The role of physical modelling in advancing port design is demonstrated by means of a case study in which three-dimensional physical modeling is used to guide the design of an offshore logistics support base being developed at an unprotected site on the coast of Brazil. The project was driven by the need for a safe harbour for offshore supply vessels, to prevent vessel damage and damage to the dock and berth during normal operations, as well as during extreme storm events. A 1:70 scale model of the proposed supply port and a portion of the surrounding bathymetry was designed, constructed, operated, and then modified to simulate several alternative layouts and design concepts. Froude scaling laws were applied to estimate prototype behaviour from observations and measurements in the model. The physical model proved to be an effective method for assessing the operability of the new port in various metocean conditions and for optimizing its design. It allowed the design team to investigate and assess the impact of many factors influencing wave conditions and the corresponding behaviour of a moored drill supply ship in an efficient and cost-effective manner. The important influences of wave direction, wave height, wave period, and water level were investigated, as were the sensitivities to ship location, loading condition, mooring configuration, mooring line pretension, and mooring line stiffness. Numerous modifications to the port layout were also investigated, which included lengthening the main breakwater, altering the entrance geometry, constructing a new offshore breakwater (of several different lengths), and widening the navigation channel. The outputs from the physical model study have been used in combination with information on the local wave climate at the site to assess operability and estimate downtime due to adverse weather for different port layout and breakwater configurations.