I explained the effects of the included angles of 3 position lines or of the distances between the observer and the objects upon the accuracy of ship's position. And I also compared the accuracy of ship's position by 3 position lines with that by 2 position lines. So it will be solved how to decide 3 position lines to obtain the best accuracy of ship's position. Now I studied each accuracy of ship's position by 3 position lines having equivalent random error and different one. The former, I believe, will be useful to select 3 heavenly bodies on nautical astronomy, and the latter to select 3 objects for Cross Bearing method.

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The writer made careful examination of every method to express the error boundaries of ship's positions fixed by two position lines, in the former paper ; he concluded that the probable ellipse system was the excellent one, theoretically and practically. However, in the case of fix by three position lines, to draw an ellipse, three quantities (the length of major axis, the length of minor axis, the orientation of the major axis) are necessary and yet one can not find an approximation to do it, accordingly troublesome construction is necessary. The writer studied on 95 per cent probable circle to meet the convenience of practicality. By making use of this method one can easily draw 95 per cent probable boundaries, in the case when the accuracies of three position lines are alike, by means of a single quantity.

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Ship's positions fixed by many position lines have normal distribution of two dimensions. As compared with the error boundary of two position lines, we get two equivalent position lines for many given position lines. From this consideration, we obtain the radial standard deviation σ in the case of many position lines.

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If the survey is made by the 200kc echo-sounder with sharp beam, the almost true shape of sea bottom is obtained within the error of 4% for the slope of bottom of 50° and 1% for 20°. We made survey by the 200kc fish-finder at the fishing-ground off Sanno, Odawara City on occasion of late. The difference, between the survey map by the 200kc fish-finder and that by the 14.5kc fish-finder the beam of which is not so sharp, is clear at the station where the shape of sea-bottom is complicated. The former is much more detailed and shows more closely the depth obtained by fisherman's experience than the latter. And the survey is easier by 200kc than by 14.5kc.

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The location of ground fish by a fish-finder is one of impotant problems in the Japanese trawl fishing. The authers have accumulated various fundamental experiments on this problem, the results of which have been already published in our Technical Report. On the basis of those experimental results, we have tentatively manufactured the three fish finders of new types. These three apparatuses are designed under the conditions for increasing the discrimination power between the fish school and the sea bed. The main characteristics of these apparatuses are as follows ; [table] These three apparatuses are installed aboard one of the two boat trawler of 100 gross tons ; and the transducers on her same side planking. The followings are the experimental results. (1) The capacity of each apparatus for detecting a single ground fish were measured 180 meters when the boat was stopping. When the boat was cruising, the capacity of 50kc apparatuses drop to 100 meters because the running attenuation of ultrasonic wave and the running noise were measured, while the 200kc apparatus is not disturbed by any influences. (2) After we made a continuous observation of the ground fish behavior with the fish-finders, the whole day from morning to night every day, the fish school was clarified to move with the migration of D.S.L. ; namely, during the night the recording paper was filled only with single fishes or D.S.L. and any fish school did not appear. In the morning when the sky was gradually turning gray, the D.S.L. began to go down slowly at the rate of 20 to 30 meters per hour ; and about sunrise, above the D.S.L. appeared the fish school, which went down slowly and finally reached in the neighborhood of sea bed when the D.S.L. disappeared near sea bed within two or three hours after sunrise. In the day time, we could find many fish schools near the sea bottom. But in the evening when the D.S.L. which began to rise slowly in the rate of 20 to 30 meters per hour appeared on the bottom. the fish school also began to rise toward the sea surface and disperse about sunset and finally the record showed the state of night. (3) We have observed the vertical distribution of ground fishes in the three layers of 0 to 2 meters, 2 to 4 meters and 4 to 10 meters above the sea bed. We sumed up the total length of fish schools appeared on the recording paper every trawling time and layer during the whole experiment period. The results show that in the major tide the fish school is more numerous mainly in the layer of 2 to 10 meters ; but in the neap tide mainly in the lowest layer. In this fishing ground there was a tendency that the catch of ground fishes at the major tide was smaller than that at the neap tide. I believe that this tendency is supported by the abovementioned results.

