Ocean-going vessels having a load carrying module supported from a pair of spaced apart hulls by legs. The legs may be articulated in two places to provide control of the spacing of the two hulls and to control the elevation of the module off the water. Dynamic control of the articulation may control the response of the vessel, such as to sea conditions. The legs may include aerodynamic surfaces, fixed or controllable, that may be used to aide buoyancy and/or enhance stability, such as by assuring the bow of the hulls does not rise excessively. The hulls preferably are at least partially inflatable, with techniques for installing flexible fuel tanks within a preexisting inflatable hull being disclosed. Also disclosed are modular pressure control systems for controlling pressures in inflatable hulls having a multiplicity of separate inflatable compartments.