Most long-range sail boats and motor yachts have a GPS or chartplotter for navigation, but for serious ocean-crossing voyages, vessel owners should consider adding a satellite compass for improved accuracy and fuel efficiency.
“In boating, fuel and time are the two most important aspects,” said Satish Narayan, vice president of sales and marketing at ComNav in Richmond, B.C. “When you have a good accurate heading, the autopilot gets a nice straight course, saving time and fuel.”
Garmin, Furuno, Simrad, B&G and ComNav all offer satellite compasses that can be installed on new boats or added in an aftermarket installation. Most integrate with a multifunction display or chartplotter and are NMEA 2000 or 0183 compliant.
In addition to providing a more accurate heading, a satellite compass reports pitch, roll, yaw heave, rate of turn and other data. It updates more quickly than a GPS position and works while the boat is stationary. Satellite compasses use the Global Navigation Satellite System to sense direction, too, so they’re not affected by onboard magnetic interference. Gyrocompasses use the rotation of the earth to sense true north and are not affected by magnets.
The U.S. Coast Guard auxiliary says it allows for an error of 3 degrees on a fluxgate (electronic) compass because the unit is affected by the magnetic anomalies noted on nautical charts and is disturbed by nearby metal objects and other electronics. “This is a major problem for some boat owners, especially those with metal hulls,” the auxiliary said in a statement. “Eliminating the heading error can improve fuel efficiency when navigating by autopilot because it makes paths shorter and reduces the boat’s tendency to “hunt” for a heading.
Ken Englert, owner of Maritime Communications Inc. in Marina del Rey, Calif., said that gyroscope compasses on large vessels are expensive to purchase, own and maintain. “Someone would call us with a problem with a gyro compass and we would have no way of servicing them,” he said.
New and Improved
Eric Kunz, senior product manager at Furuno, explained, “The satellite compass doesn’t care about magnetic elements or weather or location. With gyrocompasses, one of the issues is the fact that as you travel east and west, you lose accuracy. As you approach the poles, the farther north you get, a gyrocompass loses accuracy.”
The Furuno SCX 21 and SCX 20 are the company’s flagship satellite compasses. The only difference between the two is that the SCX 20 is NMEA 2000 based and the SCX 21 is compatible with NMEA 0183. The SCX 20 has won five National Marine Electronics Association awards in the sensor category.
Furuno first introduced a satellite compass in 2002 and the SCX 20 was introduced in 2020. What sets apart these two apart from competitive units on the market is that they have four GNSS antennas, making them the most powerful satellite compasses available.
“When we developed it, one of the Achilles’ heels of satellite compasses was the two-antenna design,” said Kunz. “The four-antenna design can calculate a heading solution from any one of the baselines including the crossover lines and that creates six baselines.”
Kunz explains that there are multi-path interference possibilities for any satellite compass system. “On most sailboats and cruising boats, it’s hard to mount a GPS compass in a location where it’s going to work reliably well,” said Kunz. “If there’s any structure above the GPS on the vessel, the reflection can cause variations in the arrival time of the signal to the unit.” The SCX 20 and 21 include a motion sensor that provides heave, rate of turn and heading plus sensors for temperature and atmospheric pressure. For a backup, they also have an internal magnetic compass.
The four-antenna configuration lets the SCX 20 and 21 figure out if one antenna is encountering an error. If so, it will shift to allow the others to deliver accurate data. “It can figure out which ones that are encountering this kind of error and eliminate them,” said Kunz.
The SCX 20 and 21 have a 10-inch by 8-inch footprint and weigh about three pounds. The antennas have a load equivalence number of four. LEN is a number used to express the amount of current used from the NMEA network. The units can integrate into a chartplotter or multifunction display; retail pricing starts at $1,295.
Other Choices
ComNav’s G2 and G2B GNSS Satellite Compasses were developed to improve the accuracy of autopilot navigation compared to a magnetic or a fluxgate compass.
The company uses a triple satellite configuration and the units are on an MCAN chartplotter combined with AIS. The G2 and G2B support GPS and GLONASS satellites and are engineered to exceed a sealed IP67 rating for water resistance. The units come standard with heave, pitch, roll and rate of turn as standard output and a 49-foot serial cable. A 98-foot cable is an available option. ComNav pre-programs each unit with default settings for heading, rate of turn, course over ground lat/long position and time and date. Five baud rates are selectable.
“A lot of good information is received simultaneously if you’re using more than two receivers,” said Narayan.
He estimates that 90% of the installations done with G2s are in a retrofit. The antenna and central processing unit take up minimal space. A sensor provides the position over the globe and it updates almost instantaneously, doing quick calculations to provide an estimated time of arrival based on speed over ground and direction. The G2 with the 49-foot cable retails for $3,400 and has been approved for International Maritime Organization standards. It integrates with compatible MFDs and chartplotters.
One of the largest marine electronics suppliers, Garmin Marine, offers the MSC 10 satellite compass in black or white for a sticker price of $1,149.99, according to the company website.
“Garmin was the first to deliver a marine positioning receiver and antenna using multi-band GNSS support and we’re pleased to bring this innovative technology to our customers with the MSC 10,” the company said in an email. The MSC 10 uses L1 and L5 GPS frequencies plus multi-constellation support from Galileo, GLONASS and beiDou to provide positioning and heading accuracy within 2 degrees. It also has an integrated attitude heading reference system.
The MSC 10’s LEN value is 6, the unit size is 6.1 inches by 13.1 inches by 3 inches and it weighs 28.6 ounces. The plastic housing is waterproof to an IPX7 rating and it comes with a 19-foot, 8-inch-long cable. Garmin says it can be installed as original equipment or in an aftermarket application and provides an installation manual online for DIYers. The company can refer customers to professional installer as well.
Maritime Communication’s Englert says that installing a satellite compass is not labor intensive. The time and cost would depend on the access. His company charges $195 an hour for labor. Sailors and motor yacht owners who want to cover long distances should find the increased accuracy and improved fuel economy that come with a satellite compass worth the investment. n