A unique demonstration of lighthouse technology was featured in Sturgeon Bay and Kewaunee during the Door County Maritime Museum Fall Lighthouse Festival this past weekend. A cannon, a steam whistle, and a small diaphone horn were the centerpieces - showing (and sounding!) the evolution of lighthouse fog signal technology throughout time.
Jake Heffernan, VP of the Friends of the Kewaunee Pierhead Lighthouse and the Chairman of the City's Lighthouse Preservation Committee has done extensive research on the subject of fog signals and their workings. The signals on display are small compared to the signals actually used for fog use, but that allows Heffernan to travel the region giving presentations on the subject, sounding the signals.
On Friday, Heffernan and his wife Heather were at the Sherwood Point Lighthouse near Sturgeon Bay for two scheduled presentations on the topic. They were joined by Bob Desh, (USCG Ret) who trained the duo on the safe handling of their new exhibit, a brass cannon. Desh had joined the Heffernans at Sherwood Point for the same presentations in June, and had fired his own cannon to simulate the Boston Fog Cannon. So impressed were the Heffernans that they purchased their own cannon to add to the presentation.
The first fog signal in the US was at the Boston Lighthouse long before the colonies declared their independence. The lighthouse off of Boston Harbor was built in 1716, and in 1719 was given a cannon to signal ships in poor visibility. The cannon took an incredible 4 lbs. of gunpowder per shot and was fired every 30 minutes in thick weather.
Left: a sketch of the original 1716 Boston Light. This light was blown up by British soldiers during their retreat on June 14, 1776. Center: Boston Lighthouse fog cannon photographed on-station
Right: Little Brewster Island and the Boston Lighthouse. The cannon can be seen on the ground to the left of the tower
To demonstrate the Boston fog cannon on a manageable scale, Heffernan and his wife use a small cannon which takes 1/2 fluid ounce of black cannon powder per shot. Below, the cannon is fired at the Sherwood Point Lighthouse during a demonstration on the Friday of Lighthouse Weekend.
Once the Industrial Revolution introduced steam whistles to the world of lighthouses, navigation during poor weather became a little easier. Whistles used for fog signals were usually 10" in diameter and around 20" tall. These were some of the largest steam whistles made, taking an incredible volume of steam (and later compressed air) to sound. The sound power was incredible, but the sound was hardly unique. Ships and factories alike all used steam whistles. Only the characteristic (the duration of the blast and the time between blasts) told the mariner they were hearing a fog whistle and not another whistle. Fog whistles were meant to be deep toned, to allow the sound to carry as far as possible. (Lower frequency waves travel further than high-frequency waves)
Video above: Moving a 10" diameter steam whistle, sounding a 10" diameter plain whistle on air, sounding a 10"diameter chime whistle on air
To show how a steam whistle works and sounds on a manageable scale, and to illustrate how the bell size of the whistle effects the pitch of the tone, Heffernan uses a 5" diameter whistle with a piston inside that changes the resonant distance inside the bell. Simply - it's a 5" diameter slide whistle.
The video below shows Jake and Heather sounding the 5" diameter Lunkenheimer Fire Alarm whistle for attendees at Sherwood Point Lighthouse.
The next step in the evolution is sirens - this is an important transition because it gave the tone more depth and power. In the operation of a siren, a spinning, slotted disc (known as the rotor) rotates inside a similarly slotted fixed disc. (Known as the stator)
Air is drawn into the discs, then forced through the slots as the rotor spins. The action of the air "puffing" through the slits then being chopped off as the holes pass is the physical process which sound is created. The faster the rotor spins, the higher the pitch we hear with our ears.
Furthermore, each one of the slits acts as a separate "voice." The voices are stacked on top of each other, providing a more powerful tone. Early sirens were powered by steam, later by compressed air, and finally by electric motors. Early sirens still took a very large volume of air but the uniqueness of the tone differentiated it from other ship or factory whistles.
Left: a fog siren driven by an electric motor, prior to installation in the Alcatraz Lighthouse, CA
Center: A compressed air fog siren on display at the Maine Lighthouse Museum in Rockland
Right: An air raid siren, showing the numerous ports which generate sound. The rotor can be seen blocking most of the holes in the stator.
