Journal of the Kansai Society of Naval Architects, Japan

The position of ship's centre of gravity is usually measured by inclining experiment. The existence of various errors is inevitable in the measured value, as the above method is not direct but indirect. The aurhors made an attempt to investigate the actual variance of the measured positions of C.G. based on sister ship groups. Samples are picked up from the defunct Japanese Navy vessels, whose trial displacements lie between 2,000t and 3,000t. According to the investigation, the following became clear; (1) Distribution function form of measured values is Gauss' normal distribution. (2) In our investigation range, 90% confident intervals of standard deviations for displacement, KG, GM are as follows; [table]

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Recently in Japan, Miserable disasters to fishing boats and small vessels are frequently reported. On the other hand the general demand of seamen on improvement of habitability and accommodation has a tendency to enlarge continuously the deck structure of vessels. Such circumstance is apt to make ships roll heavily or "lurch" by the heavy abeam wind pressure and will bring the ships in distress in the worst condition. Consequently heeling moment of the wind pressure must be a critical factor for the safety of vessels at sea as well as maneuverability and dynamic stability. For the numerical estimation of heeling moment on a vessel, there are only two or three simple theoretical formulae and very few experimental results outside of a report by Okada, which deals with experiments carried out in 1952 on models of a small passenger vessel and of two fishing boats to find out the heeling moment due to the wind pressure at angles only under as small as 30°. A series of wind tunnel experiments, using models of three types of vessel, for the study on the effect of heeling angle up to as large as 70°were carried out. As the results of the experiment the empirical formulae on wind force, heeling moment and position of the centre of wind pressure were obtained. It must be specially noted that the centre of wind pressure is 15 to 25% higher than that of side area.

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Designing the stairways in ships, it is important to know their function in the case of emergency. In general, however, the research and investigation of human action are very difficult, because it is affected by the psychological and physiological factors. As a first step, the authors made a number of surveys of the speed at which passengers ascended or descended the stairways in normal condition. The results are shown in Fig's 1&sim;4, compared with the data of the stairways in buildings. In addition, the auhors investigated the "rise and tread" of the stairways and the results are shown in Fig's 5&sim;7.

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In the design of the mechanical ventilation of air duct system the motor fun is usually designed to have enough capacity to exchange the whole air in the assigned compartments with fresh out-door air at required frequency with all terminal air ports fully opend. The dimensions and laying of the air ducts must be determined so as to satisfy the requirement. This is an arduous task. We have derived a new basic formula applicable to the calculation of the ventilation ducts, assuming that the all air resistances, including duct friction, bend and orifice resistances, are proportional to the square of air velocity in the duct, and also adopting the equivalent length of duct which makes the calculation easy. This formula has analogy to that of electric circuits, and the calcultaion can be made in the same way as in electric circuits.

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