From the horses mouth.
"In fact Vrolijk isn’t convinced foilers are any faster and they did the research. In the early stages they employed designer Sebastien Schmidt to do a study on what it would take to make Bertarelli's 41ft cat, Le Black, foil and they also had a meeting with the L’Hydroptere team who were keen for them to build a bit inshore version of their foiler tri. According to Vrolijk their VPP has shown the foilers to be occasionally as fast, but no faster than their cat with its long and exceeding fine hulls.

“This system is not easy to put on two foils, so you have to put it on more foils and then you add it up and it doesn’t work. It flies, but it is not fast! Plus all the problems with controlling the foils. Maybe in 10 years….”