Boaters could find navigation more difficult if a proposal by a private company to use radio frequency bandwidth right next to the existing GPS radio bandwidth is granted, a national boater-advocacy group says.

BoatUS believes the proposal, for which a 30-day public-comment period is now under way, would threaten the reliability of the GPS system across the United States.

"This is a remarkably short comment period for an issue that has such dire consequences for America's boaters and every other GPS user in the country," BoatUS Vice President of Government Affairs Margaret Podlich said.

At issue is an unusual conditional waiver granted in January by the Federal Communications Commission to a broadband wireless communications provider, LightSquared, to permit the dramatic expansion of land-based use of mobile satellite spectrum. This spectrum, or frequency bandwidth, is directly adjacent to the frequencies used for Global Positioning System (GPS) communications.

The company has proposed building 40,000 ground stations.

LightSquared's high-powered ground-based transmissions from these stations have shown to cause interference in hundreds of millions of GPS receivers across a wide range of uses, including aviation, marine, emergency response and industrial users such as delivery and trucking companies.

A new report requested by the FCC says, "all phases of the LightSquared deployment plan will result in widespread harmful interference to GPS signals and service and that mitigation is not possible."

Recreational boaters lost their only other viable navigation system, LORAN, when the Department of Homeland Security shut the system down last year.

At that time the U.S. Coast Guard urged mariners to shift to GPS-based navigation systems. Boaters rely on GPS-enabled chart-plotters to steer clear of navigation hazards, keep them in the safety of deep-water channels, or even get them home when storms shut down visibility.

"They are a critical piece of safety gear," Podlich said of boat-based GPS systems. "What will boaters do if they are unreliable, and how will the US Coast Guard's new emergency search and rescue system that stands watch over 36,985 miles of coastline, Rescue 21, remain effective since it relies on GPS?"

Boaters and other GPS users are urged to speak upĀ and send their comments to the FCC and their members of Congress opposing this proposal.