ABSTRACT

Investigations on the stability of a discus-shape buoy have been carried out by two different ways in order to determine the most suitable shape, size and weight for a discus-shape buoy hull which would survive environmental conditions that might be encountered in the oceans.

There have been a few related studies being done on this Subject [1]. But it may be stated that there might have been no such systematic investigations as these presented in the paper.

The two ways are as follows:

  1. General considerations of the effects of the parameters such as diameter, weight, center of gravity, and freeboard on the static stability of the buoy. They can be done through total static stability curves obtained for, the various kinds of the buoy with the aid of computer's computations

  2. Model tests to find the critical size and weight for the discus-shape buoy hull at which point the buoy would be overturned by breaking waves and strong winds.

INTRODUCTION

A discus shape telemeter buoy with a diameter of 6-meter moored in a depth of 900 m in the Japan Sea, was overturned during a storm in March, 1972, when an average velocity of wind was estimated about 30 m/sec [2]

Oceanographic telemeter buoys? would be required to gather and transmit safely information about the oceans to shores without being overturned even by severe environmental conditions of waves, winds, and currents.

The purpose of this paper is to determine the most suitable shape, size, and weight for a discus-shape buoy hull which would survive very severe environmental conditions that might be encountered in the oceans through theoretical computations and some experiments on the stability of the discus-shape buoy.

In this considerations, the effect of a mooring line is neglected in order to simplify the analysis and for the reason that the mooring line can provide a considerable amount of restoring force [1].

STABILITY CURVE

It is, in general, one of the useful methods for the stability of a floating body to investigate the total static stability curve for the body. The total static stability curves for the buoys were obtained by digital computer's computations.

The righting moment of a buoy is expressed as W GZ, where W is the weight of the buoy, and GZ denotes the righting arm. The righting arm GZ can be obtained by the following equation.

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These computations were made by approximate integration of the submerged volume of the buoy hull.

When the static stability curve is required, it is necessary that intersections of the water line and the longitudinal station cross-section have to be read for a number of longitudinal station cross sections, and it takes much time to draw the stability curves. However, since the discus-shape buoy hull consists of a circular cylinder and a frustum of a circular cone, the shape of the longitudinal station cross-section can be expressed as a hyperbola for the part of frustum and as a straight line for the part of cylinder.

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