Yachts tend to roll uncomfortably while at anchor, causing discomfort to the crew and passengers, generating additional stresses on equipment, and making such operations as embarking and disembarking hazardous activities. Currently, there is a dearth of data regarding roll motions at zero forward speed for hull shapes dominated by large appendages. Hence, an experimental study into the effect of large appendages on roll motion was undertaken. The model test results are presented, showing how changes in appendage geometry alter the roll response.

This paper reports on work conducted to date investigating the downwind performance of yachts in waves. The main objective of this research is to develop numerical models, resulting in computer software, that may be incorporated into a VPP to predict the mean velocity of a yacht when sailing downwind in waves. The software will be used to investigate how design parameters, such as hull and appendage shape and sail and rig configurations, affect the performance of yachts sailing downwind in waves. The forces acting on the yacht to be investigated are as follows: • wave induced longitudinal force. • hull resistance forces. • sail forces. A numerical model has been developed for each of these forces and incorporated into a longitudinal motion time domain simulation. The simulation predicts the velocity, heave and pitch of the yacht. Experiments have been conducted at the Australian Maritime College's Ship Hydrodynamics Centre to validate the wave force and resistance numerical models. Experimental results have been compared with theory and conclusions drawn.

Computational methods for calculating the flow of the wind over a yacht's sails have been developed over many years. Amongst the pioneers in this field were Milgram (1968), Thrasher ( 1979) and Register (1983). These methods are under continuous development and refinement, for example Fiddes (1996). This paper presents the results of a case study using such a computational model. In this study the upwind performance of the International Mirror Class dinghy is investigated, with particular regard to the interaction between the jib and main sail and the effects of raking the mast aft. The latter point was of particular interest since the British sailors had adopted this rig set-up in preference to a vertical mast and were able to dominate the racing, particularly in lighter winds. The work presented here is part the Australian Maritime Engineering Cooperative Research Centre's (AME CRC) Yacht Technology Research Program. This program involves the development of computational techniques for predicting yacht performance. Two of the principal tools are the velocity prediction program (VPP) and a vortex lattice model which is used to compute sail forces. After a presentation on the Yacht Technology Research Program at the recent Sailing Science Conference in Hobart, Tasmania (Couser 1997), the author was approached by Norm Deane2 and Steve Walker3 with the aim of using computational methods to investigate the aforementioned phenomenon. This work was undertaken since it contributed to the ongoing validation and improvement of these numerical methods and provided an ideal opportunity to apply theoretical sail analysis methods to a practical problem.