In view of design and evaluation of systems, the author considered the fundamental composition and the functional relation among each components of the position fix system, figuring the reliability diagam. Consequently the system reliability P was shown as P={P_E∧(P_O∨P_C∨P_R∨P_S∨P_F∨P_L∨P_D∨P_W∨P_N)∨P_E}, where P_E, P_O, P_C, P_R, …P_N are reliability of dead reckoning, celestial navigation, coasting, radar navigation…and satellite navigation subsystems respectively.

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The studies are based upon the measuring records taken by the Japan Maritime Safety Agency at 12 monitoring points within the coverage of the Kita Kyushu Decca Chain during about one year (1969-1970). Additionally, supplementary measurements were carried out at two points during 72 hours. These observations were made by following data ; 6 days every month, every minute and 1030-1130 (daytime). Constant deviations of both each pattern and each point were obtained. The characteristics of these deviation were correlated each other at the next points in the Red and Green pattern. Monthly standard deviation showed that±1-3 cel corresponded to about ±10m near the base line except the point where to poor propagational conditions. Of course, the nature of the deviation suggested that the propagation velocity used were unsuitable, the reasons why of these phenomenon were presumably affected by the mountaineous profile along the each path. Especially a large amount of deviation of Purple pattern at Hososhima might be influenced by the nature of the route which across the sea and the steep mountains several times. The meteorological conditions will be affected the deviation and these introduced two types of variation. Approaching the front, high pressure and typhoon, a peculiar variation will be occured synchronously at several points.

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In fall of 1970, Decometer readings were carried on simultaneously at four points, every 10 min. in daytime and 5 min. at night during 72 hours continuously. The consideration of selection of these points was made carefully in order to analysis data under uniformal propagation conditions. The constant deviations at each point and pattern were found respectively, but the correlation between the distance from the transmitter and the deviations could not ascertain clearly. Because the author considered that a large amount of deviation at each point might be introduced from the neighbouring interference on account of geological position. In the case of Red pattern, however, 3 points are positioned nearly on the great circle, and also, the deviation increased was proportionaly to the distance from the transmitter. The stability of Purple pattern is ±2-3 cel during, daylight, correspond to the distance in about 7-12m. To the contrary, from the transient time or so the Decometer readings will be oscillate gradually and progressed to night variation like the sine wave. These phenomenon are presumably introduced from the contamination of the skywave. Since the night variation is a large, the phenomea was caused by the variaton of the virtual height. The phenomena above could not analysed at the present time.

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The servo type SMD compass has been reported by the authors before. This time, two pairs of SMD bridges are used, one being fixed fore and aft and the other transverse. Each output from the SMD bridge is given to the oscilloscope acting X-Y, and then the brilliant line showing the direction appears on the CRT. In this paper, theoretical and experimental investigations on the CRT presentation type SMD compass are reported.

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A collision avoidance system is devised which is composed of a ship-borne radar and a conventional VHF communication system with some additional devices. Ship-borne radars and VHF communication systems are used quite widely today. The functions of the system are listed below ; (1) collision warning by a buzzer which is equivalent to a horn of a car. (2) identification of a target with which a collision may occur by giving a mark on the radar scope as well as identifying lamp display. (3) exchange of information on manoeuvrings and others through VHF telecommunication. An evaluation test at sea was executed in the vicinity of Port Yokohama where "Noji-ma", a patrol ship, was employed as the target and "Sumida", also a patrol ship, was calling station. The functions of the system were almost satisfactory and the covered range was up to 3.5 miles for the range of "Low Sensitivity" of the radar receiver. However, interferences from other radars as well as other VHF transmitters were obser-ved occasionally, since the congestion of the ship traffic as well as electromagnetic wave are heavy in the port. The tested system has this shortcoming, however, the authors feel that if the system is produced very economically, its merits are beyond its shortcoming.

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The technics of echo-sounding from the surface of ice, which had been tried at the frozen lake, Harunako, were applied to sounding at locations near Syowa Station in Antarctic in 1967 and 1968. This is very important for the research of topography. The echo sounder was designed and manufactured to be usable at the polar region. In order to make the transducer contact with the surface of ice, grease was used in stead of water. The maximum sounding was the depth of 405m through the ice the thickness of which was 140cm. The precise topographical charts were drawn with this echo-sounding and the technics of determination of accurate sounding positions on the surface of ice.