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When a ship navigates northward or southward, the deviations of the magnetic compass vary according to the change of intensity of geo-magnetic field. It is caused by the change of B_0 or C_0. coefficients of the theoretical formula of deviation. As the result of analyzing B_0 by P/λ & c/λ, and C_0 by Q/λ & f/λ, the values of c/λ were positive in three compasses of both old and new Umitaka-Maru and those of f/λ were not always negligibly small. The above-mentioned fact will show the necessity of a new type adjustor concerning this observation.

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We surveyed the character of ice floes, floe berg, and pack ice during two monthes from January 7th. to February 28th. at the Lutzow Holumbukta bay of Antarctica. In this reserch we examined the report of Dr. Ekman about the drift and set of pack ice near Antarctica coast. The drifting' rate of the pack ice is 1.9〜2.4% of velocity of the wind and its set is leftward 2〜3 points from the wind direction in Antarctic Ocean.

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In 1956, prof. H. Riehl of the Chicago University and H. W. Haggard of the U.S. Navy published some results on the prediction of 24-hours hurricane motion in the Journal of Meteorology of American Meteorological Society. The writer thought that the methods were useful to the ship officer to predict typhoon motion. So he applied the principles to the prediction of 24-hours typhoon motion in the south western part of the North Pacific. The results which the present writer obtained seemed fruitless, but mainly this was owing to the scarcity of data, or the poor accuracy of present weather maps. Therefore, the methods should be evaluated in future investigations.

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We have several surveys on the subject and get the following results ; (1) On the Koso-maru, which has cargo winches of Ward-Leonard system, the current rushes are small and, therefore, the voltage variation is also small. (2) On the Sanuki-maru and Arizona-maru, which have cargo winches operated by pole-changing induction motor or by commutator motor, the current rushes and also the voltage variations are quite large. (3) The voltage dip is almost proportional to the current rush ; the ratio of these two values are nearly equal to the transient impedance of alternator.

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In the movement of a sailing boat, the forward driving force named thrust and the force tending to drive the boat sideways vary according to the various alterable factors e.g., the speed of the wind, the direction in which it acts, the speed of the boat, etc. In this papar, the writer, with the figures which Eiffel has given for a thin rectangular aerofoil of 6: 1 aspect ratio and various arch, calculated the coefficients of thrust and side force against the direction of real wind from bow and the ratio of the speed of the boat to the speed of the wind. Then, making use of those calculated results, some considerations about the following subjects are presented by the writer with some assumptions. (a) The angle of attack in which the thrust is greatest. (b) The lee way of the sailing boat. (c) The course of the boat in the case when the required time for sailing to get to a weather side destination is minimum.

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As buoyant materials of life-saving appliances aboard, we have been using Balsa, Cork and Kapok because of their characteristics remaining buoyancy for a long time in the water. And, some of Plastic foam are adopted for them by recent technical progress. However, buoyant force of these materials, one of fundamental abilities not only as materials but also as appliances, is tested in fresh water internationally. Tests carried out at Durban by the Society of Master Mariners on March 11, 1957, reported that kapok-filled life jackets sank in oily-petrol, light diesel oil-water in short time. Authors wanted to test and examine more the force remaining buoyancy of buoyant materials in oily water and oil, which might have been out of question in deciding their fitness for practical use heretofore. Therefore we have researched influences of Petrol, Gas Oil and Fuel Oil to Kapok, Cork, Balsa and Polystyrene foam by model-tests etc., at the first step of the investigation. The conclusions to which authors have come as a result of above tests are: a) Kapok is much affected on buoyancy by Petrol and Gas Oil, while more or less by Fuel Oil. b) Polystyrene foam has no durability to Petrol. c) Cork and Balsa are almost not affected by these oils, etc. And, thinking of danger of lives at the sea casualties, especially of that in oil tankers, we should decide their fitness of life-saving appliances by tests not only in water but also in oil hereafter.

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