Getting Started

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:
Specifications for the
inertial measurement
units used on board
the Kerkyra.

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.