Toru Katayama

Porpoising oscillations of very-high-speed marine craft

Experimental and theoretical investigations on porpoising of a planing hull at high forward speed up to Froude numbers Fr = 6.0 (Fr = U √gLOA, where LOAdenotes the overall length of ship) in calm water are conducted. Captive model tests and forced motion tests are carried out to measure the hydrodynamic forces acting on the hull. The results reveal that without any exciting force, such a craft can porpoise as a self-excited oscillation originating from the existence of coupling restoring coefficients of different sign in a coupled system. The results also show that significant nonlinear effects for motion amplitudes appear in the restoring, the added mass and the damping coefficients. The measured hydrodynamic forces are compared with the results of an existing prediction method including nonlinear effects, and show a good agreement with them. Simulation of porpoising in calm water is carried out using the predicted hydrodynamic forces in a nonlinear equation of motion. The calculated results are in fairly good agreement with experimental ones.

Parametric Roll Resonance of a Large Passenger Ship in Dead Ship Condition in All Heading Angles

Although it has been widely believed that a ship in dead ship condition has the largest roll motion at resonance condition, the authors found that, because of parametric roll resonance, a kind of ships has significant heavy rolling in beam waves with slightly smaller period of the half value of its natural roll period if the roll damping is small. In the present paper, model experiments to measure ship motions of a large passenger ship in waves with various heading angle are carried out to confirm the region of heading angles where large parametric rolling appears. The results demonstrate that parametric rolling appears at wide region of heading angles and disappears in certain heading angles.

Experimental and Numerical Studies on Roll Motion of a Damaged Large Passenger Ship in Intermediate Stages of Flooding

Measurements of roll motion of a two-dimensional scale model of a damaged large passenger ship are carried out during flooding process. The experimental results demonstrate that large and slow roll motion sometimes appears in the intermediate stages of flooding. The appearance of the large roll motion significantly depends on location and size of damage opening. It is also confirmed that the simulated results are in fairly good agreement with experimental ones.

Experimental Investigation on Capsizing and Sinking of a Cruising Yacht in Wind

This paper describes the main finding of the investigation of the sinking accident of a 6.45 metre-long cruising yacht in September 2003 in Japan. Responding to the request from Japan’s Marine Accident Inquiry Agency, the authors executed a model experiment in beam wind for identifying the time-to-sink as well as stability calculations with and without water inside the yacht. The results indicate it could capsize when the wind velocity exceeds a threshold. Because of an opened hatch on the deck, water initially enters into the cabin. After capsizing, the water ingress process stops. However, if wind is strong enough to incline the capsized yacht, the yacht starts to return to upright condition but this transition stage provides an opportunity to further flooding. By systematically changing wind velocity in the experiment, the time to sink was recorded. In conclusion, the critical wind velocities for capsizing and sinking were estimated, and reasonably well explain the reason of this accident.

A Study on the Characteristics of Roll Damping of Multi-Hull Vessels

In this study, for a catamaran and a trimaran as multi-hull vessels, the characteristics of the roll damping are investigated experimentally. A free roll decay test and a forced roll motion test with and without forward speed are carried out. The results show that the roll damping of them is much larger than that of conventional mono10 hull vessels, and the component created by side-hull accounts for a significant rate for trimaran. Especially, at the condition without forward speed, the interference of waves created by hulls are significant, the measured roll damping values by different experiments are different on the basis of different water surface condition created by hulls. Moreover, the simplified prediction method is proposed.