It is known that the steadieness of magnetic compass are disturbed by rolling of the vessel. The damping period of magnetic compass card has been occasionally synchronised with the period of rolling of the vessel. We have found that damping curve of magnetic compass card has been related with the period, viscosity or temperature of the liquid, diameter of the card, magnetic moment of the compass, and horizontal magnetic force on the earth. On account of above reason ; if we know some elements, we can easily find out one of the rest. This experiments should be coutributed to konw the condition of magnetic field in the vessel and to determine the dimension of the magnetic compass which is newly designed by the requirement of ship owner.

View full abstract

1. We investigated the present condition of illuminating means including radioactive luminous paint to the dial navigational instruments to rationalize uisual navigation by exponding look out of range and hastenning adaptability to darkness. 2. In addition to above, we found pattern of rational proportion among length, breadth, and space interval of scale etc., of dial experimentally to make it easy to read, to lesson measuring time of taking bearing etc. 3. Examined actual effect of radio-active luminous paint and showed a procedure to the definitnition of the practical brightness of it.

View full abstract

In order to obtain the probable error of Loran lines of position measured by a number of ships at sea, the present writer distributed to each of the ships a printed form to be filled with observed errors. The method of obtaining error is as follows: Estimating the position fixed by cross beraring or Radar at coasting and the position fixed from astronomical observation in ocean respectively as the correct ship's position, the error is represented by the length of a perpendicular drawn from the above-mentioned position to Loran LOP. Here, the error of Loran LOP can be expressed as formula (1) of the present article. Let a…geometrically non-variable error [numerical formula]…error on the baseline due to the error of the measurement of time difference. △t…error of the measurement of time difference (μ.s.) φ…the angle between the two stations from the observer cosecφ/2…the factor of geometrical precision. Thus, if from the deta collected from the ships a number of observed errors (e) and their angles (φ) be found, then substituting each of them in formula (1), the values of a^2 and b^2 can be odtained by the method of least squares. Transforming them into probable errors, formula (5) and (6) are obtained. The results of the calculation are shown in Table 1, and they are, expressed graphically as curve B in Fig I and II. Besides, curve A in Fig I and II represent the probable error of LOP, which was estimated from an American literature.

View full abstract

Ship's inclination is divided rolling by wave cycle and other lists. For rolling by wave cycle, we can avoid its risk by alernation ships course and speed. Viz cosα-(1.25√<Lw>-Lw/Ts)/Vs α: angle between ships head and wave head. Lw: wave length. Ts: ship's rolling period. Vs: ship's actual speed. For other list, we are requested following fotr terms. (1) θmax≦25° (2) Ds≦0.08m (3) θrange≧60° (4) GM=B/12〜B/42 Ds: Dynamical stability arm. B: Breadth We can always estimate good KG limitted these four term's lines according to draft change.

View full abstract

The author believes that the reason why from the practice of seamen every vessel under way keeps out of way of small rowing boats and fishing vessels or boats which are permitted to carry a white light on the Regulations for Preventing Collisions at Sea, is not due to what they are considered the vessels at anchor. And it being not for avoiding the immediate danger, both sides of them should not take a measure to keep out of their ways at the same time against each other ; namely they should not apply Article 27. These small rowing boats and fishing vessels or boats have no special privilege and they have the same rights and obligations on the Regulations as the other vessels. Accordingly, it is natural that the risk of collision should be avoided against the precaution required by the ordinary practice of seamen or by the special circumstances of the case, and that should be done before the vessel approaches. within the range so as to involve the risk of collision.

View full abstract

The compass card in the liguid type magnetic compass bowl has deviation of angle on the horizontal plane as the vessel makes turning. Here we call it waked angle. By the results of our various experiments, the waked angle has hardly relation with the diameter of compass card or the area of the card, and the clearance between inter-side of the compass boul and the outer side of the compass card shows no big influence upon the waked angle when the clearance is over 10mm. Besides them, no influence was revealed by the clearance on the compass casd surface, magnetic needle, roughness of the compass card or inside surface of the bowl, thickness of card, luber's line, etc., and a little inflance was revealed by damper.

View full abstract