Final answer:
The triangular sail that was more effective at catching the wind than the traditional square sail is called the lateen sail, enabling ships to sail against the wind and contributing to the navigational advancements of the fifteenth century.
Step-by-step explanation:
The triangular sail that was better able to catch the wind than the square sail which was previously used is known as the lateen sail. This advancement in maritime technology allowed ships to sail against the wind through a process called 'tacking'. Originating in the Middle East with Arab sailors, and later being adopted in Europe, the lateen sail was combined with the square sail to produce three-masted ships capable of greater maneuverability and navigation confidence. This technological enhancement, along with the sternpost rudder from China and navigational instruments such as the astrolabe and magnetic compass, fundamentally changed seafaring and allowed European navigators to venture into the open ocean beyond the sight of land.