AUVAC

AUV Design: Shape, Drag and Practical Issues

Twenty years ago, autonomous underwater vehicles (AUVs) were an infant technology, and there was an absence of evolution to guide designers in deciding the fundamental shape and size of their craft. Since this period, researchers have tried a wide variety of AUV shapes and sizes, including torpedo shapes, like the National Oceanography Centre’s (NOC) Autosub and Hydroid’s (Pocasset, Massachusetts) REMUS; laminar flow bodies, like the early Kongsberg Maritime (Kongsberg, Norway) HUGIN vehicles; streamlined rectangular styles, like Atlas Elektronik GmbH’s (Bremen, Germany) Sea Otter; and multihull vehicles, like the Woods Hole Oceanographic Institution’s (WHOI) Autonomous Benthic Explorer (ABE). Each came with a vision of fulfilling a certain set of requirements and an oceanographic niche.

Most early AUVs were designed with a cruising speed of around two meters per second as a compromise between long endurance (requiring a slow speed) and making reasonable progress. It is probably true to say that most have fallen short of achieving the combination of design speed and range.

This has occurred for a variety of reasons. For instance, increased drag associated with antennae, lifting lugs and sensor protrusions, among other things, may have been glossed over, and the build is often heavier than anticipated – which is invariably overcome by carrying less energy (batteries). In addition, the propulsion efficiency may be less than hoped for due to poorly designed or matched propellers, and the expected battery energy density can be less than expected due to cold temperatures, high current drain or incomplete manufacturer’s data. It is easy to overlook the energy overheads for premission checks, transit times and so on in the initial design estimates.