Tuesday, January 3, 2017

Windy New Year

When driving through the rain in 43ºF (6ºC) weather to go windsurfing, I sometimes almost understand those who question my choices. Perhaps even more so when rigging in the rain and warning my fellow addict about the dog poop on the small grassy area, only to discover that I had just put my boom into a big pile of poop.

But things get better once you get out, you say? Or do they? I knew that the shape of my sail looked bad, but could not figure out why until I was on the water. There, I noticed that the bottom camber was not on. How do you spell "dahh!" again? But it was not all bad. I had to switch mittens, anyway, since the open palm mittens that I had just "improved" by removing some stitches now did not stay on my fingers anymore, and my fingers started to hurt. Meanwhile, Jerry was having fun on the water. Wave gear is so much easier!

Eventually, I made it out with a properly rigged sail and open-palm mittens that kept my fingers warm. 15 minutes later, we had made it to the speed strips right behind some dunes. The ocean on the other side was very angry, but the inside was nice and flat. We started the back-and-forth sailing - Jerry with nice jibes and duck jibes, me with lots of stops to check the speed from the last run. Again and again, the GPS watch would show only 28 or 29 knots - 30 seemed unreachable. That was a bit of a surprise, after just recently hitting 30 knots in almost every run at the Kennedy Slicks, in 5-10 mph less wind! Playing around with mast foot position and outhaul did not help; I barely managed to get one run with a 30-knot reading. Considering that I had perfectly flat water, often caught nice gusts in speed runs, and (for a change) did go deep enough downwind in half of my runs (130º), I should have gone at least a couple of knots faster.

So obviously, I need to identify a culprit. It is absolutely inconceivable that it was my fault that I was slow! Seriously - I did feel like I had things under control most of the time.

One potential cause is the current. One the top end of the runs, it was quite strong, probably several knots. But at the bottom end, it was barely noticeable, so that only explains (at most) half of my slow runs.

So I'll blame the sail. One speed guru told me that it's the wrong sail for me, and perhaps he is right. It's also 8 years old now, and had a few repairs. I lost one of the cams a while back, and replaced it with a random one that seems way too loose and a bit too big. Maybe the correct cam would help? After all, "cam" is short for "camber inducer", and the "inducing" refers to the profile in the sail (of which I did not have much, even with almost no outhaul). Time for another "dahh"?

But all the little problems aside, it was a real fun session. The water felt a lot warmer than the water in Cape Cod Bay or Nantucket Sound, and it was shallow at both ends of the runs, so taking breaks was easy. Jerry and I had big stupid grins on our faces most of the time.

Here are today's GPS tracks:



Friday, December 30, 2016

Never Trust Software!

I develop software for a living. So when I say "Never trust software!", you should trust me! What does that have to do with windsurfing? Let me start my explanation with a couple of screen grabs. Here's the first:

These are my "alpha" numbers from a windsurfing session 3 days ago. The best one was only 7.27 knots! That was a bit disappointing, since a few of my jibes were pretty nice.

An "alpha 500" is a 500-m run with a jibe in the middle where the two ends have to be within 50 meters. Since I was not really watching where I was going, I assumed that the two "arms" of the alpha were too far away. That's easy enough to verify - when I changed the "alpha proximity" number in GPS Action Replay from 50 m to 60 m, I got a 20.85 knot alpha. Here's the section from the GPS track:

You can see that the two ends of the 500 m track are indeed more than 50 meters apart, which is why GPS Action Replay did not count it.

But when I analyzed the same track today using the program GPSResults, I got very different results:

This program thinks that my best alpha was 20.296 knots! Obviously, at least one of the two programs is not trustworthy!

Looking more closely, I noticed that GPSResults has shorter run length for the first three alphas, ranging from 444.8 to just 100.6 meters. Indeed, the two legs are less than 50 meters apart a little to the left:
So - which of the two programs has it right? Let's check the exact definition of what "alphas" are in speedsurfing (from http://www.seabreeze.com.au/forums/Windsurfing/Gps/GPS-Team-Alpha-Racing-Explained):

 "All results must have a total distance covered that is less than or equal to the maximum distance"
Based in this definition, GPSResults is correct, and GPS Action Replay has a bug in its alpha calculation. However, the other GPS speedsurfing web site has a slightly different definition:
"Software calculated speed over ‘one’ run of 500 meters with a gybe and a proximity at the startpoint of 50 meters."
Here, the "less than" is missing, and GPS Action Replay actually would be the program that calculates alpha correctly.

Most days, it makes no difference if we say "less than" or not - since the jibe is the slowest part of the run, extending to the full 500 meters usually gives the best alphas. But as I have shown, not always!

I assume that the difference in definition was not intentional, since both sites allow the use of both analysis programs. Maybe they can agree on using just one definition?

Tuesday, December 27, 2016

Slick Fun

I don't know if the wind Santa is still around or what it was, but we got another warm and windy day today. WSW, high tide, and a predicted drop called for a session at the Kennedy Slicks. That's one of my favorite spots. Very flat water right next to the breakwater - but it's deep, so no worries about running aground.
Nina likes it shallow, but she nevertheless decided to join me for a speed session. I rigged for the wind, which was hovering around 30 mph - a 6.3 m race sail sounded about right. That would usually mean a 5.0 for Nina, but she believed that the predicted rapid drop in the wind was just waiting for her to get onto the water. So she rigged a 5.8. That's the ancient KA Koncept with a small and high mast cutout. At the bottom of the cutout, the boom is still at Nina's eye level!
I had to struggle a bit with my 6.3 in the gusts, but kept it somewhat under control. But my fighting meant that the 5.8 was way too big for Nina - and a high boom is about the last thing you want when overpowered. But she seemed to be doing fine on her first run out.
I quickly got numbers above 30 knots on my Locosys GW-60 GPS watch. That does not happen very often, so it made me quite happy. But I stopped frequently to keep an eye on Nina, who was struggling. There's absolutely no danger at the Kennedy Slicks - the worst case scenario is that you'd drift for 15 minutes and come ashore half a mile downwind (or perhaps a 20 minute swim if you don't want to walk back). But after a second run out and a bit of struggling, Nina sailed back to shore, and called it a day.

I helped her derig, and stopped sailing a little while later, too. It was a short session with just 7 runs, but 4 had a top speed above 30 knots .. not too bad. Despite the shortness and no playing around at all with gear trim, the session ended up as my third-fastest of the year. I love December sailing!