Saturday, November 26, 2011

The case for Dry Case armbands

When using a Genie GT-31 for speedsurfing, you need a waterproof armband. This post explains why I think that a Dry Case armband is much better than the often recommended Aquapac armbands. Let's start with a picture of the Dry Case armband with a GT-31:
The Dry Case bags use a vacuum seal, which has several advantages over Aquapac bags:
  1. Without air in the bag, there is no excess pressure that pushes water into the bag when the bag is submerged. 
  2. The vacuum causes the plastic from both sides of the bag to stick together. They remain stuck together even when you open the bag - so if the bag developed a hole, water would not fill the entire bag.
Up until recently, I had always used Aquapac armbands to hold my GT-31 (either a medium or a large bag). However, I always noticed that the insides of the bags where getting wet after just a couple of uses, even if the bags were clean and did not show any cracks or holes. After using bags for a few months, they would often develop cracks which let a lot of water in. Since the GT-31 is waterproof for immersion (but not for high-speed windsurfing crashes), that was not a problem. I just put some clear tape over the crack, and the combination has worked fine for me. Eventually, I had to replace a bag or two, though, when the cracks got to big.

However, our fellow Fogland Speedsurfer Sabah has not been so lucky. After a recent session, he noticed that his entire Aquapac bag had filled up with water, and that the GPS turned off. He could not get it to turn back on even after drying it, and trying to recharge it. I took his GPS apart a few weeks later, and this is what I saw:
You can see a lot of corrosion on top of the battery pack and on different parts of the circuit board - apparently, a lot of salt water made it into the case. A close look at the housing reveals problems at the three top screws that hold the upper and lower part of the housing together: one mount is broken off completely, one partially, and the third on is cracked. Most likely, the GPS housing was damaged either during a bad crash where the arm hit the mast or board, or maybe when the GPS was dropped. That alone would not have been a problem - the GPS was still working fine at the beginning of the session. But together with the tendency of the Aquapac bags to develop leaks, it eventually killed the GPS. I tried to rescue it by rinsing with water, but I was way too late. By now, the corrosion as so bad that some parts of the electronics just fell off.

I think the GPS would still be working if it had been in a Dry Case bag instead. I found the Dry Case bag through luck when I needed a waterproof armband in Hatteras, and the only one I could find was a Dry Case armband at WindNC. I have since used the Dry Case several times to hold an Android phone so I could have GPS Speed Talker tell me my speed while sailing, and it has remained perfectly dry so far (I am sure that an Aquapac case would have let water in by now). The Dry Case has a microphone connector which is not needed for the GT-31, but the connector in the bag is actually useful: if you put it on top of the GPS close to the push buttons, you can prevent accidental pushing the buttons while sailing.

It remains to be seen how long the Dry Case really will remain dry. But as I said, I think it is already doing better than the Aquapac armbands. The plastic material seems sturdier and less likely to develop cracks; and using vacuum to get the air out of the bag and to make the sides of the bag cling together is a great idea. When I am using it with my phone, I'll keep double-bagging the phone in a little clear plastic bag. That has been overkill so far, but why risk a $130 piece of electronics that is not waterproof? I also added the little piece of brightly colored plastic. With the phone, the bag may sink in water, even though the armband itself is floaty. That should not be problem with the GT-31, since the GT-31 is "floatable". The armband on the Dry Case also is sturdier than on the Aquapac cases, but all armbands can slip off, especially when using dry suits or no suit. The brightly colored plastic may just make it easier to find the GPS when it's floating in the water. Of course, it would be even better if Dry Case would come with brightly colored (or at least white) arm bands in the first place...

Tuesday, November 22, 2011

Windsurfing Point Judith

Last Sunday, we went windsurfing in the Point Judith Harbor of Refuge for the first time. We had picked the spot because the weather forecast called for very warm winds, which often decouple in Kalmus and Fogland at this time of the year. Point Judith sticks out into the water and is surrounded by water from 3 1/2 sides, so decoupling is much less of a problem (as the wind graphs from warm days from the previous weekend showed).

