Thursday, June 22, 2017

Ducks Fly Fast

Ducks can fly - why can't I? It's not for lack of trying:
Maybe I need to flap harder? Or maybe I need to grow a pair .. of wings, that is. Probably won't happen.

The picture is from a session two days ago at Kalmus. After sailing back and forth for 9 hours the day before (I call that "distance sailing"), it was time to do something different - a bit of old school freestyle. I'll refrain from doing any freestyle as long as I have any excuse - "the water is cold" or "I did not sail much recently" being two of my favorites. So I still count the Duck Jibe as a freestyle trick. It's tricky to catch the sail after throwing it! Works better than trying to fly, though.

The crash in the picture above was harmless - perhaps all that flapping helped, after all. A little while later (and a little more tired), I had a better crash. If you've learned the Duck Jibe, maybe you remember the "Plank Walk": when your mast hits the water, and your gear suddenly stops, but you keep going ... straight off the nose of your board. That's pretty much what I did. Here's the GoPro footage:
That was fun! As a little bonus, I set my top speed of the day during my brief flight, according to my GPS:
I was three knots faster than in my second-fastest run! If you believe the GPS, that is. I really don't think that I was airborne for longer than 2 seconds - I would have flown about a 100 feet in that time! So let's look at the data more closely:

Here is the narrative to what happened:

  • I slowed down a bit during the sail duck, from 22 knots to 18.5 knots
  • When the mast hit the water, the board came to a sudden stop. Not so my body! Since my foot was still in the strap, the upper body did not just keep the speed, but actually accelerated from 18.5 to 26 knots within 0.4 seconds
  • I hit the water shortly thereafter. As soon as my hand was deeper than about 2-4 inches, the GPS watch lost reception, since water absorbs the GPS signal. We can see that point #24220 is not the expected 0.2 seconds after the previous point, but rather 1.6 seconds. So 1.4 seconds worth of data are missing.
  • GPS chips are made for cars, not for windsurfing. Cars often loose GPS reception, for example in tunnels or under bridges; but usually, they keep going at roughly the same speed and direction as before.  So the GPS chips go into "dead reckoning" mode, assuming that the "car" is still traveling at the same speed, and predicting the speed and new position.
Well, I may be many things, but a car I am not. I did stop when I hit the water. Speedsurfers traveling twice as fast as I did may bounce a few times before sinking, but I did not. So the GPS guessed wrong about how far and fast I traveled when I had no GPS reception. It corrected it's mistake very shortly thereafter: in point #24221, it adjusted the position by about 20 meters, roughly the same amount that it guessed wrong in the first place. The two points with large distances easy to see in the tracks:
For this particular file, only one of the three GPS speedsurfing programs gives the correct 2-second top speed. That is GPSResults, which refuses to use data points that have longer-than-expected time gaps. Both GPS Action Replay Pro and ka72.com use such data points, and therefore give an incorrect maximum 2-second speed that is "dead reckoning inflated" by about 3 knots.

Using accuracy estimates (SDoP filtering) to identify the "guessed wrong" data points could have worked, but would have required a threshold of 3.0 knots; the current threshold of 4.0 used by GPSResults would have let the bad points through. An "average SDoP" filter with a threshold of 1.5 that I had proposed earlier would have easily identified the bad points, and avoids the potential issues with invalidating larger stretches of data if single points are missing.

Now if I can only convince myself to duck jibe at the end of speed runs, maybe I'll finally get a 35 knot top speed...

Wednesday, June 21, 2017

Fun at Kalmus

It finally felt like summer today! Not that I'm complaining about windsurfing 5 out of the last 6 days, but fog in June just feels wrong. Today was sunny!!
After doing a bit of distance sailing two days ago (206 km, almost the distance of 5 marathons :-), I was a bit tired yesterday - but today was just perfect, with SSW wind and low tide. The 5.6 m freestyle sail felt so easy after 6 and 7 m freeride and 7.8 m slalom sails! Here's a short video from today:

Friday, June 16, 2017

Bump and Bay

Southeast wind all day - where do we go to play today?
Our home spot Kalmus is a S-WSW spot. In SE, it gets wind shadow from Great Island - the little island that extends down from Lewis Bay.
The usual SE playground is West Dennis (marked with an "A") in the map. But besides the $20 fee and a drive that seems to take forever during tourist season, the birds have taken over - the usual windsurf spot is blocked off.
Next to Monomoy Island (marked with a "B") on the map might also be a great spot to find some flat and shallow water. But you'd definitely also find a lot of seals, and the occasional Great White Shark. And someone who does not want to drive to West Dennis now certainly would not want to drive twice as far!
So it was time to check out a closer spot: Oregon Beach in Cotuit. I had tried to sail there a few times before, but the wind never cooperated. But let me zoom in a bit to show you why I had not given up on it yet:
That long sandbar is called Popponesset Island. It's about 800 meters long and just a few feet high - potential speedsurfing territory! I had checked it out once on a longboard, and it looked promising near high tide. The other thing you may notice is the color of the water on the right: green instead of blue means shallow! Nautical maps show depths of 1-3 feet to almost 1/2 mile out. Freestylers like shallow since they fall a lot. Speedsurfers like shallow because it reduces chop.
We started windsurfing shortly past low tide. As usual, Nina was on freestyle gear (90/4.7), so I also chose my Skate 110 and a 5.6 m freestyle sail. It was surprisingly bumpy in front, but after the first 30 minutes, the wind filled in nicely. I had fun doing mile-long runs over to Dead Neck. But when I checked with Nina, she said she did not like it much - the chop was a bit disorderly, the wind a bit gusty close to shore where she wanted to practice freestyle, and she even had found a few deep spots where she could not touch ground.
So now I had a perfect reason to check out Popponesset Bay! The sandbar in front would reduce the chop, and the inside should be shallow enough to stand - so off I went. Getting there from Oregon Beach (where you need a Barnstable resident sticker for parking during the season) was easy, and the bay was shallow, chop-free, and windy! I turned around to tell Nina, but discovered that she had followed me, and was waiting on the ocean side beach near the tip of the island.
We spent the next hour sailing inside Popponesset Bay - here are today's GPS tracks:
Let's zoom in to have a closer look at the inside sailing:
The Google Earth image shows a shallow section in the middle of the bay. When we started sailing, a lot of this area covered by a foot or less of water; at some spot, it was just ankle-deep. In view of a great wind forecast for the next week, I had no desire to once again prove my skills in discovering shallow spots at full speed, so I stayed a bit further to the inside of the bay. The runs there were about 450 m long, about the same as at Fogland inside the bay. Closer to high tide, similar runs further up would also be possible. With a slightly more easterly wind direction, runs right next to the Popponesset Island would beckon .. we left that for another day.
We sailed back when it started raining. Overall, the spot was not quite as good as I had hoped for, but it was still plenty of fun. There's definite speed potential inside the bay, ideally during ESE and within 2 hours of high tide. However, runs are a bit on the short side, and getting there on a really windy day would require braving some not-so-small chop on speed gear. On summer weekends, boat traffic might also be an issue, but today, we only saw two or three boats coming into the bay. Now if someone could just turn off the rain that usually accompanies easterly winds...

