Semi-submersible vehicles have low-profile platforms above the water surface while keeping most of their hulls below waterline. In addition to reduced detectability, these craft may potentially have good seaworthiness and hydrodynamic advantage at fast displacement speeds. In this study, exploratory tow tank tests and computational fluid dynamics simulations were carried out with a Suboff model in configurations relevant to semi-submersible vehicles. At different speeds, the optimal drag-lift ratio is found to occur at different submergences, whereas the downward suction force monotonically increases with increasing speed and decreases with increasing draft. The lift center exhibits non-monotonic behavior at variable speeds. Computational simulation results demonstrated good agreement with experimental data and provided insight on contributions of pressure and friction drag components and flow features around hulls. The presented data can be useful for developers of semi-submersible vehicles.

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