The launch is at the Salty Brine State Beach, right next to the Block Island ferry. From the suburbs west of Boston, the driving time is about the same as to Kalmus in Hyannis, 75 to 90 minutes. Here are some pictures:
There's a decent sized paved parking lot, and more parking right next to it at George's Restaurant. The beach is sandy and more than a mile long - plenty of space for kiters and windsurfers:
The sailing area is surrounded by jetties, which create a protected triangular area that is about 2 km long:
In addition to the hope for steadier winds, we had been attracted by the jetties, hoping that they would create flat water for speed runs. But when I went sailing, I discovered that the harbor had a nice, long, rolling swell that was just too much fun, so I never bothered sailing up close to the jetties. I did go for a bit of long distance speed, and got some numbers that were pretty good for the conditions (22 knots for the nautical mile and 17.8 knots for 1 hour).

I thought that the place was amazingly easy and fun to sail, and the other advanced sailors all like the spot, too. However, pur newbie Jeff, who only started windsurfing about a year ago and is still working on getting comfortable in the straps, found the conditions not quite to his liking. It did not help that the shore break got the better of him when he came in, and broke his mast. I did not see this happen, but the shore break did not really look bad enough to break masts - I think he had a lemon, and some bad luck. Here are a couple of pictures that show the shore break a bit:

Like Sabah in the picture above, Dani had a lot of fun even though he arrived after the wind had started to go down:
Fred caught a wave on his way in and was smiling ear to ear about it:
The wind died down in the afternoon, and only the guys on the bigger gear were still planing. In the morning when we came, some of the very friendly local sailors had been out on 4.2 - 4.8 m sails, but the wind drop had been in the forecast. We did not get any of the huge ups and downs that Fogland and Kalmus had the same day, so the "no decoupling" definitely worked as expected. On the downside, this means that Pt. Judith won't get thermals in the summer - but then, the somewhat small parking lot would be filled with beach goers, anyway, and I am not even sure if windsurfing even is allowed during the summer season. But for the remaining 9 months of the year, Point Judith is a great spot! At some parts of the harbor, for example near the openings in the jetties, the swell ramped up to chest high, and got pretty steep; it also had a bit of cross chop there, great for jumping, but not nearly as "voodoo"-like as Kalmus can have.

It was great to once again see so many members and friends of the Fogland Speed Surfer team show up, including Fred, Bart, Dani, Sabah, Jeff, Graham, and of course the lovely Nina. The spot definitely has potential for long distance speed, and maybe even for top speed under the right conditions. The water felt quite a bit warmer than on Cape Cod, as can be seen on the sea surface temperature image:

 We will definitely be back!

Monday, November 21, 2011

Closer is faster

One of the great things about being part of a speedsurfing team is that you can examine the tracks of better team members afterwards and learn from them. The first time I went windsurfing with Dean, I learned that I needed to go a lot deeper downwind for top speed. Even now, a year later, I often discover that I did not go nearly as deep downwind as I thought when I look at my tracks in the evening.

Our great little speed session at Egg Island two days ago has provided some more material for learning to sail faster. Both Nina and I improved our previous top speeds by about 3 knots, but there is still a lot of room for further improvement. Here is a comparison of the GPS tracks from our fastest runs (my track has the blue label):
The biggest obvious difference is where we reached our top speed. My top speed was close to the sand bar, where the water was very flat; Nina's top speed was pretty far out in the bay, where the chop got sizable. The main reason why she stayed away from the sand bar was that she was afraid of hitting ground at shallow spots. I had walked the entire length of the sand bar at the start of the session, so I was comfortable getting closer to it, but I still stayed about 40 meters away from it. In most of my runs, I felt that the chop was limiting my speed - as soon as I approached top speed, the chop got so high that I throttled back to avoid crashes. I find it pretty amazing that Nina hit her top speed that far out. Yes, she was on a 49 cm narrow F2 Missile that handles the chop (even) better than my 58 cm wide Fanatic Hawk, but still. As for the top speed difference, keep in mind that Nina almost never goes for speed; that she weighs next-to-nothing, at least compared to me; and that she was using a 4.5 m wave sail instead of the cambered larger race and speed sails that Dean and I were using.