Tuesday, June 13, 2017

Longer Is Funner

You'd think watching coupling and decoupling should be fun. It's not, at least if it's the wind. I did that yesterday, so I know. We got ready to leave several times when the wind meter went up to 18 mph, only to see the wind drop again 15 minutes later.

Today was a similar hot day. When the wind meter started playing the same up-down-up-down games again, I had enough. I put my F2 Lightning in the van, drove to Kalmus, and went out with my 8.5 m V8. Here's what happened:
Simply put: lots of fun! The wind was very iffy near the shore; a few guys who tried to go out on shortboards got very frustrated. The longboard, though, was fun from the very start. I toured a mile upwind to the Kennedy Slicks, where the wind seemed more consistent; then I crossed over to the point. The wind was great again on further away from Kalmus; however, I had to go really slow close to the point, because the many rocks there were barely visible at high tide. The swell on the outside was quite big, but I was out there all alone, and did not want to push my luck.

After about 90 minutes, the wind picked up to averages around 23 mph, and became more steady. Blowing sand was a clear indication that gusts were above 25, and my 8.5 was starting to feel a tad big. I also regretted that I had put in only the three rear-most footstraps - I could get in, but I could not find a nicely balanced position, and constantly had to push the nose of the board downwind. Maybe the Lightning thought it was a shortboard? More likely, though, the fin was not right for the conditions. I briefly thought about rigging smaller, but clouds were coming in, so I did not think the wind would stay up long - and indeed, it went back to its nasty up-down-up-down ways before I made it home. But I'm not complaining - I had two hours of most excellent longboard fun. Fully planing in the rear footstraps, with what feels like 10 feet of board in front of you and in the air, is an almost surreal experience. So, playing with coupling and decoupling winds is fun - you just have to bring the right toys.

Monday, June 12, 2017

Too Hot

The wind has been sparse this spring on Cape Cod. So when the forecast for yesterday started to look good a full week in advance, and then stayed good the entire week, we got excited. But unfortunately, the temperatures also started to climb - to the mid-80s (30ºC) even on Cape Cod, and into the 90s inland. With the water temperatures still in the 60s, the dreaded decoupling threatened. And it came:
iWindsurf wind meter readings for Kalmus 6/11/2017
For comparison, here are the meter reading for Hatch Beach, where the wind was sideshore / offshore:

We made it to the water early enough to catch the best half hour of the morning wind, and stopped as soon as the wind dropped, hoping for a second session in the afternoon after it cooled off. The short pickup at 4 had us return to the beach; but by the time we arrived, the wind had dropped down to 13. We spent the next 2 hours talking to friends in the parking lot, and rigged the next time the wind picked up. It was another false alarm! But this time, we waited it out on the water, and were rewarded after half an hour of shlogging. It got better and better during the next hour, until it got dark and the sand was blowing. Everyone (about 5 windsurfers were left) came of the water tired but happy.

While the heat was to definitely to blame for the lack of wind in the middle of the day, it also has warmed up the water quite nicely. A 3 mm short-sleeved wetsuit is plenty warm, and requires frequent falls to avoid overheating - summer is freestyle time! Nina is now seriously thinking about the loop, so I practiced a few chop-hop exercises that might help. One is jumping far rather than high, and keeping speed; the other one is trying to kick yourself in the butt with the back foot, while keeping the front leg at least somewhat extended. I'm pretty sure some teaching gurus have said that both of these exercises help with the loop - but regardless of that, they are also fun. For once, neither my knees nor my ankles complained about the bit of jumping around, but it may have helped that the total time on the water was less than 2 hours. I also got my first Carve 360s of the summer season, so I was pretty happy. Here are the GPS tracks (a bit shifted to reduce the long break between the sessions):
Today was even hotter than yesterday. The wind tried to come up a few times, but it never lasted more than 15 or 30 minutes. There is some hope in the forecast for the end of the week ... there's always hope.




Wednesday, May 31, 2017

Reader Comments about Filters

In response to my post about the "60 Knot New Speedrecord", a reader had a bunch of comments. I answered the first comment in the comment section of the original post, but he came back with a whole bunch more. Mathew wrote:
"Thanks for writing up a follow up. It should be pointed out that the acceleration filter shouldn't "per point" as highlighted in the follow-up... it should apply from last-good-point until the next point which doesn't breach the threshold. Also - and this example highlights it - once a filter has been breached in the middle of a run, the remainder of the run must be discarded [ most of the time ]. The problem here isn't that we dont understand what type of filtering is required - we already do know -> the problem is that the auto-filtering of the software analysis, doesn't match how humans do it. ie: if your data isn't clear, then then the data from that run shouldn't be used. [ Which is why we use two, three or four GPS's.... ] ... In the RealSpeed example, with 3ms-2 (5.5 kns-2) it takes about 3 seconds for the threshold to not be exceeded [ (20.8-4.5) / 5.5]. Since a new threshold is breached within 3 second window, the new window needs to be calculated... and so on. Thus about 7 seconds or so should be dropped.
A standard practice in all sciences, is to drop data that is completely bogus -> thus all "simple filtering" should be applied first, then apply SDoP filters last. [ Caveat: big-data analysis doesn't work this way generally speaking, as the algorithms are sometimes more accurate using bogus data. ] It would be useful to implement the filters accurately, then apply it to these examples vs. applying a simple SDoP filter.
... the point is -> SDoP/SDoS isn't a panacea - it doesn't replace simple physical constraints of the sport. Indeed humans naturally apply a few more physical constraints, ie: even though 3ms-2 is the threshold, it is completely unlikely to that you will sustain 1/3G acceleration for more than a few seconds simply because the drag component goes up very quickly [ vs terminal velocity of about 30m/s ]. "

This is pretty long, so let me just restate what I think he is saying in simple terms:
  1. We know that acceleration in speedsurfing is limited to less than 5.5 knots/second
  2. When looking at GPS tracks, that allows us to identify artifacts without any doubt. If the speed shoots up from 5 knots to 20 knots between 2 data points, we know something is wrong.
  3. If software could implement this "physical constraint" in filters, that would allow the identification of artifacts without SDoP filters.
  4. However, just throwing out single points where the acceleration is above the threshold is not good enough (as I had illustrated in response to his previous comment).
Before I go into a detailed analysis about these points, let me say that I mostly agree with Mathew. For example, the typical acceleration in speed runs is less than 2 knots per second. For example, check out one of Boro's recent traces where he got close to 40 knots:
Let's zoom in on the speed run in the middle:
I selected the region where the acceleration was highest, or close to it. Within about 4 seconds, he went from 31 knots to 36 knots - that's an acceleration of about 1.25 knots/second. So if we accept that this is a typical track, then a threshold of 5.5 knots/second seems rather safe. But is it?

Let's look at what the current default in the most accurate GPS analysis software is, GPSResults. For 5 Hz GPS data, the acceleration filter defaults to 8 m/second(squared) - that's 15.55 knot. That's about three times as high as what we said! Why does GPSResults not use the 3 m/s2 that Mathew suggests?

Well, theories are all nice and good, but it's always better to look at real data. I went through a test set of about 200 GPS files from GW-60 watches and GW-52 units to see how many of these files had points with an acceleration above 3 m/s2. The answer: 125 of 197. That's about 2 out of every 3 files! If we'd implement a filter with this threshold, it would remove good runs from the majority of files.

