US2489755A - Lift gauge for floating drydocks - Google Patents

Description

1949 F. c. CZARNECKI I 2,489,755

LIFT GAUGE FOR FLOATING DRYDOCKS Filed March 7, 1944 d 7 INVENTOR 2 /{,,,ATT0RNEY Patented Nov. 29, 1949 UNITED .STATES PATENT -OFF|CE 4 Claims.

Thesubject has to do with the docking of ships; for repair and maintenance or reconditioning by means .of a'floating drydock of either sectional and self docking or single unit type, military or non-military. Docks of this character. areused to lift men of war, cruisers, plane ,.carriers, destroyers or other navy ships, or merchant cargo vessels or tankers. Throughout the entire process ofv lifting, holding andre-launching many types ofvessels, it is highly important and necessary that sectional uplift .be kept equal to or close to'the ships weightfor the given section. It is customary to equip the varioussections of such docks with gauges which register depth of draft and also depthof water ballast in each compartment or section. Various types of gauges or instruments are used for this purpose. From the readings of these gauges and by reference to previously .prepared tabulations, curves and charts, the required lifts onthe various sections of .the vessel, .by the corresponding sections of the .dock, aredetermined and controlled to match the requirements of any particular ship. This process is attenuated andalso subject to possible errorin calculation. .Error of this sort is hazardous and may result in permanent damage. to the ship, or dock, or both,.if they arestressed .incorrectly. It istherefore very desirable to .have lift gauges which automatically indicate the net lift on the ship by the respective dockcompartments or sections so that ballast water is controlled and the sectional lifts accurately adjusted to conform'with the requirements of any particular ship at all times during raising, carrying, holding and re-launching.

Further objects and advantages of my.invention will be apparent from the following descriptionconsidered in connection with the accompanying drawing, the single figure of which; is a more or less diagrammatic view of. a preferred embodiment of my invention.

Referring to the drawing, reference character [designates a pressure bell which is subject to varying water pressures resulting from changes in the draft of the drydock. The upper part of bell l is connected by means of a conduit 2 with the upper end of the lower leg of a U tube 4. Preferably interposed in the conduit 2 is; an air dryer'3 to prevent the passage of'water vapor from the bell to the U tube.

Disposed within the lower leg'is an insulating core 9 upon which is wound a spiral resistance coil. This coil includes three sections 6,"? and 8' of different pitch. The section 6. has a resistance per inch corresponding tothe'change in buoyancy of the dock as the wing wall thereof emerges from the water in ,whichthe dock is floating. Section I has a resistance per inch corresponding to the change in buoyancy of the dock due to emergence-from the waterofthat 2 portion of the pontoon section from the pontoon deck level to the .bilge knuckle, while section8 has a resistance per inch corresponding to the change in buoyancy of the dock caused by. the emergence of that portion thereof from the bilge knuckle to the bottom of the dock.

.Disposed intheupper leg of the U tube 4 is an insulatingcore I0 upon which is wounda resistancevcoil having sectionsfi, '1 and 8 of the same pitch ,.as the sections designated by like reference characters on thecore 9. ,However, it will be noted that the resistance coil in the upper legis' inverted with respect to that in the lower leg and the lower end of the resistance coil in the. upper leg is at the same level as the upper end. of. the resistance coil. of the lower leg. The upper end of the upper leg is subjected to atmospheric pressure through the conduit II in which is, preferably interposed an air dryer I2 for preventing the entrance of atmospheric moisture.

The ,U tube' i contains sufficient mercury so that ,when no pressure is applied to the lower leg through theconduit 2, the mercury level stands at the, upper end of the lower resistance coil and at the lower end of the upper resistance coil. The apparatus so far described will be referred to' hereinafter as unit D, and it will be apparent that, the-level of the mercury therein Varies with changes in draft of the drydock, an increase in draftcausing the level to fall in the lower. leg and to rise in the upper leg.

A similar unit B includes a pressure bell 2| which, is subjected to variations in pressure due to changesin the head of ballast water contained within the drydock. The bell is connected through a conduit 22 to the upper end of the lower leg ofthe U tube 24. Disposed within this leg is an insulating core 29 on which is wound a spiral resistance coil having sections 26, 21 and .28. .The resistance per inch of section 26 corresponds to change in buoyancy of the dock resulting fromballast water drawdown in the wing section, the resistance per inch of section 2?. corresponds to change in buoyancy caused by ballast water drawndown from the deck level of. the pontoon section to the bilge knuckle, while the resistance. per inch of section 28 corresponds to.. the,.change in buoyancy of the dock caused by ballast water drawdown from the bilge knuckle to thebottom of the dock.

An insulating core 3ilis disposed in theupper leg of the U tube 24 andis provided with a winding identicalv with that on core 29 except that it. is. inverted. As was the case in unit D, the lower end of the winding on core30 is substan tially, level with the upper end of the winding on the core 29and the U tube contains a sufficient quantity of mercury so that when the level is the same inbothrlegs itstands atthetop of the lower .coil and atthe bottom of the uppercoil.