Now let's compare my runs with Dean's. Dean has been playing the speed surfing game a while longer, and he got a lot closer to the sand bar. Here is a comparison of my fastest run to his second-fastest run of the day:
He was about 1.6 mph faster than I was by staying closer to the sand bar. He reached his top speed right at the tip of the sand bar, where the water was flattest. He then kept close to his top speed for several hundred meters into the bay, which speaks for his skills and the chop-handling ability of his Tabou Manta board.

In my four fastest run, the top speeds were very close to each other (57.24 - 58.23 kmh). In contrast, Dean's fastest run was quite a bit faster (62.98 kmh) than his second-fastest run (60.64 kmh). Here is the comparison of our fastest tracks:
Dean was much closer to the sand bar for the entire run, and the smoother water enabled him to accelerate much faster and to reach a higher top speed. It is quite amazing what a difference 100 feet can make! It is quite unlikely that I would have beaten his speed even if I had sailed so close to shore, but I probably would have picked up another knot or two.

For Nina and myself, one goal for the day had been to practice the Slingshot. We definitely had this in mind while sailing, and played around with it somewhat. I don't think that I did one that was good, mostly because the chop on the approach to the sand bar made it seem advisable to start going a bit downwind earlier for more control. Looking at the tracks now, I think that might have been a mistake: holding a steeper angle longer to get closer to the sand bar before bearing off probably would have been faster. But I might need a few more days of practice before I approach a sand bar at 25 knots with the plan to Slingshot myself downwind just a few seconds before hitting it at full speed!
One thing worth mentioning is that I was using the GPS Speed Talker application the entire time that day. It sure was nice to here it telling me 30, 31, 32 knots! The top speed on the Android phone was 0.5 knots higher than from the GT-31, but overall, I think it was pretty accurate, and definitely helpful.

I had planned to use Nina's bluetooth-enabled BGT-31 with the Speed Talker app, but when I tried to set this up, I discovered that updating the firmware on the BGT-31 apparently has removed all bluetooth options from the settings - the menu items are simply missing! I know that they were there initially, because I tried to hook the BGT-31 up to my Mac when we got it. I tried re-installing the older firmware version from the Locosys web site, which worked - but it did not restore the bluetooth menu items! So if you have a BGT-31, think twice before "updating" the firmware version!

Saturday, November 19, 2011

The Egg Island Slingshot adventure

My lovely wife had recently posted a link to a description of the "Slingshot" manouvre in the Windsurfer International Magazine, and we were dying to try it out today. After hearing about how flat the water at Egg Island in Lewis Bay can be, we decided to imitate the freestylers who often sail to there from Kalmus. We were on the water just before low tide, where the chops is small and regular, so Nina decided to sail the F2 Missile. She had tried it only once before, with limited success, but her sailing has improved a lot since then, and she has been on small (72 and 77 l) boards quite often. So this time, she did just great.

The water behind the sand bar at Egg Island was beautifully flat. The wind was a tad more gusty, especially at the approach to the sand bar, but nevertheless, these were almost ideal speed conditions, with wind averages around 30 knots. Nina quickly broke her old personal bests, reaching almost 50 kmh. Dean got his best speed outside of Hatteras, with more than 34 knots. Your's truly sailed while listening to the GPS Speed Talker, and it quite often spoke of 30 and 31 knots. At the end of the day, my 2 sec top speed was 31.4 knots (58 kmh), and I even broke the 30 knot barrier in the 5 x 10 second average. Being on my 5.8 KA Koncept certainly helped - but Egg Island at low tide sure is a great speed spot. Now why again did I never sail there before in SW winds?

