Patent GB-760429-A (GB)
Title: Improved apparatus for the estimation of the correct distribution of the cargo in a ship
IPC: B63B9/00
Filed: 1954-05-12
Abstract: 760,429. Electric analogue<SP> </SP>calculating apparatus AKTIEBOLAGET GOTAVERKEN. May 12, 1954 [May 16, 1953], No. 13961/54. Class 37. Apparatus for estimating the cargo distribution of a ship for correct values of trim and hull bending moment about an arbitrary reference plane dividing the longitudinal section of the ship, comprises a first group of series connected resistances adjustable in correspondence to the respective products of the weights and distances from the plane of the cargo loaded in the several compartments on one side thereof, a second group of series resistances adjustable in similar manner to represent the products of the cargo weights and distances on the other side thereof, a first variable additional resistance proportional to the total moment of the bulk weight of the ship and the hydrostatic displacement lifting force about the plane, a second variable additional resistance proportional to the arithmetic sum of the moment of the hydrostatic displacement lifting forces and of the bulk weights of the fore-and-aft portions of the ship about the reference plane, and a switching device whereby either of two alternative balanceable bridge circuits may be set up, in the first of which one branch comprises one group of series resistances and the other branch comprises the other group of series resistances in series with the first variable additional resistance and in the second of which one branch comprises both groups of series resistances and the other branch comprises the second additional variable resistance, there being provided alternative balancing potentiometers interconnecting their respective bridge branches and adjustable to restore balance and indicate on calibrated scales the trim and the longitudinal bending moment of the loaded ship about the reference plane. It is shown that the trim t of a loaded ship is given by and the total bending moment M is given by about an arbitrary reference plane, where v = weight of cargo in each compartment. Lx = displacement of each cargo element from the reference plane. f<SP>1</SP>(h) = the total moment of the bulk weight of the ship and of the displacement lifting force about the reference plane. f<SP>11</SP>(h) = the reciprocal function of the trimming moment necessary to produce at a given draught a unit variation of trim between stem and stem. f<SP>111</SP>(h) = the arithmetic sum of the moments of the bulk weights and the displacement lifting forces for the fore and the after parts of the ship about the reference plane. #<SP>1</SP> denotes algebraic sum. #<SP>11</SP> denotes arithmetic sum. A balanceable bridge circuit (Fig. 3) comprises ranges of series resistances 11 to 14 and 15 to 18 adjustable to represent the products of the cargo weights in compartments 1 to 4 and 5 to 8 (Fig. 1) and their distances L<SP>1</SP> to L4 and L5 to L8 from an arbitrary reference plane XX, inter. connected by equal resistances R<SP>1</SP> across a current source 9 and on-off switch 10. Series resistances 19, 20 are provided respectively adjustable to represent the values f<SP>111</SP>(h) and f<SP>1</SP>(h) defined above, together with alternative balancing potentiometers 21, 23; the system being arranged by ganged switches O<SP>1</SP>, O<SP>2</SP>, O<SP>3</SP> to function (as shown) with resistances 11 to 14 and 15 to 18 in series as one arm of the bridge interconnected with the other arm comprising resistance 19 by potentiometer 23, or alternatively to function with resistances 11 to 14 and 15 to 18 in opposite arms interconnected by potentiometer 21; the latter arm also comprising resistance 20. When the bridges are respectively adjusted for balance indicated by galvanometer 25, potentiometer 21 indicates trim t on scales 26, 27 calibrated for different draught values, while potentiometer 23 indicates total bending moment on a calibrated scale; referred to the plane XX in each case. The apparatus may be assembled as a transportable structure unit (Fig. 4, not shown) embodying plans of the ship's hold space and with variable resistances accommodating up to 25 cargo compartments.