Traditionally ships have been designed to fulfil the contract performance in calm water. More recently, however, the efforts in the IMO have resulted in the introduction of the Energy Efficiency Design Index (EEDI) to quantify and restrict greenhouse gas emissions from ships. The powering performance of future ships should be optimised for the wave and wind conditions it is going to meet during its operation. For these reasons the ship designers have an interest to develop ships with minimum resistance and optimal propulsion for real world conditions at open seas. Accordingly, the number of propulsion tests carried out either in seaway or in regular waves at HSVA is steadily increasing.
Propulsion tests in head seas account for a large portion of all dynamic propulsion tests performed at HSVA. The Side Wave Generator, however, allows the generation of oblique and short crested seas in the main towing tank. A new towing arrangement was recently developed to allow measurement of ship resistance also in oblique seas, giving impulses on ship hull design and optimisation. This is important as the highest resistance values are not always encountered in head seas, but in bow quartering seas.
The combination of towed resistance and propulsions tests provide information on the efficiency of the propulsion in seaway. The new towing arrangement helps designing ship hulls for optimum performance in seaway and in choosing the best propulsion point for a given ship design. The propulsion tests in waves can be carried out both as free-running tests or in a captive mode.