The final fog signal demonstrated is the diaphone. The diaphone was originally invented as an organ stop for the Wulitzer pipe organ. A Canadian inventor named John Pell Northey modified the organ tone generator to create the Diaphone Fog Horn. Northey began manufacturing several sizes of diaphone horns for various uses under the Diaphone Signal Company of Toronto. Organized by size, referred to by "Type," the Type A diaphone is the smallest, going up to the massive Type K. The most common diaphone sizes in the world became the Type F and two-tone Type F2T in the United States.
The diaphone's sound is generated inside a slotted cylinder. A similarly slotted piston is driven forwards and backwards by air pressure. Air is forced through the slits in the cylinder. As the holes in the piston line up with the cylinder, powerful puffs of air are pushed through the slits and immediately chopped off.
As with a siren, this chopping action is the physical process which creates the sound.
As with a siren, each slit segment within the piston provides its own "voice" to the horn. With each one of these slits generating sound at roughly the same frequency (pitch), the sound emitted through the resonator is far more powerful than a whistle - which only generates sound through a single opening.
The Type F weighs approximately 500 lbs fully assembled and takes a high volume of air at 35 psi to sound. By contrast, Heffernan's Type B diaphone generates air the same way and consumes far less air and only weighs about 40lbs. So efficient is the Type B diaphone, that it can be sounded using a 30 gallon shop air compressor, with air pressure regulated to 35psi at the horn.
The Type B diaphone was seldom used for fog signal use, however it did find use at several US Light Stations, such as Two Rivers Pierhead on Lake Michigan, Fourteen Foot Shoal Light on Lake Huron, and Point Iroquois Light on Lake Superior.
The Type B was far more commonly used inland, for fire signal use. The horn's power and fast responsiveness when air is applied allows it to be used to sound a pattern of blasts to give volunteer firefighters information about the incident they are being called to.
The compressed air horns of the past have been mostly eliminated. Those that remain use vibrating metal discs to generate their sound and are not nearly as powerful as the diaphone.
Modern fog signals use an electromagnet to oscillate the air, creating a tone similar to a modern school "bell."
These signals are typically activated as needed by boaters and sailors. By tuning their VHF marine radio to a dedicated frequency (83A in our region) and keying the microphone 5x, they are able to activate the fog signal as needed rather than relying on fog detection equipment or having the signal sounding continuously.
The video below shows a real-world activation of one of these modern air oscillating signals.
Capt. Robbo of Nor'Door Cruises (Friends of Plum & Pilot Islands) activates the modern fog signal on the Minneapolis Shoal Light, located halfway between Door County and Escanaba in the bay of Green Bay
Heffernan's air setup consists of a 50-gallon air tank with a gasoline engine driving the air compressor. When the whistle is being used, an additional 120 gallon air tank is connected to the main tank to allow for a total of 170 gallons of usable compressed air.
Towed on a trailer, Heffernan parked the tanks next to the Sherwood Point Lighthouse for the presentations on Friday. The Door County Maritime Museum sold tickets to the presentations, with the proceeds benefiting the Kewaunee Lighthouse.
On Saturday while volunteers opened the Kewaunee Lighthouse for public tours, Jake parked the trailer at the base of the pier and demonstrated these signals for passersby. Unfortunately, a strong southeast wind drove waves onto the pier, forcing the lighthouse to close early at noon, but close to 50 visitors braved the spray to tour the lighthouse in the 2 hours it was open.
Several bright-eyed groups stopped to chat with Jake as they passed through, who fired the cannon and blew the whistle and horn for them.
Jake Heffernan is booking presentation dates for the 2025 season. If your group is interested in a presentation on the Evolution of Fog Signals, send Jake an email.
(Note - presentation locations are encouraged to be out of residential neighborhoods due to the noise generated during the demonstrations.)
The demonstrations and their equipment are funded by the Heffernans and do not use non-profit funding. Proceeds from these demonstrations benefit the restoration of the Kewaunee Pierhead Lighthouse.
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