Answer:
Piloting:
The ancient Greeks developed the phenomenon of piloting which made ocean exploration easier. Piloting is a technique in which a reference is set so that a person does not get lost while navigating.
Prediction of tides:
Pytheas, a Greek geographer, discovered that tides could be predicted in an ocean, based on the phases of the moon.
Lines of Longitude and Latitude:
Eratosthenes was a Greek mathematician who calculated the circumference of the Earth and formed the lines of longitude and latitude which was an essential concept for the exploration of oceans.