Exploratory Study of Design Parameters and Resistance Predictions for Semi-Submersible Vessels

Unmanned semi-submersible vessels were recently proposed as a military logistics concept. ?ere is currently little guidance to inform the concept-level design of these hulls as there are few existing vessels or established design lanes to serve as a benchmark; existing low-cost methods for prediction of hull resistance and motions in the surfaced and in the submerged condition do not readily lend themselves to the semi-submerged case. By nature of their operation at the free surface at high keel-depths, semi-submersible vessels have proportionally larger resistance than both conventional ships or deeply-immersed submarines due to the increased wave-making resistance. ?e potential for reduced waterplane area when deeply immersed can lead to surface suction eff ects and seakeeping concerns that are not readily predicted. In this study, a parametric analysis is presented relating the hull form coeffi cients, immersions and operation speeds of both early era submarines designed to operate mainly at the surface and modern narcotics smuggling vessels. Illustrative histograms of hull parameters show the signifi cance of the slenderness ratio, Froude number and prismatic coeffi cient, all terms related to the wave-making resistance. ?e physical explanation for these trends is discussed using a combination of existing surface ship standard series at the large beam to keel-depth ratios available, as well as computational ?uid dynamics (CFD) and tow tank testing of a SUBOFF hull at various surfaced conditions as a representative generic model of a semi-submersible. Results showed that drag is highly dependent on the degree of immersion. Drag dependence on immersion level, in addition to the traditional design factors, have implications on the operations of long-distance class of military logistics vessels from both detectability and range perspective.