knowledge of gravity: increased their knowledge of tides, sailors could predict when the depth of water near the shore would decrease which exposed dangerous rocks.
astronomical chart: is any map of the stars and galaxies. mariners relied on these maps to guide ship's direction, especially before the introduction of compass, using the skies to help them determine their location.
astrolabe: allowed sailors to determine how far north or south they are from the equator.
compass: is a primary direction-finding device used in navigation. the magnetic compass allowed sailors to steer a ship in the right direction.
lateen sail: used by arab traders and in the indian ocean, it was able to catch wind from either side of the ship allowing it to travel in both directions.
new ship designs: by adjusting the ratio of length to the width of a ship, adding or reducing number of masts, and use different types of sails.