Effects of fin stabilizer configurations on semi swath resistance

Abstract

The installation of the fin stabilizers on the Semi Small Waterplane Area Twin Hulls (Semi SWATH) vessel reduces the disadvantages of its low restoring force. The important role of the fins in increasing the lift force on Semi SWATH brings the need for the hydrodynamic assessment, including the effect of fins on the Semi SWATH resistance. In this thesis, the resistance and wake wash of the Semi SWATH model with separation over length ratio, 0.35 and 0.30 were investigated. The investigation considers the fin stabilizers’ configurations, which change the induced drag and lift and flow pattern around the hulls. Numerical simulation was carried out to examine the mentioned criteria using the ANSYS CFX software with build in Reynolds Average Navier-Stokes (RANS) code in deep and shallow water conditions. Validation of the numerical result was based on the experimental result, which was performed in towing tank at the Universiti Teknologi Malaysia. It was discovered that the computational result showed up to 11% maximum average error. This error is larger as compared with other catamaran computational cases, which is mainly caused by the limitation of the computational tools in producing good computational grid and simulating the turbulence free surface flow in the complex hull form. It was concluded that the fins’ installation angle changes the pressure distribution and wave propagation around the hulls, which increases the total resistance up to 70.9% in deep water and 40.3% in shallow water by average. The resistance increment from shallow water effect for the hulls with 15º fin angle showed 56.5% reduction compared to the bare hulls case. An extended parametric study in shallow water concluded that the total resistance enlargement can be avoided by 27.7% from the appropriate hull and fin parameters, including smaller water depth, larger hull separation distance and small angle of fore fin stabilizers. The findings of the research can be a guideline for the modification of the fin stabilizer configurations for the catamaran and the extending application of Semi SWATH in shallow water region.