This is an innovation that will reduce skin friction between free water, and a hull of a ship, or rowing shell, or racing craft, etc. on the bottom horizontal surface.
Here, a watercraft is shown with an empty, airtight bottom cavity, filled with slightly pressurized air, which pressure requirement would likely be less than 0.5 psi for every foot, measured from the very bottom of the ship to the free water line.
Thus, if the waterline on the side of the boat is 3 ft. above the (flat) bottom, then an air pressure of less than (3 ft x 0.5 psi/ft. =) 1.5 psi would probably be required.
The function of this "submerged air bubble", is to replace the solid bottom surface material of the craft, in the sense of being in contact with the water.
Primarily because gasses are much less viscous than liquids, the friction between free water, and the moving craft, which now has the bottom-bubble's lower surface as its "keel", is much less than what would be found with a solid-surface contacting the water.
The upsides are improved performance and economy in terms of fuel efficiency. The downsides are additional complexity in construction and operation, due to the concave geometry and air system. Also, because of the tendency of fluid/gas interfaces to remain level, and other factors, the conventional hull's resistance to rolling and pitching (and the associated "righting moments" induced by the usually progressively increasing submerged volumes) would be somewhat lessened for small angle deflections.
This affect is mitigated however, by the isolated cavities at the front and sides which, when the ship is tilted, still retain their air volumes, and comparatively-long moment-arm torque-righting effects. The overall affect in serious weather, is not deeemed significant, due to the very shallow depth of the bubble cavity, where for example, its flooding when the bow might emerge from the water, would not be noticeable.
On large ships where little operational pitch or roll is encountered in ordinary conditions, only a short cavity depth would be required - and the potential for fuel savings would be very high.