| 1914 - Submarine Signaling
The following paper was written in 1914 following
the successful testing of the first electro-mechanical sounding system, the
Fessenden Submarine Oscillator. This instrument was invented by Dr. Reginald
Fessenden of the Submarine Signal Company, an early forerunner of a major
electronics and defense company. As the name of the company suggests, the
primary goal in developing the Fessenden Oscillator was to communicate between
ships and between ships and shore facilities. The idea was to "protect shipping
with a wall of sound" that would allow vessels to better determine their
position as well as to communicate with shore facilities and other vessels.
Apparently the concept of using the oscillator to determine depths was an
afterthought. Ironically, although today there are some applications for
submarine signaling, the primary uses for the descendants of the Fessenden
Submarine Oscillator are in the measurement of depths, generation of sidescan
sonar imagery, and in the observation of other geophysical and physical
oceanographic parameters.
Submarine
Signaling: The Protection of Shipping by a Wall of Sound and other Uses of
the Submarine Telegraph Oscillator
R.F.
Blake
Abstract:
Submarine signaling has been greatly advanced by
the introduction of a powerful sound transmitter and receiver called the
“Fessenden telegraph oscillator.” By means of this, telegraph messages
can be sent and received through the water by moving ships and for short
distances speech can be transmitted, icebergs can be located, and soundings
taken instantaneously.
The apparatus consists of an oscillating electric motor-generator which has
a strong electromagnet surrounding a central core and the magnet is a copper
tube which acts as a closed secondary to the core winding. This copper tube
is attached to a large diaphragm. When the alternating current passes through
the core winding it induces a current in the copper tube, which being free
to move, vibrates back and forth, thus setting the diaphragm in
vibration.
This apparatus is installed in a ship so that the
face of the diaphragm is in contact with the water and its vibrations set
up sound waves in the water. Signals have been sent a distance of 31
miles.
The oscillator can also be used as a receiver.
Sound waves striking against diaphragm cause the copper tube to vibrate,
thereby generating a current in itself which is induced in the core winding.
A telephone receiver in the armature circuit enables the observer to hear
the sound.
COMPARED with other forms of transportation, the
amount of energy necessary to transport water-borne freight is very small
and its cost would be cheap indeed if it were not for the dangers of the
sea. We have fogs and rocky coasts, shoals and icebergs, currents and storms
to guard against, and these add immensely to the expense. Of this we have
had a very recent instance, for, as the result of the loss of the Titanic,
vessels carrying passengers are now constructed with a complete double bottom
extending above the water line; in other words, instead of a single ship,
we must now have two complete ships, one entirely enclosed by the other.
And the loss of the Empress of Ireland indicates that even this may not be
adequate.
Bit by bit the dangers which beset the early navigators
have been overcome. The chart told him the best course to take from one point
to another. The mariner’s compass enabled him to maintain his course
when the stars were blotted out by clouds. With sextant and chronometer he
located his position, with log and soundings he guarded himself when a sight
could not be obtained. More recently wireless telegraphy has enabled him
to call assistance in time of danger. But with all this, many dangers remain.
The more important of these are due to fog.
The North Sea, the English Channel and the Grand
Banks, the New England coast, the western coast of the United States, British
Columbia and Alaska, and other points are all of them subject to fogs, sometimes
lasting for weeks at a time, and it is therefore not surprising that thousands
of lives are each year still lost at sea.
And there is not loss of life; the pecuniary loss
is also very great. It is no unusual occurrence for a score of steamers to
be tied up at one time, unable to enter harbor on account of fog or of the
combination of fog and rough weather.
In such a case, the loss to the steamship companies
in interest and depreciation on ships and cargoes and in wages may easily
amount to more than fifty thousand dollars per day, and this loss occurs
not once but frequently during a year, and on many routes.
In addition to this, the danger of collision in
fog adds very considerably to the cost of insurance, and some of our worst
disasters have occurred in this way.
