Blubber and compliant coatings for drag reduction in water I. Viscoelastic properties of blubber and compliant coating materials

The dolphin and some related marine mammals are noted for small hydrodynamic drag, and a delay in the onset of boundary layer turbulence with increasing Reynolds number. In 1957 Kramer suggested that a compliant biomaterial coating on the dolphin is responsible for the decreased drag, and drag reduction was reported during 1960–1962 by Kramer for towed underwater bodies covered with coatings to simulate the dolphin skin. However, attempts to reproduce and verify Kramerʹs results have been unsuccessful; results reported are contradictory. Characterizations of the viscoelastic compliant materials used are inadequate, and a quantitative knowledge of the viscoelastic properties of the biomaterial coating of marine mammals for comparison with proposed synthetic drag reduction coatings is needed. The data reported here include values of complex shear compliance (J∗ = J′ − iJ″), shear modulus (G∗ = G′ + iG″), with the mechanical loss tangent (J″J′ = G″G′), and shear sound velocity and attenuation in the frequency range of 2 to 1000 Hz for samples of pilot whale blubber and for several compliant coating materials. A brief description of an automated measurement system for the dynamic mechanical properties mentioned above, requiring 3 to 5 seconds at any frequency between 2 and 10,000 Hz, is also included.