Here are my GPS tracks for the day:

 It was nice to see Nina work on speed for once, and she found sailing the Missile "very interesting" (in a good way). After I short break, I borrowed the 4.5 m wave sail that she had sailed all day for some bump and jump fun.  Graham and Martin were still out, and they both worked on loops. I saw some very nice tries, and at the end of the day, Graham actually made it around and water started out of a loop attempt - congrats! The pain on the back will eventually go away :)

Thursday, November 17, 2011

Why wind forecasts drop

In recent weeks, the wind forecasts on have often shown this annoying pattern:
  • the wind predictions 5 or 6 days out look great, and remain great for a few days
  • about 2 days before, the forecast suddenly drops and looks a lot less impressive
For example, the forecast on Monday may predict 30 mph winds for the weekend. This stays more or less the same until Wednesday - but on Thursday, the forecast drops to the low 20s. This happened a lot in the last few weeks. Almost every time when we went sailing, though, the actual wind was much stronger than the most recent forecast, and closer to the stronger forecast from a few days before. 

What is going on? Well, let's have a look at the iWindsurf forecast tables for Kalmus from this morning. The default tables show the "Quick Look":
Until yesterday, the forecast for Saturday called for wind in the upper 20s to low 30s; now, it shows mostly low 20s. Sunday is still looking a lot better in the table above, but dropped a few miles later during the day.

A look at the different computer models sheds some light on what's happening. Here are the tables from the GFS model:
The tables from the NAM model don't look quite as good:
Both are run by NOAA. The NAM model has a finer geographical resolution (12 km vs. 35 km for GFS), but gives predictions only for 84 hours, compared to 7 days for the GFS model. The "Quick Look" table on iWindsurf will use the NAM model if it has data for the entire day, and the GFS model otherwise. So in the example above, it shows NAM data for Saturday, and GFS data for Sunday.

This time of the year, it seems that the GFS model always predicts stronger winds  than the NAM model, at least for the Cape Cod area. So when the iWindsurf "Quick Look" tables switch from the GFS model to the NAM model, it seems that the wind forecast has suddenly dropped. In reality, however, the wind prediction from the GFS model may not have changed all all, or even gone up!

I do not know why the GFS model seems to make better wind predictions than the NAM model at this time of the year, but I'm glad it does. As I am writing this, the latest NAM model runs predict 23-25 mph for Saturday (that's 5 Beaufort for our European readers), while the GFS predicts 27-29 mph (6 Beaufort). My bet is that we will see 30+ mph again!

So, if you are making plans for windsurfing on Cape Cod for the weekend, check the GFS tables! Just keep in mind that when it gets too warm, decoupling at onshore beaches may cause winds to be a lot lower than predicted. That will hopefully not be an issue on Saturday, but it could be a problem in Kalmus on Sunday.

Tuesday, November 15, 2011

Four funtastic days

We just had four fantastic days of sailing - here are the wind graphs:
We sailed three different spots to catch the best wind each day; the only spot we sailed twice, Skaket, had very different conditions on the two days we sailed. Here are the three spots on a map:
It's easy to see why we chose Skaket for the WNW wind on 11-11, Kalmus for SW on 11-12, and Fogland for SSW on 11-13: they are the spots with the best fetch for the given wind direction. In addition, Kalmus typically has thermals that increase the wind in SW, and Fogland can have thermals and channeling in SSW. Why we picked Skaket on 11-14 is explained below.