Aside from those dangers peculiar to fog, there
remains a number of others. A continuance of cloudy weather or abnormal ocean
currents or both, may throw the navigator out of his reckoning and place
him on a rocky shore a score of miles away from the safe route he assumes
himself to be following.
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The United
States Revenue Cutter Miami close to an iceberg similar to that which
destroyed the Titanic. On April 27, 1914, Fessenden oscillator was
tested off the Miami and received signals both from an ice berg and
the bottom.
(Courtesy
of
NOAA
Photo Library.)
Click image for larger
view.
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Icebergs
still remain a menace in spite of all the efforts which have been made to
guard against them. From time to time, statements have been made that apparatus
has been devised which is capable of locating their presence, but in every
instance in which such apparatus has been tested it has proved a
failure.
The history of systematic marine protection by
means of lighthouses and beacons does not go back very far. It is true that
there were a few lighthouses such as the Pharos of Alexandria centuries ago,
but even in quite recent years a European Government received a petition
for compensation from the inhabitants of a sea coast district on the ground
that the erection of a lighthouse had deprived them of one of their principal
sources of income, to wit, luring vessels on nearby shoals by means of false
lights.
The systematic employment of sound signals for
marine protection is of still more recent date and has never been carried
out fully, in spite of the fact that many of our greatest scientists, for
example Tyndall and Rayleigh, have devoted special attention to this
matter.
One reason for this is that sound signals produced
in air are very erratic in their range and intensity, so much so as to be
on many occasions absolutely misleading. This is due to the fact that when
a fog-horn is blown, the sound may be carried by the wind or may be reflected
or refracted by layers of air or different densities, with the result that
the sound may be audible many miles away while there may be a zone of complete
silence extending from a few hundred yards in front of the signal to a distance
of four or five miles.
As this phenomenon is by no means infrequent, the
result has been to discredit more or less this type of signal, and it will
be evident that the knowledge that a siren had been installed at a certain
dangerous point might prove a source of danger instead of a
protection.
As
already stated, many eminent men have worked upon this problem, but it was
not until Arthur J. Mundy, of Boston, suggested the use of water instead
of air as the medium for transmitting signals and proved its value by practical
demonstration that any great advance was made. Water has many advantages
over air for this purpose.
1. In the first place, it is free from the dangerous
zones of silence which occur when the signals are produced in air.
2. In the second place, the absorption of the sound
is much less in water and consequently the signal is not only absolutely
reliable but is transmitted to a distance many times greater than when it
is transmitted through air.
3. The sound is not carried away by the wind in
stormy weather, as is the case with the siren.
4. It is not affected by atmospheric disturbances,
as in the case of wireless.
5. It permits of the accurate determination of
the direction from which the sound is proceeding, which is not the case with
either the air siren or wireless telegraphy.
Some recent instances where ships have signaled
by wireless that they were in distress but have had to remain without assistance
for many hours, and in one instance for more than a day, because their location
could not be determined by the vessels coming to their aid, will be familiar
to every one.
All these advantages indicated clearly years ago
the advisability of developing apparatus for signaling by means of sound
waves transmitted through the water itself.
But it is one thing to conceive the idea, and another
thing to develop a practical system, and it may be of interest to know that
up to the present time the sum of a million dollars has been invested in
developing submarine signaling, so far without monetary return.
The first method which was employed for producing
the sound was through the striking of a bell and the method of receipt of
the signals was by means of a microphone attached to the skin of the ship.
Neither the original bell nor the original microphone attachment was
satisfactory.
It would be impossible in the space permitted to
discuss even briefly the innumerable experiments made with different sizes
of bell, with different materials for the bell, with different methods of
producing the blow, the precautions taken to eliminate electrolytic action,
with different types of microphone, with different methods of mounting the
microphone on the side of the ship, with the experiments made to minimize
water and other noises. It will be sufficient to say that finally the work
of Mundy, Wood, Fay, Williams and others resulted in a completely practical
system.
