In the late 1400s what led sailors to being able to travel farther away from the coasts?
Several innovations in the 1400's helped to make changes to European sailing ships, enabling them to mount longer expeditions, carry more cargo, and sail against the wind.
The quadrant and later astrolabe, combined with a greater understanding of astronomy, enabled captains to stargaze and better place their ships in positions on the high seas, in which a lack of visible land had made positioning difficult. The Chinese compass invention also serves such a point in determining location.
Movement by rowing through oarsmen had been common since Roman days, such men also took up a lot of space, so adding more masts (from 1 to 2 to 3 as the caraval emerged) allowed more wind to be caught for coastal sailing as well as freeing more room for cargo, as the later carrack demonstrated.