Apparent Wind Fun

Windsurfers know about apparent wind. I mean the physical concept, not the "apparently, there is no wind when I want to sail". Apparent wind is the combination of "true wind" (the wind we feel when standing still) and "induced wind" (the wind we feel when we stick the hand out of the car window). We can all add the direction vectors in our head, and end up with the strength and direction of the apparent wind, right?

Or so I thought. I learned about apparent wind a while back, when the original Windsurfer was a new board. Back then, we were typically going much slower than the wind. Let's look how the apparent wind changes for a windsurfer going at half of the true wind speed:

When our slow windsurfer is going upwind at an angle of 60 degrees to the wind, the apparent wind has an angle of about 45 degrees. When turning downwind to a 120 degree course, the apparent wind changes angles to about 90 degrees. That's a 45 degree change in apparent wind angle for a 60 degree change in course. Our sailor will have to open up his sail as he turns downwind almost to the same degree as he changes his course.

The curve above applied more than 30 years ago when I learned windsurfing, and it stuck with me. I never really considered how faster gear would change things until recently, when the apparent wind issue came up in our "International House of Speedsurfing" on Cape Hatteras. So I took a closer look, starting with the GPS tracks from Roo, the fastest sailor in the house. The program GPS Action Replay Pro lets you look at "Polar plots", which show the maximum speed at different sailing angles:

There's lots of interesting information in this plot: The maximum upwind angle was close to 60 degrees

• The top speed was reached at an angle just below 120 degrees (it was quite choppy)
• Maximum upwind speed was around 20 mph, maximum speed near 120 degrees was 34 mph.

The wind speeds that day were in the high 20s, with gusts just above 30, so Roo's top speed was just a tad faster than the wind speed. Let's look at the speed vs. board angle on a graph:

Board speed and apparent wind speed are show relative to to maximum wind speed. When going upwind at a 60º angle to the wind, the apparent wind was 40% higher than the true wind; when on a downwind speed run at a 120º angle, the apparent wind dropped to be roughly the same as the true wind. 

What I found somewhat surprising was the lowest line in the plot, which shows the apparent wind angle. It changed from just below 40º when going upwind to just below 60º when on a speed run. That's a change of just 20 degrees for a direction change of 60 degrees! Compared to the 45 degree change that we had seen for our slow windsurfer in the first diagram, that's a lot less. Our speedsurfer barely has to open up his sail by only 20 degrees when going from pinching hard upwind to full speed downwind!

Another thing I found surprising was that even when pinching upwind, the apparent wind angle was still about 40º. That's more than I would have thought. Over the years, I have had several experienced speedsurfer point out that windsurfers often tend to oversheet (once they got used to going fast). Roo also caught me oversheeting when he followed me to check my technique. He blamed the sail I was using, since it has a short boom and was developed for "light weights" (which I am not). But a wrong idea about what the apparent wind direction was probably also caused me to oversheet! 

I got a few of things to look out for when speedsurfing in the future: 

• don't sheet in so much when going upwind or on a beam reach
• don't open the sail too much in a sling shot
• double-check your angles by comparing them to faster sailors, and/or by using GPSLogit and an Android phone to announce the actual speeds when sailing, and/or move your hands and harness lines closer together when speedsurfing to develop more sensitivity for the sail.

I suggest that my speedsurfing friends stop reading here. But anyone interested in loops should keep reading, because apparent wind strength and angles also play a role on speed loops. 

I admit that my interest in learning to loop had waned a little bit in the last couple of year, but the recent reminders that life can be short and come to a sudden, unexpected end have re-kindled my interest. So I started to think about loops again; to watch loop videos over and over; and to replay lectures about looping in my head.

One of the confusing things about looping is that spin loops can be initiated in many different ways. Some of the suggestions I have heard are:

1. Jump high and sheet in hard!
2. Whatever you do, try the first loops when going deep downwind!
3. Stomp on the tail to practically stop the board, while moving the depowered sail to windward-forward!
4. Take off at a slight upwind angle to get height, let the wind turn the nose of the board downwind a bit, then just hold on for the ride!

Some of these suggestions directly contradict others. But there is solid support for each of these suggestions. The last suggestion may be the one that is heard the least often, but it comes from a PWA pro who routinely throws some of the most beautiful loops ever seen, often on perfectly flat water. All the suggestions have helped many windsurfers to learn the loop. Nevertheless, some experienced teachers who have taught dozens of student to loop are convinced that other approaches to teaching are dangerous/no good/wrong. How confusing!

