We have an error curve of Direction Finder only after installed the equipment on board, so I think it shall be convenient to know error value approximately and to decide the DF antenna's position to make less error before actual setting. It is well known that the DF error caused by surroundings, the hull of the ship, the masts, the funnel, the rigging, the stays, the derricks etc. This paper shows how to take the approximate error due to the hull by using a scale model. The principle of this experiment is as follow that the electromagnetic field disturbed by the hull is similar to the electric current pattern around dielectric in the equability current field. I selected our college training ship "Fukae Maru" as test boat, and made that model in scale 1/90・In consequence, it can be confirm that the data of this test shows to resemble to actual error.

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It is often observed that some decrease occurs in the sounding capacity of echo sounder when a shen runs at fast speed. The main reason of such decerase is thought that the ultrasonic wave transmitted from the transducer installed on the bottom is disturbed by the bubble layer occuring under the ship bottom. The ultrasonic wave is attenuated by the bubble layer, and its attenuation decreases as the frequency of ultrasonic wave increases, as clarified by the Laboratory as well as by field experiments. In order to obtain data for a actual ship, we installed two types of echo-sounder of 13 kc. and 200 kc in frequency in a 220 ton steel fishing research boat and observed the influence of bubble layer on the echosounder. The transducers of echo-sounders were installed in the same condition at ship bottom as shown in Fig.2. The result shows that the 200 kc echo-sounder was not affected by the bubble layer under the condition of slight sea and ship speed at 11 kt. But in the case of 13 kc echo-sounder under the same coditions, attenuation was observed in the ultrasonic wave by more than 10 db and the increase of noise reached as much as 30 db. In this way it has been found that the sounding capacity of a 13 kc echo-sounder falls as low as 400 meters even though it registers at 4, 000 meters when the ship is in stop. From these data it may be concluded that a 200 kc echo-sounder is sufficient for the echo-sounding up to 500 meters and that for the echo-sounding abovs 500 meters it is necessary to use an echo-sounder of lower frequency, such as 13 kc. In the latter case, a great care must be taken for the selection of position where the transducer be installed and for the technique of such installation so as to avoid the harmful influence of bubble layer.

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The underwater telemeter to measure the depth on of trawl net board a boat, for which ultrasonic waves are used, is developing in several countries. In Garman type, 30kc megneto-striction type transducers the transmitting surfaces of which are set upward or downward are mounted at the trawl net, the recorder is installed on board a boat, the transmitters and the transducers are joined by a cable, and the depth of the net and the distance between the net and the sea-bottom are measured on board the boat. In American type, about 25kc ultrasonic waves are used as the carrier and the depth of the net and the water temperature are transmitted by FM and AM. They are studied also in our country. The underwater telemeter has many problems, for example, the noises, the wake and the beam of ultrasonic waves. We made the underwater telemeters for which 50kc and 200kc ultrasonic waves are used as carriers and made experiments on them. The results of experiments are as follows. (1) In case of 50kc, the attenuation due to the gathering of bubbles in the wake of the boat is big and S/N ratio was small due to noises of the boat. In case of 200kc, these influnences were hardly found. (2) For the underwater telemeter we can use 200kc ultrasonic waves as a carrier unless the distance is not so long. If we use 200kc, we can make the small transducers. In this case, we should use the lens which makes the beam wide, because the influence due to the shaking of the net is big.

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Since 1912, the magnetic survey of the whole Japan and the adjacent areas of Japan was carried out by the Japanese Hydrographic Office. The results of these magnetic surveys were published as the magnetic chart of the adjacent seas of Japan. In construction of the magnetic chart, magnetic variation was calculated from the following empirical formulae on geographical distribution which is expressed by the quadratic function of latitude ψ and longitude λ, δ=δ+aλ+bψ+cλψ+dλ^2+eψ^2. From July 11 to 20, 1960, the 1st magnetic survey at sea was carried out with the magnetic compass for navigation by the survey ship "Takuyo" of the Hydrographic Office around the west coast in Hokkaido and Siriyamisaki. From the magnetic survey, it was found following results. 1) Departure of the observed magnetic variation at sea from the empirical formulae are considered to be less than ± 1°. Therefore, the magnetic chart constructed by Japanese Hydrographic Office is correct for navigation. 2) It has been reported by navigator that there are local magnetic disturbances at several areas in Hokkaido, but it was found that there are no local disturbance more than ± 1°from the results of the magnetic survey for navigation.

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A sail transforms its profile according to the alteration of the state of air currents around it. Therefore, when the profile of a sail is known, the pressure distribution on the profile and other aerodynamic characteristics of the sail can be estimated. In this paper, the author studied theoretical solutions for an arbitrary profile of a sail in two-dimensional flow. Let the profile of a sail, the force P right to the sail, produced by the pressure of both sides and the tensile force T acting parallel to a sail surface be expressed by equations (1), (2), (3), with parameter x, their geometrical relations being shown in Fig.1, where α is angle of attack. Whereupon, the function F_2(x) of pressure distribution expressed by (2) is obtained as (4), and lift coefficient C_L, drag coefficient C_D, moment coefficients around leading edge (C_<ma>) and trailing edge (C_<mb>) and the position of centre of pressure are given by (7), (8), (14), (15), (16) respectively, with function F_1(x), C_T and chord length C. An accurate coefficient of tension C_T is determined by the actual measurement only. Therefore, its approximate quantities are presented with some assumptions referring to theoretical lift coefficient of a circle and experimental values of sail model Nr 1814 at Gottingen.

