A system to create and maintain a gas/vapor cavity about a hull surface includes a fence selectively extendable above and below the hull surface. A gas venting means is positioned beneath the hull surface downstream from the fence. The vented gas can be used to create a gas/vapor cavity downstream from said fence and cover the hull surface. A heat source is also positioned downstream from the fence and beneath the hull surface. The heat source is capable of heating the hull surface to create or maintain the gas/vapor cavity on the hull surface. A sensor and controller can also be provided to control the cavity.