Part 1

THE SPERRY GYRO-COMPASS, BY THE SPERRY GYROSCOPE CO.

_Copyright,_ 1920 THE SPERRY GYROSCOPE COMPANY BROOKLYN, N. Y., U. S. A.

DESIGNED, ENGRAVED AND PRINTED BY

THE

SPERRY

GYRO-COMPASS

THE SPERRY GYROSCOPE CO.

MAIN OFFICE AND FACTORY

MANHATTAN BRIDGE PLAZA. BROOKLYN, N.Y.

THE SPERRY GYROSCOPE COMPANY

_Boston, Mass._ 60 VIRGINIA STREET

_Great Lakes District_ 828 GUARDIAN BUILDING Cleveland, Ohio

_San Francisco, Cal._ 52 DAVIS STREET

_Main European Office_: THE SPERRY GYROSCOPE COMPANY, Ltd., 15 Victoria Street, London, S. W. 1

—REPRESENTATIVES—

_France_

COMTE A. DeCHAMBURE 37, Rue Bergere Paris

GEORGES BREITTMAYER 20, Rue Taitbout Paris

F. J. DELVES 20, Rue Taitbout Paris

_Spain_

F. WEYDMANN Victoria 2 Madrid

_Holland_

TECHNISCH BUREAU VAN LEENT Nassaukade 17 Ryswyk

_Italy_

F. P. CAMPERIO Via Bagutta 24 Milan

_Sweden_

GRAHAM BROS. Stockholm

_Denmark_

C. KNUDSEN 11 Kobmagagade Copenhagen

_Norway_

OTTO PLATOU Skovveien 39 Christiania

_Japan_

MITSUI & CO., LTD. Tokyo

MITSUBISHI ZOSEN KAISHA, LTD. Tokyo (For Ship Stabilizer)

_Chili, Peru & Bolivia_

WESSEL DUVAL & CO. 25 Broad Street New York

THE SPERRY GYROSCOPE COMPANY

_Manufacturers of_

GYRO-COMPASSES GYRO SHIP STABILIZERS GUN-FIRE CONTROL APPARATUS NAVIGATIONAL INSTRUMENTS NAVAL AND COMMERCIAL SEARCHLIGHTS

_Putting the Earth to Work_

When the earth was thrown off from the sun and commenced rotating about its own axis, there was developed a force generated by the earth’s rotation. For countless centuries this force has been at work, but no one has ever been able to harness it to serve the purposes of man. But now, through the efforts of Foucault, Hopkins, Sperry, and other noted scientists, this force has been put to work. It serves to direct a thousand ships in their courses.

Of course, this is not the only force which has been used to guide ships. Since 1297 A.D. mariners have used magnetic attraction as the force by which to guide their vessels. For centuries seafaring men sailed only in wooden ships, and were therefore satisfied with the magnetic compass. Then came steam and steel. Navigation then instead of being a hit or miss game of chance became the exact art of directing a ship by the shortest possible course in the quickest possible time.

Now that ships cost millions of dollars to build and thousands of dollars per day to operate, time has become the most essential element in navigation. The development of ships from the sailing vessel to the ocean greyhound has been one of the marvels of modern times. But the development of the magnetic compass has not kept pace with the development of the ships which rely upon it. Many of the great trans-Atlantic liners are guided by practically the same type of compass as that which Columbus used on the _Santa Maria_. The compass on the wooden _Santa Maria_ pointed to magnetic north with a fair degree of accuracy, but the compass on the steel greyhounds must contend with many distractions.

For years magnetic compass designers spent their efforts to produce compensating devices that would annul the effects of all external influences, so that the magnetic compass would be free to indicate only the direction of the earth’s magnetic lines. Very little has been done to improve the compass itself—it still depends upon the attraction of the Magnetic North Pole. The Sperry Gyro-Compass differs in principle from any other compass. It is not magnetic. It derives its directive force, not from magnetic attraction, but from the earth’s rotation.

There is certainly a crying need for this new type of compass. A ship now-a-days costs millions of dollars and carries cargoes usually equal in value to that of the ship. It has been estimated that inaccuracies in navigation attending the use of the magnetic compass cause a yearly loss of ships to the value of $70,000,000. No estimate can possibly be made on the value of lives lost on these ships.

Millions of dollars are spent each year on charts, lighthouses, buoys, geodetic and hydrographic surveys, and on compilation of notices to mariners. Notwithstanding all of these, ships must ultimately depend upon their compasses for their safety and efficiency of navigation.

Inaccuracies in navigation can be eliminated by the use of a reliable compass. The Sperry Gyro-Compass puts the earth to work. It utilizes a force which is as unvarying as the law of gravity, a force that cannot be interfered with by any other influence.

