We revisit experimental studies performed by Ekman on dead-water (Ekman, 1904) using modern techniques in order to present new insights on this peculiar phenomenon. We extend its description to more general situations such as a three-layer fluid or a linearly stratified fluid in presence of a pycnocline, showing the robustness of dead-water phenomenon. We observe large amplitude nonlinear internal waves which are coupled to the boat dynamics, and we emphasize that the modeling of the wave-induced drag requires more analysis, taking into account nonlinear effects. Dedicated to Fridtj ¨ of Nansen born 150 yr ago (10 October 1861). In this paper, we present detailed experimental results on the dead-water phenomenon as shown in the video by (2008). The material is organized as fol- lows. In the remaining of this section, we briefly review the different studies of this phenomenon, either directly related to Ekman's work or only partially connected to it. Section 2 presents the experimental set-up. The case of a two-layer fluid is addressed in Sect. 3, followed by the case with a three-layer fluid in Sect. 4. The more realistic stratification with a pycnocline above a linearly stratified fluid is finally discussed in Sect. 5. Our conclusions, and suggestions for future work are presented in Sect. 6.
Internal waves were generated by a ship using the ‘dead water’ effect in areas where the water contains a strong near-surface density gradient. The effects of these internal waves on wind waves were examined. The principal measurements were slope statistics of the wind waves and horizontal currents in the internal waves. The effects on the wind waves were always observable from an aircraft; however, in measurements made only along the ship's track the effects of the internal waves were not always readily distinguishable from other factors that influence the wind wave field. By using statistical techniques, relationships have been established between the wind waves, the internal waves, and the wind velocity. The principal finding is that the wind wave field is relatively more sensitive to internal wave currents at low wind speeds than at high wind speeds. Numerical values are given.