Seakeeping-performance comparisons of monohull, catamaran, and SWATH crew-transfer vessels in operationallimit sea states
Muhammad Zaid bin Zainuddin,MooHyun Kim,Krish T. Sharman,Suqin Wang
Abstract
Three different hull forms, monohull, catamaran, and SWATH (small waterplane area twin hull), of similar displacement and principal dimensions are designed for the systematic comparisons of their seakeeping performances in sea state 3 and 4, which is considered as the typical operational limit of CTVs (crew transfer vessels). The RAOs (response amplitude operators) of the three vessels for various wave headings were calculated from potential theory and BEM (boundary element method) in the frequency domain. In parallel, the time-domain simulations including viscous drag effects were also conducted for their motions in sea state 3 and 4 by using an independent in-house program, CHARM3D, which compared well against the frequency-domain results. When comparing seakeeping performance in sea state 3 and 4, the SWATH vessel outperforms both the catamaran and the monohull. The SWATH's 6DOF motion amplitudes are about half of those of catamaran and monohull since its heave-roll-pitch natural frequencies are much lower than the peak frequencies of incident waves in sea state 3 and 4. Therefore, we found that a SWATH can be operated up to a higher sea state 4 while a monohull and a catamaran can be used up to sea state 3. Our simulations also examined the three CTVs positioned about 10 m behind a monopile wind turbine structure of 10 m-diameter, by using our in-house two-body CHARM3D hydrodynamic interaction simulation programs. The two-body simulation results show minor shield effects in motions when operating behind the monopile. Again, SWATH shows the best seakeeping performance compared to other vessels.