How the Earth’s Rotation Is Utilized

Any wheel rotating at a high speed about its own axis, and free to place itself in any plane, is called a _Gyroscope_. The _Gyroscope_ is the instrument which utilizes the earth’s rotation as a force to direct the course of ships.

Suppose you were to place such a small wheel supported by its axis upon a larger wheel which also is revolving. The rotation of the larger wheel would so influence the smaller wheel that its axis would point in the same direction as the axis of the larger wheel. Why this is the case does not concern us here. Let it suffice that the larger wheel will cause the smaller wheel to behave in this manner. This is in accordance with a natural law. This law operates as unfailingly as the law which causes an unsupported body to fall to the ground.

Suppose the larger wheel happens to be the earth, which in reality is a revolving wheel. Suppose further, the small wheel is a Sperry Gyro-Compass. In accordance with this natural law just outlined the smaller wheel, or Gyro-Compass, will point its axis in the same direction as the axis of the earth, or, in other words, to the true or geographical North Pole. This explanation of the principle of gyroscopic motion is necessarily crude. The principle itself has been established beyond any reasonable doubt. It can be proved by mathematics to the satisfaction of the most exacting scientist and has been demonstrated, throughout the navies of the world, to practical seamen.

The final result is that we have a principle which enables us to construct an instrument which will place itself in the true geographic north and south meridian, and that it responds to no influence or impulse other than the earth’s unvarying rotation.

_How a Compass is Used_

The purpose of a compass is to indicate direction. The relative position of the North Pole to any point on the earth’s surface is called North. We figure all direction from this conception. This geographical North Pole is called the True North. About 800 miles from this True North Pole is a spot which has a strange magnetic attraction. The needle of the magnetic compass, if undisturbed by local influences, points to this spot, and not to the True North Pole. This spot is called the Magnetic North Pole. This mysterious attractive spot is not stationary. It moves about from year to year within a wide circle.

Inasmuch as the navigator must refer to True North, he must determine the angle or variation between True North and Magnetic North as indicated by his magnetic compass. This determination is made comparatively easy by using charts which express in degrees the difference between Magnetic North and True North for any point on the earth’s surface.

Such a chart is shown in Figure 3. Also on each chart used by a navigator for a particular locality there is marked a compass rose in which is recorded the variation for that exact spot as of a certain date, and in addition the rate at which the variation changes annually, Figure 4.

Navigation along a coast line where sights can be taken on buoys or lighthouses is simple, and is termed “piloting.” This, of course, can be done without the aid of a compass.

Upon getting to open sea the mariner checks his position in a similar manner, by observing the position of his ship in relation to the position of the sun, moon or stars. Between observations the position of a ship is determined by “dead reckoning.” The distance it has traveled from the last known position is measured by the ship’s log and the direction is indicated by the compass. Very often for days at a time, owing to weather conditions, it is impossible to get an observation or sight on a celestial body. During this run the navigator is dependent entirely upon the compass. The slightest error in the compass, due to variation or deviation, in such circumstances will cause the ship to be miles out of its course, and the actual position will be far from the calculated position.

_The Ideal Compass_

If you were to conceive of a compass which would be free from all the troubles and errors found in most compasses, which would relieve you of all the worry and care the present compass requires, a compass which would be accurate and reliable, a compass which would be the Ideal Compass under all conditions, you would undoubtedly conceive of a compass that had the following characteristics:

1. It must point True North.

2. It must free you from the necessity of making calculations and corrections.

3. It must free you from compensating the compass for errors.

4. It must free you from the burden of swinging the ship, or otherwise taking the deviation of your compass.

5. It must not be influenced by inherent magnetism of the ship.

6. It must not be influenced by any change in the character or disposition of the cargo.

7. It must not be influenced directly or indirectly by any temperature changes.

8. It must not be influenced by the roll or pitch of the ship.

9. It must not be influenced by any weather conditions.

10. In the event of failure, or error, it should give instant warning.

Comparison of the Magnetic Compass with the Sperry Gyro-Compass

Let us compare the Magnetic Compass with the Sperry Gyro-Compass and determine which more nearly approaches the Ideal Compass.

True North

The Magnetic Compass

The Magnetic Compass does not point to True North, it points to Magnetic North, which is about 800 miles from the True North Pole.

The Sperry Gyro-Compass

The Sperry Gyro-Compass, which is not a Magnetic Compass, and is not affected by a magnetism of any sort, and derives its directive force from the earth’s rotation, points True North. It does not point to the Magnetic North Pole.