Well, apparent wind can also be very confusing to students. So there probably is a role for apparent wind in the loop! Let's see what we can find.

We will start with a simplified description of the loop: The loop is a catapult where the board is in the air and the feet are in the straps. 

We all catapulted when we learned to use the harness. Most of us did not like that, and quickly learned not to catapult. But we probably all remember that a sudden gust of wind can cause catapults. Sheeting in too quickly can have the same effect. Right away, this explains approach #1 to the loop: "Jump high and sheet in hard".  You'll get a lot more power in the sail and will get catapulted. Just make sure you are high enough in the air! A 10 ft wave on Maui to jump of works really well here. But for flat water loops, this approach can be downright dangerous.

Approach #2 ("do it downwind") is advocated by many windsurfers who have seen others get hurt by approach #1, or got hurt themselves. By going onto a deep downwind course before jumping, the chances of hitting your gear and getting hurt are drastically reduced. However, the downwind approach has one big problem: it is hard to jump when going deep downwind! Also, your apparent wind will be much less than the true wind, so there is just not enough wind to cause a catapult!

I know several very good windsurfers who tried to learn the loop with the downwind approach, but got nowhere. However, I also know several high-level freestylers who learned the loop with a variation of the downwind approach: they were working on Grubbies, and ended up looping instead. I have also seen "first Grubby" videos where the ending looked more like a loop than a proper Grubby, so the number of "Grubby loopers" is probably much higher.

One thing that you must do when learning the Grubby is to stick the nose of the board into the water to "create a rotation point", as the Tricktionary calls it. In a good Grubby, the board rotates 180 degrees, then slides backwards fully planing with you leaning forward on the board and backwinding the sail clew first to initiate another 180 degree rotation. But when learning the Grubby, there's a good chance that you kill most of the speed when sticking the nose into the water, with your board turned just a bit. As a result, your apparent wind increases to the true wind speed, and you get catapulted. Congratulation, you just landed your first loop!

The 3rd approach, "Stomp on the tail", is usually just a part of the entire instruction. I have seen some beautiful loops that clearly take this approach; but I have also seen beautiful loops that do not include tail stomps, even on flat water. This has confused me. What had me even more confused was a description "you stomp on the tail and stop the board, but your body keeps moving forward". That simply did not work for me. I can stomp on the tail to get a nice board wheelie, but all my weight must be on the back foot to do so, which means my body stops just as much as the board.

So let us look at what happens to the apparent wind if we go deep downwind, say to 150º off the wind, and stomp on the tail to kill speed. That's easy enough to do with plenty of apparent wind calculators on the web; I used this one. We'll assume that the true wind is 25 mph, and that our initial speed is 20 mph (typical for choppy conditions on freeride gear).

• Initial apparent wind:
  12.6 mph, angle 97.5º
• Apparent wind after slowing to 10 mph:
  17.1 mph, angle 133º

So the apparent wind has increased by 4.5 mph, and moved around by 35.5 degrees. If we had the sail luffed at the start, if will now be fully powered: we get catapulted! If we happen to the the board out of the water and pull up with the back foot, we'll get our first loop.

Now finally to the 4th approach: jump slightly upwind, move the rig towards the wind, let the nose turn downwind, and hold on! This loop advice is somewhat unusual, but it comes from Tonky Frans, not someone to take lightly when it comes to loops! Let's see what happens to the apparent wind here, again assuming 25 mph wind and 20 mph board speed:

• Initial apparent wind:  29.6 mph, angle 45.3º
• Apparent wind after the nose turns 20º downwind: 26.9 mph, angle 57.5º

This time, our apparent wind direction changed by only 12.2 degrees. But keep in mind that the nose of the board turned 20º downwind, so that the total angle change is actually 32.2 degrees! If the sail was luffed at the start, it is now nicely powered - without any active sheet-in! We're just holding on to the sail so that it does not get ripped out of our hands. Note that the apparent wind is much stronger than in our previous 150º downwind scenario (26.9 mph vs. 17.1 mph), meaning that the catapult will be more violent. That's good, because we have to turn the nose of the board an extra 50 degrees!