So what threshold would work? In the test set, the highest acceleration within the top five 10-second runs was 6.35 m/s2. If you're wondering what the data look like, here's a screen shot from my analysis software:
At the second point in the table, the doppler speed jumped from 25.562 knots to 28.03 knots - that's about 2.5 knots faster in 0.2 seconds! Looking at the track, the spike is quite obvious. It looks like random noise added on top of a much smaller real acceleration; in the next data points, the speed goes down again. Overall, though, this run looks good - there's no reason to discard it.

So even for this small set, we'd need a threshold close to 7. If we'd look at more test data, we'd probably find a few tracks with even higher numbers, so the threshold of 8.0 that GPSResults uses for 5 Hz data seems quite reasonable. Unfortunately, having to use a higher threshold throws off Mathew's argument a bit. 

The higher threshold is needed because the higher frequency data from the GW-60 and GW-52 devices has a lot more noise. That's not a problem - since we have a lot more data points, we can average out the noise. But trying to implement this in a filter will be quite a bit more complicated than it seems at first glance.

If we examine the current versions of 4 different programs to analyze GPS data (GPSResults, GPS Action Replay Pro, ka72.com, and RealSpeed), it appears that only one of the four has a reasonably implementation all filters that are known to work, and uses them by default when calculating speeds (I am talking about HDoP, SDoP, minimum number of satellites, and acceleration filters). Three out of the four programs are missing one or more of these filters, and/or require a separate manual step to apply them. This is for very straightforward filters: "if the value is above (or below) the threshold, mark the point as bad, and do not use it to calculate speeds". It would be a great improvement to see these simple known filters implemented in all four GPS analysis programs.

But even the most accurate program, GPSResults, currently fails to identify some artifacts that can occur when the data quality is marginal (but not obviously bad).  For this particular problem, better filters would be needed - for example filters that use average SDoP errors for short-term speed (or standard error estimates, which also consider all error estimates in a region, not just single points). For errors that result from "dead reckoning"-type overstatements, acceleration filters would not help at all - the very cause of the error is that the software inside the GPS tries to keep speed relative constant when the GPS signal is bad. So far, though, the level of interest in implementing better filters for such artifacts seems darn close to zero.

Let me finish with a comment on Mathew's pointers towards scientific and "big data" analysis. There are some interesting similarities between large-scale DNA sequence analysis and GPS analysis. I worked in large scale DNA sequencing at the beginning of the Human Genome Project (HGP), when the data were analyzed very much like GPS data are still analyzed for records: with some computer help, but also a lot of human checks at any problem regions. During the first years of the project, progress was very slow, and many scientists doubted that the project would finish on time. The first big breakthrough came when someone developed accurate "quality scores" - a measure how likely the sequence data points were to be correct, which is very similar to SDoP values. As soon as these quality scores were widely used, many analysis bottle necks were removed; the accuracy of the "final" results increased dramatically; and throughput jumped. The quality scores were one essential part that enabled further dramatic improvements which allowed the Human Genome Project to finish ahead of its deadline. Early on, I did a little bit of research to evaluate both the accuracy and the usefulness of the "SDoP-equivalent"; the results surprised me positively on both counts. 

In the early phases of the HGP, we did something that is very similar to the wearing of "2, 3, or 4" GPS units that Mathew mentioned - we'd also generate data several times over. We had lots of complex rules and highly educates scientists to check on any discrepancies; but in the end, we ended up with "finished" data that had orders of magnitude more errors that what late could be done completely automatically, using accuracy estimates (and proper filters and analysis algorithms).

So yes, I may be somewhat biased towards seeing the usefulness of accurate error estimates.

Saturday, May 27, 2017

Overstating Speed by 4 Knots

This is a geeks only post. You've been warned.

I love my GW-60 GPS watch, and it has worked great for me. However, recent problems with accuracy that both Boro and Denis on our team had seen made me wonder how often such issues arise. I had never seen them in my data, and I often looked closely enough that I would discover them. But many speedsurfers just quickly analyze the data to get their speeds, and upload those speeds, trusting whatever the software tells them.

So I went on a little fishing expedition on ka72.com. I searched for downloadable GPS sessions from May 15, 2017 onwards, and downloaded data files that were from GW-60 watches. Then, I looked at the tracks in detail in GPS Action Replay Pro and GPSResults, searching for examples where the 2 second speed was overstated.

After checking 15 files, I found one with a problem:  the top speed was just a few seconds of 25-knot speeds, in the middle of what looked like a longer swim. That's not how top speeds are reached! Sure enough, the GPS analysis software came to different results: Ka72.com and GPSResults gave a top speed of 25.3 knots, but GPSResults gave only 21.37 knots - 4 knots less! Let's look at the data:
This windsurfer had set up his watch to record only if the minimum speed exceeded 5 knots. The middle graph shows the speed: it was below 5 knots for about 4 minutes, with a few seconds where he supposedly sailed a lot faster than during the test of his session. The tracks on top show that this was at the very end of a run, after turning around - very suspicious! The accuracy graph at the bottom confirms the suspicions: the watch new that it did not have good data, and gave the data near the spike a much higher error estimate than the test of the track. Which, by the way, is why GPSResults did not include this region when it looked for top speeds.

Here are the data points in this region:
All data points in this regions have +- numbers between 3.2 and 4.957 - in other words, they are junk and should be ignored. For this screen shot, I forced GPSResults to behave badly by turning the filters off. The two other analysis programs, GPS Action Replay and ka72.com, always behave badly with data like this - they do not have SDoP filters.

In both this and the previous example of speed artifacts, the errors occurred during prolonged times where the windsurfer apparently was in the water, probably swimming, trying to waterstart, or resting. In such situations, GPS watches are more prone to artifacts because of where they are typically worn: on the wrist (instead of on the upper arm or helmet like other GPS devices). That means the watch will be under water much more than a GT-31 or GW-52 GPS, not getting any GPS reception because water absorbs the GPS signal. But at times, the watch may be close to or just above the water, and get a signal for a short time. At that point, the GPS chip has to re-acquire the satellites, and calculate the current position from scratch - which can introduce big errors, especially if the reception is marginal. In the tracks and the non-doppler speed graphs, there are often big jumps and spikes when this happens. Usually, that's not a problem with doppler speeds (which is exactly why we use doppler speeds for GPS speedsurfing!): single speed spikes from position adjustments just disappear in the doppler speeds. But when swimming with the watch close to the surface, we sometime see multiple spikes in the speed graphs. When that happens, the error can "go through" to the calculated doppler speeds, which is what we see in the graphs above.

Many speedsurfers may never see issues like this one because they sail in shallow locations, nail their jibes, and/or waterstart quickly very time they crash. But if you have a session where you spend a considerable amount of time in the water, then the chances of errors like the one described here are significant. Sometimes, it's obvious - Denis knew he had not set a new world record. Other times, it's not; in the example above, the 2 second speed seems reasonably close to the 10 second speeds, at least at first glance, so the result was posted to the GPS Team Challenge. In this case, it did not affect anything; but similar problems could happen during faster sessions that count for the monthly ranking.