The submarine bell in use on the lightships is
actuated by compressed air stored in a reservoir. The actuating wheel has
projections mounted on it so that when the wheel revolves a number of strokes
follow each other, the different intervals being peculiar to the different
signal stations so that the captain of a ship by counting the strokes of
the bell can determine what lightship is producing the sound.
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Tank
attached to skin of ship for receiving submarine signals.
(Courtesy
of
NOAA
Photo Library.)
Click image for larger
view.
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In
order to receive the sound, it has been found absolutely necessary to suspend
the microphone in a tank of water, for this is the only method of cutting
out the water noises and the noises due to machinery, etc., on board the
ship, which otherwise drown out the sound of the bell.
One of these small water tanks, containing a microphone
of a special type, is attached to each side of the bow inside of the ship.
From each tank wires are run to a device which is called the indicator box,
so arranged that by throwing the handle to one side, the starboard microphone
is connected to the telephone, and throwing the handle to the other side,
the port microphone is connected.
It will be obvious that once the bell is picked
up, the captain has only to turn his vessel until the sound is heard with
equal intensity on each side, to know that his ship is then pointing in the
direction from which the sound is coming, and in this way he can take compass
bearings of the nearest lightship or lighthouse fitted with a
bell.
How many vessels and how many lives this device
has saved even in the few years during which it has been in use, it would
be impossible to tell. Less sensational than the wireless telegraph, it may
be questioned whether its actual practical utility to the merchant marine
has not been greater.
Compressed air, or an
electromagnetic mechanism, may swing the hammer, or the bell may be operated
by the waves themselves. A type much used is a bell buoy which may be anchored
off a shoal, and will give submarine warning day and night without further
attention. A large vane extends from one side of the mechanism. As the buoy
swings up and down in the water, the vane by means of a ratchet compresses
a spring which automatically releases and operates the bell hammer.
It will be evident that, even if no further development
had been made, the system would be and is a complete and practical one. Its
universal adoption would greatly minimize if not entirely prevent disasters
due to errors of ship position.
But with the very success of this system, it became
evident to those in charge of its development that still further advances
might be conceived as possible, especially in three directions.
1. Suppose the sound-producing apparatus could
be so constructed as to be operated from moving ships by a telegraph key.
If this were achieved, it would be possible for one ship to signal to another
in fog, to communicate its position, its direction and its speed, and eliminate
all dangers of collision. It would also be possible to signal between submarines
or between battleships and submarines, and to communicate between battleships
in action without interference from the enemy and though all masts were shot
away.
2. Suppose the range of the sound-producing apparatus
could be extended so as to cover a radius of 25 or 50 miles. Then it would
be within our power so to encircle the coast of every nation, with what has
been felicitously termed “a wall of sound,” that no vessel under
whatsoever circumstances of loss of reckoning, of variable currents, of fogs,
and storms could approach the coast without being warned of that fact and
notified of its exact position on that coast and of the direction of the
nearest lightship.
3. If the sound-producing apparatus could be
constructed so as to be actuated by telephonic currents, it would be possible
to transmit speech through the water.
It will be of interest to consider some of the
difficulties which had to be overcome before the desired results could be
obtained.
The most serious of these obstacles was the fact
that water is almost incompressible.
Now
since sound is a compressional wave in the medium through which it is
transmitted, it is evident that any apparatus which is to transmit sound
through water must be capable of exerting very great force. In the bell,
this is accomplished by the hammer blow of the clapper, and any electric
or other apparatus which is to be used for submarine signaling must have
a force comparable with that produced by the impact of a hammer or an
anvil.
A second and very grave difficulty arises from
the fact that if the water is to be compressed, some material object must
be set in motion to compress it, and that object, which must have sufficient
mechanical strength to stand the stress , and must therefore be of considerable
size, must start from rest, reach its highest velocity, and come to rest
in one-thousandth part of a second, if a musical note having a pitch of five
hundred per second is to be produced. The forces of acceleration thus
necessitated are very large.
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Demonstrating
listening device, very similar to a telephone, used on board ships with submarine
signaling apparatus.
