Velocity

2014

NovAtel's Annual Journal of GNSS Technology Solutions and Innovation

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Kerkyra 2014 For more Solutions visit http://www.novatel.com velocity 33 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 differ- ent 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 want- ed to get a sense of how actual measurements would compare to the "gut feel," and that meant measuring the effects of small sail trim adjust- ments to see how the boat responded. He want- ed 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. "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 collect- ing the data and looking and seeing what was of interest. Here's a different type of motion on a dif- ferent type of vehicle, let's put our equipment on and see how it behaves." With all that in mind, Thistle and his No- vAtel 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® sys- tems mounted midship. The enclosure hous- ing 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). This configuration of equipment enabled them to measure the key dynamics of a ves- sel: heading, pitch, yaw, and roll. Further- more, the dual-constellation receivers would reduce any problems encountered from shad- owing by the mountainous coastline and high roll angles. The Race Despite the Van Isle 360's formidable reputa- tion, Mother Nature threw the Kerkyra's crew a curve. Instead of fighting complex wind pat- terns 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 NovAtel equipment used during the race Two SPAN receivers (dual constellation GPS+GLONASS receivers) Two GPS-702, GG Pinwheel® antennas IMU-CPT, a commercial grade IMU LCI, a tactical grade IMU FigURe 1: The boat motion is from right to left. The detailed data shows the difference between a well-executed tack (at left) and the loss of headway and speed (indicated by the series of compressed position f xes) resulting from a poor tack (at right). A drawing of the Kerkyra.

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