AGRICULTURE
Setting Sail
Yacht racing has been a sport for many centuries, and sailing technology has been evolving for millennia. But the advent of GNSS and inertial technologies has brought a new level of precision to the sport. Those who watched the America's Cup race coverage in the fall of 2013 witnessed the state-of-the-art instrumentation used on board for navigation and by race monitors for tracking competitors' performance.
When NovAtel Aerospace Program Manager, Owen Thistle, decided to enter the 2013 Van Isle 360 International Yacht Race with a sailboat named Kerkyra, he knew it would be a challenge. Competitors typically encounter tight inside passages with swirling tidal currents and complex wind patterns, and frequently end up sailing overnight in high winds and rough seas on the outside shore of the island.
Undaunted, Thistle joined by two other NovAtel colleagues, CTO, Pat Fenton, and VP of Operations Mike McAloney-set out to undertake what Sail Magazine has characterized as “North America's toughest coastal race.”
Given their professional calling in precise positioning, the crew also took on a secondary mission in the race: to accurately record the boat's position, attitude, velocity, and acceleration. The trio of NovAtel engineers wanted to get a sense of how data from GNSS and inertial technologies would compare to the “gut feel” a sailor has when he makes an adjustment, and to see what insight this type of data would bring to the sailing experience. “We have a strong emphasis on innovation at NovAtel, and innovation has as much to do with understanding the problem as it does with creating a solution,” Thistle says. “Customers are very familiar with their tasks and challenges but they don't necessarily know what our technology is capable of doing. So, I thought it would be a good exercise to think about what my ideal yacht racing instrument would be and how we might approach that with our technology.”
Conversely, the race offered the NovAtel team a chance to experience their company's products from a perspective more like a customer's. NovAtel creates products that customers integrate into end user solutions, making the team one layer removed from the end application, Thistle says. It's important for the team to actually use the technology, because it gives them a better feel for what the end user experiences and how that experience can be improved.
Thistle says, “This venture gave us a great opportunity to remember what it can be like to try to install and run equipment in environments that are not always easy. It's very different from working in a lab on horizontal surfaces with good power supplies. We were dealing with salt spray, boats moving, and people trampling over cables.”
This experience also helped the NovAtel team to appreciate the amount of data their equipment provides and how to extract and apply that data optimally for a specific application.
This wasn't the first time an employee applied a GNSS application to a hobby. In 2011, Applications Engineer, Andrew Levson, incorporated two GNSS antennas and dual-frequency receivers into a specially tailored skydiving wingsuit1. Why? He wanted to see if GNSS technology could help skydivers improve their performance. He planned to set new Canadian records for both distance and formation flying, and with his wingsuit jumps, he intended to prove NovAtel's OEM615™ receiver and ALIGN® heading technology would provide accurate positioning, heading and velocity measurements to help him train and achieve those goals.
This day-long wingsuit jump inspired Thistle to fuse GNSS with his passion for sailing. Sailing technology continues to evolve, and GNSS and inertial measurements are starting to play a role in the sport, specifically in highend races like America's Cup Race where the boats are almost perfectly matched, and even the slightest change in sail trim or design can give racers an edge. “This was about putting the equipment on something that has different challenges and different types of motion to see what we can learn about how it behaves,” Thistle says. “We do try to walk a mile in our customers' shoes when we can. In this case, there was significant value in going and trying to use the equipment to take measurements under what we thought would be very difficult circumstances.”
What they hoped to measure
Through the Van Isle experience, Thistle wanted to get a sense of how actual measurements would compare to the “gut feel,” and that meant measuring the effects of small sail trim adjustments to see how the boat responded. He wanted to know if details in the logged data would provide useful feedback if the crew had access to it in real-time.
For example, tacking is the maneuver used in upwind sailing whereby the boat's bow is turned into and across the wind so that the sail is filled from the other side. Some tacks, of course, are better than others, as shown in Figure 1.
Figure 1
“We also wanted to look at ways to improve on current instrumentation,” Thistle says. “A good example is you typically use instrumentation to measure the velocity of the boat, but that gets affected by the rolling and pitching and yawing motion of the boat. We thought maybe we could use inertial measurements to subtract that part out and get a more smooth measurement of the boat's velocity. A lot of it was a matter of collecting the data and looking and seeing what was of interest. Here's a different type of motion on a different type of vehicle, let's put our equipment on and see how it behaves.”
