US3334608A

US3334608A - Method and apparatus for establishing draft and trim of a vessel

Info

Publication number: US3334608A
Application number: US542516A
Authority: US
Inventors: Nemoto Hirotaro; Shibata Kiyoshi
Original assignee: Ishikawajima Harima Heavy Industries Co Ltd
Current assignee: IHI Corp
Priority date: 1963-03-16
Filing date: 1966-04-14
Publication date: 1967-08-08
Anticipated expiration: 1984-08-08
Also published as: SE342791B; GB1029725A; NL6402719A

Description

g- 1957 HARDTARO NEMOTO ETAL METHOD AND APPAFATUS FOR ESTABLISHING DRAFT AND TRIM OF A VESSEL 3 Sheets-Sheet 1 Filed April 14, 1966 INVENT RS MPO 777/90 Ma 7'0 k7 yosw/ SW54 7% ATTORNEYS g- 3,1957 HmoTARo NEMOTO ETAL 3,334,608

METHOD AND APPARATUS FOR ESTABLISHING DRAFT AND TRIM OF A VESSEL Filed April 14, 1966 5 Sheets-Sheet 2 ATTORNEYS Aug. 8, 196 HARQTARO NEMOTO Ema. 3,334,608

METHOD AND APPARATUS FOR ESTABLISHING DRAFT AND TRIM OF A VESSEL Filed April 14, 1966 3 Sheets-Sheet 5 D N K LO (D I g $2 LI. 5 a.

INVENTORS H IROTARO NE MOTO KIYOSHI SHIBATA m m M BY 24 ii ATTORNEYS United States Patent 3,334,608 METHOD AND APPARATUS FOR ESTABLISHING DRAFT AND TRIM (IF A VESSEL Hirotaro Nemoto, Tokyo-to, and Kiyoshi Shibata, Solrashi, Japan, assignors to Ishikawajima-I-Iarima llukogyo Kabushiki liaisha, Chiyoda-ku, Tokyo-t0, Japan, a company of Japan Filed Apr. 14, 1966, Ser. No. 542,516 Claims priority, application .lapan, Mar. 16, 1963, 38/1 3,377 9 Claims. (Cl. 114-74) This application is a continuation-in-part of our application Ser. No. 351,940, filed Mar. 16, 1964, and now abandoned.

This invention relates to a method and an apparatus for attaining and maintaining the values of draft and trim of a ship hull at a predetermined Value, and in particular to a method and apparatus in which the values of the draft and trim of the ship hulls are automatically calculated and controlled.

Merchant ships are provided with a warning mark on the central portion which should stand above the water line. Further loading beyond this limit is forbidden by international law. Therefore, when the central portion of draft reaches this mark during the loading, the loading operation must be stopped regardless of the condition of trim. Even in this case the predetermined trim may be realized if oil is removed from one place to another within the vessel, but this method is not recommended. Especially when the loading operation is fully automated, failure to arrange a good order for loading operation may result in failure to realize the predetermined trim, making it impossible for the ship to leave port.

In commercial shipping, such as oil tankers, the draft and the trim of a ships hull are determined by the loading of the ship. In such ships, it is known to load certain portions of the ships hull with water ballast to establish a setting of draft and trim in the ballast condition. As the tanks of a ship are gradually loaded with the water ballast, the ship both tends to increase draft or sinks, or to slant. The change in the state of a ship may be considered in two stages under the assumption that the angle of inclination remains relatively small in magnitude. In the first stage the ship sinks vertically in proportion to the magnitude of the loading, and in the second stage the ship is slanted while maintaining a constant displacement. In the loading the tanks on a ship, in which the major portion of the hull area is composed of loading tanks, such as in a tanker, the final displacement of the ship does not guarantee the desired level of draft and trim, the trim being the difference between the draft in the fore perependicular of the ship and the draft in the aft perpendicular of the ship. If the loading is continued in the second state of sinking in an effort to correct the value of the trim, the displacement of the ship will increase and the ship will sink beyond a required level of draft of displacement.

One method of solving this problem would to move the liquid from the aft tanks to the fore tanks, or from the fore tanks to the aft tanks. This method however has obvious disadvantages in accuracy and complexity and in the time required for the performance of this operation. In order to overcome this problem, two alternative methods have been devised, the first being that the fore and aft tanks are alternately loaded, and the second involving the simultaneous loading of the fore and aft tanks, in which the loading operation for one part is stopped and the ship is sunk to the predetermined position, while the remaining liquid is poured into the tanks in the other part, until the ship sinks precisely to the desired draft. In this operation the loading of tanks with the water ballast is not resumed once the initial loading has been completed.

