Methods and apparatuses for both reducing and increasing water-side drag of marine vessels are disclosed, to enhance vessel operation and control. The hull of a marine vessel employing the invention would be sectionally constructed, to form a rigid structure. A short central bow section terminating in a primary lateral hydrodynamic step and a longer adjacent aft central hull section are disposed between narrow outboard hull sponsons having large length-to-width aspect ratios which provide substantial buoyant support for the vessel, enclosing an open-channel conduit under the vessel's aft central hull section. Outer water-side surfaces of the elongate outboard hull sponsons are contoured similarly to common racing shells and finished smooth, to delay or prevent flow separation and pressure drag. A shallow-draft aft central hull section having a shingled multi-step bottom surface abuts the central bow section adjacent the primary lateral step. A forced ventilation system provides a continuous air supply under the aft central hull section adjacent the primary lateral step during ahead propulsion, forming a lateral dynamic plenum which occupies its separation zone. A thick layer of air bubbles flows adjacent the shingled bottom surfaces of the aft central hull section during ahead propulsion, preventing flow separation and water-side pressure drag. When ventilation air supply is stopped during ahead propulsion, water-side flow separations develop large pressure drag forces on the vessel's hull, effectively braking the vessel's forward speed. The invention's teachings may be applied to the design of high-speed buoyantly supported marine vessels of all types, including both small craft and large ocean-going vessels.