Day 1: Skaket, WNW, 30-40 mph
We had good memories of gentle waves at Skaket in NW winds, and when we arrived about 90 minutes after high tide, the waves looked perfectly manageable for us flatwater sailors, despite the strong winds that sandblasted us and made rigging a bit more difficult. We rigged the smallest sails we typically use (3.7 for Nina, 4.5 for me), and used the smallest boards: the Angulo custom 72 for Nina, and the Goya One 77 for me. We were soon joined by Ron, who lives just a few minutes away. By the time we hit the water, the waves had gone down a bit, and were just perfect for wave newbies like us. Despite the wind being almost straight onshore, getting out was easy. I absolutely loved how flat the water was between the waves! After mostly sailing bigger boards in the last couple of months, it took me a few attempts before my jibes were dry - but one of the nice features at Skaket in WNW winds and medium water levels is that you can go for mile-long runs parallel to the shore, and still touch ground when you fall in. The boom cam video below shows how flat the water was between the waves:

We had to stop after 90 minutes because it was getting quite shallow, but it was almost getting dark, anyway. We stayed overnight in Hyannis, where we met up with Jeff, Graham, and Manish. They had sailed in Chapin, and reported gusty conditions with some voodoo chop - it seems we had picked the better spot.

Day 2: Kalmus and Kennedy Slicks, 35-40 mph
The forecast for the day called for SW wind in the low to mid 20s, but sun and swarmer temperatures. Based on recent weather patterns, I expected a significant thermal boost, and was not disappointed. We hit the water at 11:30 am, and I did a few runs with my Skate 110 and a 5.5 m sail, but that combo quickly got to big, and it was time to go down to 4.5 and 95 l. As we were getting close to high tide and wind averages picked up to 35 mph, the famous Kalmus voodoo chop came. Here's a picture of young Master Graham having fun:

In the steep waves with lots of cross chop, jibing and even controlling the Hawk 95 became a challenge, so I decided to cruise upwind a mile to the Kennedy Slicks, where Dean was going for speed runs. By now, it was getting a bit crowded on the water, anyway, and I really wanted to be on the nice, flat water next in the Hyannis Port harbor.

Getting upwind was easy enough, since I had plenty of power. On my last run out towards the jetty, I heard a snapping noise, and my harness lines suddenly seemed a bit longer. When I jibed and tried to hook back in, I noticed that one side of my harness hook had broken off! I hooked in, anyway, but it took only about 10 seconds for the other half to snap, too. Sailing without the harness is something I just don't do - lazy me usually hooks in first thing, and accelerates later. So I chickened a bit and sailed back to shore without even getting into the foot straps - stupid idea, that just resulted in things taking 3 times as long, with a lot more pressure in the sail. When I finally made it to the shore, my lower arms were burning.

Dean did not have a second spreader bar, but he was nice enough to offer me to take turns with his harness. Fortunately, that was not necessary, since a local windsurfer who was just taking pictures offered me a ride to Kalmus to pick up the spreader bar I had bought two days before, but foolishly not used. Thanks so much for the ride and the ride back (and sorry that I forgot your name)!

So I finally made it out onto the "Kennedy Slicks" right next to the jetty in the Hyannis Port harbor - and slick they were! About 100 feet from the jetty, the chop was about 2 inches high - chitter-chatter chop, my favorite kind. What's better than waterstarting in the foot straps, going up to 25 knots in a few seconds, going downwind and accelerating to almost 30 knots, and then entering a jibe at full speed on perfectly flat water? Carving a nice, wide arc at 50 kmh is something to dream about!

Once at the Slicks, I wished that I had the 5.5 non-cambered race sail that was still lying in Kalmus, rather than the 4.5 m wave sail. Dean was on a 6.3 m cambered race sail and slalom board, and hit almost 33 knots (61 kmh). I barely managed to break 30 knots, and that only for one second. Still - this was the first time I hit 30 knots, so it counts! I also managed to make my second-best jibe ever, with a minimum speed of 12 knots - not bad for a mid November day:)

Dean let me use his equipment for one run, and that was just wicked scary. By then, I was getting tired, and I neither wanted to get catapulted at full speed, nor did I want to break his gear, so I sailed as slow as seemed possible. But there's only so much you can slow a slalom board and sail down in 35-40 mph winds, and my speed was still about 28 knots. With a bit more practice on this gear and fresher forearms, 10-second averages above 30 knots should have been no problem. Next time...

