Marine Compass

Timeline

1. 1451–1453Lisbon and Portuguese Atlantic ports · LisbonRoyal-sponsored Portuguese expeditions were all equipped with dry compasses before departure; this type, with a rotating magnetic needle fixed on an axis beneath a 32-point compass rose, gave stable readings on a pitching deck and, together with the astrolabe, formed the twin core instruments of Portuguese ocean navigation.
2. 1453–1456Golden Horn naval shipyard, Constantinople (Istanbul) · IstanbulAfter Mehmed II captured Constantinople, he greatly expanded the Ottoman navy, rebuilding shipyards at Kasımpaşa with captured or hired Byzantine and Genoese craftsmen, and equipped many galleys (kadırga) with marine compasses, quickly giving the Ottoman fleet precise navigation in the eastern Mediterranean and Aegean.
3. c. 1457–1460Gulf of Guinea, West African coast · Gulf of GuineaApproaching the equator, Portuguese navigators noticed significant changes in magnetic declination, began systematically recording magnetic variation data, and combined compass bearings with Polaris altitude measurements (latitude sailing), developing a composite method to maintain directional accuracy south of the equator where Polaris was lost, providing key technical reserves for later voyages around the Cape of Good Hope.