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UBC Theses and Dissertations

The influence of hullform parabolization on the powering, seakeeping and economic characteristics of the UBC-Ferry Gould, Kevin John


This work is a hydrodynamic study of a displacement vessel using numerical and experimental methods to improve efficiency. A new hullform is developed that will have significantly reduced wave resistance, lower power requirements and reduced fuel consumption. This process is termed waterline parabolization and can reduce the wave resistance of a parallel mid-bodied displacement vessel by increasing the overall beam of the ship, through the addition of parabolic amidships bulbs. Two approaches have been taken: a “constant displacement” design producing a new hullform with shallower entrance and exit angles, and a “retro-fit” design where amidships bulbs are added to a parent hullform increasing the displacement. Optimal shapes for the amidships bulbs are developed numerically using a potential flow code based on Dawson’s method coupled with a Matlab optimization routine. Tow-tank tests at Istanbul Technical University (ITU) confirmed that amidships bulbs could reduce the effective power (PE) by 15%. Given the improved powering with parabolization, this thesis also compares the seakeeping characteristics of the parent, “constant displacement”, and “retro-fit” hullforms at high sea state conditions. A strip theory program called SHIPMO PC is used to compare the three different hullforms. Added resistance in waves, roll motions, pitch motions, heave motions and acceleration levels are quantified. There is no significant change in the seakeeping performance except for the roll motions, where there is a shift in the natural frequency of response. This shift is indicative of increased roll stiffness for parabolized hullforms with constant KG’s and increased GM’s as independent variables. Limited tow-tank tests were completed at ITU and they confirm numerical added resistance predictions in head seas between parent and “retro-fit” hullforms. Finally, a route specific cost benefit analysis of a “retro-fit” amidships bulb for the UBC-Ferry is done. Benefits include a variable fuel savings of 44000 L/year and a reduction in capital costs of installed power of 59,500$. The capital construction costs of the “retro-fit” would be 23,900 $/Tonne, and the payback period would be 18 years. Other then cost, the “retro-fit” would have an improved EEDI (Energy Efficiency Design Index) rating and reduced impacts on the environment.

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