Testing the Costa propulsion bulb with a view to its use on modern ships 1

After a historical summary on the development of propeller guiding apparatus reference is made to the effect of the Costa propulsion bulb. A series of tank tests with this device and with relative test arrangements are described; results are given which were obtained with self propelled models. Then, the results obtained on full size ships are discussed and the importance of evaluating service results by means of modern statistical methods and of effecting comparative trials according to standardization rules is emphasized. As often as possible additional vibration measurements and steering trials should be made. The improvements obtained with Costa propulsion bulb on models and full size ships are then compared and the existing differences explained. Recent flow experiments gave a further means of studying fundamental phenomena, e.g. the influence of the Costa propulsion bulb can directly be observed. In conclusion it is stated that model tests with Costa propulsion bulb are both a valuable help to recognize the influence of certain features in bulb design and a proof of the effectiveness of the bulb on modern ships.