In water cornering at speed... In this photo, they appear to be exiting a turn. No way to determine what speed they are running, but the tunnels are fully saturated. In my mind, this begs the question of bow wave interaction with the sponsons and the turbulence created by the same. Water is being displaced upwards into the tunnels, which is then forced around and down the inside edges of the sponsons. This is mixed with a lot of air passing through the tunnels. My point is… considerable turbulence. Turbulence can (and does) induce drag.