Story by John Vonderlin
Email John: firstname.lastname@example.org
I found a book titled, “Fogs and Fog Signals of the Pacific Coast of the United States, Pub. for the use of shipmasters, owners, and agents interested in the commerce and navigation of the pacific coast (1888), ” that partially answers one of the mysteries that has been repeated in a number of my postings about shipwrecks. That mystery is, how could so many ship captains and crews swear they never heard the fog whistles when the lighthouse or signal keepers and nearby residents just as vehemently swore they had heard them continually? I had assumed exhaustion, drunkenness, dereliction of duty or insurance fraud was involved to some degree by one or both parties, in most of the incidents. Perhaps, that wasn’t the case, as the book seems to indicate. Perhaps, the heavy layers of fog our coast is subject to, and its effect on sound waves was, at least in some cases, the answer.
In the Coastside area there were three fog stations at the time the book was written, Ano Nuevo, Pigeon Point, and Montara, As you can see from the chart I’ve attached, as of July 1st, 1888, the Ano Nuevo station had been in service 11 years, 10 months, and the Pigeon Point and Montara station,11 years 11 months. During that slightly more then a decade all three stations had been operating the maximum during the month of September with totals of 1,671 total hours during that month for Ano Nuevo, 1,784 hours for Pigeon Point and 1,636 for Montara. That is about 1 out of 5 hours in that month. The minimum month for all of them was April, with 408, 385, and 412 hours respectfully, or between an an hour and an hour and a half a day.
At this time Ano Nuevo had a 12 inch steam whistle that sounded a blast for 10 seconds, followed by a 35 second quiet interval. Pigeon Point also had a 12 inch steam whistle that alternated between a 4 second blast, followed by a 7 second quiet interval, then followed by another 4 second blast, but followed by a 45 second quiet period. Being so close together, it was critical that a shipmaster could tell the difference between the two. Montara had a 5 second blast followed by a 23 second interval.
Later in the book I found mention of the problem of not hearing the fog whistle, even though it was sounding. It read:
“At this station, (Ano Nuevo) which is six miles south of Pigeon Point, some experiments have been made that indicate an area of inaudibility as existing not far from the whistle. The steamer Shubrick, in 1875-76, was run in three different directions from the whistle during the experience of fog, while the whistle was blown regularly all the time. Captain Korts, in charge of the vessel, says that in running in a northwest direction straight from the signal and to the windward, the sound was heard up to the third mile, and then lost, regained at four miles distance. In running southeast–i.e. with the wind– the sound was lost near the second mile and was not heard again until the fourth mile was reached. In moving straight out from shore, in a southwest course, the sound was heard continuously for the whole four miles. The fog in those trials did not reach above 150 feet above the surface of the ocean, and upon going to the masthead Captain Korts, found that immediately over the signal it was swelled up in an unbrella-like shape, and was very thin at the summit of this dome, the steam of the whistle showing through it.
These experiments, as well as the experience of Capt. Whitelaw already quoted, indicate that when sound signals are generated in one medium, whether that be a clear atmosphere, or more or less dense fog, the sound waves have great difficulty in passing from that media to another.”
Captain T.H. P. Whitelaw, who for many years had had the occasion to note the audability of sound signals on this coast while affording relief to wrecked vessels and recovering material from such, had said: “Clear spaces in fog banks alter or interrupt the course of the sounds of signals. When sound strikes the thick strata it is deflected upward–sent overhead– and so lost; and when it passes into lighter strata or open spaces it is heard again”
As an illustration of this phenomena he drew this diagram and explained it as follows:
“Approaching Point Bonita, and when about 6 miles distant (A) I have met a wall of fog and could hear the siren on the Point plainly. Passing through this I have encountered a clear space (B) in which the siren was not heard. The fog seemed to arch overhead, touching the sea again at (C) about 3 miles from the Point. Here the siren was heard again and as soon as we passed into the open space (D) it was heard but faintly, and wholly lost when within about a mile and a half of the Point.”
He goes on with more diagrams and observations, but I think his point is made. The book ends with a whole list of conclusions that the shipmaster should not make about where there ship was, based on what they did or did not hear from a fog signal station. The paranoia that I would have felt after reading them would have made me a permanent landlubber back then, especially if I had to navigate anywhere there was fog, particularly at night.
While modern instruments have made many of these matters moot, if you want to know more about the dangers they faced, even after the great improvement of having fog stations built on previously even more treacherous coasts, Archive.org, has another book you might want to read. It was written in 1881 and is titled, “Aberrations of Audability of Fog Signals.” It documents how boats had run ashore an eighth of a mile from a fog whistle station and never heard it, and explains why. Somehow Sea Serpents seem less scary now. Enjoy. John