Improvement of the low-speed control authority of an AUV through hull shaping

Often it is necessary to operate an autonomous underwater vehicle (AUV) under conditions where the specific gravity of the vehicle varies by as much as 3%. For AUV systems without a variable ballast system that have to operate at low speeds, this can severely restrict the operational envelope of the system. This paper explores the limits on control authority as a function of vehicle speed and specific gravity for a typical AUV and then shows the effect of increasing the hull elliptic cross-section on vehicle control. Increasing hull lift through various devices is shown to be propulsion-limited as a result of the increase in induced drag. An example is shown where the drag of the vehicle at its lowest speed is higher than the drag at its maximum speed.