He had attempted the solution of a certain problem which he had not solved, and every day of leisure, even every occasion of effort and every word of flattery, must have quickened in him new wishes to take the prize which seemed so near, and to achieve the possibility which had thus far eluded him.
From time to time, therefore, he had addressed new memorials to the sovereigns proposing a new expedition; and at last, by an instruction which is dated on the fourteenth of March, in the year 1502, a fourth voyage was set on foot at the charge of the king and queen,--an instruction not to stop at Hispaniola, but, for the saving of time, to pass by that island.

This is a graceful way of intimating to him that he is not to mix himself up with the rights and wrongs of the new settlement.
The letter goes on to say, that the sovereigns have communicated with the King of Portugal, and that they have explained to him that Columbus is pressing his discoveries at the west and will not interfere with those of the Portuguese in the east.

He is instructed to regard the Portuguese explorers as his friends, and to make no quarrel with them.
He is instructed to take with him his sons, Fernando and Diego.

This is probably at his request.
The prime object of the instruction is still to strike the mainland of the Indies.

All the instructions are, "You will make a direct voyage, if the weather does not prevent you, for discovering the islands and the mainland of the Indies in that part which belongs to us." He is to take possession of these islands and of this mainland, and to inform the sovereigns in regard to his discoveries, and the experience of former voyages has taught them that great care must be taken to avoid private speculation in "gold, silver, pearls, precious stones, spices and other things of different quality." For this purpose special instructions are given.
Of this voyage we have Columbus's own official account.
There were four vessels, three of which were rated as caravels.