The Coast Guard will replace unreliable automatic fog detectors at 17 Maine lighthouses with “on demand” fog horns that mariners activate with VHF radio signals.

The Mariner Radio Activated Sound Signal (MRASS) devices are turned on by keying a standard VHF-FM radio five times consecutively on VHF channel 83A. The fog signals then start their sounding cycle, running for up to 60 minutes following each activation, Coast Guard officials said.

It’s the latest in the decades-long automation of aids to navigation, and will replace VM-100 fog detectors. The VM-100 system is a 1990s generation of fog detectors that measure light and atmospheric conditions to control when fog signals should sound.

But the devices take considerable skill to calibrate and maintain, and parts are getting scarce. Replacing them with on-demand calling will increase reliability, the Coast Guard says. Eight sound signal systems have already been replaced in Maine and New Hampshire since October 2009, and ultimately this is a national program.

After each conversion, the Coast Guard will reach out to local stakeholders directly, put out Safety Marine Information broadcasts, and announce the change in the Local Notice to Mariners. Permanent changes will be made to nautical charts and the Coast Guard Light List.

“The MRASS devices will replace aging fog detectors that are prone to failure, expensive to maintain, and require specialized training to preserve”, said Capt. Michael Baroody, commander of Coast Guard Sector Northern New England. “We believe giving the mariner more control is an effective way to enhance the coastal aids-to-navigation system.”

But the changeover has plenty of skeptics in coastal Maine, with questions about reliability, and potential danger for smaller boats and transient mariners who are not familiar with Maine’s intricate coastline. The Coast Guard delayed the rollout of its system by a year so it could talk more to coastal communities about their concerns.

Maine lighthouses to be converted:

  • Browns Head Light: Vinalhaven, ME
  • Burnt Island Light: Boothbay Harbor, ME
  • Cape Elizabeth Light: Cape Elizabeth, ME
  • Dog Island Light: Eastport, ME
  • Egg Rock Light: Egg Rock, Frenchman’s Bay, ME
  • Fort Point Light: Fort Point, Penobscot River, ME
  • Goat Island Light: Cape Porpoise, ME
  • Goose Rocks Light: North Haven, ME
  • Heron Neck Light: Green’s Island, Vinalhaven, ME
  • Marshall Point Light: St. George, ME
  • Owls Head Light: Owls Head, ME
  • Portland Head Light: Cape Elizabeth, ME
  • Sequin Light: Sequin Island, ME
  • Spring Point Ledge Light: South Portland, ME
  • Two Bush Island Light: Spruce Head, Penobscot Bay, ME
  • West Quoddy Head Light: Eastport, ME
  • Whitehead Light: Whitehead Island, Penobscot Bay, ME