The writer showed that the agrounding was a calamity of the sea depended upon the error of the observation and or estimation of ship's position and that the probability of the agrounding amounted to about 10^<-2> in a case (mathematical model) and it was greater than that of collision.

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Collision between two vessels is caused by various conditions. In fact, I can point out that there is not enough look out and that the various actions taken to avoid collision are not done in ample time. About 30% of the vessels that collided caught sight of the other vessel at a distance less than 3 times the length of the ship, and about 70% of the vessels that collided took action to avoid collision at a distance less than 3 times the length of the ship. We think that to avoid collision, we must keep good watch and that any action against it should be taken in ample time.

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The hand steering in harbor is probably not substituted for any other instrument for the time being. Then miss-steering is apt to cause a casualty particularly for giantio ship. We obtained the following results by inquiring of many quartermasters about miss-steering: 1) 93% of miss-steerings occur in the case of no gesture in giving order. 2) 68% of miss-steerings occur in the case of right answer back for order. 3) 58% of miss-steerings occur in the "stand-by" situation. 4) 79% of miss-steering in the "stand-by" situation occur within first half an hour of steering watch.

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The width of effective area of bridge pier, which is an important factor to calculate possible capacity of a fair-way, is obtained for small boats from observation, made on the Sumida River, Tokyo. Statistical manipulation is made for frequency data of separation of boats and the edge of bridge Pier. The width of effective area is obtained to be about 2a+3Lpp for small boats. Such value for tnain barges is 2a+80m, where 2a is the width of bridge Pier. The speed of boats under the bridge (Eitaibasi) shows little change compared with that in ordinary condition.

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The effective area of ships in narrow straits is investigated in search for the influence of tidal current to the navigational traffic capacity. The observation was made in the Kanmon Straits from Aug. to Sept., 1967, by "Programmed Radar-Photograph Method". This method is developed for this study, and turn out to be very useful. The results of the survey are given as follows. [numerical formula] and [numerical formula] where r and s are the length and width of the effective area respectively, and L and u are the length of ships and the speed of tidal current (L_0 and u_0 are 50 meters and 2 knots respectively).

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The consumption of time and cost on the processing segment is considerably high as compared with the movement segment on the transportation of exporting general cargoes. It is the equal on the ship's operation. Then, it should be reduced the consumptions of time and cost on the stagnant process of ship and cargo, as much as possible. First of all, it should be rationalized of the management of ships and port facilities. The authors investigated the means of rationalization of management of ships and port facilities based on the physical distribution cost of general cargoes around the Yamashita pier terminal at Port of Yokohama. The scope for researching of cargo processing were limited to the receipt and handling, storage in a transit shed, transfering to ship side via apron of pier and by barge and ship's loading etc. On the other hand, the scope for ship's operation in the port were limited to the berthing process including with the waiting times for berthing at outer harbour. As results of investigation, it should be managed for the sake of reducing of physical distribution cost, as follows: (1) It should be managed to reduce of ship's waiting time for berthing.and berthing period for the loading, because the influence of demurrage is considerably high. (2) The annual tonnage of cargoes which are delivered, should be increased in the interests to level down of cost due to port facilities. But, it should not be exceeded over ρ=0.75 that is utilization factor of berth. (3) The total loading tonnage per ship should be incrased in the interests to cost down of ship's management. (4) The loading tonnage of cargoes via apron of pier should be incresed decreasing the cargoes by barge for the sake of increasing of the loading efficiency.

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As the accuracy of a ship's position fixed by the cross bearing method or the horizontal sextant angle method is determined by way of functions of distances and intersecting angles, in most cases, the closer one stands near any object the better he can get a highly accurate position, and on the contrary, the farther away from it, the poorer accuracy he can obtain. However, the extent of inadequate accuracy is subject to the relation between the three objects and the observation point, so it is not easy to know the whole aspect. To know them, the author calculated the probability densities of every point, and draw accuracy contours of the ship's positions. [Fig.3 (a) (b) (c) (d) (e) and Fig.5 (a) (b) (c) (d) (e)] The process of the drawing of the maps is somewhat troublesome, but if one examines those maps closely, he can see the main points of this paper.

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When the artificial satellite is used as aids to navigation, its positional error is inevitable. We must consider its effect on the line of position. In case of one target, the displacement of the target corresponds to the displacement of the line of position. The author analysed the case of two targets. The angle between the two or the difference of distances may be measured. The displacement of the two targets are classified into parallel displacement, rotation and dilatation. The displacement of position line by the difference of distances from two synchronous satellites is calculated and is showed in figures 4 and 5.

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At this time, we developed the new equipment, that was "Course Recorder", which was able to receive Loran-C signals on the X-Y Plotter. Then in December, 1968, we made the experiments on Osaka Bay and the Coast of Tomoga-shima installing this equipment on "TENYO" of Hydrographical Department of Maritime Safety Agency. The conditions of receiving are almost good, so in future we think that we get the good results in utilizing Loran Navigation.