3,334,608 Patented Aug. 8, 1967 Loading is conventionally conducted by the ships crew by a proper combination of the above mentioned methods. However, the performance of this operation requires as crew having experience and skill which would not always be the case in commercial shipping.

It is therefore an object of this invention to provide a method and apparatus by which the desired level of draft and trim can be attained.

It is a further object of the present invention to provide a method and apparatus for automatically loading the ship in a manner to achieve the predetermined level of draft and trim.

It is a further object of the present invention to provide a method and apparatus for maintaining the predetermined level of draft and trim of an ocean going vessel, once this level has been attained by the loading of the vessel.

In accordance with the above objects, the present invention provides for separate tanks displaced along the hull of the ship which control the trimming of the vessel by letting liquid into or out of the tanks. When either of the centers of rotation, fore and aft, reaches the predetermined level, which is automatically computed on the basis of either of the drafts at stern, or the draft in the midship and the trim, the charge or discharge of the fluids to the corresponding tanks is suspended.

The same procedure is effected in the other tank when it has reached the predetermined level.

Further objects and features of the present invention are detailed with greater particularity in the specification and drawings in which:

FIG. 1 is a schematic view in side elevation of the interior of an oil tanker illustrating features of the present invention; I

FIG. 2 is a top plan view of the vessel shown in FIG. 1, showing in schematic form the various piping arrangements by which liquid is passed between the two tanks;

FIG. 3 is a schematic view of a vessel showing the various design points which are used in the analysis of the inventive method and apparatus;

FIG. 4 is a schematic of the fore portion of a vessel showing one type of remote draft indicator;

FIG. 5 is a schematic cross-section of a vessel showmg another example of remote draft indicator; and

FIG. 6 is a block diagram of the apparatus of the present invention.

In the drawings in which like numeral represent like elements, there is shown an oil tanker having a hull 1 in which are disposed liquid tanks 2, 3 and 21 each of which 1s supplied with liquid from a main pipeline 4 by means of pipes branching from the main pipeline. The branchmg pipes in each tank are equipped with a bell mouth 22 and valves 6, 7 and 23. Main pipeline 4 is generally led to the upper deck through a a pump room 24 aft the cargo tanks. In a preferred embodiment of the present invention, as incorporated in an oil tanker, tanks 2 and 3 are spaced apart from each otherin the fore and aft sections of the vessel. Tanks 2 and 3 may be used as the two tanks for controlling the trim and draft. In loading the craft, arbitrarily selected cargo tanks 21, between the tanks 2 and 3, are first loaded. However, towards the end of the loading operation, when it becomes necessary to control the trim and draft of the vessel, only tanks 2 and 3 are loaded, and not any of the others at that time.

The principles of operation of the present invention will now be described with reference to the showing of FIG. 3. Assuming that fore tank 2 is loaded with a quan- 0 tity W of sea water ballast while hull 1 is afloat at the water line 8, in even keel condition, the hull 1 may then he considered as sinking in a first stage, in parallel posithe bow, and at the pump 5 which is placed in tion, from the water level 8 to the water level 10 to displace a volume of sea water equal to the volume of sea water added to its ballast tank 2; and, in a second stage, as rotating about the point 12 until it assumes the indicated position with respect to the water level 9. In the ensuing theoretical discussion, the following designations which are conventional in the art of ship design will be employed:

TPC is the weight required to sink the hull parallel to the base line by one unit of draft; MTC is the value of moment required to initiate a unit trim to the hull at the water line;

I is the horizontal distance from the point of intersection 12 to the center of gravity of the sea water ballast W (which is negative if the center of gravity is forward of the intersection 12 and positive if it is aft of intersection 12);

H is the vertical distance between the water line 8 and 10, that is the depth which the hull has sunk, and t is the value of the trim, i.e. the difference between the fore draft and the aft draft expressed in units of length. Therefore, we have:

