Keeping both GPS and sextant onboard is advisable

I was sailing as the chief mate on an oceanographic ship working in the Adriatic Sea between Italy and Croatia. It was the evening 4-8 watch, a clear night with little ship traffic as we were following a grid of tracklines laid out by the scientists. I walked over to the starboard GPS receiver to get my 1900 position, and was surprised to find that there was no readout. A check of the port receiver showed there was no readout there, either. Neither the captain nor I could figure out what was wrong, and then half an hour later the display on both receivers came back on. This continued to happen each time we entered roughly the same area while crisscrossing our grid throughout the night. The following morning the chief Italian scientist overheard the captain and me talking about the GPS problem and said, “I think that your signal was jammed by a local military base here on the Italian coast, a holdover from the war in Bosnia.”

At first I was skeptical that our GPS signal could have been jammed. Then the captain reminded me of an incident a few years earlier when the master of Point Sur, a famous research vessel based in Moss Landing, Calif., noted that the GPS readout on his ship didn’t work while the vessel was in the harbor and up to a mile offshore. Other vessels in the harbor reported the same thing and it continued for weeks on end. After involving everyone from the U.S. Navy to local yacht owners, the culprit was found to be the television antenna on a small pleasure boat which was creating strong interference, jamming the GPS signal on every vessel in the port.

GPS, or NAVSTAR GPS as it’s officially called, utilizes weak radiowave signals currently generated by about 30 satellites 12,000 miles above the earth. As a result, it can be jammed or rendered unusable relatively easily — naturally or intentionally. A strong solar storm could completely knock out the system, according to a recent National Academy of Sciences report. Other militaries can jam GPS signals intentionally. Early on during Operation Iraqi Freedom, U.S. troops captured six GPS jamming units reportedly developed in Russia. Our government can also pull GPS from public use without notice due to national security concerns, a decision then President Bush announced in 2004. GPS is not a new technology. It’s been 20 years since the first GPS satellite was launched into space, and many of the original satellites will soon be at the end of their useful life. Some GPS satellites have already begun to fail, the latest falling out of service just weeks ago. A report issued by the U.S. Government Accountability Office in April 2009 pointed out that although the aging GPS system is due for upgrades, the Air Force is facing delays, huge cost overruns and technical snafus, and is falling behind schedule on modernizing the system. The report noted that the Department of Defense admits that over the next few years the satellites will go out of service faster than they can be replaced.

A shutdown of the GPS system could have disastrous consequences. The Federal Aviation Administration (FAA) is currently using a GPS-based system to guide some commercial airplanes, and is implementing a complete changeover at airports nationwide. Imagine if GPS failed shortly before a fully loaded airplane touched down going 185 miles per hour in zero visibility.

Losing GPS capability would have calamitous effects on shipping. The Automatic Identification System (AIS) relies on GPS and is used to direct/monitor vessel traffic in major ports. Without GPS input AIS would essentially be rendered useless, putting our ports at increased risk for collisions, oil spills and breaches of security as vessel traffic authorities would be unable to identify and track thousands of vessels in harbor areas around the country. Offshore, the numerous drillships worldwide which use GPS input while in active dynamic positioning mode could fall off station, possibly ripping out pipe and causing oil spills as a result. For all close quarter situations, an effective backup to GPS is obviously needed — and available.

Enhanced Long Range Navigation (eLORAN), is the next generation of LORAN, a radio navigation network that has been in use for decades. It has a reported accuracy near that of conventional GPS positioning in coastwise and harbor applications, and uses the infrastructure that is already in place. Its effectiveness is a result of solid-state transmitters, advanced software applications and uninterruptible power sources, along with a new generation of shipboard receivers. Because the signal is much more powerful than GPS, eLORAN is not nearly as susceptible to jamming. In February 2008, the U.S. Department of Homeland Security announced that eLORAN would be implemented as a national backup for a GPS failure — but funding squabbles threaten to scuttle this implementation. Even when fully installed, however, eLORAN’s effective coverage would only be several hundred miles offshore.

The International Maritime Organization mandates the use of GPS or some type of electronic navigation system onboard oceangoing ships, but makes no such requirement for celestial navigation equipment — a time-tested means of determining the ship’s position at sea. I was the mate on a 323-foot ship running from Seattle to Alaska several years ago that didn’t have a ship’s sextant onboard. I remember thinking then how odd it is that the Standards of Training, Certification & Watchkeeping code requires deck officers to show proficiency in celestial navigation — but SOLAS (International Convention for the Safety of Life At Sea) doesn’t require ships to carry a sextant! I would like to see SOLAS Chapter V, Regulation 19, amended to require every oceangoing vessel to have a sextant, along with the appropriate books and tables to make the necessary calculations, as a backup to GPS in case of a failure while the ship is far out to sea.

I believe that the development of new technology is vital to the modern merchant marine, but we should not forget that even the best technology can fail. The money to upgrade our GPS system and fully implement eLORAN needs to be allocated, in my opinion, to help keep our American ports and coastal areas safe. Adding a requirement that oceangoing ships carry a sextant and celestial navigation equipment would then give mariners the navigational backup capability we should have — wherever we need it.

Till next time I wish you all smooth sailin’. •

Kelly Sweeney holds the licenses of master (oceans, any gross tons) and master of towing vessels (oceans), and regularly sails on a wide variety of commercial vessels. He lives on an island near Seattle. You can contact him at

By Professional Mariner Staff