In all 4 approaches to the loop, we must get the sail suddenly loaded up, so that we get catapulted around. In the first approach, the load-up is initiated by actively sheeting in; in all the other approaches, the load-up is "automatic", caused by changes in the apparent wind. In reality, most loops will probably use a bit of a mix of the "active" and the "automatic" sheet-in, but at least in theory, either approach alone will work. Regardless how the sail is loaded up, the mast must pushed to foward-windward with an extended front arm: more to windward for a horizontal rotation, more to forward for a vertical rotation (I hope you jump high enough if you do it this way!). So, pick your approach and go looping!

OBX-Wind Pictures and Results

The OBX-Wind week was fantastic, and there were hundreds of pictures posted on Facebook. But an email from a friend just reminded me that not everyone is on Facebook, so I'll post a few pictures here, along with links to more pictures and the full results. Results first:

Men's Open

1. Kurosh Kiani
2. Dan Preece
3. Arnold Roest

Men's 6.5

1. Gaetan Lauzon 
2. Michael Wazewski 
3. Ron McKay

Women's Open

1. Nina Schweikardt
2. Leanne Torrie
3. Andrea Dietrich

Women's 6.0

1. Carole Ausant
2. Martine Monett
3. Annabel Ferguson

More than 100 racers were registered, and about 95 racers finished at least one race. According to the GPS tracks, a race was 16 km long! Full results are on OBX-Wind.com.

We also had a little GPS speedsurfing competition going on on ka72.com. Here are the final results:

The competition was pretty intense, as evidenced by 4 winners in the 5 different categories - Roo, Dean, Al, and Nina. Dean took the overall leadership despite still being in pain from trying to ski through some trees a few weeks earlier. In my eyes, another big winner was Dani, who got back onto the water after overcoming some troublesome health issues.

Nina outclassed everyone in the distance category by sailing 223.13 km (a bit more than 5 marathons) - on the day of the long distance race! She had sailed about 80 km before the racing started. She was quite happy to have the races in the middle, since she finds going back and forth a bit boring. But she was rather unhappy that the wind died at around 6:30 pm. She came in when here 7.0 m race sail was not big enough anymore to get her planing - just 3 km shy of the women's world record spot on the GPS Team challenge.

Since Nina had beaten my top speeds several days in a row before, I tried hard to beat her in distance - but luck was not on my side. I sailed about 100 km before the race started at 10:30 am, and maybe I was getting a bit tired as I came in for the jibe at the second mark. Two pictures tell the story:

I'm on the blue and white Gaastra sail on the right side. I was in to top 20% or so for the race, which I was happy enough with. And then ...

I made a big splash. That is a questionable tactic in any race. Usually, long distance races are a bit more forgiving - you got plenty of time to make up distance. But unfortunately, I had once again practiced my Karate skills on the sail, which did not like my elbow. Not one little bit - the tear was huge, and forced me to drop out of the race and take an early lunch break.

The afternoon was not much better. After thinking that perhaps distraction from other racers had contributed to my morning fall, I had decided to not join the second race, and sailed about 1/2 mile downwind of everyone else. When the race was over and the water was getting less crowded, I decided to sail back upwind ... and immediately had a violent spinout. Violent enough to break a footstrap screw. I had lost the fin! That was the same fin that I had run aground with at full speed a few months earlier. The top did not have a brass nut, but the screw still seemed to fit well enough. I had used the fin for several sessions after building it back up with Marine-Tex and sanding it. But sailing 140 km in a session apparently was too much, and the screw had worked itself loose. I walked back a bit, trying to find the fin in chest-deep water, and checking for any obstacles in the water that I might have hit, but found neither. I was quite far out, almost at the reef. I tried to sail with the harness tied around the back of the board, which was possible, but very tedious on my 96 l board. So I took the opportunity to check the water depth by walking most of the way to shore. Yes, it's shallow enough - hip-to-chest deep most of the way for a 6 ft guy. By the time I got to shore more than 2 hours later, I was tired and rather cold. Here are the GPS tracks:

A few more pictures from the race and the week:

Open winner and PWA pro Kurash Kinai showing how to jibe

Party at Ocean Air

Speed clinic with Roo

JR, Nina, Mike, Chrissy

Organizer and 4th place racer JR

Phil showing that freestyle gear can be fast

JR, Kurash, Mike and Chrissy

Al, Bart, Nina, Dean, Peter, Mike

Winning with style

Dani's birthday party

Nina freestyling

Plenty more pictures here and here, and also on Facebook - check Windsurfer Photos and OBX-Wind. Many thanks to the organizers (especially Mike, JR, and Chrissy), helpers, local stores, sponsors, and the East Coast Windsurfing Association. Also thanks to Dylan from ka72.com for setting up the speedsurfing competition!

