Bellows on Demand
Though the sound of a fog horn is heard bellowing through the misty mantle much less these days, the audible warning capacity it offers the mariner remains a part of navigational safety – and lighthouse life.
Gone are the days of fog horns sounding 24/7 at remote, offshore light stations or automatically being activated by fog detectors such as the Videograph-B and VM-100 when fog reduced visibility below a three or four mile threshold.
Today, if you hear a fog horn sounding, it has been activated by the mariner on demand via what is called a mariner radio activated sound signal system (MRASS). In Maine, the United States Coast Guard installed the first MRASS system at Whaleback Lighthouse in Kittery during 2011.
Four years later, the Coast Guard introduced this on-demand system at a larger number of lighthouses in Maine, and by 2019, just about every lighthouse with a fog horn in the Pine Tree State was outfitted with this technology.
Why the change?
For starters, there were several operational and support issues surrounding the VM-100 fog detectors last in use. In 2014, Matthew B. Stuck, Chief of Waterways Management, First Coast Guard District, noted, “If we had the capacity to support the VM-100s in perpetuity, we would do that. But the decades-old system is starting to break down with greater regularity, and as the manufacturer is no longer producing the units or parts to fix them, the Coast Guard must begin to make the transition away from it.”
Aging equipment and a lack of available parts may have caused an increase in discrepancies, but this was only half the story. When the fog detectors failed, the public was becoming less and less tolerant of the fog horn sounding for hours or days on end. Residents living within earshot of a lighthouse did not want to listen to a fog horn blasting away on sun-splashed days with unimpeded visibility upon the water.
As Lieutenant David Bourbeau of Coast Guard Sector Northern New England explained at the time, “The current technology used for triggering fog horns is at least 30 to 40 years old and requires a lot of battery power. It also has a tendency to fail and, when it does, the fog signal will operate continuously until the problem is fixed. This can be a real annoyance for neighbors of shore-based fog horns, and a threat to mariners who rely on the distinctive signal different fog horns produce to help fix their location on the water.”
A change was necessary. Thus, the Mariner Radio Activated Sound Signal (MRASS) system was adopted and installed at lighthouses.
The primary fog horn used by the U.S. Coast Guard with the MRASS system is the FA-232 sound signal, which was manufactured by Automatic Power. The FA-232 has a range of a half-mile. If two FA-232 sound signals are stacked one on top of another (referred to by the USCG as an FA-232/02), the horn’s range is increased to one mile. Solar-charged batteries generally operate the horn, but it can also be made compatible with commercial powered lighthouse sites as well.
So how does the pure tone, omnidirectional FA-232 sound signal work?
The process is relatively straight forward. The horn’s power supply is mounted within a self-contained emitter housing, which is accessed by releasing the V-band that secures the dome to the emitter. The entire assembly stands 3-feet, 7-inches tall, weighs approximately 120-pounds and is waterproof and corrosion resistant.
Inside the emitter housing, the FA-232 is comprised of three electrical components: oscillator, timer and driver. The oscillator converts the DC input to the appropriate frequency, which furnishes the characteristic tone of the signal, while the timer provides the coding and the driver serves as the horn’s speaker assembly.
The turned steel drivers vibrate at a precise frequency and are acoustically coupled to the air through the horn. The sound signal’s solid state power supply inverts the DC input to AC at the proper frequency to resonate the diaphragm contained within the emitter housing. Essentially, the sound signal emitters are electromechanical vibrators.
The acoustical level of the FA-232 is 122.7 decibels, and as a guide, the sound signal is generally not located more than 100-feet from the water for best results. Though built as omnidirectional sound signals, the FA-232 can be converted to a directional sound signal by installing plugs in the emitters where sound is not desired direction-wise.
Now that you know how the FA-232 sound signal operates, let’s turn our attention to how the fog horn is activated. Here is where we come back to the Mariner Radio Activated Sound Signal system.
The action required to activate a fog horn is simple. Mariners use a VHF radio – keying the VHF radio a minimum of five (5) times consecutively (within a ten second time period) on channel 83A. This action will activate the fog horn, which will then sound for 45 to 60 minutes, providing ample time for the mariner to utilize the horn’s navigational safety benefits when transiting the area.
Listen to Electrician’s Mate first class Chase Miller of U.S. Coast Guard Aids to Navigation Team Southwest Harbor, Maine, explain how the MRASS system works…
Did You Know?
According to the 1970 International Dictionary of Aids to Marine Navigation (IALA), the “Usual range of a sound signal is the distance at which, in foggy weather, an observer has a 50 percent probability of hearing a sound signal when he is situated on the wing of a ship’s bridge in an ambient noise level which is equal to or greater than that found on 50 percent of large merchant vessels, propagation between the sound signaling apparatus and the observer being affected in relatively calm weather, with no intervening obstacles.”
Nice piece! Years before MRASS was installed, our foghorn was activated whenever Boston Light’s foghorn sounded. Made for a loud summer at Graves when workmen at BL set their scaffolding in front of the sensor for six weeks. -D Waller