Shallow water catamaran wash : simple characterisations for a complex phenomenon

This thesis explores catamaran generated wash in shallow water, with the specific goal of simplifying this highly complex phenomenon into user friendly characterisations. The wash caused by marine traffic in coastal or inland waterways can have significant effects on waterway users and shore goers within the littoral zone. Typically wash is a minor irritant affecting only the enjoyment of others. However, given certain conditions, wash can also be a significant safety hazard, with one death directly attributed to it. Vessel wash can also have a major impact on the environment with wash related environmental degradation being reported in many countries, particularly those with high speed marine traffic. The potential exists that significant and irreversible changes will occur to the environment because of it. Accordingly wash environmental impact is no longer seen as of secondary importance to successful operations, but in some cases has become the key requirement. Successful mitigation of this wash hazard clearly involves the source of the wash, being vessels and their operation. In response to this hazard, authorities have implemented mitigation strategies, typically route planning and speed restrictions, with limited success. Fundamentally, regulation without understanding of the wash phenomena cannot be truly effective. Accordingly a series of simple wash characterisations are proposed to better define shallow water wash. These characterisations can be utilised by naval architects, operators and regulators in their assessment of wash and in turn effect hazard reduction. A thesis by publication‚ÄövÑvp approach has been taken, comprising five published papers. As is the case for a conventional thesis, the outcome is of a sustained and cohesive theme throughout, (being reflected in the thesis' title). The first four papers each examine a separate wash characterisation, outlining performance in shallow water. These papers were the outcome of physical tests held in the Australian Maritime College model test basin, Tasmania. The first and second papers, on wash decay and divergent wave angle respectively, both confirmed that these parameters vary significantly with water depth, (as well as displacement and hull form), and can be utilised as shallow water characterisations. The third paper investigated unsteadiness that was recorded during experiments and it was concluded that this is due to soliton generation. Furthermore, such highly non-linear waves are known to be a significant safety risk. The fourth paper provides proof of concept that wavelet analysis is successful in characterising vessel wash. The wavelet methodology allows differentiation of various hull forms from their wave patterns alone. The fifth and final paper is a summary of the thesis findings, placing them within the global context of existing vessel performance indicators such as resistance, propulsion and manoeuvring. In turn this paper establishes that the simple wash characterisations proposed are a significant extension of existing wash knowledge and also incorporates a new and novel method of wavelet analysis. Accordingly the thesis achieves its goals of clearly defining shallow water wash and establishing a series of simple wash characterisations.