While this particular problem here may be specific to GPS watches, and maybe even the GW-60 watch, I have seen similar artifacts in GPS data from all kinds of devices, including the long-time "gold standard" GT-31. Typically, it's easy to recognize such problems if you look at the your GPS traces, and examine your doppler speed graphs for the top speeds. In GPS Action Replay, I also find the "SDoP" graph quite useful to identify problem areas. I don't find GPSResults quite as intuitive, but then, GPSResults does a much better job at filtering out problem areas automatically, so the results are more likely to be accurate in the first place. Hopefully, we'll also see similar automatic filtering soon on ka72.com and in GPS Action Replay Pro.

Thursday, May 25, 2017

60 Knots - A New Speedrecord?

Short answer: no. Before I get to the long answer, let me warn you: this is another one of my geeky posts. I reckon it may be of interest to about 5 or 10 windsurfers in the whole world! You've been warned.

This all started when our "United Speedsailors of America" team member Denis posted results from a recent session. He had uploaded his results to ka72.com, and it showed that he had reached 2 second speed of 59.88 knots:
Denis does around 40 knots on a regular basis, so he is wicked fast. But he also knew that he definitely had not broken the world record for 2 second top speed (55.23 knots by Antoine Albeau on the Lüderitz Speed Channel). Even the ka72 results hinted in that direction: his best 10 second speed was just 30.1 knots.
Furthermore, Denis often sails with Boro, who just recently had his own problems with GPS accuracy,  so he was very skeptical about what his watch tried to tell him. He had also worn his old trusted GT-31 GPS unit, and that had reported a top speed of only around 30 knots.
World-famous speed surfer and GPS guru Roo (yes, he is from Australia!) immediately looked at the tracks, noticed that during the time of the supposed record speeds the "sat count dropped to 6/7", and came to the conclusion that due to "the surrounding mountains the sats that were just above the horizon produced poor signals which caused the anomoly".

Well, this seems to make sense - Denis and Boro are windsurfing on a mountain lake, so the mountains around it must be too high! Since almost everyone else is windsurfing in flat terrain, maybe we can just ignore their problems? That's simple! Simple is great! Right?

Not so fast, cowboy! Sure, there are 10,000 ft (3,000 m) mountains around Washoe Lake. But the lake itself is at 5000 ft elevation, measures 2 x 4 km, and is in a valley that extends more than 10 km from each end of the lake. So a lot of the sky and the GPS satellites will be visible. So let's look at the tracks:

The doppler speed graph from his GW-60 watch is shown on the top in red; for comparison, the GT-31 data are shown in blue at the bottom. The GW-60 data show 3 spikes: 2 above 50 knots, and one above 70 knots! Before we jump to any hasty conclusions, let's zoom in on the largest spike:


We can see that the blue (GT-31) graph shows a speed close to zero around the time of the spike. In other words, Denis was most likely in the water at that time. There are few things that kill GPS reception as well as a few inches of water! We can also bet that Denis wore his watch on his wrist, and the GT-31 on his upper arm, so at times, the watch will have been deeper under water. Sure, the watch should not show a spike like this .. but I have seen similar spikes in GT-31 data in the past (and do not usually see them in GW-60 data, even when I fall a lot). As Forest Gump said: "It happens".

But let's not stop there - let's look at the actual data points:
Pay attention to the "+/-" column, which shows error estimates for the speed (also called "SDoP", for "Speed Dilution of Precision"). The SDoP values start at around 2, but then quickly jump up to 4.957, which is where they stay for a while. At the first line of the highlighted area, we can also notice that the time between data points jumped from 0.2 seconds to 16.6 seconds - for more than 16 seconds, the GPS did not have enough reception to calculate speed. Denis, where was your hand?

If you wondered why the +/- numbers never got higher than 4.957, give yourself a geek gold star! That's simply because the SDoP numbers are stored as a single byte in the .sbp files, and the highest number possible corresponds to 4.957 knots. In plain English, an SDoP of 4 or higher indicates complete junk.

So, the watch actually knows that these data points are junk! Any analysis software should now, too! As guru Roo correctlu pointed out, GPSResults completely ignores the problematic data points, and gives top speed results that are practically identical to the results from the GT-31 unit. GPSResults has an SDoP filter, and by default refuses to include any regions with SDoP values above 3.0 (for 5 Hz data). The big question remains: what about other software?

Many Australian speed surfers analyze their results on ka72.com, and Denis did. However, it appears that ka72.com either does not use SDoP filters, or does not use them correctly. If we assume that Denis' problem had more to do with putting the watch under water than with being surrounded by mountains (which was not a problem when he was not swimming), then this problem might affect many other speed surfers, and needs to be addressed (there's also a problem with the alpha 500 numbers being wrong for this track).

Now, how about my favorite GPS analysis software, GPS Action Replay Pro (GPSAR, which I used to create all the screen shots above)? Unfortunately, the results are not pretty:
GPSAR calculates a top speed of 64.55 knots! Based on the settings shown in the speed dialog, GPSAR does not have any SDoP filtering at all, and thus arrives at incorrect results.

So, here's the bottom line:
  • Accuracy estimates are fantastic to automatically identify bad data can lead to very large over-estimates - even fake "world records"
  • ka72.com and GPS Action Replay Pro do not appear to have functioning SDoP filters at this point in time; any data analyzed with either software should be carefully checked!
  • GPSResults has SDoP filters that can correctly identify artifacts such as the ones described here; however, as I have shown in a previous blog entry, the default settings may not be adequate to catch smaller errors, which can overstate speeds by a knot or two
--
As mentioned above, Denis's data files are available on ka72.com. I also made zip files with the data from my previous post about GW-60 accuracy for Boro's data and for the 6-GPS test drive.
--
Added May 28, 2017:
In a comment to this post made today, Mathew made the bold statement "You dont need SDoP - just have a sensible acceleration filter". Well, acceleration filter can indeed be helpful to identify some problems, but they can not identify all problems that SDoP filters can find. The program GPS Action Replay does have an acceleration filter, but using it (which is an extra step that most users won't do) does not fix the problem. Applying a 3 m/s2 acceleration filter in the current version of GPSAction Replay (5.23) removed 801 points from Denis' track:
But afterwards, the speed table still shows a top 2 second speed that is 17 knots to high:
That's a little better than the 64.55 knots before the filter, but still wrong. Perhaps this is a bug in GPS Action Replay that could be fixed - but acceleration filters can, by definition, only identify some artifacts: those with too much acceleration. In case of artifacts that remain high for a few seconds, acceleration filters will fail. Here's an example, using RealSpeed and the problem trace I described in my next post:
Here, the speed increases from less than 1 knot to 20.5 knots in 0.2 seconds, and then to 24.7 knots. After that, the speed remains around 23-25 knots for more than 2 seconds. The acceleration filter identifies the first 2 points, and also a few points at the end of the artifact (shown in red); but the points in the middle have low acceleration and look fine to the filter, which is why they are shown in green. Even after applying the acceleration filter, this data set still gives a 2 second "top speed" that is from an artifact, and 4 knots higher than the real top speed in this track. But the SDoP values in this region, which are all above 3, make it very clear that the data cannot be trusted and should be discarded.

Another example of errors which acceleration filters cannot catch, but SDoP filter can, are the more subtle 1-2 knot errors that can result from using an underhand grip in speed runs, with the watch facing downward and the lower arm blocking the GPS signal. It remains to be seen, however, what the best thresholds and implementation details for SDoP filters are that can catch such artifacts, without throwing out "good" data where just a single data point has higher-than-usual error values. That requires looking at a bunch of GPS files in detail to see how to separate the good from the bad, and will take a while.

