It is originally recognized that the Akashi Channel is a narrow one provided in Rule 25 (a) in Regulations for Preventing Collisions at Sea, but it has been recently claimed that the traffic control should be required in this channel. In this thesis we investigated the present conditions of application for Rule 25 and studied how the traffic control should be, and came to the conclusion that this channel should be divided into three narrow ones.

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The auther intends in this paper to discuss the cause of sea disasters. There are many studies on cause of sea disasters. Most of those had only searched for the responsibility of operators and technological cause. However the cause of sea disastrs are very complicated. So, Auther propose that it's investigation carry out many sided-operational, technological, and labour,

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Collision between two vessels is caused by personal and various other conditions. We have studied the circumstances of collision about the tonnage of the vessels that have collided, the kind of certifications of the crew concerned, and the action taken to avoid collison. And we have reached the following conclusions, though they may appear to be commonplace: (1) The captain should be strict in carrying out his duty, and give his crew enough guidance and superintendence at ordinary times. (2) The man on duty should watch most attentively. (3) When visibility is limited, the international rules should be followed regularly. (4) The regulations regarding lights should be obeyed faithfully. (5) Every action to avoid collision should be taken positively and when there is ample time for it.

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The Marine Traffic Simulation Program Language I. (MSPL I) was developed to analyse and obtain the characteristic of the marine traffic systems. This language consists of about thirty commands and has been written using the PL/I (Program Language One) for IBM 360-75 Data Processing Systems.

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New Law, which is planned to be established, should apply to all vessels in the Japanese territorial waters, instead of present Port Regulations Law and Cabinet Order for Navigation in Specified Water Area. The reason for the new regulations to be established, is to change or improve the fault of present regulations to accomodate with the existing state of present sea trafic. The Draft of new regulations is consist of 95 articles excluding annex and will particulary sets up new rules for navigation of channel, separate route and in or out of harbour etc. including new penal code.

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The facilities and layout of the Principal berthes for Gigantic Tankers were analyzed, to find the suitable type of the berth to keep the proper moorage of the vessels, and to practice the safe mooring operation of crews. As the result of investigations, the writer could point out the recommendable layout, and desirable construction of the Gigantic Tanker berth, viewing from the point of proper moorage and safe operation.

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We know some problems of position fix cannot be solved. What is the defect in necessary conditions for them? The author studied the theme by analytical geometry. All observations are expressed in equations, loci of which are called position lines. Number of unknown variables is the sum of the number of unknown factors and two (due to lat and long of ship's position). Number of the equations must be equal to the number of unknown variables. Then, it is necessary and sufficient for position fix that the Jacobian (function determinant) of the equations is not zero. Geometrically, the condition means that position lines must have a cross and that the coordinate system must be defined without ambiguity. Some examples are discussed in detail.

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First, I drew the contours of constant probability density of Decca fixes in the adjacent waters of Hokkaido and Kyushu, using the "probaaility density formulae." Secondly, by comparing these of Loran fixes with the abovementioned contours, I tried to make a practical chart of Loran and Decca coverages, with which navigators could select the appropriate chain and pair of the Decca system or the triplet of Loran stations to obtain the most accurate fix in the ditto waters in daytime and at night.

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The SS3 rate of Loran C by visual receivers at Yamakawa was measured in spring 1968, comparison with the data of 1967 : 1) The constant deviation of TGG of the Y chain was made again, and the deviation that is introduced from the both observations was about -2.6μs. When the Loran A was measured five years ago, the author obtained the minus deviations along the "Kuroshio" in the south western waters of Kyushu. The reason mainly in the former case, howerer, may be due to the velocity of waves. But the author would not dare to discuss the problem in present stage. 2) The pattern of the both values, W and Z chain, showed "dish" type, namely the normal change. (Fig.2) But the jumping phenomena were regularly recorded in twilight. 3) The pattern of X chain at Yamakawa were similar to that at Tanegashima, neverthless, the distance between the both position is about 40n.m. each other, moreover one observation was carried out in summer, and the other in spring.

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Adding the former report 1, the accuracy of time difference readings and its position lines were investigated. Though there are still some problems left in the utility of the Loran C system by using a manual visual receiver-indicator, the accuracy of both time difference readings and its position lines were much better than the actual Loran A navigation system.

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Phase velocity of C.W. transmitted from the four Decca stations the Hokkaido Chain were investigated, by using the decometer readings at 59 points, 40 of which were on board, while the others in land. Although phase velocity are different in various transmitted paths, the seasonal variation in an individual path is comparatively small. In order to obtain the most appropriate hyperboric lattices for practical use, more precise investigations on propagation of waves are desirable.

