Effective collision diameter, D, is calculated from number of collisions on three congested waterways, Uraga Suido, Akasi kaikyo, and Kanmon kaikyo, using a simplified equation, [numerical formula] where P, ρ, and V_<rel> are the collision rate, the density, and the relative speed respectively. This equation is deduced from the general equation introduced by the author by assuming the lengths of all ships are equal. The collision diameter thus obtained is 0.4〜1.8×10^<-4>L for collision of ships going in one direction and 1〜3×10^<-4>L for collision of ships going in opposite directions. These values allow estimation of collision rate on fairways where traffic quantity and distribution of ship size and density are known.

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Weather adjustment by backlash of the autopilots is now in common use, and, though there is much room for improvement, is getting more and more widely used bscause of its simplicity and its low cost. Our object here is to investigate the most suitable weather adjustment by backlash-how to minimize the loss caused by steering to correct the course deviation and then lessen the frequency of steering. In order to achieve the object, we adopted the technique by simulation and, exercising random disturbances upon the automatic steering control system, calculated the amount of the responses. As a result of these investigations, we could finally formulate the optimum adjustment: To adjust backlash to twice or three times the standard deviation in the case of rate control and to once or twice the standard deviation in the case of proportional control.

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This is a study on the estimation of responsive characteristics of a ship motion in waves by the use of an analog computer. In this paper, according to the rolling test and the curve of statical transverse stability of the ship, each coefficient of the equation of motion for the ship rolling was determined on the model ship shown in Fig.1 and Table 1. Then, the equation of motion was simulated on the analog computer. The block diagram is shown in Appendix A-1. As to the equation of motion in eq. (1) and (2), the responsive characteristics of the ship motion were calculated by the analog computer. The results of the calculation are compared with the experimental results which were obtained through the tank experiment for the above mentioned model ship. It is shown that the calculated results agree with the experimental values. Then, as an example of this method in practical use, the responsive characteristics of rolling motion of the fishing boat are calculated by this method and discussed.

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The paper presents four diagrams of the reverse stopping distances, by means of which most average navigators can obtain the informations about the backing manoeuvres of their large tankers. The diagrams do not represent the analysis of actual ship tests, but the mere results of calculation based on the assumed ships which are regarded as representative vessels having the average performance of present-day large tankers. The results appears to be available for the turbine-driven vessels, but for diesel ships there are something to be desired.

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Assuming the fluid perfect, the two-dimensional calculations are obtained for the forces and moments, which act on the body from the surrounding fluid, when the motion is not steady. The effects on one elliptic cylinder are approximately calculated by means of the image method and the conformal representation, when there exist two elliptic cyinders, which may be moving with any velocity in any direcion respectively. The forces and moments consist in two parts, the one (P_1 and M_1) due to the instantaneous stream line condition, the other (P_2 and M_2) due to the unsteady condition of flow, that is, the rate of change of velocity potential on the surface of the cylinder. One elliptic cylinder represented by C_1, the long axis=2a(1+C^2_1/a^2) and the short one=2a(1-C^2_1/a^2), is moving with U in direction of the long axis. The other cylinder by C_2, the long axis=2b(1+C^2_2/b^2) and the short one=2b(1-C^2_2/b^2), in position of f.e^<iβ> from C_1, is going with V in direction of the long axis angling α with U. The force and moment on the C_1 cylinder are approximately [numerical formula] direction (from the course of motion): π+3β-2α [numerical formula] where, s=V/U, k=b/a, σ=a/f, ・x_1=C_1/a ρ: density of fluid From these results, some simple cases are considered and the forces and moments are shown in Figs.

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The writer showed that what is the substance of lookout in the navigational system from a ergonomical point of view and what is the basic elements of the lookout automation.

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When one power-driven vessel found other vessel of same kind under way, on her way, and each approaches relatively so as to involve risk of collision, it should be considered whether crossing relation and crossing rule are applied or not, between these two vessels.

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The writer suggested that the collision using with radar are based upon the mistake or blunder in the handling of radar data. So he devised to show the radar data in the visual shape of the model ship instead of spot or line in the aid of the graphic display the same as in the condition of the visual navigation.

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The infringement of the Regulation for preventing collisions at sea, presumes some negligence on board. But in case of special circumstances, the negligence is not blamed. I want to find out general rules for such occasions through the decisions at the Maritime Disaster Inquiry Agency 63, 64, regarding such cases as any neglect to carry light, or any neglect to keep a proper look-out.

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The dense winter fog crippled Inland Sea Services for two days, Feb. 12 and Feb. 13 of 1969 was so called radiation fog and many collisions and agrounds were reported around the Inlad Sea region. So the author investigated the winter radiation fog in western Japan with the object of forecasting it synoptically and locally using the surface and upper meteorologlcal elements. Analyses indicate the following features. (1) Migratory high prevailed in western Japan in synoptic surface map. (2) Cold core was seen in the central area of the Inland Sea in local map. (3) The distribution of saturation deficit was nil or very little. (4) The deviation of maximum temperature and minimum temperature were very little at Takamatsu and Okayama. (5) The area of divergence was extended in the central part of the Inland Sea on Feb. 1200z. (6) Warm core was seen off Kyushu and Shikoku in synoptic 850 MB map. (7) Inversions were analysed in ascent curves at Shionomisaki and Yonago. (8) Air pollution from the seaside heavy industrial zones like as Hanshin, Mizushima, Sakaide, Hiroshima, Ube and Kyushu heavy industrial zone were considered to be the important factor of fog occurrence in the Inland Sea region.