OBX-Wind Racing

Avon, Cape Hatteras, NC: More than 100 windsurf racers; 2 long distance races to the reef and back - 20 km per race, 40 km total. Support from two local shops and many sponsors. Lots of smiling faces. A great day for windsurfing in the US.

GPS Speedsurfing at OBX-Wind April 16-22

The OBX-Wind Festival will take place in Avon, Cape Hatteras, NC next week! It will be a fun event with demo gear, a long distance race, and lots of action on the water. It is organized by the folks from Makani fins and Mike Burns, with support from the ECWA, local windsurfing shops and many sponsors.

This sounded like too much fun, so Nina and I decided to drive down for the week, even though we already had a vacation in Hatteras booked for the ABK camps in May (which will also be great!). Several other members of the "United Speedsailors of America" team on the GPS Team Challenge will join us in our house at Island Creek, and other team members had already booked their vacation on Cape Hatteras for this week, so we will have a crowd of speedsurfers on the water!

As part of the OBX-Wind week, we will have a couple of GPS competitions going. One is pretty informal, easy, and "all-inclusive" - just show the speed reading on your GPS to the official on the beach when you come from the water (and also before you go, so we know you did not get the speed while driving in your car!). There are no restrictions for this competition - any windsurfer with a GPS can participate, regardless of the kind of GPS you use.

But we will also have a number of pretty serious speedsurfers there, including several guys who have beaten 35 and 40 knots. For these folks, we have set up a semi-serious competition on KA72.com. Here's a screen shot of what this will look like:

This competition will be on the web at https://www.ka72.com/Groups/Group-Activity/groupid/26 (you need to be a registered used on ka72.com to see the page, but registration is free).

To join the competition, you need to:

1. Have a GPS device that is approved for the GPS Team Challenge (a Locosys GW-52, GT-31, GT-11, or a Canmore GP-102). Data from other devices, like GPS watches or GPSLogit, will not be allowed.
2. Register at ka72.com (registration is free).
3. Join the "OBX-Wind Speedsurfers" group.
4. Upload your data to ka72.com (after logging in first!). Data should be uploaded the same day, and must be uploaded before the end of the competition on Friday, April 22nd, 5 pm.

The OBX-Wind Speedsurfers competition will score five different speed disciplines, and determine the overall winner based on rank in all 5 disciplines. The disciplines are:

• 5 x 10 second average speed

This is the average speed for the fastest five 10-second runs of a day. This discipline is often considered the most relevant "top speed" category in GPS competitions.

• 100 m

This is the average speed for the fastest 100 meter run of a day.

• One hour

This is the average speed for one hour. Avon is ideal for this category, with 5 km runs out to the reef and flat water. This requires a bit more stamina than the first two "top speed" categories, as well as decent jibes.

• Total distance

This is the total distance sailed during a calendar day. 200 km are almost easy in Avon if the wind is right!

• Alpha 500

This is the most technical discipline: the average speed over a 500 m run with a jibe in the middle; the end points must be within 50 meters. It requires blistering speed on a beam reach, a great jibe, and great acceleration after the jibe.

Most of these disciplines are also used for the GPS Team Challenge. One difference is that we replaced the "2 seconds" top speed category with the "100 m", since the 2 second category is quite prone to errors from spikes in GPS data. We also dropped the "nautical mile" category that the GPSTC uses, since that would have made the competition somewhat too distance-oriented.

If you would like to join the competition, but do not have a valid GPS unit, try to get in touch with me in Avon. I will have a limited number of Canmore GPS units and waterproof armbands for rental. There will be a rental fee of $10/day, plus a security deposit of $60 (since the GPS units can easily be lost or damaged in  crashes). If you don't know who or where I am, ask around Island Creek - folks like Mike, JR, and Dean will be able to point you in the right direction. Keep in mind that I plan to spend most of my time on the water, though!