With all that in mind, Thistle and his NovAtel colleagues installed two GPS-702-GG Pinwheel® antennas (capable of tracking both GPS and GLONASS signals), one on each side of the stern, connected to a pair of SPAN® systems mounted midship. The enclosure housing the SPAN receivers also held two different grades of Inertial Measurement Units (IMUs), each linked to a SPAN-SE GNSS receiver: a commercial-grade IMU-CPT and the more precise tactical-grade LITEF LCI-1. Both types of IMUs incorporate Fiber-Optic Gyros (FOG) and Microelectromechanical System (MEMS) accelerometers, but with markedly different performance characteristics (see Table 1).
|
TABLE 1: |
Gyro Bias (deg/hr) |
Roll Accuracy (degrees) |
Pitch Accuracy (degrees) |
Heading Accuracy (degrees) |
|
| LCI-1 | <1.0 | 0.007 | 0.007 | 0.018 | |
| IMU-CPT | 20.0 | 0.020 | 0.020 | 0.060 |
This configuration of equipment enabled them to measure the key dynamics of a vessel: heading, pitch, yaw, and roll. Furthermore, the dual-constellation receivers would reduce any problems encountered from shadowing by the mountainous coastline and high roll angles.
Despite the Van Isle 360's formidable reputation, Mother Nature threw the Kerkyra's crew a curve. Instead of fighting complex wind patterns and intense waves, during most of the race they encountered a different kind of challenge: virtually no wind at all.
The June 2013 Van Isle 360 turned out to be one of the calmest races of its kind, and the team spent most of their time trying to gather enough of the imperceptible breezes to coax the boat to each leg's finish line-and on many legs that didn't happen until at least 10 minutes after the time limit expired.
“We had some decent periods of wind but the most remarkable thing was how calm it was overall. We had very flat water,” Thistle says. “That was disappointing in a few ways. We were out there to measure motion and there wasn't much. And we were out there to complete race legs, which was hard to do with those light winds.”
All this equipment and nothing to measure? Well, not quite. Even in the lightest breeze and stillest waters a boat experiences motions detectable by IMU measurements.
“We had one night of rough water on the outside coast, and for me it was interesting to look at the measurements of what the boat was actually doing compared to 'gut' feel,” Thistle recalls. “I will not forget my three-hour 'off' shift when I was trying to sleep up in the bow that night. It was the closest I've come to losing my lunch since I was about five years old. I was sharing the bed with two sail bags and a bunch of emergency gear, and I felt like a tomato being tossed with the other ingredients in a salad-sometimes finding myself on top of the gear, sometimes underneath.Tired as I was, I couldn't wait to get out of bed.”
Figure 2 shows what some of the true boat motion looked like that night.
Figure 2
Figure 2a
Nonetheless, the long intervals with very little acceleration encountered during the 2013 Van Isle 360 race presented a real challenge for gyro and accelerometer technology. A key difference between the entry-level and high-performance IMUs carried on board the Kerkyra is the drift in gyro bias in low-dynamic conditions. High dynamics allow for alignment of the IMU output, but long periods with relatively small accelerations cause measurement errors to accumulate and create a bias in the output. The sailboat provided good examples of this effect (see Figure 3).
Figure 3
What They Learned
Despite the calm seas, the NovAtel crew not only had a chance to learn about the gear they brought on board, they had to make sure it was running properly and collecting data throughout the race.
The SPAN receivers logged inertial and GNSS measurements that could provide postrace insights for enhancing future performance.
“When you make an adjustment on the boat to improve performance, you're going by feel,” Thistle says. “Part of my interest in it was to see if you could bear out in the data what you felt you were doing to improve the performance of the boat. This made me realize some of these fine tunings may have made improvements, but that's very hard to measure with all the motion going on in boat and all the variables. It's hard to separate those different factors.”
The position data they obtained gave an accurate record of their route, providing the type of detail that Thistle and the rest of the crew agree would be valuable training data if presented in near real-time.
“I had some ideas about [real-time tracking in this race] but had enough to prepare without it,” Thistle says. “Even now, after looking at the data, I can see it would take more thought to figure out what is the best information to provide in real time and what is the best way to present it.”
The team at NovAtel considers the experiment a success. “There is a wealth of good measurement data from this equipment,” Thistle says. “I can see how it might be combined with wind and sail trim information and 'mined' to draw more conclusions about how best to sail a boat. This would take a lot more work, but some racing programs spend millions of dollars to optimize their boats and crews.” He adds, “It's important for companies to encourage people to try things like this. It's not really a failure if you go looking for something and you don't find it. It's all learning. We had some ideas but, in general, we said, 'let's go out and study this motion and capture it.'”
Even though Mother Nature changed the race dynamics, they learned a lot about each other during the process, and worked as a true team as they debated how to fill those sails, fix broken equipment, and solve various challenges that came up along the way. The team element is one of Thistle's favorite aspects of sailing, and he loves the interaction and ideas that come into play as they face each challenge.
Aside from all the technology, how did they do in the race? “We had a great time,” Thistle says with a smile. “We didn't really keep track of who won. But if there was a prize for best instruments or biggest fish...”
The next Van Isle 360 is slated for June 2015, and Thistle hasn't ruled out the idea of entering it. He tries to enter one race a year, and the thought of tackling those high winds and rough seas may lure him back yet again.