Day 3: Fogland, SSW, 20-35 mph
Our friend Dani made the call to go to Fogland, and that turned out to be the right call - Fogland was windier than Kalmus (probably because of the more southerly wind direction and channeling in the Sakonnet river). Again, it was sunny, and warmer still than the day before - almost 60 F (15 C). Quite a few windsurfers showed up, including many team members from the Fogland Speed Surfers - Dani and Sabah, Dean, Jeff and Graham, the two Freds, and a few others. Nina and Graham were working on freestyle the entire day. Nina's duck jibes are getting good, she is now making most of them dry, and she also work on Vulcan pops and body drags. I'm not sure about all the things that Graham worked on, but I saw some nice Willy Skipper tries, and here's one that was caught on camera:
I spend an unfortunate amount of time fiddling with my equipment. My first runs were with a 7.9 m North S-Type sail from Dani and my 118 l slalom board, but just then, the wind was picking up, with gusts of 35 mph. So I switched to my trusted old Hawk 95 and my Matrix 7.0 sail, which worked beautifully the rest of the day (after putting the second back foot strap on again that I had taken off for all the recent play in choppier waters). Even though the winds were a bit gusty, everyone was having fun, and the Fogland Speed Surfers set 5 new personal bests - Fred and Sabah for the nautical mile, Dean and I for 1 hour, and Dean also for alpha. Nice to see so many friendly and happy faces on the water!

Day 4: Skaket, SW, 25-35 mph
The wind forecast for the day was calling for SW in the low- to mid twenties again. We had not planned to go sailing, but when I saw perfect meter readings of 24-33 mph in Kalmus, we just had to go. Dean joined us, but just before we got to Kalmus, the meter readings had dropped to mid teens - bummer! By now, the air had gotten too warm - the warm winds did not reach the surface near shore anymore. It was plenty windy inland, and about 10 miles out at sea, but not on the south-facing Cape Cod beaches.

When decoupling like this is an issue, the beaches on the north shore of Cape Cod often do better, since the land warms up more, and the wind gets all the way down to the ground and then does not lift quickly enough when the offshore breezes hit the cold water. Indeed, the Skaket sensors were still showing averages near 30, so we drove half an hour to Orleans.

At the shore there, it did not look very windy - a few white caps on the water, but in Kalmus, this amount of whitecaps would have indicated maybe 20 mph winds. So Dean and I rigged 7 meter sails again and went out, while Nina was still rigging her 4.5. What a nice lesson in not trusting your eyes in unfamiliar conditions! As soon as we left the shore, the wind almost blew us off the water, and we were back in within 5 minutes to rig down. I sailed the next 90 minutes on my 5.5, at first fully powered, and still planing 90% of the time when the wind dropped towards the end of the session.

It was very interesting to see how different the ocean surface was in the side-shore winds near high tide. Instead of the regular waves with flat water in between that we had had a few days before in onshore winds, we now had high chop with some cross-chop. It was enough to make things interesting, and for Nina to have a lot of fun working on her wave riding skills; but it was not nearly as bad as the voodoo chop in Kalmus in similar conditions. I had no problems jibing my Hawk 95, and to my surprise, actually made most out my outside jibes dry. I always thought that my outside jibes were worse because of the chop, but maybe it's more of a "which hand is in front" thing - the chop was coming from the opposite direction compared to almost all other places we sail. The chop also had a slight angle to the wind - going out meant hitting the chop straight-on, while sailing back in allowed for some nice speed runs more parallel to the chop. Dean actually managed to hit 30 knots, and both of us got nautical mile averages that were close to the ones from the day before. Skaket definitely has some speed potential, at least for long distance!
So we sailed 4 days in a row in 20-40 mph winds, in a variety of different spots and different conditions. Even the same spots offered very different conditions: Kalmus a choice of voodoo chop right in front, or flat water at Egg Island or the Kennedy Slicks; Fogland perfectly flat water in the bay, and nice rolling swell in the river; and Skaket very different waves and chop in different wind directions. All this with lots of sun, and temperatures that ranged from fine to "too hot for 5-4 semi dry" on day 4. IMHO as a non-wavesailor, the Cape Cod - Rhode Island areas definitely has a big advantage over Maui when it comes to variety of sailing conditions. Pick your spot right, and mix it up, and the fun will be endless!

