Comments and Notes on the Lateral Control of SWATH and OHF Ships, O'Neill, Mar 1988 (0127)
This paper looks at the lateral plane control aspects of SWATH (Small Waterplane Twin Hull) type ships with particular emphasis on the Tri-hull versions like the O'Neill Hull Form (OHF) concept. This paper complements the work done on the longitudinal plane control aspects of SWATH ships of "Comment and Notes on the Control of SWATH Ships" by William C. O'Neill, April 1987. To assess the effects of basic physical parameters of SWATH ships on the lateral stability and control characteristics, one must have a method of calculating the four basic lateral plane derivatives which determine a ships lateral stability and maneuverability. Two radically different approaches, one empirical, one analytical, for predicting the lateral plane derivatives were assessed as to their applicability to Tri-hull SWATHS such as the OHF. Since neither of these approaches in their present form was really applicable, new expressions to predict the lateral characteristics are developed. The lateral plane derivatives calculated from these expressions match the available test data for eight different SWATH ships with accuracy more than sufficient for this task. These newly developed expres-sions are then used to assess the effects of change in geometric parameters and different rudder configurations on the maneuverability of SWATH type ships. Based on these assessments, the paper closes with a list of conclusions and recommendations.