The deeper the lifting surface the larger the waves can be. You need the waves to not have too much of an impact at their peak while the foil still being under

The deeper the lifting surface the larger the waves can be. You need the waves to not have too much of an impact at their peak while the foil still being underwater at the trough. Unless the foils can extend and rectract[1], the depth of the lifting surface impacts minimum draft of the ship as well. 1: Or fold, though with folding foils, you need to transition from foiling to floating where the water is deep enough, then float into the shallower water.