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The author studied the estimation method of the fading zone where the remark signals disappear. These dead zones for the ramark navigation are caused by the interference between direct wave and sea-reflected that with phase difference of nπ So ; the distance may be estimated from the following formula well-known [numerical formula] where h_1 ; height of ramark antenna h_2 ; height of radar antenna d ; distance λ ; wave length The apparent height of antenna, howezer, is decreased influenced by the carvature of the earth in the long surface propagation. The author tried to estimate the distance and breadth of dead zone with effective heights in consideration of the distance effect. A practical sea experimental value is about 10% in distance and 2 or 3 times in breadth.

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A ship, generally, consists of many targets which have individual radar cross section. So, in case of observation by marine radar, the echo from the target ship can be divided into several complex echoes. In this paper, the author is considering how simulation is suitable for the purpose of analyzing and predicting the echo power from a ship, using the electronic computer to calculate and make the curves of echo powers under various simulations.

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On fixing the ship's position at sea, three or more position lines are necessary to avoid an inaccurate position due to accidental errors. Though an error ellipse of astro-fix is defined only cut angles of the lines, we usually reject position lines because of their large error, if the cocked hats are too large. What is the criterion of the rejection. The author goes steps further and introduces a statistical test for the criterion and the least square method for the estimation of accidental errors. Under this treatment the confidential area of the fixed position can be calculated by hand or a digital computer.

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Since early times, some kinds of semi-conductor have been known as sensitive material for magnetism in which the Hall effect occurs. Recently semi-conductor called SMD (Sony Magnetodiode) has been made and said it is more sensitive than Hall effect elements. If the direction of the earth's magnetic field is detected by SMD, the system will become simple and moreover the bearing is put out as the voltage signal. It is also possible to make repeater compass. In this paper, the theoretical and experimental investigations on the SMD is described and the possibilities for the SMD compass are informed.

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It is very essential to have a full knowledge of reliability of navigation equipments, on which few reports have been seen so far. In this paper the writer intends to clarify the reliability of bottom logs by statistic disposal of failure data. The results of the researches are as follows: -1. The initial failure period lasts for 1 year after installation, then the random failure period follows it until 11 years after installation. 2. The reliability functions in the random and the wearout failure period are given as the following equationsr respectively ; [numerical formula].

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For the continuous recording of the sea noise which are caused by several sound sources such as moving vessels and fishing gears with complicated motion in the sea, the present method to collect information through the cable between the hydrophone and the recorder on deck of the ship is slightly difficult for use. Therefore, the authors have built newly the underwater tape-recorder as the system of direct recording without cable which can be easily attached to these moving objects. The new apparatus was shackled to the head-rope of the square part of the trawl-net, and the sea noise under trawling was recorded at the mouth of the trawl-net by it and in the laboratory was analyzed by the soundspectrograph. Here have been reported the techinical consideration on it and some of the results. 1. Underwater tape-recorder was effective sufficiently for the recording of the sea noise which was caused by moving fishing gears and others. 2. After several acoustic experiments, the calibration of the absolute sound pressure is given in decibel re 1μ bar on this report. 3. On the sound spectrum, the frequency distribution of the sea noise, which recorded at moving net of the otter trawler and of the two boat trawler, is ranged over DC to 5, 000Hz and the dominant frequency zone is the range of 500Hz to 700Hz. And then the sound pressure is about 21dB on the otter trawler and about 11dB on the two boats trawler, 4. Some of misagreements on the sea noise between otter and two boats trawler are recognized: at the range of low frequency the noise of two boats trawler is shown lower level of sound pressure than otter trawler, but at the high frequency range is shown inversely.

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Recently, we have already some equipments which are consisted of analogue and digital computing devices, such as cargo handling and navigation system. And now, a tendency to promote the computerization of merchant ships has been rapidly arised around the world. We have studied on collision avoidance calculation in this paper, which must be considered in computer controled ships. As a result, we have got a guidance of further investigations from this study.

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When a ship rolls because of waves, it drifts. After experimentations Prof. Suehiro and others reported that the drift caused by heavy rolling is greater than that caused by smooth rolling. The authors have experimented with the drifting of ships for several years on a rough ocean, but according to our studies, the drifting is not greater when the waves are larger and less great when the waves are smaller if the wind velocity is the same. In this paper, we compared the driftings when an anti-rolling tank was being used and when it was not. The method 1. This experiment was carried out on the Hokusei-maru (273 G/T) a fishery training ship of Hokkaido University, in the North Pacific Ocean. 2. The corner reflector which was connected to the salmon-gill net was selected as the datum point of experiment. In this case, the reflector was allowed to drift together with the ship according to currents and waves, but it felt no effect from the wind in spite of the movement of the ship. 3. Observers on the ship measured the distance and the bearing of the reflector by radar every 30 minutes and calculated the drift by solving the triangle. The anti-rolling tank was used on and off every 30 minutes alternately. The observations were made for several hours each day for 11 day. The results 1. As shown in Fig.1 the ship drifts almost the same whether it rolls a lot or a little. (here: wind velocity was less than 11m/sec) 2. The relation between the wind velocity and the drift is shown in Fig. 2(a) and (b). 3. The direction of drifting is closely related to the ship's head (shown in Fig.5), and the drifting distance can be calculated from the wind velocity. Consequently, if one knows the drifting characteristics of his own ship, he can estimate the position to which the ship has drifted.

