When superhydrophobicity can be a drag: Ventilated cavitation and splashing effects in hydrofoil and speed-boat models tests

Abstract

Abstract Superhydrophobic surfaces are expected to reduce the hydrodynamic drag on marine vessels due to the lubrication effects of the naturally sustained thin air-layer plastron. By conducting model-tests with a hydrofoil-boat and a speed-boat, we demonstrate that the application of a nanoparticles-deposition-based superhydrophobic coatings on marine vessels can also lead to hydrodynamic effects that significantly increase the drag. In the case of the hydrofoil boat, the use of superhydrophobic coating resulted in plastron-enhanced ventilated cavitation and the formation of water jets that reduce the speed of the boat by more than 30%. In the case of a towed speed-boat, the use of nanoparticle-deposition superhydrophobic coating on the hull affected how the boat splashes water but did not change the net drag on the boat during the transition to the high-speed planing mode of operation. The use of a superhydrophobic coating on the speed-boat propeller was found to inhibit its surface piercing and prohibit the transition to the planing mode, resulting in up to three-time lower speed. These novel effects of the superhydrophobic coating should be accounted for together with the anticipated reduction in friction drag in the design of advanced marine vessels.