Visualization of three-dimensional shipping water flow on running ship foredeck was conducted at the wave basin of NMRI. Two high speed video cameras, a mirror and synchronous stroboscopic sheet light were mounted on starboard deck and the shipping water on portside deck was observed through the transparent current plate attached along the centerline of the model ship. In this paper, the experimental technique for flow visualization is briefed. High speed video images are presented to show three dimensional features of shipping water motions. And the results of their PIV and PTV analysis are presented together with measured time history of incident waves, model ship motions and impact pressure on the deck.
Impact load due to green water shipping is one of the most severe hydrodynamic load acting on ships. Shipping water often damages containers, hatch cover, equipment and superstructure on the deck. In the extreme case, severe green water hits and breaks the bridge windows, floods electronics and disables all functions of the ship for navigation. In this manner, green water shipping is dangerous for ships. However, number of past studies concerning the shipping water is not so much and understanding of the phenomenon is insufficient even now. In Japan, Tasaki (1961) is known as a pioneer of shipping water study. He conducted a series of model experiment and measured the impact pressure on deck together with the shipping water volume. In his detailed report, he presented measured data and discussed the influence of various items such as freeboard, swell up of free surface due to forwarding speed of ship and relative water level at the stem. Following this work, Goda and Miyamoto (1976) studied shipping water impact pressure using a one-dimensional dam breaking model. Mizoguchi (1988) conducted an experiment of shipping water and analyzed its motions numerically.