1 W ZW TPC and MTC Intersection 12 is referred to as the center of floatation at the water line 10 and can be assumed to be invariable when the angle of inclination is small. Referring to the diagram of FIG. 3 once again, the triangles defined by

points

16, 17 and 18, and by

points

11, 12 and 15 are similar triangles, so that the horizontal distance between the intersections 11 and 12 may be expressed by:

where L is the length between perpendiculars which is an idiomatic phrase used in naval architecture meaning the distance between aft perpendicular and fore perpendicular, and often referred to as the length of the ship. This distance is shown as a horizontal distance [0 between the

points

16 and 18 in FIG. 3. Substituting the expressions for H and T from Equation 1, in Equation 2, we obtain (3) L- I 1 W/TPC' L-MTC Accordingly, the horizontal distance 10 between intersections 11 and 12 is independent of W, and since the intersection 12 is invariable at the water line 10 as shown above, intersection 11 is invariable regardless of the value of W. It is to be noted, however, that intersection 11 moves to some extent in response to the water line since MTC, TPC and I all change with the position of the water me. 1 In a similar manner, another intersection point could be found in a similar manner which would correspond to a situation in which the ballast is charged in the aft tank 3. This point is not shown in the figures but can easily be calculated in the manner discussed above. From FIG. 3 we arrive at the equation (4) dA=d+ r in which la is the horizontal distance between points 11 and 32; d is the vertical distance between

points

31 and 20;

L is the horizontal distance between

points

16 and 18;

t is the vertical distance between

points

17 and 18; and dA is the vertical distance between points 11 and 19.

Since t is negative in the case of trim by the how, the right side of this equation shows the difference of vertical distance between

points

31 and 32. In a similar manner we obtain the expression lb dB-d-i-t dB corresponds to the above-mentioned dA when the condition of trim by the stern is in existence with the aft tank loaded with sea water.

lb corresponds to la when the above condition is in existence.

The liquid supply to the tank will cause a change in the slanting of the ship floating on the water. Even in case there is no slanting, the ship will sink by the weight of the liquid supplied.

The change of position of the ship may occur in the following ways:

(a) The ship sinks vertically according to the amount of loading;

(b) The ship is trimmed without changing its displacement.

In FIG. 3, the water line 10 shows the condition involved in (a), and water line 9 shows the condition involved in (b).

Thus by calculating beforehand the values of Za/L and lb/L at various levels of the draft, and setting these with the respective level of the predetermined draft at the center of the hull in its final state, one can estimate, given the predetermined values of the draft d and the trim t in the final state, the values of the draft dA and dB at the points of intersection 11 and the point of intersection when the ballast is charged in the aft tank 3. This second point is not shown in the drawings for the sake of clarity. Therefore, by determining the value of draft and trim, or by taking the difference between the values of the fore draft and the aft draft at every moment, and transmitting these values to the control room through suitable conducting media, such as electricity or hydraulic pressure, the values of dB and dA may be calculated from these values at each moment by means of the above equations.

FIG. 4 illustrates one embodiment of an aero-type remote draft indicator. A pipe 16), in which lower end 46 terminates at the bottom of the hull 1, is open to the water. Another air pipe 41, which is open at the lower end thereof, is installed within opening 46. Compressed air is passed first through a flow controller 42 and is forced out by a nozzle 43 at the lower end 46 of the pipe 41. The compressed air, which exhausts from nozzle 43, is collected in pipe 40, with the result that the equivalent volume of sea water in the pipe 441 is in turn forced out through lower end 46. The upper end of pipe 40 is closed, and a pipe 44 of relatively smaller diameter extends laterally from the upper end of pipe 40, to a manometer 45 located in the control room. As air is spurted into the lower end of pipe 40, the sea water in pipe 40 is replaced by the air, and the surplus spurted air is released into the sea through the end 46 of pipe 40. Consequently, the air pressure that is equivalent to the water pressure of the corresponding depth is indicated by manometer 45. It is of course an easy expedient to read the value of the draft in electrical signals by installing a pressureelectricity transformer in place of manometer 45.

FIG. 5 shows another example of a remote draft indicator. A pipe 51 is installed through the outer side of hull 1 and extends from the bottom to the top of the hull as shown. The lower end of pipe 51 is open to the sea near the bottom of hull 1, while the upper part of pipe 51 is equipped with a sound transducer 52 which is constructed to transmit a downwardly directed sound wave, and also receives the reflected sound waves. A transmitter 53, housed in the controll room is electrically connected to transducer 52. As pipe 51 has an opening 55 for the escape of air at the upper part thereof, sea water easily occupies pipe 51 to the level of the sea water outside when the ship is afloat. Transducer 52 which receives the signals from transmitter 53, transmits the sound waves downwardly at preselected intervals of time. A portion of the transmitted signal waves are reflected by the surface of the water in the pipe at level 54 and are reflected to transducer 52 having a corresponding time lag. Transducer 52 receives the reflected sound Waves and transmits these waves to a receiver housed in the control room. By the measurement of the time lag between the transmitted and received signals, the level 54 of the surface of the water then prevailing in the pipe can be determined. This time lag may be directly read out by suitable means which are well known in the art, and which are therefore not further described herein.

