Consisting of 128 warships including royal vessels, ships from the King of Castile's vassals, and several others that had been sent by the Castilian-allied monarchs of Portugal and Granada, this large fleet had been entrusted to the Genoese admiral, Egidio Boccanegra, who was seconded by two of his relatives, Ambrogio and Bartolome.

The Aragonese disposed of ten galleys, a nau, and several small craft garrisoned by companies of crossbowmen, besides a line of siege weapons.

Despite its inferior size, the fleet managed to repulse the Castilian attacks in a two-day battle that saw the first use of naval artillery: a bombard was mounted aboard the Aragonese nau and her shots heavily damaged one of the biggest naus of Peter I.

King Peter I of Castile, who was present at Sanlúcar during the event, felt offended and demanded that the Genoese vessels be liberated from Perellós.

[8] Its castle, however, held out for longer, and when a storm drove most of the Castilian fleet ashore, including six hired Genoese galleys, Peter I had to set them on fire and return to Castile through Murcia, defeated.

[9] The naval forces gathered at the port of Barcelona consisted of ten well-armed galleys, several sailing ships and a very large vessel following the appearance of Peter I in the city.

[3] All the vessels were covered by a shoal known as "Las Tascas", which stretched from just before the Convent of Sant Nicolau de Bari to the road of Regomir.

[5] One of the biggest Castilian naus was hit twice by the fire of a bombard mounted aboard the largest Aragonese nau, which demolished its castles and left it dismasted.

Peter IV gathered a force of 50 galleys collected from Collioure, which he entrusted to Admiral Count of Osona with Cardona as vice-admiral.