Bulletin of the Kansai Society of Naval Architects, Japan

Rceently the author has experienced that a vibration of a ship was violently increased,through the quadrant and steering engine, by the unsuitable rudder form and steering apparatus. The cause of this vibration being attacked theoretically and numerically, the rudder form was partly altered and the strength of the buffer spring changed with the success of reducing the vibration.

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In the present paper the authors calculate briefly the tensile force in the towing rope of harbour tugboat due to sudden velocity increase of the tug relative to the ship towed, and discuss the effect of the buffer spring of towing hook. The conclusion drawn is as follows; the shorter and stiffer the towing rope is, the more effectively the buffer spring operates, for the tension in the towing rope varies proportionally to the square root of the effective spring constant of the rope.

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Some problems on the mechanical trigger are treated in this paper. A method of calculating the strength of the first lever is derived and the mechanism of mechancial trigger is discussed under the the following items; the dynamical effect of the falling weight, the frictional resistance between the second and the third levers, and so on.

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It is difficult to treat theoretically wave-absorbring devices of experimental tank. In the previous experiments of small size, the author obtained some results with waveabsorbing sloped boards and wave-absorbing cages containing some ragged materials such as scraps of cane. The present expermients of full size in the experimental rolling tank (30^m×2.8^m×2^m) of the Naniwa University have given nearly the same results as those of the formers. The results obtained are as follows:- (1) The best angle of wave-absorbing boards to the water surfacer is from 10゜to 15゜. (2) The loger the wave-absorbing board is, the more effective it is. When it is too long, however, it does net operate efficiently and its best length is about half as long again as the wave-length. (3) Wave-aborbing cages with suitable length and arrangement give good results, and (4) Wave-absorbing cages set on wave-absorbing board give excellent results. So far as his experiments are concerned, the wave absorbing arrangement used in his experiments will turn out effective with some improvements.

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