The Ideal Compass

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Sperry Gyroscope Company
I

F 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.

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.

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 sub­per­ma­nent mag­ne­tism is in­duced in its keel, hull, and plates. It causes a com­pass dev­i­a­tion classed as “semi­cir­cu­lar.” 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.

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.

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.

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.

                                                                                                                                                                                                                                                                                                           

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