Wednesday, May 24, 2017

Lightning in my Harbor

Lightning is the only thing that gets windsurfers off the water. But sometimes, Lightning may be the only thing that gets windsurfers on the water. Obviously, I'm talking about two different things.

The thing that got me on the water today is shown in this picture:
It's an F2 Lightning from 1987. I got it a few months back for $100. What a steal! Of course, it needed some work - a few little holes needed patching; the footstraps were falling apart and needed to be taken off; the mast track needed an hour of my attention before I figured out how to make it work again; and the daggerboard gasket needed to be replaced (with a few layers of sail repair tape for now). The picture above is from its brief maiden voyage at Fogland last week. Since then, I started to work on putting some footstraps on, and got the mast track working again, so I was dying to test it. When the Chapin wind meter showed averages around 14 mph today, with gusts to 17, I just had to go! The GPS tracks tell the story:
For comparison, here are tracks from an earlier session on a 117 l slalom board with the same sail:
The slalom session had quite a bit more wind (gusts up to 24 mph), but the tracks are more the typical back-and-forth session (I had to use a weed fin, which did not help). In comparison, going upwind on the F2 Lightning was not only 10 times easier, it also was a lot more fun - the longboard railed up very nicely! I played around with the upwind stance Andy Brandt had shown me last year - front foot sideways on the daggerboard knob, with the lower leg lying on the board, and the body far out over the water - that worked amazingly well! The top speed on the Lightning also was quite good - almost 24 mph, compared to 28 mph on the slalom board - but again, gusts were 7 mph on the slalom day! It really helped that going upwind on the longboard was so wicked easy; that made long, deep downwind runs easy, too. But the biggest difference was when the wind dropped down to 12 mph during the last third of the session. On the slalom board, that would have meant boredom and pain - there's simply no fun to be had on slalom gear unless it's planing. The Lightning, in contrast, was still fun, slowing down proportionally to the wind strength, instead of dropping suddenly from 20 mph to 6 mph as the slalom board would have done. The $100 I spent for the F2 Lightning were the best $100 I ever spent on windsurf gear!
Some of the readers with excellent memory may remember the title of this post, and wonder why I called Barnstable Harbor "my harbor". Well, that's simple: I had it all for myself! There were a couple of fishing boats out - maybe one every few of square miles. But otherwise, the harbor was all mine - as it is most of the time when I windsurf there. Not that I'd mind sharing - it's big enough, and one of my all-time favorite windsurfing places!

Monday, May 15, 2017

The Fastest Way To Get Faster

Some people who saw me driving around today looked at me in a funny way. Was it because I had my arm out of the window in 54ºF (12ºC)? Or maybe because I had 6 GPS units strapped to my arm?
In case you're wondering: I was wearing two yellow GW-52 units on top; two GW-60 PGS watches on the wrist, one facing up and one facing down; and a GT-31 plus a third GW-52 at the bottom.

As fascinated as I am with GPS speedsurfing, even I need a good reason to strap more than $1000 in GPS devices on my arm and go for a drive. I had one! I wanted to reproduce what Boro had accomplished recently. Boro wanted to start using his GW-60 watch, and compared it to his trusty old GT-31 GPS units. He got substantially higher speeds from the GW-60 watch:
  • 2 seconds:
    37.99 knots GW-60, 36.29 knots GT-31
  • 5x10 seconds:
    33.71 knots GW-60, 33.20 knots GT-31
That's 1.7 knots more for 2 seconds! It takes me (and others) years to improve my speed by that much! In many other tests, the speed of the watch had been much closer to the speed of other GPS units - was his watch broken, or was there another cause?

Looking at Boro's GPS files, it was obvious that his speed data had unusually high error margins of +- 1 to 2 knots; that's at least 2 times higher than usually, and about 5 times higher than what can be achieved with good GPS satellite reception. The error margins were about 2x higher when he was going the direction of his speed runs than when he was sailing back.

The first suspicion was that he was using an undergrip, with his watch hand closer to the mast, on his speed runs, and Boro quickly confirmed that this had indeed been the case. The human body is a very good absorber of GPS signals, and the GPS gurus had been very concerned about this very scenario - watches faces down towards the water, with an arm between them and the GPS satellites. I quickly did a little test walk with a couple of GW-60 watches on my wrist, one facing up and one down, and was able to reproduce the roughly 2-fold increase in error estimates if the watch is facing down.

But could such an increase in speed errors cause the observed difference in speed? There are some theoretical arguments against that: if the error is random, and we collect data at 5 Hz, we get 10 data points for 2 seconds, and 50 for 10 second runs. Average error should sometimes go up, sometimes go down, so that the total error should go down the more points we have. With 10 points, we'd expect the error to go down about 3-fold; with 50 points, about 7-fold. With data like Boro's that have about 1.5 knots error estimates, the expected error for 2 seconds is just 0.5 knots; for 10 seconds, it's closer to 0.2 knots; for 5x10 seconds, even lower.

So, something just is not right here. Instead of boring you to death with more theory and statistics, let's get back to my little drive. The idea was simple: let's just see what actually happens if we go for a drive with a bunch of GPS units, some facing up towards the satellite, some facing down. Somewhere in the middle of the drive, turn the arm around by 180 degrees and see what happens! And, most importantly - what's the effect on the top speed?

Let's start with a look at the speeds:
This is about 15 minutes worth of data from 6 GPS units - a bit too much information to see much. I deleted a few data points in the middle, where I turned my arm around. I also split the tracks into 2 segments for each device, before and after I turned the arm. So each device was pointing up for one segment, and down for the other.

Let's jump straight to the 2 second speed results from the first segment:
Four units show top speeds close to 28 knots: all the units that were facing up, and the GT-31. But the GW-60 watch and the GW-52 unit that were facing down show speeds that are almost one respectively 2 knots higher! Let's look at the data in detail:

The top graph shows the doppler speed, the bottom graph shows the error estimates. What stands out is:
  • Two speed curves are substantially higher than the others: the black (GW-52 #3) and the red (GW-60 #2). 
  • The same two GPS units have error estimates in this region that are about 2x higher than the other units,
  • The observed error is not random. Both the red and black speed curves stay about 2 knots above the other curves for 8-10 seconds (40-50 data points). If the error would be completely random, this would be extremely unlikely to happen by chance; winning the jackpot in a lottery is more likely.
I can only speculate why the error becomes non-random at high SDOP values, but there's a likely guess: when the signal quality gets too low, the firmware starts to rely more on "dead reckoning". GPS chips sometimes use dead reckoning when no GPS signal is available, for example in tunnels. A sensible firmware implementation would start using increasing amounts of dead reckoning as the signal quality decreases, rather than a single "all-or-nothing" threshold. There are several indications that something like dead reckoning is causing the observed error characteristics, but that probably deserves another post.

