Background: Drag evaluation and prediction are integral to maximizing the efficiency of nautical vehicles. Yet, the total force exerted by a fluid on a body is difficult to predict. One source of drag that remains poorly understood with significant effects for vessels traversing stratified waters is the dead-water phenomenon. It represents the dramatic increase in drag associated with internal waves created by the body itself. This phenomenon has been studied in the literature for surface and submerged vessels separately, but little attention has been given to directly comparing the two.Methods: Our research investigates the dead-water effects by comparing laboratory outcomes for both submerged and surface body experiments in stratified and unstratified fluids. To do this, we tow a cylindrical body with a constant force through a tank of water until the velocity of the towed object becomes uniform, when the drag force balances the towing force. For each scenario, we used four different towing forces.Results: By comparing the drag coefficient measured in each case, we find that the stratified contribution to the drag coefficient is comparable for surface and submerged bodies. The change in the drag coefficient caused by stratification is always positive in these experiments but is much larger for speeds lower than the maximum phase speed of the system.Conclusions: This implies that the dead water modification to the drag coefficient does not depend on the location of the body, which is an important consideration in determining the depth of maximum efficiency for vessel transport.
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