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An officer on duty on a fishing vessel was watching a drift net or long-line going a-drift after it had beeh set. Whenever, if he can estimate the relative position of the ship in relation to her fishing gear during drifting without recurring to an object (flag, light, reflector, radio buoy), he can employ the method to watch the gear effectively. For example, the authors made the experiment with the drifting of the Oshoro-Maru, a fishery training ship of Hokkaido University, in the Bering Sea, and tried to express the direction and distance of the drift by parameters with the ship's head and wind velocity.The experiment 1. The corner reflector connected to the drift net was selected as the datum point of the 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. 2. The observers on the ship measured the distance and the bearing of the reflector by radar every 30 minutes and calculated the drifting by solving the triangls. Observations were made several hours each day for 14 days. The results are as follows: 1. The relation between the wind velocity (W) and the drift is shown in Fig. 2. 2. The relation between drifting coefficient (K) and the ship's head (α) is shown in Fig. 3. Accordingly, the drifting velocity (U) is expressed by the following equation, U=(a-bα)√<S/Sw>W. 3 .The direction of drifting is closely related to the ship's head (shown in Fig. 8), accordingly, the drifting direction (β) is expressed by the following general equation, β=a+bα, and the coefficients a and b are based upon the ships' drifting characteristics. 4. 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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In this paper we describe problems on a controllability of ships when very large vessels proceed through the middle-channel of the strait of Kurushima, and also as to whether it is safety enough. An output of irregular yaw motions of ships caused by a turblent flow was replaced with an input of Equivalent Rudder Angle δ_e, which is expected to generate the same yaw motion of ship, and the equivalent rudder angle was used as a new guidance to estimate the yaw angle of very large vessels in the turblent flow. In order to obtain the steering-pattern that eqauls the turblent flow effect, tests by full sized ship were carried out on a training ship (G. T. 360t) and passenger ships (G. T. 2, 900t). From the results simulated for very large vessels by using a digital computer and the experimental data, it can be considered that the ship-maneuvers in the turblent flow are not so difficult as it is imagined.

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Authors dragged JIS-stockless anchor (18.63 kg) and JIS-stock anchor (19.04 kg) at a constant speed 25mm/s in mud sea bottom. The results obtained from these model test were given as follows ; 1) When JIS-stockless anchor dropped vertically from a height of 1m, a ratio of dragging pull to anchor-weight reached to 4.16, but in a short time its ratio decreased to 1.23. Also the ratio in condition when the anchor was able to bury reached to 5.43, and the instability occured within the dragging distance of 4.2 times anchor-length and then the ratio decreased to 1.49. 2) The dragging pull of conventional stock anchor indicated a constant value 5.38 times anchor-weight and it had never turned on a axis of anchor-shank. It may be quite all right to considered that JIS-stockless anchor in mud bottom is not trip, as often pointed out.

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Look-out should be vigilant, even if other ship has no Lights, it may be negligence not to see and avoid another ship. An overtaken vessel is not ordinarily obliged to keep watch astern so long as she showing a proper stern light, holds her speed and course, and taken any action to avert collision.

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There seems to be some confusions in construing, applying and obeying Article 12 of Japan Port Regulations Law. So this paper offers, tentatively, the conditions under which to apply this Article and the points to be agreed upon borh in construction and practical operation.

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Comparing the operation of liner boats with that of timber carriers, the authors have tried the rationalization of timber carriers. During one round voyage of American-log-carriers and Lauan-carriers, their operations are examined. Besides conditions of operations at Nagoya and other discharging ports are examined. The number of ships for statistics was as follows: Nagoya Others American-log-carriers 66 54 Lauan-carriers 263 49 The term was about one year, from Nov. 1969 to Oct. 1970. As the result of investigation, they found that the great obstacle of rationalization was the high ratio of anchoring hours to one round voyage. Especially the shortage of anchoring hours at discharging ports was necessary. The main cause of the extension of anchoring hours is that the ratio of waiting hours to moor and waiting hours to discharge cargo is high. The solution of these problems are enlargement of timber ponds, consolidation of port facilities, rationalization of cargo-working and security of skilful laborers.

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The authors brought forward a definition of the meeting in the marine traffic flow. According to their definition, the encounter, one situation of the meeting, is a situation that the course of a certain ship is the value between plus 135 degrees and plus 225 degrees from the course of the reference ship, the crossing, another situation of the meeting, is a situation that the course of a certain ship is the value between plus 45 degrees and 135 degrees or between plus 225 degrees and 315 degrees from the course of the reference ship, and the overtaking, the other situation of the meeting, is a situation that the course of a certain ship is the value between plus 315 degrees and plus 45 degrees from the course of the reference ship and the speed of the reference ship is greater than that of a certain ship. They obtained the number of the meeting from the simulation of the middle of Tokyo Bay. Farthermore, they proposed the definition of the randomness and obtained the values.

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The Kanmon Strait studied here is located on one of the most imoportant maritime traffic route in Japan. In addition to snch a topographic disadvantage as the narrow and meandering course with strong tidal current, the recent advance in the exploitation of the adjacent areas with many newly settled spur tracks made the traffic volume increase and the passing course of respective boats complicated. These need the urgent improvement of the traffic facilities in this strait basing on the fundamental studies. As the first step of the study, the present report described the outline of the accidents in this strait basing on the records during the period from 1962 to 1969. And the results are summarized as follows: 1. The change of the number of accidents per year caused by the traffic of about 1000 vessels a day could be represented as follows: y=3.18x±47.64 where y is the number of accidents in the year of (x+1960). This increase in the accidents was chiefly in the collision, as shown by the following relation: y=3.11x+3.04 2. These meant that the improvement should be aimed at how to protect the passing vessels from the collision. 3. The recent increase in the collision was chiefly of the vessels larger than 1, 000 gross tons, although about 70% of the collision was of those smaller than this size. 4. The rate of collisions, p, number of collislons per passing vessel, increased with its gross tonnage keeping the following relation: P=0.46x^<0.59>X10^<-5> where x is the size of the passing vessel in gross tons. 5. It was hard to find a clear relation between the hourly change of the number of collisions and of the traffic volume. 6. The collision in this strait could be characterized by that of going vessel against the anchoring one especially in the Moji area of the kanmon Harbor during daytime and in the Mutsure area at night.

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