停止せる推進器進航の抵抗

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When an ordinary Merchant ship, afloat on deep still water under no wind condition, is proceeding ahead by her own inertia only, her propellers having been completely stopped and her speed length ratio K/√<L> (where K is speed in knots and L is L.P.P. in feet) is less than 0.4,resistances acting upon the ship are principally skin resistance and the resistance of stopped propellers dragging through the water, as the wave making resistance is practically negligible. The present paper deals with the above mentioned dragging resistance of stopped propellers of a ship longer than 400 feet, proceeding at a speed from 8 to 3 knots. The loss of kinetic energy in ft. tons of a ship of W tons displacement, in the course of an interval between the instant when her velocity was v_1 ft. per sec. and the instant when her velocity became v_2 ft. per sec., can be calculated as follow : - Loss of K.E. in ft. tons=[numerical formula], Where g is acceleration by gravity in ft. per see. per see. (32.2 ft.). If we denote the distance in feet, travelled by the ship in the said interval by S at a mean velocity [numerical formula] ft. per sec., Total Resistance in tons=[numerical formula] From this quantity, deduct the calculated skin resistance at the same mean velocity, then we obtain the dragging resistance (in tons) of stopped propellers at the said mean velocity. In order to find the propeller dragging resistance, by means of the above theorem, the author made two actual experiments, when he was in command of S.S. "Tajima Maru" and "Katori Maru", 15 and 8 years ago respectively, the summaries of the results of experiments being given in Tables I and II. Successive velocities were obtained by throwing short wooden logs overboard, one after another, from the forward end of a measured fore and aft distance on board ship, having watched the thrown wooden logs right abeam of the after end of the measured distance, and noting intervals in seconds : care was taken for the procedure that when the 1^<st> log bore right beam of the after end of the measured distance, the 2^<nd> log was to be thrown overboard without delly from the forward end of the same, and so on. In Tables I and II, T, t, and v are instants at which logs were thrown over-board in H.M.S., intervals in seconds, and velocities in ft. per sec., respectively. All v's are converted into K, which represents corresponding speed in knots. Total resist ances (R in tons), skin resistances (R_f in tons), and propeller dragging resistances (R_p in tons), are calculated at successive mean speeds (K mean). In case of Table I relating to the "Tajima Maru", R(tons)-R_f(tons)=R_p(tons), while in case of Table II for the "Katori Maru" some corrections were made as will be seen from remarks at top lines of the tables and also in Table III.N.B. All the tables and remarks for the same, are written in English, for convenience of foreign readers. Graphical curves, showing relations between speeds and the dragging resistances of two stopped propellers of the two ships, are as shown in the figure, the irregularity of actual results being faired. Examining the graphs and adopting some guess work, the author compiled his own formula as follow : - [numerical formula] , where, R_p (tons)....dragging resistance in tons of stopped propellers, n........number of propellers, d........diaometer of each propeller, in feet, K........Speed in knots. Keeping notations W, g, k, R(tons), R_f(tons), R_p(tons), n, and d, the same as before, let S, hero after, represent the area of wetted surface in sq. ft., or the area mutiplied by such numbers as 1.1,1.2. 1.3,...., in accordance with the foulness of the wetted surface itself, and let us also assume [numerical formula]. Then we have [numerical formula], Substituting (S) for S+90nd^2,[numerical formula]. As one knot corresponds 1.688 ft. per see., the loss of kinetic energy in ft. tons, of the ship, in an interval while her speed drops by 1/2 knot from K knots
社団法人日本船舶海洋工学会の論文
1936-03-20

停止せる推進器進航の抵抗

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