On the drag reduction and heeling stability of a heeled planing air cavity hull

Abstract

The air cavity planing hull enables the feasibility of running at a low drag-to-lift ratio at high speeds by reducing the wetted area. During the voyage, the ventilation rate and heel are essential parameters for the performance of the air cavity ship (ACS). In this study, three-dimensional Reynolds-averaged Navier-Stokes equations coupled with the volume of fluid method (RANS-VOF) are applied to examine the characteristics of the ACS across a wide range of ventilation rates (Cq = 0–1.120) and heel angles (β = 0–5 deg). The drag reduction and cavity morphology of the ACS are well predicted by the numerical method. The difference between the predicted total resistance and the experiment is less than 5%. The air cavity gradually develops from the meniscus growth cavity (MGC) (Cq ≤ 0.168) to the bottle neck stable cavity (BNSC) (Cq ≥ 0.336) with increasing Cq. Once a stable cavity form (i.e., BNSC) is established, the excessive ventilation would expand the tail air leakage opening in width and thickness. Under the effect of the heel, air coverage and drag reduction are diminished with a critical heel angle (β) of around 2 deg. When β ≥ 2 deg, the cavity shape gradually degenerates to the one-side branch cavity (OSBC). The air coverage also has a negative effect on the heeling stability, which means that the smaller heeling moment may cause a greater heel angle. More importantly, the restoring moment reduction monotonically decreases from 54.3% to 7.1% with the increment of heel angle, which deteriorates the heeling stability of the ACS.