His first adventure, in 1415, was the defeat of the Muslims at Ceuta (Morocco), which helped open the African coast to exploration. Henry experimented with ships and navigation during this venture, which led to designing of the caravel, a long and slender ship (by comparison) with lateen sails, that would be used by his Portuguese explorers on their long voyages. Also the navigational instruments, such as the astrolabe, quadrant, and cross-staff, were developed to fix a ship's position. His captains kept logbooks of their voyages to document their experience for the knowledge of others. They also used flat maps to record longitude and latitude thereby simplifying cartography methods. Navigation and seafaring during this period was dangerous, harsh and unforgiving; positions had to be known (in order to know one's way back), the winds, weather changes, currents changed drastically in different locations and small wooden ships could be broken at sea. Supplies of food and water could easily run out during these voyages, and disease could strike. Superstition and fear was also an important passenger on these voyages, and only a few crews were clear of the obstacles associated with sailing alone in the ocean sea. What is known is that the Portuguese Atlantic islands were not unknown; a growing body of documents had shown that the islands were known to sailors. But most important is the language used by Prince Henry's personal chronicler, who wrote that the Prince "ordered [them] to find the islands" (referring to the Portuguese navigators and captains), rather than just sending his fleets into the unknown to discover what they could.