SSC San Diego TR 1801, August 1999

Approved for public release; distribution is unlimited. iv " The dolphins usually swim ahead of the ship, or sometimes alongside, but never in the ship's wake. Unlike sharks, which follow ocean liners for their refuse, dolphins merely come up to play, sometimes jumping right out of the water, darting across the bow waves and even diving under the ship. They are never covetous and never beg. On the contrary, the are the envoys of Neptune, the God of the Sea, and as such they accompany the ship and see it safe to harbour. " E. OBJECTIVE The principal objective of this project was to perform a comprehensive review of performance, kinematics, and swimming hydrodynamics by dolphins and other cetaceans. This report describes information obtained from the available literature including published research and technical reports from English-speaking and Russian sources. The project team specifically studied routine and maximum swimming speeds, morphological design related to hydrodynamic performance, drag reduction, swimming kinematics, thrust production and efficiency, behavioral strategies employed for energy economy when swimming, and maneuverability. SYNOPSIS Research into dolphin swimming has been guided historically by the false assumptions of " effortless , high-speed " swimming. Drag-reduction hypotheses were developed from these assumptions. A survey of the reported swimming speed estimates show that speed is inversely related to duration (i.e., the faster the speed, the shorter the duration). Reported maximum speed estimates range from 8 to 15 m/s. The body and control surfaces are highly streamlined. Dolphin body and control surfaces are similar to the design of manufactured high-performance structures. Drag estimates obtained from experiments on towed models and gliding and actively swimming animals were used to investigate drag-reduction mechanisms including compliant dampening, dermal ridges, secretions, boundary layer heating, and skin folds. There is some indication that the fluke oscillations may control boundary flow and prevent premature separation although the character of the boundary layer (laminar versus turbulent) remains in dispute. Symmetrical, sinusoidal fluke oscillations in the vertical plane produce thrust. Whereas the amplitude of the stroke remains constant over a routine speed range, frequency increases directly with speed, and pitch angle and angle of attack decrease with increasing speed. Hydromechanical models provide reasonable estimates of thrust power and efficiency, although the simplified assumptions of the models (i.e., rigid planform, simple geometric design) do not provide exact solutions. Propulsive efficiencies are 0.75 to 0.90. These efficiencies occur within the optimal range of Strouhal …