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A
third difficulty arises from the fact that in order to telegraph a speed
of twenty words per minute the time allowable for a single dot is very small.
As the average word consists of five letters, and the average letter has
a length equivalent to seven dots, an apparatus capable of telegraphing at
the rate of twenty words per minute must be capable of making seven hundred
dots per minute, or a single dot in something less than one-tenth of a
second.
If the signal is to have individual quality, so
as to be readily distinguishable from other noises, and so as to be separable
by resonance from other notes, each dot must consist of at least ten
impulses.
Thus we arrive at the conclusion that whatever
device is used, it must be capable of producing at least 100 compressional
waves in a single second, in order to telegraph satisfactorily at the rate
of twenty words per minute.
If this same apparatus is to transmit speech through
the water, it must be still more rapid in its action and must be capable
of producing several thousand compressional waves per second.
The above were the three main difficulties in the
way. Of course there many others -- for example, the apparatus must not weigh
too much; it must be simple in construction; it must be easily applied to
the ship; positive in its action; must not require adjustment after being
once set up and must be able to stand all kinds of ill-treatment at the hands
of unskilled operators. It will be unnecessary to go over the ground taken
by the development, and we will therefor proceed at once to describe the
apparatus as finally developed by Professor R. A Fessenden.
The device used is termed an oscillator and its
construction is shown in cross-section in the drawing, Fig. 1.
In the drawing, the iron of the magnetic circuit
and the copper tube are shaded. The magnetizing coil is cross-hatched. The
moving part is the copper tube A. This lies in the air gap of a magnetic
field formed by a ring magnet B, built up in two parts, as shown in longitudinal
section in Fig. 2.
The ring magnet is energized by the coil C, and
produces an intense magnetic flux which flows from one pole of the ring magnet
across the air gap containing the upper part of the copper tube, thence through
the central stationary armature D, thence across the other air gap to the
lower pole face of the ring magnet and thence through the yoke of the ring
magnet back to the upper pole face.
This field is very much stronger than that in the
ordinary dynamo, there being more than 15,000 lines for each square centimeter
of cross-section. Around the armature is wound a fixed winding, which we
will call the armature winding, and which is reversed in direction so that
one half of the winding is clockwise and the other counter
clockwise.
When an alternating current is passed through this
armature winding, it induces another alternating current in the copper
tube.
Only by this construction has it been found possible
to obtain the enormous force and rapidity necessary to compress the water
and to overcome the inertia of the moving parts of the mechanism.
In order to apply this force to the work of
compression, the copper tube is attached to solid disks of steel, which in
turn are attached to a steel diaphragm one inch thick which may be made part
of the side of the ship. In practise [sic] the tube is provided with lugs,
and is held between two disks drawn together on the tube by a one-inch
vanadium-steel rod and a right- and left-handed screw thread.
Telegraphing is accomplished by means of an ordinary
telegraph key placed in the main armature circuit.
Although an ordinary telegraph key is used, there
is no sparking at the contacts. This may surprise electrical engineers familiar
with the sluggish action and vicious arcing commonly found associated with
the operation of electromagnetic apparatus of this size and power, more
especially in view of the fact that a very high frequency is used, five hundred
per second, and that there is no laminated iron used in the construction
of the apparatus.
The secret of this lies in the fact that the armature
has substantially no self-induction, and no eddy currents are generated in
the apparatus. This is because the copper tube forms, as will be seen, the
short-circuiting secondary of a transformer, of which the armature winding
is the primary.
This eliminates the self-induction of the armature
winding. In addition the upper and lower portions of the winding are wound
in opposite directions, and therefore there is no mutual induction between
the field coil circuit and the armature circuit. With this construction,
the amount of magnetic leakage in the armature circuit is very small, only
a trifle more than if the armature core were of wood, and as there is no
alternating magnetic flux in the iron, there are no eddy currents.
As regards the capacity in kilowatts of this apparatus,
it is large. The armature, being wound in grooves in the armature core, so
as to withstand the mechanical forces acting upon it, is well
cooled.
