Abstract The development of the aluminium shipbuilding industry has seen greater demands put upon the design of faster and larger vessels, particularly in the high speed ferry industry, and increasing loads put on existing vessels. Because of this the fatigue performance of marine grade aluminium alloys has become a limiting factor for design, especially with regard to severe service conditions. Far more information is required, such as the load spectra acting upon the structures and the effects of physical and metallurgical properties, to allow designers to cope with these increased requirements and maximise the performance of the vessels. New grades of marine aluminium alloys have appeared recently, which claimed to improve properties that will aid the designer. CSIRO-MST has begun an in-depth evaluation of the fatigue performance of two marine grade aluminium alloys. Optimisation of welding procedures, post-weld treatments and an understanding of how weld metallurgy relates to the fatigue performance are the major goals. The information produced in this study will allow ship designers and builders to take full advantage of the latest developments in marine grade aluminium alloys. It will also provide the constraints that can be used in the design of larger and faster high speed vessels.