put longboards on top of our van. But other thing are very demotivating. As most of you know, the event was run by a German couple. Germans expect that if you give a word, you stick to it (well, at least Nina and I do!). If a local shop or the representative of a big windsurfing company says he'd bring or send items for the event raffle, and then does not, that's a big disappointment. For the local shop, we are fortunate enough to have another local shop that has always supported the ECWF (Inland Sea Windsurfing). For the large company, we will try hard to separate the person who apparently forgot his promises from the company (which we love), but it's not easy. And just for future reference: no, it it not ok to come to an event, to not register, to not sign the liability waiver, but to insist on racing on equipment that the event organizers and race director have specifically excluded from the races. You are free to disagree, of course, but just joining a race on equipment that was deemed too dangerous for this event is extremely inconsiderate and arrogant. Stating that you would "stay away from everyone", and then later posting picture where you are right next to several others in the middle of the race? Priceless. (Other words come to mind, but shall remain unwritten)

I run a small company. We have often presented our products at meetings where we had access to a number of potential customers. Every single time, we had to pay for this opportunity - often thousands of dollars. For the ECWF, we did not ask for money, since giving the local windsurfers the opportunity to test gear was more important for us. We did, however, ask for at least a small contribution to the raffle, which gives windsurfers an extra reason to join the event. Despite promises, we did not get anything. We thought that a company might at least contribute to the cost of getting one of their team riders to the event, especially in a year where they have a significantly increased marketing budget since they changed their name. Again, nothing. Well, "Denken ist Gl├╝ckssache".

I am trying hard to focus on the great people I got to know at the event, or who I have known and who have participated and/or helped again, rather than on the few negative experiences, but it's a bit of a struggle right now. So unlike last year, where we started getting the permit for the next event soon after the event, we won't plan next year's ECWF Cape Cod before our trip to Australia. There, we'll attend a few events and races, and speedsurfing on some of the top spots in the world, and wave sailing in some of the best waves in the world, will hopefully put things into perspective.