Navigation in the 1600's was very primitive compared to modern day. Sailors depended on the compass and their knowledge of the stars to pinpoint locations. Until the compass, a device with a magnetic needle that always points north, was perfected in the late 15th century, ships stayed pretty close to home except for the very brave or foolhardy. They used very primitive tools such as a jackstaff to help compute their position. With a jackstaff, sailors could measure the Pole Star's distance from the horizon and find their position at sea. Another device was the lead and line. A sailor held a lead weighted with lead over the side on the ship to measure the depth of the water. The navigator would point the straight edge of a quadrant at the pole star or midday sun to measure its height in the sky. This would tell him how far to the North or South the ship was. A divider was used to measure distances on charts and could determine how much farther it was to the ship's destination, and how far the ship had already traveled. A traverse board was used together with a compass and sand glass. Every half-hour the pegs were moved to show the direction and distance traveled by the ship. Another device was the astrolabe which was suspended for a ring, and the naviagator moved the alidade, or central rod, until it lined up with the North Star or the sun. Practical experience was as important as instruments. A good navigator could judge the depth of the water by its color and he would watch the sky for birds and and sea for floating debris or twigs. Both might be signs of land.
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