The copper tube has no insulation to be affected,
and on account of its large cooling surface and high permissible temperature
of operation, can carry very high currents without injury.
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A large passenger
ship with its Fessenden oscillator in the water ready for use. In "Submarine
Signaling," Scientific American Supplement, No. 2071, pp. 168-170, Sept.
11, 1915.
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When
the oscillator is placed on a vessel or hung overboard from a lightship,
a large water-tight diaphragm is attached to the oscillator. This particular
type of oscillator was first tested by suspending it in twelve feet of water
at the Boston lightship and the signals were heard plainly with a microphone
lowered overboard from a tug at Peaked Hill Bar Buoy, thirty-one miles away.
Since that time tests have been made with oscillators installed in the fore
peak tank of the Devereux, a collier of the Metropolitan Coal Company, and
also with an oscillator mounted on a diaphragm made part of the hull of the
vessel. The signals have been heard upwards of twenty miles from the Devereux
running at her regular speed of eight knots. Full power has not been employed
on any of the tests, and it is more than probable that much longer distances
can be obtained in the future.
In addition to the tests already described the
oscillator has been temporarily installed on submarine boats, and proved
itself of immense value and demonstrated that a flotilla of submarines equipped
with oscillators will be able to make a combined attack on an enemy, only
one need to show its periscope in order to direct the others, or all of them
can be directed by the mother ship. It therefore makes possible a whole field
of submarine maneuvers heretofore out of the question; and perhaps most
important, it removes the principal danger these boats have had to face,
the risk of being run into.
So much for the apparatus when in use as a sound
generator. The signals produced by the oscillator can of course be received
by water-immersed microphones of the usual type, but one would perhaps not
anticipate the possibility of using the oscillator as a receiver, in view
of the fact that the diaphragm is of solid steel, and weighs, with the copper
tube and its attachments, considerably over 100 pounds; but the oscillator,
like the ordinary electric motor, is also capable of acting as a generator,
an on account of its high efficiency as a motor, is a very efficient
one.
The same oscillator is therefore used for sending
and for receiving, a switch being thrown in one direction when it is desired
to telegraph under water, and thrown the way when it is desired to listen
in.
In addition to telegraphing and receiving messages,
the oscillator can also be used for telephoning under water. Sentences have
been transmitted at 800 yards and conversation at more than 400 yards, and
this was accomplished with the use of an ordinary telephone transmitter and
6 dry cells.
It seems evident, therefore, that with more power
much greater distances can be reached. Long distances are not, however,
necessary, as even with a distance of one mile it will be readily understood
that this method of under-water telephoning will be of great use as a means
of communicating between submarines while submerged, and between ships in
the fog, as the captains of vessels can talk directly to each other, instead
of transmitting and receiving through a telegraph operator.
Some other uses to which the oscillator may be
put may be mentioned briefly.
One which will at once suggest itself is the steering
of torpedoes by sound under water. The idea of so operating torpedoes is
not a new one, and has occurred to a number of inventors, but until the present
time no method of accomplishing it has been developed. With this new source
of sound, however, the method should be practicable.
Another use is as a means for obtaining soundings.
If we take a commutator wheel, with one live segment and two brushes, one
connected to the alternating-current generator and the other to the telephone
receiver, it will be evident that when the commutator segment makes contact
with the brush connected to the generator, a sound will be produced by the
oscillator. When the live contact passes away from the brush, the sound will
cease. This sound wave will travel outward and on reaching the bottom will
be reflected and travel back again to the ship. Meantime, no sound will be
heard in the telephone receiver, but if the brush connected to the telephone
receiver be shifted in the direction of rotation of the commutator until
it makes contact with the live segment of the commutator, at precisely the
instant at which the reflected sound wave has come back and impinged on the
oscillator diaphragm then a sound will be heard. Since sound travels in water
at a velocity of approximately 4000 feet per second, if the distance be 100
feet, the time taken by the sound in traveling from ship to bottom and from
bottom to ship will be approximately one-twentieth of a second.
In April, 1914, some tests were made on the U.
