Foghorn

The fog horn is a horn for generating sound signals or fog signals in the shipping industry. It was invented in 1851 by Celadon Daboll and solved in the second half of the 19th century from gradually the fog bell, which was too bad to hear. Other alarm methods such as the firing of a cannon had proved ineffective. The fog horn is used in shipping even in poor visibility as a warning to protect road users from too dangerously close to the coast or to other ships.

Principle of operation

Daboll joined the principle of sound production on the clarinet with the directional sound radiation of a trumpet: Compressed air is passed through a small metal plate and puts it into vibrations. The sound thus produced then leaves the horn directed on the horn. This type fog horn after its inventor in the English language area called Daboll trumpet.

For compressed air generation were mainly compressors, which were driven by steam engines or Stirling engines and coal-fired or oil. Mid-19th century but was also occasionally used to drive the air pump a horse treadmill.

Range

Foghorns can be identified at sea by their rhythm, typical forms are, for example,

• 3 s on, 27 s off
• 4 s on, 16 s off
• 5 s on, 8 s off, 5 s on, 42 s off

The sound frequency of a foghorn is as low as possible chosen because the attenuation of sound in air increases with increasing frequencies.

Large fog horns produce a sound pressure level of 140 dB (A ) and thus result in a range of 3 miles ( 5 km), according to some information even 8 NM ( 13 km) or as in the report from 1872 20 to 25 miles. Good fog horns for pleasure boats can reach 116 dB ( A) at 220 Hz and are still 500 meters away to hear.

Alternatives

Beginning of the 20th century, many Daboll trumpets were replaced by more effective principles. These include

• Fog Horns with membranes
• Steam fog whistle, invented by Robert Foulis
• Fog sirens
• Diaphone.

Further signal equipment on a ship are the Colombsche signal apparatus, the Takelure and Typhon.

Artistic use

In 1997, Jason Gorski experimented on the beach in San Francisco on scrap, air-operated fog horns. They were 70 cm long, weighing 30 kg, had a membrane diameter of 8 cm and produced 140 dB ( A). Gorski replied the beach visitors and the police with his concert in some confusion. He modulated tones generated by regulating the air supply and by introducing objects into the horn. During his performance, he wore a special full-body sound protection suit. According to his information, the sound spectacle was best enjoyed in one to two miles away.

Hyler Bracey built some fog horns in a bizarre vehicle. His pictures can be taken well, the dimensions of the horns.

Others

The " International Regulations of 1972 for Preventing Collisions at Sea" ( Collision Regulations ) provide for fog horns.

Since 2002, large vessels are required to have a " digital listening posts " (IMO regulation MSC 99 (73 ) ): a microphone captures sound signals 70-820 hertz; determined, a digital filter, if the sound of a fog horn comes. If so they are reproduced on the bridge by loudspeakers. There are also devices that can detect and indicate the direction from which the signal comes.