Fortunately, the forecast for the next few days shows very little wind - but it looks like it will pick up again on Saturday, for another windy and warm weekend. November rocks!

Tuesday, November 8, 2011

Summer winds in November

In the summer, Cape Cod is often the windiest place on the US East Coast, with southwest winds that are boosted by thermals. This summer was an exception, with very few windy days. But it looks like the summer winds are finally coming - in November! Here is a wind graph for Kalmus from the last two days:
Sunday was nice enough, with averages near 20 mph for about 5 hours. Monday was even better, with averages above 20 the entire day, and 3 hours with winds between 25 and 30 mph. Both days, the actual averages were 5-10 mph higher than the forecast. Looks like we got a nice thermal boost, despite the short days! All that sun made the temperatures of around 50 degrees F (10 C) for both air and water quite tolerable. Sunday's low forecast and moderate winds drew only about 6 windsurfers to Kalmus; Monday better forecast and higher winds attracted a several more, including Martin, Drew, Bruce, and a few others.

I think the crowds will get even bigger next weekend, which starts on Friday with Veteran's Day. The weather has been so warm that the water temperatures are going up a bit, and the wind forecast looks great:
The predicted winds of 25-30 mph would be lovely enough - but with a 5 mph thermal boost like earlier this week, we may see low 30s. Even Sunday, which looks a tad weak in the forecast, could end up being very nice with a bit of thermal boost.

Friday is still 3 days away, and wind forecasts this time of the year have the annoying tendency to look good a few days away, only to go down the closer we get. However, this seemed to be more the case for NW winds, and less so for SW winds, so I'll remain optimistic. Hope to see you all on the water this weekend!

Monday, November 7, 2011

GPS Accuracy: GT-31 vs. Android Phone

I finally managed to get some recorded GPS tracks from my Android phone for comparison with the GT-31 data from the same run. Just listening to the GPS Speed Talker app, I knew there were some spikes in the GPS data from the phone. Here is an example:
According to the GPS data from the Android phone, I hit 30 knots here. I wish! Within one second, the speed jumped from 24 to 29 knots, and stayed around 30 knots for 3 seconds. That's using the Doppler data - according to the GPS position data from the phone, I actually hit 40 knots!

The tracks show that the GPS points from the phone are not accurate here. I was going straight - I did not suddenly go upwind and accelerate 5 knots within one second. The jibe in the lower right corner also shows that the GT-31 is much more accurate: the blue curve from the GT-31 shows a nice curve; in contrast, the red curve from the phone GPS wiggles all over the place.

I have seen spikes in GT-31 data, too, but they tend to be rare (as long as you look at the Doppler results), and are usually very easy to identify. Most of the time, it's just a single value that's wrong, which gives a very sharp peak. Also, GT-31 spikes tend to be linked to crashes (although that's not always the case). Either way, they are easy to see and remove.

The 4-second, 5-knot spike shown above it the worst in the 2-hour recording, but there are a number of other spikes, too. Many of the other spikes affect only one point, which seems to be off by 1-2 knots (an example is in the track before the jibe). More than 98% of the time, the speed values from the GT-31 and the phone are very close.

So using an Android phone with the GPS Speed Talker app can be helpful, although one has to take the announced speeds with a bit of skepticism. Perhaps other phones are more accurate, although the only thing I have seen was a description that some other phones have less accurate GPS units. Posting results from Android phones to sites like or the GPS Team Challenge is, at best, questionable. The standard filters in GPS action replay did NOT remove the spike above, and my 2-second speed for the day would have been 4 knots to high. There are obviously good reasons why these sites suggest to use GT-31 units.