Another question that arose was whether the problems are specific to the GW-60 watch, since it apparently has a GPS antenna that is smaller than the antenna in the GT-31, and thus possibly inferior. Let's look at the error estimate graphs from the "up" and "down" segments to get an idea. I color-coded the graphs so that blue indicates "up", and red indicates "down". Here's the GW-60 watch:
The SDOP values roughly doubled when I turned my arm so that the GPS was facing down. Here's the same graph for a GW-52:
Pretty similar, again with a marked increase when the GPS unit was faces down under my lower arm. Finally, let's look at the GT-31:
The GT-31 was facing down during the first segment, and up in the second segment. Again, we see much better data accuracy with the GPS facing up towards the satellites. Note that I sometimes had to take my hand into the car to turn, and that I may not always have had the arm oriented perfectly up or down, but the overall trend is clear: all three devices show the same trend towards much degraded accuracy of the GPS is worn facing to the ground.

Here are some conclusions and suggestions from this analysis (some of these points just re-iterate what others have stated many time before):
  • When using a GPS watch, make sure that the watch is facing up during your speed runs! If you use an undergrip on your front hand, wear the watch on the inside or (even better) on your back hand. Or get an armband extended and wear the watch around your bizeps - it will get better reception there. For the best GPS reception and the most accurate data, consider mounting it on your helmet (if you wear one).
  • The GPS analysis software may need to be modified to deal with poor quality data better. For example, the default SDOP cutoff of 3.0 that GPSResults uses for 5 Hz data seems too high, as the example above and Boro's initial experience show.
  • While the examples I have shown here focus on speed over-estimates, it's just as possible that the error goes the other direction, and the speed is under-estimated. Here's an example:
The red track is from a downward-facing watch, and the speed happens to be several knots too low just around the maximum speed for this region. So wearing the watch facing downward during speed runs may not just be the quickest way to pick up a knot or two - it may also be the quickest way to loose a knot. So - keep it up!

Monday, May 8, 2017

Fun With Eddie's Pictures

We had a couple of nice windsurf sessions at the "Kennedy Slicks" in Hyannis Port Harbor yesterday and today. Eddie took some pictures both days - yesterday from Hyannis Port, today from Kalmus, about a mile away. Here is a picture from yesterday:
I'm about 200 feet away from the pier in this picture. The wind had dropped a bit when the picture was taken, so I'm hanging really low. I had wanted to stop a few minutes earlier, but went out again when I saw that Eddie was just setting up to take pictures.

For comparison, here is the picture from today:
In this picture, either I have shrunken a lot since yesterday, or the wall is noticeably taller. Some shrinking happened - I was on a 7.0 today and a 7.8 yesterday, so the mast length was about 460 cm compared to 480. But mostly, the wall was taller.

Some of you may think I'm telling stories. Some may grow concerned about walls in the water suddenly growing. Some may astutely observe it's not the same section of wall in the two pictures. But those of you who have windsurfed at the Kennedy Slicks will remember that the spot is quite tide dependent. We don't have a lot of tide in the Nantucket Sound - the different between high and low tide today was only about 3 feet. According to the the tide tables, the tide was about 1 to 1.5 ft lower when today's picture was taken.

Since we've got the pictures, know the mast lengths, and have too much time on our hands, we can calculate the height of the wall above the water. Yesterday, it was about 140 cm; today, it was a bit above 200 cm. Most of the difference was from lower tide levels; the remainder could be from some small differences in height between the different sections, or from slight chances in wind direction that pushed more water towards shore yesterday compared to today (it was SSW-SW yesterday, compared to WSW-SW today).

Why does it matter, you ask? Well, thanks for asking! You just gave me an excuse to post today's GPS tracks:
I got my top speed of the day in the second run. All top 5 speeds were in the first 30 minutes; after that, I could not break 30 knots again, no matter how hard I tried. But the readings from the nearby iWindsurf meter show that the wind actually was a knot or two stronger in the second half of the session. So I should have been able to go faster after the first 30 minutes!

From the beginning to the end of the session, the tide dropped by about 0.8 ft, according to these tide graphs. That's not a lot, but it made quite a difference in the wind quality close to the wall - the wind became a lot gustier and weaker, at least in the really flat section within a 100 or 200 feet of the pier. Nina, who was freestyling and playing with waves, verified that this was a localized effect - when she sailed away further from the wall, the wind became steadier and stronger.

That a higher wall due to a lower tide will impede the wind more is not exactly rocket science, but what surprised me was that even a change of less than one foot made such a noticeable difference. When I stopped sailing, the predicted tide level was at 1.55 ft. At more than 2 feet, the wind gets a lot steadier; at 2.5 ft or higher, the disturbances from the wall are quite small, even when sailing within 150 ft of the wall. The higher tide levels come with a slight drawback: a lot of water can gush through the big holes that are in the first third of the wall close to shore, which creates "general unrest" in the water in the near-shore section. But then, I need to practice speedsurfing in chop, so I'll borrow a quote from Coach Ned: "It's all good".

Friday, May 5, 2017

May May Be Good

Some will probably say I'm jinxing it. My answer? Listen to the great Stevie Wonder! Superstition ain't the way! So I'll just say it: May may be good.
The start has been very good - we have windsurfed 3 of the first 5 days. My kind of sailing, too: flat water! We started at Kalmus twice, but I escaped the bumps by sailing to the Kennedy Slicks one day, and to Egg Island the other day. Why, you ask? Check out this short movie from the Egg Island day:

There are very few things I like more than going full speed into a jibe on perfectly flat water. Amazingly enough, I'm still improving my jibes, even after tens of thousands of tries. Yes, that's right - tens of thousands. A good windsurf session has 50 to more than 100 jibes. Multiply that with 150 sessions per year. Repeat for a decade or three, and you might discover the actual number may be larger than 100,000. Do you need any further proof that I'm a slow learner? But it's fun!

The major thing I have been focusing on recently was to switch the feet as soon as the clew moves forward. It's only six years ago Matt Pritchard told me I should do: "imagine a line connecting your foot and the clew - when the clew moves, your foot moves". In my defense, I have been playing around with not switching the feet at all during the jibe as a way to get into switch stance. That's fun, but not the best way to cure "slow feet". Even in the first jibe in the video above, which is pretty decent, I'm still stepping just a little bit too late. But as the Beatles said - "it's getting better all the time".

The thing that made the recent flat water excursion real fun was that Nina joined me every time. When I sailed up to the Kennedy Slicks, she just followed. That confused the wind a bit, so it dropped soon after. But the next time at Kalmus, it was actually Nina who suggested that we'd sail to Egg Island. Twist my arm!  I got so excited that I did not even think of switching back to my slalom board that was on the beach, because the typical WSW bumps were a bit too large for this wannabe slalom sailor.

Today had some strong wind in the forecast - easterlies in the mid-20s. The rain that easterlies always brings even held of until after noon, so we set out early. After checking out West Dennis and finding it (a) empty and (b) not looking attractive at all, we drove back to East Bay. Nina almost jumped out of the van when we drove close to our home - a mix of temperatures near 50ºF (10ºC), no sun, and previous bad experiences at East Bay had reduced her motivation to windsurf today to almost zero. But somehow, we both ended up at East Bay, where not a single white cap was to be seen inside the bay. But there were some on the ocean, so we decided to rig, anyway - 6.0 for Nina and 7.8 for me, with 99 l and 117 l slalom boards.

To cut a long story (semi-)short, we had a blast. The wind started out good and got better. The water was flat in the middle, and near shore even flatter. So what if it started raining towards the end? We were getting tired, anyway. Thanks to the perfect conditions for laying down jibes, both Nina and I ended up with new personal bests for alpha 500 (that's a 500 m run with a jibe in the middle). Nice!

