A new phenomenon in interference effect on catamaran dynamic response

Interference effect between catamaran demi-hulls has been considered as an adverse fluid-solid interaction; the narrower separation distance between the two hulls, the greater drag force acts upon the catamaran. However, this study is aimed at introducing a novel phenomenon contrasting outcome in semi-planing and planing regimes. As speed and accordingly the Froude number increase the catamaran transits across different modes, free surface profile becomes complicated and so does the interference effect as well as the prediction of catamaran dynamic response. The situation will be even more complex if demi-hull separation narrows where nonlinearity in interference effect is more pronounced. So, free-running tests in six degrees of freedom as well as obtaining fluid flow characteristics using computational fluid dynamics were conducted for a high-speed catamaran vehicle with asymmetric non-prismatic demi-hulls to tackle the problem. The results of catamaran dynamic response reveal that not only is drag reduced substantially up to 15%, but also trim angle diminishes by 30% as hulls separation distance decreases in semi-planing and planing modes. In other words, with increasing speed, and decreasing trim angle by 2.3o, the current method achieved the goal of consequently reducing the risk of porpoising instability, without the increase of delivered power.