While the king of Portugal continued to encourage his navigators to proceed to the southwards in discovering the African coast, he became anxious lest some unexpected rival might interpose to deprive him of the expected fruits of these discoveries, which had occupied the unremitting attentions of his predecessors and himself for so many years. Learning that John Tintam and William Fabian, Englishmen, were preparing, at the instigation of the Duke of Medina Sidonia, in 1481, to proceed on a voyage to Guinea, he sent Ruy de Sousa as his ambassador, to Edward IV. of England, to explain the title which he held from the pope as lord of that country, and to induce him to forbid his subjects from navigating to the coast of Africa, in which negotiation he was completely successful. He likewise used every exertion to conceal the progress of his own navigators on the western coast of Africa, and to magnify the dangers of the voyage; representing that the coast was quite inhospitable, surrounded by most tremendous rocks, and inhabited by savage cannibals, and that no vessels could possibly live in those tempestuous seas, in which every quarter of the moon produced a furious storm, except those of a peculiar construction, which had been invented by the Portuguese ship-builders.
A Portuguese pilot, who had often made the voyage to Guinea, had the temerity to assert, that any kind of ship could make this redoubted voyage, as safely as the royal caravels, and was sent for to court by the king, who gave him a public reprimand for his ignorance and presumption. Some months afterwards, the same pilot appeared again at court, and told the king, “That being of an obstinate disposition, he had attempted the voyage to Guinea in a different kind of vessel from those usually employed, and found it to be impossible.” The king could not repress a smile at this solemn nonsense; yet honoured the politic pilot with a private audience, and gave him money to encourage him to propagate the deception. About this period, likewise, hearing that three Portuguese seamen, who were conversant in the navigation of the coast of Africa, had set out for Spain, intending to offer their services in that country, John immediately ordered them to be pursued as traitors. Two of them were killed, and the third was brought a prisoner to Evora, where he was broke on the wheel. Hearing that the Portuguese seamen murmured at the severity of this punishment, the king exclaimed, “Let every man abide by his own element, I love not travelling seamen.”