For the curious, here are my GPS tracks from today:

Friday, April 21, 2017

Back

We're back. For good this time.

First two months in Texas. Typical temperatures: 60s. Typical wetsuit: 3 mm short sleeve. Nice.

Then two weeks in Dahab. Typical temperatures: 70s. Typical wetsuit: 2 mm short sleeve. Nice!

Today on Cape Cod: 45ºF (7ºC). Water a couple of degrees warmer. Except for the water coming from above, but that was just a light drizzle. It did not even hurt when 30 mph gusts made it go sideways. Yes, of course - I just had to go windsurfing in such inviting conditions! I will not let a slight drop in temperatures keep me off the water!

East wind and nobody else out means East Bay. Perfectly safe, quite flat, but a bit gusty. So I rigged a bit bigger - 7.8. The shoes were a bit fatter - 5 mm. So was the suit - I'd rather be too warm than to cold, so the Ianovated suit with tubes was called for. The mittens took some getting used to, but at least they were palmless.

Fun it was. And work. Or rather, a workout. A good workout. The Kalmus wind meter showed only 23 mph averages gusting to 28, but some other nearby meters showed a few miles more. The 7.8 felt big, so I'll believe the other meters. But maybe it was just the gloves. And the low tide: some sections in East Bay can get to shallow for 33 cm fins at low tide. Thanks to the drizzle and my glasses, seeing where it was getting to flat was impossible. That kept the session short. But the cold was beaten! I was warm or hot the entire time. Nice.

Back to Dahab:
Reef and mountain view at Speedy in Dahab

The two weeks there were fantastic. Meeting lots friendly, laid-back people restored my faith in humanity. It did not matter one bit that their faith differed from the faith I was brought up with. Windsurfing was also great: 9 of 13 days planing, mostly on 5.x (4.x for Nina), plus a couple of days with nice light wind sessions, and a couple of days of snorkeling. Nina liked it even more than I did, since she had plenty of company from other freestylers working on everything from Vulcans to Flakas and Kabikuchis. Travel warnings for Egypt almost killed tourism for the last few years, but southern Sinai is Beduin country, far removed from the trouble areas. I have never felt safer than in Dahab. Really nice.

Wednesday, April 5, 2017

No Wind Fun

After 4 windy days in a row, we actually welcomed a no-wind day today. How windy? Nina was on 3.7, 4.0, and 4.2. Thanks to all the good food here and in Texas, I was on 5.x sails most of the time, although a 4.7 would have been plenty for at least one session. And this is still not the windy season - from Mai to September or October, windless days are rare, and 4.x sails are the norm for guys.

But for now, Dahab is just as serious about the no-wind days as it is about the windy days: no wind means 0.0 mph, gusting to 0.0, for much of the day. Fortunately, this is also a great diving and snorkeling spot, so snorkeling we went. Nina is hogging the drive with the GoPro footage, but here's one screen shot I managed to grab before I had to hand the drive over to her:
I don't snorkel often, but I have snorkeled in Belize, Puerto Rico, Bonaire, and the US Virgin Islands. Today was certainly up there with the best spots I had seen before - lots of variety in both corals and fish. But the entire experience was rather unique - here is how it went down:
We walked 5 minutes from our lovely condo to the windsurf rental place to pick up our wet suits and snorkeling gear, and then walked back a minute to the street, where one of the local Beduins asked us right away if we needed a taxi - yes, we did. After a short drive that cost us 20 Egyptian pounds (LE; about $1), we arrived at the Eel Garden View restaurant right at the beach. We dropped our stuff at a table, ordered a large water (8 LE), and walked out into the water. The picture above was taken about 200 or 300 feet from the beach. We snorkeled for about an hour, and then had a great light lunch at the restaurant (Beduin tea for Nina to warm up, a hummus platter and falafel sandwich, and fresh pressed orange juice - all for less than $5). We hung out there for about 3 hours in total, before walking down the beach promenade for desert at the German bakery. Another taxi ride back (virtually all cars in Dahab are taxis!), and then we almost had to hurry - only a few more hours before we go back into town for dinner with our hosts, Toby and Fiona.

Saturday, April 1, 2017

Yum Yum

We finally got some of the wind Dahab is famous for today. I was fully powered to overpowered on 5.3, Nina switched from 4.2 down to 3.7. We sailed for a bit more than 3 hours; the wind stuck around for most of the afternoon, but dropped from high 20s (mph) to around 20. I'll use my GPS tracks to explain the three windsurfing areas here:
The area on the top left is the lagoon. The wind towards the launch at the left is partly blocked by windsurf centers and hotels, and gusty. The main advantages of the lagoon are that it's close the the biggest windsurf center, Harry Nass, and that you can stand at the right end.

The area in the middle is "Speedy", with a big reef on the right, a small reef on the left side, and about 800 m of relatively flat water in the middle. It gets flatter the closer you get to the shore, but there is a small reef behind the sandbar, so windsurfers tend to stay about 50 meters from shore. As you might guess from the tracks, I like this area a lot.

The third area is on the right side, past the reef. There's big swell there, about head to logo high today. The waves sometimes ramp up and topple over a bit, but don't really break. That spot was quite popular today. But if you have gear issues there, you drift downwind quickly, and you'll be virtually invisible between the swell. That why most centers suggest to go there with at least 3 windsurfers - one to stay with the windsurfer in trouble to "mark" him, and one to sail back to the center to get help. The Harry Nass centers actually hand out walkie-talkies so you can call for help if in trouble.

Windsurfing was a lot of fun today, but the highlight of the day was once again the evening. We first stopped at the funky Every Day Cafe for some excellent cake, and then had a beer at Churchill's bar. But the last stop topped it all: Yum Yum Falafel for the best falafel sandwiches I ever had. The cost of 4 sandwiches and two bottles of water? 28 LE, about $1.50. Ridiculously cheap, ridiculously good.

Thursday, March 30, 2017

Dahab!

We've made it to Dahab. No, that's not Dahab in the picture above. That's just a pretty picture from the flight. Of course, you know where Dahab is, but for those few who do not, here's a map:
Dahab is on the Sinai peninsula in Egypt, at the Red Sea. Saudi Arabia is just 15 miles away across the water. The area around Dahab is quite picturesque, and very different from anything I had seen before:
We are staying in a lovely little house about 3 minutes from the beach that we share with the owners, Fiona and Toby, and one other apartment for vacationers. Fiona greeted us when we arrived after the 4-hour flight from Germany and a one hour drive. A couple of hours later, Toby drove us around town, showing us where the best restaurants and "super markets" are. They had stocked the fridge before we came, and Toby took the fresh fruit and groceries we bought back to the apartments after dropping us of at a restaurant - fantastic service! We started to understand why the apartment had gotten only 5-star ratings on TripAdvisor - and many of those!
The restaurants here are very good, and there are dozens of them right on the water. We had pizza the first night which was better than 99% of all pizzas I've ever had. The cost? About $5 for a pizza and beer. Yes, it's dirt cheap here. Nina had a big meat dinner the next day, which was served with a little portable grill placed on the table, and included fresh bread and dips before and Beduin tea afterwards, all for $9. My vegetarian meal cost about half as much and was very good. This is a great place to be a vegetarian: all restaurants have plenty of vegetarian selections. Here are a few pictures:
The seafront promenade
Top level view
Rooftop dining under palm trees
"But what about the windsurfing?", you ask? Well, we knew that this is not the prime wind season (although there are plenty of expert and pro level windsurfers who are here for months). We did windsurf the last two days, but the wind was a tad on the lighter side. Nina was on 4.7 and 5.0, and had to pump quite a bit, but did get to work on Flakas both days; I was on 7.5 and a Fanatic Ray 115 (a bit overpowered when the wind picked up), and on 6.5 and a 107 l freestyle board yesterday. Today is a no-wind day (averages right now: 0 knots), but I'm hoping to get a light wind freestyle session in in the afternoon. The weekend forecast looks promising, though, with 3 windy days in a row. That should be more typical Dahab wind: our host Toby, who is about the same size I am, has a 4.8 m sail as his largest sail.

