Patent GB-1132838-A (GB)
Title: Improved device for determining the effect of cargo distribution on the bending moments, shearing forces, dead weight and draught of a vessel
IPC: G06G7/70
Filed: 1965-12-15
Abstract: 1,132,838. Vessel trimming computer. GOTAVERKEN A.B. 15 Dec., 1965 [21 Dec., 1964], No. 53205/65. Heading G4G. A vessel is divided (Fig. 1) by transverse planes A to E into six compartments I to VI; the compartmental loads being q 1  to q 6  wherein each load is given by q = W E +W P -W B  1 where WE = hull weight Wp = cargo weight W B  = buoyancy the centres of gravity of the compartments being displaced x 1  to x 6 ; and the dividing planes displaced A to E from the central plane C. The shearing force across a dividing plane N is given by where m is the total number of compartments and the plane divides compartments n, n + 1. The bending moment across a main plane C is given by where m iE , m ip  and m i3  are moments of hull weight, cargo weight, and buoyancy and m i  = qx i  where x i  is the displacement of the C.G. of the cross section from the main plane. The moment about an arbitrary plane B astern of the main plane C is given by and for a plane D ahead of plane C by where I B , I D  are distances from planes B, D to the main plane. Each compartment is represented by a resistor group (Fig. 2) wherein resistor 1 is adjustable to represent cargo weight and resistor 2 to represent buoyancy in terms of compartment draught, and are interconnected through series resistor 3 representing the hull weight of the compartment; so that the total resistance inserted represents qi. Resistors 4, 5 of critical values for respective compartments are switchably inserted to shunt the variable resistors so that the total resistance inserted represents the moment m i  of the compartment about central plane C where m i  = m 1  E + m 1  P - m 1  B and m 1  E, m 1  P, m 1  B are hull, cargo, and buoyancy moments. Circuit 6 enables resistor 2 to be short-circuited. Fig. 3 shows a circuit for determining shearing forces across any dividing plane (eqn. 2) wherein resistance groups I to VI representing the loads q 1  to q 6  in corresponding compartments are series connected in a Wheatstone bridge with variable balancing resistor 9 and galvanometer 8; switches T 1  to T 6  serving to short-circuit resistance groups situated between the appropriate switch and the galvanometer connection to select the appropriate dividing plane; adjustment of resistor 9 for galvanometer null representing the required shearing force. Fig. 4 shows a circuit for determining bending moment across plane D wherein resistance groups I to VI corresponding to the several loaded compartments are series connected in a Wheatstone bridge with unbalance galvanometer 8 and balancing resistor 10. Resistor groups V, VI representing compartments forward of plane D are adjusted to represent the moments of the loaded compartments with respect to main plane C, and Groups I-IV representing compartments aft of plane D are adjusted to represent the loads of the compartments so that their total value represents the total shear force in plane D (eqn. 2) and resistance 11 D  switched to shunt them develops a total resistance value representing the moment of these loaded compartments about plane C, so that the gross resistance of the groups represents the bending moment M D  of plane D (eqn. 5b) which is indicated by null adjustment of potentiometer 10. Fig. 5 shows a circuit for determining vessel dead weight, which resistor groups I to VI are series connected in a branch of a Wheatstone bridge with a galvanometer 8 and a multi-step variable resistor 12 and series potentiometer 13. The resistance groups are set to represent compartment cargo weight by short-circuiting buoyancy resistors 2 and hull weight resistors 3, and the bridge is balanced by adjustment for resistance 12 step by step and of variable resistance 13 over the intervals; the sum of their indications denoting dead weight. For determination of mean draught, resistance 12 is ganged to multi-step resistance 14 (Fig. 6) calibrated so that each resistance step corresponds to a draught increase due to the increase of dead weight for one step of resistance 12; such step values depending inversely upon the dead weight variable resistor 13 set for dead weight, which is switchably connected in series with calibrating resistance 17 and shunted by calibrating resistance 15, and is connected in series with multi-step resistance 14 and with balancing resistance 16 in a Wheatstone bridge with galvanometer 8 and fixed comparison resistor 18, the setting of balancing resistor 16 indicating mean draught. It is shown that the stern draught is given by where T is the trim MET = trimming moment of hull weight M BT =trimming moment of displacement M CT  = moment for unity change of trim X = distance from centre of buoyancy to stern perpendicular divided by length of vessel. Stem draught is similarly given by In Fig. 7 the resistor groups IV to VI for compartments ahead of plane C are series connected in one branch of a bridge and set to represent load moment with regard to the main plane; in series with a multi-step resistance 19 gauged for variation with multi-step resistors 12, 14 to represent trimming moment of hull weight. Resistor groups I to III for compartments astern of the main plane are connected in the opposite bridge branch in series with the variable resistance circuit 13, 16, 17 at its setting for measuring mean draught (Fig. 6) wherein resistance 15 is replaced by resistance 21 to allow for changes of the centre of buoyancy due to draught changes within the steps of the multi-step resistance. Multi-step variable resistance 14 at its mean draught setting (Fig. 6) is also series connected and the whole is shunted by a further switchable multi-step variable resistance 20 ganged to resistances 19, 12, 14 in dependence on mean draught. Adjustment of resistance 16 for null indicates the sum of mean draught and draught change caused by the difference between the moment sums of the sets of resistance groups, as a measure of stern draught. In a similar circuit for measuring stern draught (Fig. 8) resistor groups I to III for the compartments astern of plane C are series connected with a multi-step variable resistance 22 representing the trim moment of hull weight and the displacement with respect to plane C at the existing mean draught, ganged to multistep resistances 12, 14, 19, 20. Resistor groups IV to VI and variable resistances 13, 14, 16, 17 set for mean draught are switchably connected in the other branch of the bridge, resistor 15 being replaced by fixed resistor 24 and multi-step resistance 20 being replaced by multi-step resistance 23 ganged to 19, 12, 14 in dependence on mean draught. Variable resistance 16 adjustable for null indicates stem draught. Draughts of intermediate compartments are determined by interpolating on chart 25 (Fig. 9). Buoyancy resistances for the individual compartments are set to their corresponding draughts obtained from chart 25 (Fig. 9) with reference to the computed stern and stern draughts. The apparatus is assembled (Fig. 9) with an instrument panel 26 wherein knobs I 1 , I 2 ; II 1  II 2  &c set the load and buoyancy resistances for corresponding compartments; a bridgo galvanometer 8, and knobs for adjusting the dead weight multi-step resistance 12 and the other multi-step resistances ganged thereto; the intermediate dead weight variable resistance 13, the draught resistance 16, the shearing force resistance 9, and the bending moment resistance 10. Ranges of key switches 28, 29 select respectively measuring planes from A to E and the measurement functions of dead weight DW, stern draught d A , mean draught d M , stem draught d F , shearing force SF, and bending moment BM; the key switches operating through relays (not shown). A generalized circuit of the instrument is given (Figs. 10 to 16, not shown) in which the switchably selected circuits corresponding to those of Figs. 3 to 8 respectively are indicated by superimposed dotted lines. The apparatus may be modified to measure double values of shearing force and bending moment.