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.

An American Clipper, highest type of sailing ships.