Rashed Al-Qemzi topped the overall practice times at Ribadouro with an impressive lap of 45.03sec and that put the Emirati 0.19 seconds ahead of Stefan Hagin.
Alex Carella was third and Duarte Benavente was fourth out of the 28 boats that took to the water.
Drivers were permitted to practice on the course on Saturday morning but the wind strengthened during the session.
Al-Qemzi was using his 2017-specification DAC and had complained that it was getting bogged down off the start line in testing.
With a new engine fitted it responded much better.
Victory Team’s Mansoor Al-Mansoori crashed in the second practice session with Sander Sarlin and the Estionian’s boat was extensively damaged.