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The authors assumed that the thickness of the canvas and the sewed twine and the stitch were the most leading factors on which the strength of the sewed canvas was depending, although it is naturally suppose that there were a lot of factors controlling it. And the change of the breaking stress and the elongation of the canvas due to the differences in them was examined. And, appendantly, the strengh of the canvas sewed with single serial seam was compared with that double one.

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[in Japanese]

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The Lookout in the navigation watch takes the longest duty hours and has the most important part in it. But there have been many marine accidents caused by the negligence of the Lookout. Now, we studied the present condition of the Lookout, according to the datas of the marine accidents from 1950 to 1959 and the enquete about the Lookout.

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Recently explosions of Virginia coals which are carrying as North American liner's homeward base cargo occur about ten times. After investigation of the events we found them as marsh gas explosions. We examined the data of Virginia coal carrying condition on board of Philippine-Maru. We find two course for anti-explosion of coal-negative and positive. For positive course ventilation is almost only way for anti-explosion of coal. We find the way of ventilation by the model of hatch test.

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In their studies of ship's oscillations in a seaway, in order to analyse a large amount of data concernig ship's oscillations automatically in a short time, the authors used a Fourier Analyser, a kind of electronic analog computer, which was designed so work as in M.J. Tucker and T.B. Whiteley's way. A view of the whole apparatus and diagram illustrating the principle of the Fourier Analyser are shown in Photo.1 and Fig.2 respectively. By this apparatus, the spectra of ship's oscillations and wave heights were calculated on some examples which were discussed in the former paper by one of the authors. Results of the calculation are shown in Figs.8, 9, 10 and 11.

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In the previous report, authors had described that holding efficiency in various types of anchor should be researched by the characteristic curve of holding power. This paper related to model experimental results investigated in order to provide efficient JIS-stockless anchor, and we carried out tests with the model anchors in weighing 10, 20 and 30kg respectively and five anchors of similar types with partly changed anchor head in weighing 10kg each. As the results of these tests in model tank with fine sand, (1) Average coefficient of the holding power for JIS-stockless anchor in sand bottom is about 4 times the anchor weight, and these Max. power are indicated when the dragging distance reached 4 times the anchor length from the tripping location and the rotating angle are just within 45 deg. (2) JIS-stockless anchor being dropped has scarcely tendency to trip. (3) Shortening the space between the fluke gives good holding stability, although it reduces the possibility for tripping completed, and it is better to make anchor shoulder large and the conneting point of the shank high for improvement of holding efficiency.

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This investigation was worked out on the characteristics of rolling and pitching of ship loaded with Lauan Wood on deck by model experiment and the main points treated in this paper were as follows ; (a) Effect of ballast waters on rolling, taken in lower hold owing to increasing of the statical stability. (b) Effect of buoyancy of logs loaded on deck on rolling. (c) Effect of longitudinal distribution of cargo on pitching & etc.

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Following the experiments using cargo three islander model these are reported in Part 1 & 2, we carried out some experiments on mooring and riding at single anchor using model ships of Aft Engine Aft Bridge Type Vessel and Oil Tanker. The results of experiments have shown followings: 1 Aft Engine Aft Bridge Type Vessel can ride out gale easily in comparison with othir type vessels, as her yawing is very small. She will be able to ride out gale at single anchar when full loaded. In case of mooring, yawing can be checked with open hawse at angle of 45°. 2 Oil Tankers will be able to ride out gale even when at single, anchor if full loaded. As ther eason they receive less wind pressure and immerse deeper in comparison with three islanders. In case of mooring, yawing can be checked with open hawse at angle of 60°like as three islanders.

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By putting the additive in Diesel oil, it has been recognized that the heat efficiency become better on account of atomizing the spray, promoting the burning and then shortening the after-burning. Therefore, fuel consumption per B.H.P. per hour will become smaller, but the effect of this additive depending upon the manner of mixing, a few of which I have investigated.

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By using a thermal type ammeter and a recording ammeter, we measured fluctuating current of A.C. generators on board some cargo ships under loading, and from the results we discussed load factor of the generators.

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In this paper, the proper engine maneuvering during crash backing of the geared-turbine-driven vessels is investigated. The oil tanker "S. MARU" (D.W. 17900 tons, S.H.P. 9000HP, Normal Speed 16knots) is used an example. First, the variations of the values of wake fraction and thrust reduction facter in the process are founded on the basis of the actual backing test data. Then, putting that result to good use, the approximate equations of the motions of the vessel and shaftline are setted. And, the each variations of the values of shaft revolution, ships speed, turbine torque, propeller torque, and thrust for several maneuverings fixing reasonably are calculated by the Disital Calculator. These results will be utilized to make the standard of the crash astern maneuvering.

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