The upper end of the upper leg is subjected to atmospheric pressure through a conduit 3| in which is preferably disposed an air dryer 32.

Reference character 50 designates a pair of conductors leading from any suitable source of electric energy. One side of the line All is connected to terminals l5 and 35 at the upper ends of the resistance windings on the cores 9 and 29, respectively. The other side of the line is connected through an ammeter I l and a variable resistance l3 to the terminal [6 at the upper end of the resistance coil on the core l0. This side of the line is also connected through an ammeter 34 and a variable resistance 33 to the terminal 36 at the upper end of the resistance coil on the core 30.

The reference character l8 designates the shaft of a differential voltmeter having armatures El and 3?. These armatures are wound reversely with respect to each other so that application of a potential to the armature l1 produces a torque tending to rotate the shaft 18 in a counterclockwise direction, while the application of a potential to the armature 31 produces a torque tending to rotate the shaft in the opposite direction. The shaft carries a pointer 19 moveable over a scale 20 which is calibrated in tons. The armature I? is connected to the terminal l5 and to the mercury at the bottom of the U tube 5. The armature 31 is connected to the terminal 36 and the mercury at the bottom of the U tube 24.

Each of the units D and B includes a bridge circuit made up of the resistance elements in the two legs of the U tubes and the variable resistances l3 and 33, respectively. The armatures of the differential voltmeter 20 are connected across bridge circuits so as measure changes in potential thereacross resulting from unbalancing of the respective bridges caused by variations in mercury level. When the level of the mercury is the same in both legs of the U tubes, the bridges may be balanced by adjusting the resistances i3 and 33, respectively, so that zero potential is impressed on each armature of the voltmeter.

By providing identical resistance elements in both legs of either U tube, so arranged that a change in mercury level cuts in the same amount of resistance in one element as it cuts out in the other, the total resistance of the bridge circuit remains constant and consequently the current flow therethrough is constant.

Operation of lift gauge The net lift on a ship berthed on a floating drydock is the excess tonnage of water ballast removed from the necessary amount to sink the dock itself to any given draft. As water is pumped out the water depth in a ballast compartment naturally decreases. The rate of such decrease varies with the extent of the plan area of the ballast compartment. The larger the area, the less depth is required to equal a given tonnage. Thus, for the wing wall portion of a ballast dock is fully submerged and the mercury stands at the top of coil or core 30. The entire coil is short circuited or shunted by the mercury, the voltage drop is nil and there is no deflection of the gauge pointer. As ballast water is expelled, the head falls, the pressure falls and mercury meniscus 25a falls proportionally, exposing coil 26 causing a potential drop resulting in a clockwise deflection of the lift gauge pointer tending to indicate tonnage lift. As water ballast is expelled the dock (with its ship) begins to rise. Naturally any rise diminishes the displacement and hence the lift. Unit D therefore comes into play. Draft pressure is admitted to bell l and is impressed upon mercury manometer 4. The resistor coil on core I0 is likewise composed of three segments. The resistance of these segments is proportional to reduction of tonnage lift because of dock rise and also because of added Weight of dock structure as it emerges from the water. (Weight of steel or timber in air is greater than when submerged in sea water.) The same electric power source is applied in similar manner and armature l1 rotates counter-clockwise thus subtracting such decrease of tonnage lift. These operations proceed simultaneously and continuously so that the lift gauge pointer shows the net lift on the ship in long tons as indicated by the pointer and the dial face numbers.

The unit may have more or less than three segments. Three has been selected as merely representative of a typical wing wall dock with curved bottom. A graphic curve drawing recording instrument may be added to this indicating type here described, or the graphic type may be used in place of this indicating type. The system and instrument may also be designed for use on alternating current of various frequencies. In such case cores 9Ill and 2938 may contain interiors of magnetic material in order to increase the voltage drop.

In all cases the indicating or recording instruments may be located at the master control board in the control house, if desired.

These instruments are advanced in that they are rugged and can readily be constructed so that the manometers can be installed in the air ballast chambers, thus receiving pressure directly and thereby avoiding the use of complicated air bubbler pressure transmission. They are also advanced in that the closed circuit two wire transmission from manometer to control board is highly dependable.

While I have shown one more or less specific embodiment of my invention, it is to be understood that this has been done for purposes of illustration only, and that the scope of my invention is not to be limited thereby, but is to be determined from the appended claims.

I claim:

1. In a lift gauge for a floating drydock, a, first manometer having a pair of vertically extending legs, like resistance elements disposed in the respective legs, a body of mercury in said manometer, means for applying a pressure proportionate to the draft of said drydock to the mercury column in one of said legs, means for connecting the upper ends of the respective resistances to the opposite sides of an electric circuit, a second manometer having a pair of vertically extending legs, like resistance elements disposed in the respective legs of said second manometer, a body of mercury in said second manometer, means for applying a pressure proportionate to the head or water in a ballast tank of said drydock to the mercury column in one of the legs of said second manometer, means for connecting the upper ends of the respective resistances in said second manometer to the opposite sides of said electric circuit, and indicator means responsive to the difference in electrical potential between the point of contact of one of the resistances and the mercury surface in said first manometer and the point of contact of the corresponding resistance and the mercury surface in said second manometer, said indicator means being calibrated in units of Weight to thereby directly indicate the net lift of the drydock.