Monday, March 20, 2017

Texas Summary

We're back from Texas. This year was quite different from the previous two years. The temperature seemed to be almost the same the entire 2 months, with some days in the 70s in January, and days in the low 60s in March. Most of the rain came towards the end of the trip; in previous years, we saw more rain earlier on.

This year was windy! We sailed 29 days, just about every other day. That includes only one day of light wind sailing, and we love light wind freestyle. There were a few more sailable days that we did not go for various reasons - including that we were tired from sailing 3 or 4 days in a row before, with better wind. We'll go back next year, but probably without the light wind boards.

Driving back was easy this time, once the van was packed. That, however, was not so easy, since we bought a new board, two new sails, and a new mast in Corpus. All the new gear and great wind made it easy to set new personal bests in 4 of the 6 GPS Team Challenge disciplines. Corpus Christi is great for speedsurfing!

Back home, it became apparent that our house had missed us badly. Major pout attack: electricity was out in about half of the house, and neither heat nor hot water worked. But a friendly electrician stopped by within 15 minutes and got most of the electricity back up (with a second outside repair scheduled for tomorrow), and we had backup heat from a gas stove, a wood burning stove, and several electric heaters. So we waited until today to get the heat fixed; all that was needed was a new "thermal fuse" for $25. It did cost us $120 to learn that, but the repair guy was very friendly and professional, and showed up within a couple of hours after we called. He did not have the part that was needed in the van, and would have had to come back a day later to put it in; but instead, he asked me if I was "somewhat handy", and then explained where I could get the part, and how to put it in (which was trivial). 40 minutes later, we had heat and hot water again. These little outages sure make you appreciate things you usually take for granted!

We knew about the heat and electric problems before we even started to drive back, thanks to wifi thermostats and switches. The thermostat alerted us that the heat was not working when it showed that the heater was running all the time, but the temperature never reached 50 degrees. Not a problem, since we had backup electric heaters hooked up to wifi switches ... until two of the switches went offline a couple of days later. At that point, we got a bit nervous. In previous years, our neighbor would have checked on the house, but he just moved to Arizona. Fortunately, Bruce and Gerda live less than a mile away, and were kind enough to check for us. Since the electricity was out, they could not get in through the garage as planned, but they were able to peek into the basement windows and assure us that we'd not be faced with the worst-case scenario: broken pipes and a flooded basement. Big thanks to Gerda and Bruce! Also many thanks to Jerry for recommending Alex, who went above and beyond to help us get the electricity back up.


Sunday, March 12, 2017

Big Foot Problems

Have you ever had a windsurf session where your feet got bigger and bigger as time went on? That's what happened to me today! Let me show you.

It all started well enough. We did not get the usual Texas sunshine, but at least the rain that had been with us for almost a week stopped today. I had hoped to do some freestyle, but when the averages picked up to almost 30 mph, and my 5.0 m sail suddenly seemed huge, I settled for trying to jibe without falling instead. At first, things went ok:


But then, my feet started to get bigger, and I had problems getting into the straps:


As the size of my feet kept increasing, my increasingly desperate attempts to get into the straps after the jibe had me bouncing around:


When I finally got my feet back into the straps, I put them in really good. Too good, as I discovered when I tried to get them out again in the next jibe:


That hurt a bit. Clearly, my big feet required some changes. The first thing that came to mind was a duck jibe, so I tried that:


So far, so good. But I don't really do Duck Jibes. That's too much like freestyle. So how about we just copy the delayed foot work, but otherwise do a normal jibe? Let's see:

That worked! But then, I remembered what my windsurf teach guru Andy Brandt says about this jibe (called "Sail First Jibe" in Alan Cadiz' jibe video): "Don't do it!". I learned the hard way to always do what Andy Brandt says. One time in Bonaire, he told me to go in because I was tired. I went for "one more run", ruined a sail, and almost broke my nose. So something needed to change!

Fortunately, I remembered that doing a sail-first jibe with both feet in the straps is allowed - it's an "easy" way to learn sailing switch stance in the straps. So let's try that:

That has some promise! For some reason, though, planing out seems more difficult. One might argue that this is because the weight further back sinks the tail and reduces speed, but who wants to be that technical? I have a better idea: I'll blame the chop instead! Chop can be blamed for all kinds of jibe problems. Sure, Bird Island Basin does not have a lot of chop, but there is some! All I need is a place that's even flatter! So our next stop (after a brief return to Cape Cod to shovel the drive way): Dahab in Egypt! Stay tuned...

Monday, February 20, 2017

Eye Protection

I blogged about the importance of protecting your eyes from UV light while windsurfing last year, and it's time for an update. My reason to look into this was that I had been diagnosed with cataracts. "No big deal, everyone gets them", you might say. Largely true - but my grandmother died during cataract surgery, so there are darn good reasons to delay and avoid it as long as possible.
Cataracts and other eye problems are directly linked to UV exposure. Wearing sunglasses can help a lot, but has a few shortcomings - some UV rays can still enter the eyes from the sides and from reflection on the back side of the lenses; water drops can impair vision; and on partly sunny days, sunglasses can simply be annoying. I did wear either prescription sunglasses or (on cloudy days) non-tinted polycarbonate glasses almost every single day I windsurfed since last year; but my lovely wife often finds sunglasses too bothersome, and sometimes sails unprotected on cloudy and partly sunny days.
Nina speeding on a cloudy day

I have always found contact lenses much more convenient for windsurfing, and used daily disposables for years, so I'm happy to report that I am back to using contacts. But this time around, I went for UV absorbing contact lenses - specifically, Acuvue Oasys 1-Day lenses. They absorb more than 90% of UVA and 99% of UVB, making them the best UV absorbing lenses I could find. Some other contact lenses also have good to very good UV absorption, but most lenses do not - including the ones I had used until last year. I plan to also wear sunglasses on sunny days, and polycarbonate safety glasses on cloudy days; on partially cloudy days, UV exposure can actually be even higher than on sunny days. So far, the protection seems to be working - at this year's eye doctor follow-up, the cataracts seems unchanged relative to last year (after appearing suddenly within the 2 years before that).

So, if you are wearing contacts while windsurfing, double-check that they offer UV protection. If not, talk to your eye doctor about getting a different kind for windsurfing. If you prefer to use glasses, I can recommend the sports frames from Zenni.com. They are not pretty, but have worked well for me for more than 100 sessions so far, and you can get a pair of polarized prescription sunglasses for about $110.