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The most probable position is accompanied with an error ellipse--two-dimensional joint probability density. This theme has been treated geometrically in many reports, and some nomographs are given for two or three observations. In this report it is treated analytically, therefore, the calculation and display of an ellipse on account of many position lines can be done by a digital computer and a plotter. And besides, here is explained astro-fix efficiencies due to azimuths of celestial bodies ; and a new method to estimate observation error from the distance between two positions determined independently or by different persons.

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We consider that the Running Fix obtained by a bearing and two transfered position lines is equal to the fix by cross bearings from S_1 and S_2, S_3 which are advanced object S_1 and exist in the error boundary of estimated position when ship's running course or distance is wrong. (see Fig 1-b) So, we constructed contours of constant probability density for Running Fix and considered as follows ; (1) When ship's course is set, the closer the object to the ship the better and, since the dotted lines make an angle of about 70 degrees with S_1S_3, it is recommended that the first observation be made at the close angle from the ship's head, while the third bearing of the same object is observed about 20 degrees abaft the beam. This result is common with the Running Fix by two position lines. (2) When ship's course is altered at the time getting the second bearing, the first bearing should be observe at the point to see the angle between the object and ship's head to be ∠S_1 S_3S_2 in Fig.5, while the third bearing of the same object should be observed about 20 degrees abaft the beam.

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An officer on duty on a fishing vessel watches the fishing gear drifting after setting the salmon gill-net or tuna longline. At any time, if he can estimate his ship's position by any method concerning the gear without recourse to an object (flag, light, reflector, radio buoy), he can employ the method to watch the gear effectively. The authors had experimented with the drifting of the Hokuseimaru (273 G/T), and reported that the direction and distance of drifting were estimated by the ship's head and wind velocity. And for the next study, we experimented on the accuracies of estimated ship's positions based on the method, in the North Pacific Ocean. The experiment 1. As the drifting velocity and directions had been calculated by previously reported equations, some drifting positions were estimated. 2. Ship's positions can be determined by the bearings and distances of the corner reflector connected to the gill-net (length 3n.m., depth 7m). 3. Determined and estimated ship's positions are shown in Fig.2 every 30 minutes. The accuracies of estimated positions. 1. We say that the distance error is the length between the determined position and the estimated position, as shown in Fig.3, related to the drifting time every day. Furthermore standard deviations of distance errors are shown in Fig.4. 2. Differences of estimated drifting directions from determined directions are shown in Fig.5 in relation with the drifting time. And standard deviations of direction errors are shown in Fig.6. 3. Under the general condition that the drifting time is 6 to 8 hours, the distance error is 1n.m. (s.d.) and the direction error is 7°(s.d.). According to this method, we could obtain satisfactory results from various points of view for the sake of keeping watch over the fishing gear. We recommend an officer on duty to study the drifting characteristics of his own ship and apply himself to keeping watch over a fishing gear.

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The line of position by heaven body on the Mercator chart has some kinds of error. For example, there are 1. error due to the curveture of equall altitude circle 2. bearing error due to the difference between great circle bearing and Mercator bearing 3. distance (intercept) error due to the scale of Mercator chart. Usually they are so small that they are used to be negligible. But we have to understand the nature of these errors and we must know which error is bigger than other's. This paper gives a calculation some kinds of error in LOP on the Mercator and chart also some error tables. Another purpose of this paper is to investigate the formula, error due to curveture=tan (altitude)/6876. This formula gives a assumption that the equall altitude curve on the Mercator chart is a circle. This is not a circle and not a simple curve, as many bibliographies say. So this is not exact formula but approximate one. This paper gives the limit of its adaptation, exact and simple formula, some tables and digrams to obtain the error and so on.

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The measurements of Loran C were practised at Tanegasima-Yamagawa-Mejima in Southern Kyushu for two years by visual receivers. The author believed that following results are considerably reliable. 1) The receiving limits of surface wave of Loran C are estimated in 800-970n.m. from the transmitting station. Since the numbers have many parameters, these could not define exactly in this stage. 2) The refelcting height of 100kHz pulse in the D-region varies unexpectedly. This fact means that, if we use the Loran C table, the error of 4 or 5 μ sec in maximum is unavoidable. 3) The constant errors at Yamagawa observation of Y slave surface wave are found from -2.0 to -2.9 μ sec all the year round. On the contrary, the error of Tanegasima is -4.0 μ sec. 4) The X and Y signal patterns of measuring data at both Tanegasima and Yamagawa are the same, moreover they are stable. The author suggest that, even if we use the Groundwave-Skywave of both chains, the position fix in this waters is accurate.

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