2. In a lift gauge for a floating drydock, a first manometer having a pair of vertically extending legs, like resistance elements disposed in the respective legs, a body of mercury in said manometer, means for applying a pressure proportionate to the draft of said drydock to the mercury column in one of said legs, means for connecting the upper ends of the respective resistances to the opposite sides of an electric circuit, a second manometer havnig a pair of vertically extending legs, like resistance elements disposed in the respective legs of said second manometer, a body of mercury in said second manometer, means for applying a pressure proportionate to the head of water in a ballast tank of said drydock to the mercury column in one of the legs of said second manometer, means for connecting the upper ends of the respective resistances in said second manometer to the opposite sides of said electric circuit, a difierential voltmeter having opposed armature windings, means for connecting one of said windings between the body of mercury in said first manometer and one side of said circuit, means for connecting the other of said windings between the body of mercury in said second manometer and said one side of said circuit, said voltmeter being calibrated in units of weight to thereby directly indicate the net lift of the drydock.

3. In a lift gauge for a floating drydock, a first manometer having a pair of vertically extending legs, a body of mercury in said manometer, means for applying a pressure proportionate to the draft of said drydock to the mercury column in one of said legs, an elongated electric resistance element in said one leg, the resistance of said element per unit of length from the lower end to the upper end thereof varying in direct proportion to the reduction in weight of water displaced by the drydock as the draft of the latter is reduced per linear unit, a like resistance element disposed in inverted position in the other leg, means for connecting the upper ends of the respective resistances to the opposite sides of an electric circuit, a second manometer having a pair of vertically extending legs, a body of mercury in said second manometer, means for applying a pressure proportionate to the head of water in a ballast tank of said drydock to the mercury column in one of the legs of said second manometer, an elongated electric resistance element in said one leg of said second manometer, the resistance of the lastmentioned element per unit of length from the lower end to the upper end thereof varying in direct proportion to the weight of water removed from said ballast tank as the head of water therein is reduced per linear unit, a resistance element like the last-mentioned element disposed in in- 70 verted position in the other leg of said second manometer, means for connecting the upper ends of the respective resistances in said second manometer to the opposite sides of said electric circuit, and indicator means responsive to the difference in electrical potential between the point of contact of one of the resistances and the mercury surface in said first manometer and the point of contact of the corresponding resistance and the mercury surface in said second manometer, said indicator being calibrated in units of Weight to thereby directly indicate the net lift of the drydock.

4. A lift gauge for floating drydocks, consisting of a ballast manometer tube containing mercury and having one arm connected to a ballast pressure bell and an atmospheric arm connected to atmosphere, an electric resistor coil in one arm of the manometer and an identical electric resistor coil in the other arm, the coils being connected in series by the mercury, means for applying a constant voltage to the series circuit, the coils being 50 positioned that as the mercury rises and engulfs the turns of one coil it falls and exposes identical turns of the other coil so that the intensity of the electric current flow through the two resistor coils remains constant regardless of the position of the mercury meniscuses, a draft manometer tube containing mercury and having one arm connected to a draft pressure bell and an atmospheric arm connected to atmosphere, an electric resistor coil in one arm of said second manometer and an identical electric resistor coil in the other arm, the coils being connected in series by the mercury, means for applying said constant voltage to the second series circuit, the coils thereof being 50 positioned that as the mercury rises and engulfs the turns of one coil it falls and exposes identical turns of the other coil so that the intensity of the electric current flow through the two resistor coils in said second manometer remains constant regardless of the position of the mercury meniscuses, and an indicating instrument for measuring the difference in electrical potential between the point of coil contact with the mercury meniscus of the atmospheric arm of the ballast manometer and the point of coil con tact with the mercury meniscus of the atmospheric arm of the draft manometer, said instrument being calibrated in units of weight to thereby directly indicate the net lift of the drydock.

FRANK CHARLES CZARNECKL REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 98,630 Reim Jan. 4, 1870 267,856 Fennerty Nov. 21, 1882 1,120,214 Metzdorfi Dec. 8, 1914 1,131,412 Parks Mar. 9, 1915 1,133,556 Gerdien Mar. 30, 1915 1,172,650 Walton Feb. 22, 1916 1,534,909 Browne Apr. 21, 1925 2,213,485 Conley Sept. 3, 1940 2,342,587 Klemperer Feb. 22, 1944 FOREIGN PATENTS Number Country Date 281,195 Germany Dec. 1'7, 1914 352,597 Germany Apr. 15, 1922 369,610 Germany Mar. 24, 1923

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