If you want to hear how fast you are going while sailing with the highest possible accuracy, you can always use a bluetooth-enabled GT-31 (a BGT-31), and have the GPS Speed Talker app use the BGT-31 data for the announcements.

Sunday, November 6, 2011

Did Andy jinx me?

Some of my fellow windsurfers see me as a freestyler. I can't totally blame them, since I have taken 10 ABK Clinics in the past 3 1/2 years, and I actually work on freestyle thingies during the clinics. In my heard, though, I and a BAFer (that "Back-And-Force" sailor for the non-windsurfers). Ok, I put on a GPS and call myself speedsurfer, but that seems to be just a ruse, considering that I have not even broken 30 knots yet.

The one thing in my windsurf quiver that's not compatible with freestyle is my 8.5 m V8 sail. With its 2 cambers and huge mast and boom, it's about 3 x as heavy as a nice freestyle rig. I love this rig, but this year, it has given me a really hard time - I am sure that Andy Brandt has put in a jinx to get me to stop using it.

Things started in April, when I hit a fishing line at full speed, and put a big hole into the sail (check the video on YouTube). Fortunately, Gerda from WindFixes was able to fix this, and the sail was as good as new again. But then, the boom snapped during a late summer session. Ok, it was a few years old, and I always wanted to try the Aeron V-grip boom, so not all was bad.

The final  part of my big rig broke last week, when the mast snapped while sailing. I knew I had downhauled it a bit much, the cambers really did not want to rotate - but I was still about 5 cm below specs. Well, the mast was pretty old, too, and it has gotten a lot of use over the years. Still, it made me wonder if I'd been jinxed by one of the freestylers - maybe Andy Brandt himself :)

But within a day of posting about my misfortune on Facebook, two of my windsurfer friends offered me a replacement mast for free. Do you need any more proof that windsurfing makes people nicer? I got to sail my 8.5 today using a nearly new mast with a $559 list price that Dani lent me - thanks, Dani! It was quite a perfect day, too - the 8.5 got a bit big at times until I had sailed up to the flat water at the Kennedy Slicks. Lots of sun, and the air and water was not too cold: Sabah and Nina sailed without gloves and hood today, and were perfectly fine. Dani was in his new dry suit, which kept him warm and smiling from ear to ear for the entire afternoon. Great day! And the forecast for tomorrow is even better! Maybe it's a good thing that my drysuit does not deserve its name anymore - all my clothes were soaked today when I got of the water. Since I had to change out of everything, anyway, I'll probably use my 5-4 semidry wetsuit the next few times I go out. I think the semidry lets less water in than the "dry suit"! I'll have to check this baby for obvious problems soon.

A Google Earth overlay of my tracks from today can be seen here. Once again, looking at the tracks brought some big surprises - I would have sworn that my angles at the upwind runs to the Kennedy Slicks, and during my speed runs at the wall, were much steeper.

I also used the GPS Speed Talker app again today. It worked really well, except that the stupid Android phone started playing music all the time. I think it has a "music" button that got pressed accidentally by the bag all the time. Also, the phone GPS is definitely more prone to spikes than the GT-31: at one point, my speed jumped from 29 mph to 35 mph according to the phone, and stayed around 34 mph for a few seconds. I knew this was an artifact while sailing, though - I may have sped up by one mile, but definitely not by 5 mph. The GT-31 tracks don't show the spike at all. Nevertheless, I found hearing the speed all the time quite useful. The new waterproof headphones I ordered for $16 worked much better than the ones I used before, too - no pain in the ears at all, and they stayed in place for a couple of hours, despite a few crashes and near-acrobatic jibe and tack saves. Now I just have to find the stupid music button on the phone, and figure out how to disable it!