In the case of casualty at sea, capsizing was 26 of 4069 casualties in 2000 from 20 to 200 tons vessels in Japan. For over 500 tons vessels, it was only 3 of 2826. The cause of capsizing is almost stemming from bad weather. For small vessel, it is important to run into the nearest harbor as soon as possible when the sea state deteriorates. Therefore the authors have been proposing the method to get course keeping ability by spreading a sail at the foremast. In order to verify the effects of a sail, model experiments were carried out at the wind tunnel with water tank to measure wind force and moment. The model is 1.27m length with scale of 1/25 for the 150GT and 31.8m length ship. The wind force and moments were measured every 20 degrees of heading angles ranging from 0 degree to 180 degrees. The sail areas of jib type were 10% & 17% of the transverse projected area of the model. Numerical investigations were conducted using these experimental data. When the wind speed is four to five times of ship speed, namely K=4 to K=5, the course keeping ability increases and the safe navigation of small vessel in strong wind is kept by spreading our handy type sail. At that time, the vessel should run from 30° ahead to tail wind. The tracks of the model ship in base of coefficient of wind force (Ca) and coefficient of wind moment (Cna) are simulated. It gets the effects to keep steady course, nevertheless it's little to increase the speed of vessel.
展开▼
