Question 664Navigation General

The correct answer is D) the earth's magnetic field affecting the ship's hard iron during construction. Permanent magnetism in a ship is caused by the earth's magnetic field acting on the ship's hard iron components during the construction process. As the ship is being built, the hard iron parts of the vessel become magnetized by the earth's magnetic field, resulting in a permanent magnetic field within the ship. This permanent magnetism is separate from the temporary magnetism induced by the earth's field acting on the ship's soft iron components. The other answer choices are incorrect because they do not accurately describe the primary cause of permanent magnetism on a ship, which is the interaction between the earth's magnetic field and the ship's hard iron during construction.