When the transducer of the echo-sounder is equipped on the bottom of the wooden ship, it is necessary to know the penetration loss of ultrasonic wave through all sorts of wooden boards. Now we report the result that we immersed a cryptomeria board and a pine board in water in the tank and measured the penetration loss of ultrasonic wave. And we studied its relation with the number of days of immersion. We found that the loss decreased conspicuously after about a week. And we stndied its relation with the thickness of a board and the frequency of ultrasonic wave.

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The measurement of ultrasonic reflection coefficient of fish body presents a serious problem to the use of fish-finder, the solution of which has not ever been published. We measured the reflection coefficient by a new method. Through this experiment, we bound that two values measured in field tests and in tank tests are almost equal. Therefore, the future investigation will be simplified. First, matchiag transformers and an attenuator are put between receiver and amplifier. Then, the acoustic pressure of reflected wave is obtainod from the value in decibel (db) shown on the attenuator when the image on the recording paper extinguishes. Second, the curves showing the relation between the acoustic pressure of direct wave and distance and that between the acoustic pressure of reflected wave and distance are obtained with a sender, and a small magnetosrtriction receiver, going up and down over a body to be measured. These two curves thus obtained are shown in Fig 1 ; the former, in the left side of the discontinuous line and the latter, in the rigt. The difference between the two curves at the dscontinuous line is the reflection loss of that body. We measured the reflection coefficient of living Gray rock cod, Horse mackel, Flatfish, Cuttlefish, and Carp. The results showed that the reflection is closely connected with form of fish body and is in proportion to difference of densities of sea water and fish body, and square of frequency. The reflectin of ultrasonic wave from a fish body, in a cap, is not effected by its air bladder alone, but its whole body. The reflection loss from the whole body is 10-15 db less than that from the air bladder. The same may be true with other fish. (1951)

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After having investigated the real circumstances of setting wireless navigational aids about 413 fishing boats amounting to the ratio of 90% of the whole boats which have the chief base at Shimonoseki harvor, we have confirmed the following results. 1. Radio Direction Finder 32% of the whole investigated boats have the aid. The items of various boats are as follows. Trawlers: 100%, Danish seine boats: 83% Purse seine boats: 57% 2. Fish Finder 20% of the whole investigated boats have the aid. The items of various boats are as follow. Trawlers: 59% Danish seine boats: 9%, Purse seine boats: 80%, Fish carryers following to Purse seine boat: 20%. 3. Marine Radar Only one of Danish seine boats was set up with the aids at Feb. 1952, moreover, one of them are on the way of being set up and two Trawlers and a Danish seine boat are planned to set up this aids. For the future, there is a distinct tendency to set up many more to them in the fishing circles.

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Through psychological test and statistical datas of accident of communication worker, I explained here that each type of accident on the sea are more likely concerned on optical illusion or so than other reasons, and emphasized the importance to analize its background systimaticlly for getting some hint to clarify blind point of visual navigation.

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To check dredging Resistance of anchor by which she is manoeuvered easily in a harbour, we experimentaly measured it by 1.000 G.T. of training ship. (Weight of anchor: 1.2tons, weight of cable one shackle : 0.7ton.) Results are as follows ; [table]

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1. At the first step in the course of study on the establishment of job standard in an emergency, we started to measure G M of life boat of each condition, -3.61ft for light condition, 2.32ft for her boarded with reguler erew, 2.35ft for her same condition but setting oar out side, and 1.27ft for full load condition. 2. It's a matter to be checked and trained to set crew over 45 member for their fittest position in a boat in an emergency, and keep her posible stability by their rational pose and motion in boat with such small G M. 3. Another experiments are going.

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Although there are many investigations on the relations between fouling of vessel and her speed, we have not yet ample data of the similar problems on small ship, In this paper the authors attacked this problem by using the S.S. "UMIKAZE MARU" (Gross 70 tons.) of Nagasaki Marine Observatory, and obtained following results: (1) The relation between the speed and the periods from the day of cleaning of the bottom was found as shown in Fig.1. (2) The amount of decreasing of speed is rather small for the period ranging from Jan. to May, but in June (rainy seaon) the speed suddenly decreased and then the amount of decreasing became nearly same to that of Dec., that the total amount of decrement of speed was nearly 40% at the end of year.(3) The frictional resistances were calculatedform above data. (4) The time of bottom cleaning should be decided on the economical points.

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It is well known that, when a single-screw ship goes on ahead by keeping the rudder amidships, synthetic action of screw current, wake current, and sidewise pressure appon the proppeller blades causes her course deviation. In this paper the author investigated the effects of above actions to the turning circle of a ship by means of model experiment and turning trials of cargo and fishing boats. Therefore the results tested on the right handed single-screw vessels are as follows: (1) Generally the turning circle with starboard helm is larger than other circle with port helm. And this was remarkably perceived in small ships which have large R.P.M. of propeller. (2) The difference between above both turning circles is incrsased relative to small helm angle, large velocity and rudder area. According to the above mentsoned results, moreover, the forces causing the ship's course deviation are considered as follows ; (1) The sidewise forces upon propeller blades. a) If the propeller is nearer to the water surface, the differnce of pressure on the upper and lower halves of propeller disc, being caused by air suction, exerts the sidewise force on it. b) Sidewise component forces are generated upon the rotating blades, due to non-homogeneous suction current drawn in from both isles of the run. (2) The sidewise force upon rudder plate. The screw current that is influenced wake current striks both sides of the rudder plate asymmetrically, and then by the sidewise force is exerted on it.

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Fish-finders and echo-sounders applying ultra-sonic sound wave are eouipped to many fishing boats for the use of fishing operation and depth finding. But, they are not gaining necessarily satisfctory effect beacause of permeation loss by ship's bottom plate when they are eouipped in fishing boats. When transducer of fish-finder is eouipped on the bottom of a boat, the tansducer is put in a tank filled with fresh water which is fixed to the bottom plate ; when the transducer is equipped on the side of boat, the transducer is put in a stream lined cover made of steel or rubber and fresh water is used as medium to prevent running attenuation and running noise. When the ultra-sonic waves transmit through steel plate or rubber film, they are attenuated remarkably. But the permeation loss caused by steel plates and othes can be lessened by means of oil medium instead of fresh water. In this experiment, botanical oil was used and basic study was made on the influences of oil upon the cnaracteristics of ultrasonic. And the experiment shows the fact, if oil is used as the medium when the ultra-sonic waves transmit through steel plate of 10mm in thickness, it is as if a steel plate of 5mm in thickness was applied. As the result of the acove study, it isconsidered that the oscillation power of transmitter can be increase by oil and that the efficiency of fish-finder and echo-sounder can be enhnced. The study is being continued now.

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