S. revenue cutter Miami to see whether soundings could be taken in the manner
above indicated. As the commutator had not been completed a temporary apparatus
with a stop watch was used. The echo from the bottom was plainly heard not
only on the oscillator, but in the wardroom and in the hold of the ship without
any instruments whatever. The elapsed time corresponded to the depth shown
on the chart and proposed method was proved to be feasible.
The
chief object of the tests on the Miami was, however, to determine whether
a reflection from icebergs could be obtained, and this was proved beyond
question. The apparatus used was the same as for taking soundings.
A signal was sent from the oscillator, the echo
from the bottom heard, and then the echo from the iceberg came in. To make
sure that the second echo was not also from the bottom, the distance from
the Miami to the iceberg was varied from about 100 yards to 2 _ miles. The
elapsed time between the signal and the echo from bottom remained the same,
but the elapsed time of echo from the iceberg varied with the distance and
corresponded very closely to the position of the iceberg determined by the
range finder. Moreover it was found that it made no difference whether the
face of the iceberg was normal to the path of the sound or not, thus showing
that the echo was due not to specular reflection but to diffraction
fringes.
When the Miami had gone 2 _ miles from the iceberg
a heavy storm made it necessary to postpone further tests, and continued
rough weather made further tests impossible, as the oscillator was not
permanently installed but had to be lowered overboard. The echoes at 2 _
miles were, however, loud, and there can be no doubt that they would have
been heard at greater distances. (See appendix).
To sum up: The oscillator represents an important
step forward in the science of navigation. It makes it possible to surround
the coasts with a wall of sound so that no ship can get into dangerous waters
without warning, to make collisions between ships possible only through
negligence. Although no sufficient tests have been made to warrant the statement
that icebergs can be detected under all circumstances or that soundings can
be taken at full speed, what evidence there is points that way. For naval
purposes it provides an auxiliary means of short-distance signaling that
is available at all times and that cannot be shot away, and it widens the
possibilities of submarine boats to an extent we cannot yet fully
grasp.
Report
of Captain J.H. Quinan of the U.S.R.C Miami on the Echo Fringe Method
of Detecting Icebergs and Taking Continuous Soundings.*
We stopped near the largest berg and by range finder
and sextant computed it to be 450 feet long and 130 feet high. Although we
had gotten withing 150 yards of the perpendicular face of this berg and obtained
no echo with the steam whistle, Professor Fessenden and Mr. Blake,
representatives of the Submarine Signal Company, obtained satisfactory results
with the submarine electric oscillator placed 10 feet below surface, getting
distinct echoes from the berg at various distances, from one-half mile to
two and one-half miles. These echoes were not only heard through the receivers
of the oscillator in the wireless room, but were plainly heard by the officers
in the wardroom and engine room storeroom below the water line. Sound is
said to travel at the rate of 4400 feet per second under water. The distance
of the ship, as shown by the echoes with stop watch, corresponded with the
distance of the ship as determined by range finder. On account of the great
velocity of sound through water, it was our intention to try the oscillator
at a greater distance for even better results, but a thick snowstorm drove
us into shelter on the Banks again.
On the morning of April 27, anchored in 31 fathoms
of water with 75 fathoms of chain in order to make current observations....
Professor Fessenden also took advantage of the smooth sea to further experiment
with his oscillator in determining by echo the depth of water; the result
giving 36 fathoms, which seemed to me very close.
*From the Hydrographic Office Bulletin of May 13,
1914.
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Presented
at the 300th meeting of the American Institute of Electrical Engineers,
Philadelphia, Pa., October 12, 1914, under the auspices of the Committee
on Use of Electricity in Marine Work.
Copyright
1914. By A. I. E. E.
Citation:
Blake, R. F., 1914. “Submarine Signaling: The Protection of Shipping
by a Wall of Sound and Other Uses of the Submarine Telegraph Oscillator.”
Transactions of the American Institute of Electrical Engineers Vol. XXXIII,
Part II: 1549-1561. |
