Tsugukiyo Hirayama

Development of Mini-Buoy for short term measurement of ocean wave

The authors have developed a small wave buoy as “Ultra-Small-Directional-Wave-Buoy” from 1997. In recent years, The demand of short term wave measurement such as verification of wave radar system and speed trials of new ships is increasing, but general wave buoys are large, expensive and for long term measurement. For such usages, smaller and lighter “Mini-Buoy” is developed.

Free Running Model Experiment on Speed Loss in Directional Spectrum Waves

For evaluating speed loss, self-propulsion test and free running test are carried out in directional spectrum waves with a full ship model in the towing tank of Yokohama National University. Such experiments will be the first time in the world. In the free running test, the model has six degrees of freedom as in real condition, and it is controlled to run straightly by using rudder controlling system, therefore the speed loss can be derived directly by considering the relative speed against carriage by using optical position sensor. It is found that the speed loss in short-crested waves is bigger than the speed loss in long-crested waves in short wave length. The experimental results of speed loss in directional spectrum waves are compared with the results of estimation methods which are originated from the added resistance obtained by experiment and theoretical calculation.