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Today, the ramark beacon signals seem to remain just the bearing information. They will be much more valued, however, if their signals bring the navigators the land-fall distance information at which the bearing sweep appears on the rader scope first time, just likely to beams of the light-house, because, the navigaters rapidly may fix her potition easily at that time. Regarding the propagation of the ramark microwaves as those in diffraction region beyond the curvature of the earth, the author studied the estimation method by calculation the diffraction field on the Bullington Nomograph. The practical sea experiment held at Sata and Nojima, Misaki approaches have pvored this method approximately available.

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The daily and anual changes of the radar detection range were observed for more than a year from 1967 to 1968 In spring and summer, for several hours past noon of fine days, the detection range usually increases and super-refraction or duct condition is considered to occur, while, at midnight or in the early morning it decreases. In autumn and winter, few daily changes are found and standard condition or slight sub-refraction is observed for all day long.

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It would be of great value in preventing vessels from collision, if the one ship could show, by signal images on the other ship's radarscope, the measure that it has taken to avoid collision when they are in risk of collision with each other, as in thick fog. We operated two ships each equipped with V.H.F. transponder and its receiving apparatus in addition to the marine radar, making a series of experiments on the representation of the signals mentioned above. The results are as follows.

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The marine transportation has recently intensified owing to our country's economic development. The fair-way traffic volume in the Kanmon strait is about 1000 vessels a day and traffic congestion has brought about a great number of sea accidents. It is the problem of marine traffic in the harbour and narrow channel to develop securer and more efficient system of traffic control, and it is necessary for marine traffic improvement to find the actual state of traffic. From this point of view, the reserch on ship's speed under passing was conducted with radar and visual observations from Aug.30 to Sept.3 in 1967 at Oseto in the Kanmon strait. This report described the characteristics of the ship's speed under passing through the Kanmon strait.

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As a result of researches on the actual conditions of sailing of small power-driven vessels, by eye-observations and a memo-motion camera, in and around the berthes for sightseeing vessels in Toba Ko, sailing rules and sailing areas by these vessels was known approximately, and so we considered the order of sailing rules and the arrangement of sailing areas in and around these berthes.

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In order to clear the navigational disorder of powerdriven vessels, bound eastward or westward, at the southern water area of Ryuzin Sima in Kurusima Kaikyo, it was tried to set up a base line for vessels to keep as close to or far from Ryuzin Sima as practicable, on the basis of the provisions of Article 7 sub-section 2 and sub-section 3 of Cabinet Order for Navigation in Specified Water Area, now in force.

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For the purpose of prevention of shipwreck, especially small vessel, I studied some vortical disturbance off Wakasa Bay using the PPI scope photographs taken at Fukui radar site during the special co-operative observation for heavy snow fall in Hokuriku district from Jan.18 to 22 1966. Namely, first I attempted to catch the dynamic developing and moving of vortical disturbance by Fujita's Cine-Meteorology technic with 8mm cine-camera. Next, I investigated meso-scale structure of vortical disturbance by using the surface meteorological elements and, conversion method of aerological data from thier time change to space change.

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The manmoth vessels have required the accuracy of the depth in the port. I investigated the following : 1) Daily sea-level oscillations in Nagoya port. 2) The relationship between daily barometric preasure change and daily sea-level one.

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In Japan, average values of rudder areas as fractions of lateral plane area A_R/(L・dm) for the class of ships which length between perpendiculars has 40 meters or so are as follows; tug boars…1/23 fishing vessels…1/35 cargo vessels…1/46 Tokyo University of Mercantile Marine has replaced recently its training and experimental ship which it had used since 1952. This ship. "Shioji Moru II" has her values of A_R/(L・dm) of 1/38.4, and of Lpp of 37.0 meters. After maneuverability tests, it is found that she is directionally unstable, and they have fitted a fin to her stern for the compensation. Author reports here the results of Spiral Tests, the effectiveness of the fin, and propose the lower limit value of A_R/(L・dm) for the same class ships.

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When the two ships of the same type are rolling in regular waves with the phase difference of ε, the amplitude of |Δθ| of the relative rolling angle between both ships is expressed by |Δθ/θ|=2|sinε/2| derived from the equation of rolling. In this case, |θ| represents the amplitude of rolling angle of the ship in regular waves. Utilizing the above equation, the present writer discusses in this paper the phase difference on the optimum distance between both ships in rescue operation.

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When let go anchor and make it bring up or when moor on anchor in strong wind, the forces acting on anchor are dynamical ones caused by ships motion, so we have investigated the behaviours of anchors on sand bottom in such circumstances by model experiments. The results of experiments are as follows: -1) when we make anchor bring up, ship's speed affects on the behaviour of anchor biting into bottom. And if we can measure always the tension of anchor cable, it may be able to judge whether the anchor brings up effectively or not. 2) when the dynamical forces act on anchor having brought up effectively, the anchor is dredged quickly but it does not rotate or jump out the bottom. When the dynamical force is over, the anchor bring up effectvely as in initial condition. The length of dredging is not so long as several times of anchor lenght. The resistance of anchor in this circumstances, we could not analyze theoretically but we have to study hereafter experimentaly or theoretically.

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