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A survey on the effect of rudder speed upon advance and turning lag with a constant steering engine power has been published in the report presented by Nihon Kainan Boshi Kyokai (N.K.B.K.) in 1966. The said report of N.K.B.K., howewer, has paid no consideration for rudder aspect ratio. This paper treats of this subject, taking account of rudder aspect ratio, which varies inevitably with changing the rudder speed with a constant steering engine power.

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The author has investigated on the effect of elastic property of rope to the amount of the movement of ship and to the tension of the rope, in some cases of mooring the ship or towing the ship by tug. The results are as follows: -1) In case of mooring, the elastic properties of ropes do not affect to the tensions, so it is advisable to use wire ropes because the amount of the movement of ship becomes smaller. 2) But when heaving and or pitching motions, or horizontal movements of a ship are caused by wave, swell, surge etc., the elastic properties of ropes affect to the tensions, so it is better to use fibre ropes. 3) In case of towing a ship by tug or the berthing prosedure of a ship, and when tug boat or the ship having initial speed (these are nomal cases), the elastic properties of ropes affect on the tensions of ropes, so it is better to use fibre ropes.

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Splicing is a wellknown method of joinning rope by interweaving the strands, however, we have few reliable data of breaking strength on the rope spliced. Therefore, we examined the strength of steel wire ropes and synthetic fiber ropes joined by various methods of eye and short splices, as the basic research for the study of the problem. We report the results of some measurments and discuss in this paper.

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The Precision Depth Recorder (PDR) manufactured by Nippon Electric Company of Tokyo was installed in usual manner on MS HAKUHO MARU, an ocean research ship delivered by the Shimonosheki Shipyard of Mitsubishi Heavy Industries, Ltd. to the Ocean Research Institute of the University of Tokyo, in March, 1967. She is 3, 226 tons gross and 87 meters in length. In spite of its capability of sounding as deep as 10, 000 meters, we found that the equipment could not show the sea bottom at such depth when her speed exceeding 10 knots at the scale of the sea state class 3, being disturbed by the flow-noise. The flow-noise is generally attributed to bubbles in the current of water in the front of transducer. We have, therefore, investigated how to obtain the optimum performance of the equipment by installing temporarily four hydrophones under her keel between the transducer of the PDR and her FP, and we observed noises of each hydrophone. By this investigation it was verified that the layer of water current containing bubbles is generated under the bottom of ship. Though this layer is very thin near the stem but it becomes thicker as the distance from the stem increases towards the stern. We found that its thickness at the frame No. 87 was about 40cm, where the transducer has been installed. The speed of ship was about 10 knots. From the results obtained, we installed a new transducer under keel at the point of 7.1 meters from FP on the side of stern. By this reformation the aggregate performance of the equipment is greatly improved. In scheduled survey trip from November, 1968 to March, 1969, she crossed the Tonga Trench and sounnded the sea bottom. The tests were very successful. When she crossed the trench at the speed of 10 knots toward east against head wind, the echo signals were never masked by flow-noise. The maximum depth recorded is 10, 450 meters. On her westward course with the speed of 14 knots in fair wind, similar tests were performed ; the maximum depth recorded was 9, 800 meters. The meteorological conditions during the investigation were: 1) the scale of wind was class 4, 2) those of waves and swells were both classes 3. The draught of the ship was 3.80 meters at the stem and 6.40 meters at the stern.

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As the progress of the modern navigation with many elaborate electronic nautical instruments, navigation officers on duty on board must be kept at those modern instruments, and yet the speed of ships are increasing as much as the number of ships increases, the concentration becomes more violent. In spite of according to those modern instruments, the final object of the navigation is to plot the positions of the ship on the chart, and that final process must be handy and simple as much as possible than ever before. Therefore some sort of available navigational computation which may be designed on the Navigational-use Triangle are laid out by authors. It may afford navigators saving the time and getting rid of complication of consulting various kinds of multiple tables and also be accurate enough for the navigational computation daily. As well as the simplification of the navigational computation partly, the scale for the simple navigation without nautical instrument is graduated and may give good kind of the safety navigation for small crafts.

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