Until the 15th century, the Portuguese were limited to coastal cabotage navigation using barques and "barinels" (ancient cargo vessels used in the Mediterranean). These boats were small and fragile, with only one mast with a fixed quadrangular sail and did not have the capabilities to overcome the navigational difficulties associated with Southward oceanic exploration, as the strong winds, shoals and strong ocean currents easily overwhelmed their abilities. They are associated with the earliest discoveries, such as the Madeira Islands, the Azores, the Canaries, and to the early exploration of the north west African coast as far south as Arguim in the current Mauritania.