Dynamic analysis of a semisubmersible-type bucket ladder dredge
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abstract
A semisubmersible-type bucket ladder dredge is a candidate to satisfy the need of the Indonesian tin mining company, PT Timah, to recover tin deposits in water depths of 50 m and deeper. Their current vessel is a barge-type bucket ladder dredge capable of operating in depths shallower than only 30 m. In order to evaluate the dredging capability in 50 m water depth, a dynamic analysis of both semisubmersible-type and barge-type bucket ladder dredges was conducted. The vessel was designed by modifying an existing semisubmersible platform used in the oil and gas industry, while the barge-type used is a conventional bucket ladder dredge. Hydrodynamic coefficients, wave forces, and response amplitude operators (RAOs) of both vessels were computed by using the 3D linear diffraction-radiation software WAMIT. The response spectra of the vessels were obtained in head, quarter, and beam seas of sea state 4. The effect of mooring stiffness was also investigated. Besides modeling the system with low stiffness, such as a catenary mooring, the dynamic analysis was also conducted for the free-floating condition. Finally, the motion performance for the two vessels was compared for various sea conditions, and it is shown that the semisubmersible-type bucket ladder dredge performs better with smaller responses in the selected sea conditions expected in water depths greater than 50 m.