Freedom From Calculation

Every time a ship’s course is laid or changed, or its position noted, the navigator must make and apply calculations to correct the errors caused by variation of the earth’s magnetic fields, and deviation due to local conditions about the ship. Mistakes are frequently made in applying the correction factors by applying them to the wrong side. An error is thus introduced, which in magnitude is twice the correction factor. Instances are reported of ships being 200 miles out of their courses as a result.

The Gyro-Compass requires no corrections since it is undisturbed by variations or any local magnetic conditions. The reading indicated by the Sperry Gyro-Compass is not approximate—it is absolutely and immediately correct. It is not necessary to correct the course every few hours for variation—the navigator is freed from the necessity of making calculations.

Freedom From Compensation

After the navigator has made calculations for the deviation errors of the Magnetic Compass, they must be applied by means of manipulating the soft iron globes and compensating magnets. This is an operation requiring such a high degree of skill that only trained men called Compass Adjusters are qualified for the work.

The occasional turning of a thumb nut is the only compensation necessary in the use of a Sperry Gyro-Compass. No tables or curves are required. The ship’s Navigating Officer makes this adjustment with ease.

Freedom From Checking Deviation

Each time a compass is compensated it is necessary to check the compensation by checking the deviation on various headings. This may be done by the use of deflector magnets. A more exact method is to swing the ship in a circle while bearings are taken of a known object on land and the deviation noted on various headings. The sun is often taken as a reference point for this purpose.

It is never necessary to swing ship or to correct the Gyro-Compass for either variation or deviation of any kind. Where a Gyro-Compass and a magnetic compass are both used on a ship, the ship may be swung to correct the magnetic compass—the Gyro-Compass furnishing true headings. The time required is thereby materially shortened.

Influences Due to Magnetism of the Ship

When a steel ship is building a sub-permanent magnetism is induced in its keel, hull, and plates. It causes a compass deviation classed as “semi-circular.” This deviation must be compensated for.

As a ship moves through the earth’s magnetic fields in its varying quantities and directions, a temporary and varying magnetism is induced in the soft iron of the ship. The resultant deviation is classed as “quadrantal,” and must be compensated for.

The Sperry is not a Magnetic Compass. Hammering, riveting, and moving through magnetic fields may induce magnetism in the ship, but will have no effect upon the Sperry Gyro-Compass.

There is no condition of the ship or cargo for which the Gyro-Compass must be corrected.

Influences Due to Cargo

Change in the character or disposition of the cargo of the ship causes a change in the magnetic fields surrounding the compass. These changes must be compensated for.

The Sperry Gyro-Compass is not affected by any cargo. A cargo of iron ore has no more effect upon it than a cargo of cotton. You could even carry a load of strong magnets without causing the slightest deviation.

Influences Due to Temperature Changes

Changes in the temperature of the stack, due to shifting of the wind and force of draft, vary its magnetic characteristics. Consequently the Magnetic Compass is affected.

Temperature changes do not influence the Sperry Gyro-Compass.

No matter what the conditions are that change the magnetic characteristics of the stack, ship or cargo, they cannot affect the Gyro-Compass, as it has nothing whatever to do with magnetism.

Influences Due to Roll and Pitch of the Ship

The Magnetic Compass

Another error, called heeling error, is caused by the change in the disposition of the material of the ship with reference to the compass. It is brought about when the ship rolls. For example, a ship heading on a northerly course would, if rolled to port, place all magnetic material of the ship to the eastward of the compass. This pulls the north end of the compass to the eastward. The action and effect would be just opposite to this on a roll to the starboard. The result is that the needle is caused to oscillate in either direction. The helmsman in his attempt to keep “on” will cause the ship to traverse a sinuous course.

The card and needle of the magnetic compass are placed in a bowl filled with a liquid. The purpose in so doing is to make the action of the card somewhat sluggish, so that it will not follow very slight magnetic distractions or ship movements. Every time the course of the ship is changed the sluggish action, due to adhesion between the bowl, liquid and card, pulls the compass off the meridian. Official test has shown that from three to four minutes are required for the compass to overcome this “lag.” The “lag” is somewhat less in the dry card compass.

The Sperry Gyro-Compass

Not only is the Sperry Gyro-Compass unaffected by magnetic conditions, resulting from the heeling error, but before being placed upon the ship it is tested for days under conditions simulating the motion of the ship in the most severe storm.

A ship steered by the Gyro-Compass traverses a straight line course; the Gyro-Compass does not oscillate with the rolling of the ship. It is not necessary for the helmsman to use as much helm to keep the ship on her course. A great saving is made in the use of the steering engine.

There is no “lag” in the Sperry Gyro-Compass, because it does not leave the meridian, no matter which way or how quickly the ship may turn or zig-zag. Exhaustive tests have been conducted on compasses installed on torpedo boat destroyers. Even when zig-zagging at top speed in heavy seas the Gyro-Compass shows no “lag.”

