Скачать или смотреть SHIP'S MAGNETISM, PART -03, CHIEF MATE EXAM, NAV AIDS, PHASE -II, Causes, Effects & Compass devn 🧲🧭🚢

Permanent Magnetism in Ships — Clear Concept for OOW, Chief Mate & Cadets 🧲🚢
This lesson explains how ships acquire permanent magnetism and why it is important for compass correction and navigation exams.
Permanent magnetism is mainly produced during ship construction. While the ship remains in the same orientation in the shipyard, the Earth’s magnetic field continuously acts on the hard iron structures. Processes like welding, hammering, bending, heating, and electric currents further magnetize the steel — making this magnetism permanent.
🧲 How Ships Acquire Permanent Magnetism
• Ship stays in one fixed heading during construction
• Earth’s magnetic field aligns particles inside hard iron
• Welding, hammering, bending & heating strengthen magnetic alignment
• Magnetism remains even when the ship changes position later
Examples of hard iron: keel plates, bulkheads, deck plates — all retain permanent magnetism.
📌 Key Characteristics
• Does not change with time, heading, or location
• Poles created in the structure remain fixed
• Depends on heading at the shipyard and hemisphere of construction
• A ship built in the Northern Hemisphere generally has: – Blue deck (north pole up)
– Red keel (south pole down)
A ship built on the equator on an east-west heading will have no vertical permanent magnetism.
🧭 Effect on Magnetic Compass — And How We Correct It
Permanent magnetism creates deviation in the compass, affecting accuracy.
Because ship magnetism exists in an oblique 3-D direction, it is broken down into components so each can be corrected separately:
• Pa — Fore & Aft component
• Q — Athwartship component
• Romeo — Vertical / Heeling component
Induced magnetism can also be resolved in the same manner during compass adjustment.
This structured understanding makes deviation correction easier and helps in real bridge operations as well as exams.
🎯 Best For
✔ Chief Mate / Mate (MMD) exams
✔ OOW watchkeeping
✔ Deck Cadets
✔ Navigation Aids students (Phase 2)
Clear concepts here build a solid base for magnetic compass correction and deviation tables.
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