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Geosciences LibreTexts

2: Getting our Bearings

  • Page ID
    • 2.1: Latitude and Longitude
    • 2.2: Measuring Speed
      It was important for mariners to know their speed at sea. Early sailors used chip logs, which were planks of wood attached to long spooled lines containing knots at regular intervals. The plank was thrown overboard, while the spool remained on the ship. Once in the water, the plank encountered drag, which held the plank roughly stationary in the water while the attached line unspooled. The rate at which the line unspooled indicated how fast the ship moved away from the plank, and thus the ship’s
    • 2.3: Map Projections