Traveling the straight line course instead of the sinuous course, ships equipped with the Sperry Gyro-Compass have saved from one to ten per cent in time over the average schedule time required to cover their courses when steering by the magnetic compass.

Warning of Unreliability

Due to magnetic storms and any number of other causes the magnetic compass may at any time be distracted so that it does not indicate correctly. Disturbances are extraneous and their direction and magnitude cannot be determined. The navigator is constantly subject to the feeling that his compass may not be accurate—that he cannot depend on it.

About the only thing that will cause an error in the Gyro-Compass is the failure of the electrical power supply. Should this contingency occur an electric bell warns the navigator. Any disturbances must originate with the master compass and can be quickly and accurately located.

* * * * *

The Sperry Gyro-Compass unfailingly points True North under all conditions of weather, ship or cargo. It relieves the navigator of calculation of errors, and tiresome compass compensations. It makes a great saving in time required to “swing ship.” The Sperry Gyro-Compass is, therefore, the Ideal Compass.

_Advantages Attending the Use of the Sperry Gyro-Compass_

During the construction of a steel ship it is usual to build it on ways the direction of which lie in the East-West line. Should the ways be placed in a North-South line the riveting on the keel and plates tends to help the molecules of metal to place themselves parallel to the magnetic lines of force, and magnetize the metal. When placed in the East-West line the molecules of metal in the plates are at right angles to the magnetic lines of force, and are not as easily magnetized. The use of the Gyro-Compass eliminates the necessity of placing the ways in the East-West line.

After a large ship has been launched, and during the fitting out period, it is often necessary to have it swung end for end in order to neutralize or equalize the magnetism induced by the earth’s magnetic field. To swing a large ship end for end costs anywhere from one thousand ($1000) to three thousand ($3000) dollars. The Gyro-Compass is unaffected by any magnetic phenomena, and is so dependable that it makes the swinging of the ship unnecessary.

In constructing a ship it is customary to make all metal parts within approximately ten (10) feet of the magnetic-compass stand of bronze, brass or other non-magnetic material. The proximity of magnetic metals seriously affects the accuracy of the compass. All electric leads are run so as to clear the vicinity of the compass, as the magnetic fields set up by such conductors seriously influence the compass needle. Actual experience is on record that the total installation cost of the Sperry Gyro-Compass has been saved many times over by the elimination of special metals and special run of electric leads.

Before starting on a long voyage, especially with a new ship using the magnetic compass, it is customary to swing the ship through a complete circle to check deviation. To swing ship it is first necessary to pick out a suitable object on land having a known bearing to the ship. This object is used as a reference point. If at sea observations are taken on the sun. The ship is then swung through 360 degrees, stopping usually on each 15-degree heading, and noting the deviation. A table is made up showing the deviation on each of these headings. An attempt is then made to so adjust or manipulate the compensating magnets to eliminate the error found. The ship must then again be swung through 360 degrees, stopping at headings as before to check the applied compensation.

On some ships it is the custom to check the deviation by the deflector magnet method. The ship in this case is put on a certain heading and a magnet placed to one side of the compass and the deviation noted. The same magnet is then placed at an equal distance to the opposite side and the deviation noted. The difference, if any, between the readings is the deviation on that particular course.

With either method of checking for deviation, considerable time is used. It is not necessary to check for deviation or apply any compensation to the Gyro-Compass, as it is not magnetic. In fact the Gyro-Compass has nothing whatever to do with magnetism.

When at sea the Gyro-Compass affords the means of keeping to the straight-line, true course. The line A B, Figure 5, shows the straight-line course from the port of New York to the port of Liverpool. The line A C E B shows, with exaggeration, the actual course steered due to compass and other errors. At the point E the ship’s position was checked by observation of a celestial body. The line E B represents the new course set to bring the ship to her destination. This is an occurrence which sometimes happens not once but often during a voyage.

It is evident that a loss of time is involved when the ship leaves her straight line course. The inherent accuracy of the Sperry Gyro-Compass enables the ship to keep to the straight line course, and also to steer directly on true courses.

By keeping on a straight line course the ship is enabled to make a good many more miles on the same number of revolutions or turns of the propeller. Under exactly the same weather conditions a 16,000 ton liner made 370 miles in 24 hours at an average of 86.95 revolutions per minute per mile when steered by a magnetic compass, and the same liner made 377 miles with 85.61 revolutions per minute per mile when steered by the Gyro-Compass. This saving amounts to easily $50 per day for this ship. During her eleven-day voyage she saved $550. At this rate of saving the Gyro-Compass equipment is soon paid for.