During this war the French and Spanish fleet could not face the English and Dutch in an open sea battle and therefore had switched to privateering.

On 21 May 1703 a large merchant fleet consisting of about 110 English and Dutch ships transporting mainly salt, but also wine and sugar, left Lisbon for England.

The next day near Cabo da Roca (fr: Cap de la Roque) they encountered the squadron of Coëtlogon composed of five larger warships : Vainqueur (84), Monarque (90), Éole (64), Orgueilleux (90) and Couronne (76).

Vlack lost an arm and part of his shoulder, but he only surrendered when the main mast came down and the ship was on the point of sinking.

Thanks to the sacrifice of Vlacq, the convoy got away intact, meaning this Dutch defeat had little impact on the cause of the Grand Alliance.