The remote draft indicators shown in the embodiments of FIGS. 4 and 5, are only two examples of many possible embodiments of draft indicators. In practice, the methods for transmitting the remote draft data may be found in the combination of these shown or in the use of hydraulic pulse, etc. In the present invention any one of these methods may be applied, as shown in FIG. 6. Placing remote draft indicators, such as 61 and 62, in the fore and aft sections of the vessel provide indications of the respective drafts from which the trim may be easily calculated. Furthermore, as the value of d may be obtained from another draft indicator set up at the midship dA and dB may be calculated from these values through the above equations. These calculations may be made either by trained personnel, or when the indications are converted into electrical signals, electronic, electrical or other computer devices, such as a draft and trim calculator 63, placed in the control room, may carry out the necessary calculations to arrive at the values of dA and JB which may determine the values of draft inputs received from the remote draft indicating devices. As these computing mechanisms are also well known to the art, they need not be further discussed herein.

Once the value of dA has reached the value of dAo, which is the desired value of corresponding draft and trim in the final state of loading, a comparator circuit 64 in the computer which compares the calculated values of dA and dB against the predetermined values from a draft and trim reference source 65 produces an electrical signal when these signals are equal, which operates to close the valve 7 at the mouth of the aft tank 3, via a valve 7 control unit 66 and leads 67 and 68, preventing further loading of tank 3. In the same manner, the computer will produce a signal to stop the loading of fore tank 2, by closing the valve 6 of the mouth of tank 2, via a valve 6 control unit 69, the lead 67 and a lead 70, when the calculated value of dB has reached the predetermined value dBo, that is, when the draft at the position at the second intersection point of the center of rotation of the aft tank has reached the value dBo. In the case in which dB has reached dBo prior to dA reaching the value dAo, valve 6 will be closed first, and then valve 7, once the value of dAo has been reached. In the case in which a ship such as a tanker is being loaded, the draft d at the mid-ship part will first reach its predetermined value do. In this case the loading will be stopped when d has reached do regardless of the values of the drafts dA and dB.

In the unloading operation the operation described above will be performed in the reverse order. In the loading of cargo oil, similar effect can be obtained by using the cargo oil instead of sea Water as ballast. It is also within the scope of this invention that the inventive method is applicable to the loading and unloading of water ballast to the tanks of ships in general, including bulk carriers, as well as in the above mentioned reference for use on oil tankers.

As has been described in this application, the present invention provides a method and apparatus for attaining a predetermined value of draft and trim in the final state of ship loading by making use of an automatic calculation of parameters, which is efiicient in application in loading operations and the like.

While we have shown our invention in preferred embodiments thereof, it is our desire to define the scope of our invention by the claims which are appended below.

What is claimed is:

l. A method for establishing and maintaining the draft and trim of a vessel, comprising the: steps of varying an amount of liquid in each of at least two tanks disposed separately in the hull of said vessel, simultaneously establishing the level of liquid in each of said tanks, comparing the instantaneous values of midship draft and trim against predetermined values thereof, controlling the flow of liquid into said tanks to maintain the amount of liquid in each of said tanks when the established value of draft and trim corresponds to the predetermined value thereof.

2. A method as claimed in claim 1, wherein the step of establishing the liquid level comprises discharging liquid from said tanks.

3. A method as claimed in claim 1, wherein the step of establishing the liquid level comprises charging liquid into said tanks.

4. Apparatus for establishing draft and trim in a vessel having at least two tanks separately disposed in the hull of said vessel, comprising measuring means for measuring the values of draft and trim of the vessel, valve means controlling the flow of liquid to and from each of said tanks, reference means for providing predetermined values of draft and trim, comparator means connected to said measuring means and to said reference means for comparing the measured values of draft and trim with the predetermined values thereof, and control means connected between said comparator means and said valve means for controlling said valve means when the measured values of draft and trim correspond to the predetermined values thereof.

5. Apparatus as claimed in claim 4, wherein said measuring means comprises pressure sensitive means.

6. Apparatus as claimed in claim 4, wherein said measuring means comprises means for producing an electrical signal proportional to the measured value of midship draft and trim.

7. Apparatus as claimed in claim 4, wherein said measuring means transmits a first electrical signal to said comparator means and said reference means transmits a second electrical signal to said comparator means and said comparator means receives said first electrical signal produced by said measuring means and said second electrical signal proportional to the predetermined value of the midship draft and trim and produces a third signal when the magnitudes of said first and second signals are substantially equal to each other.

8. Apparatus as claimed in claim 7', wherein said comparator means transmits a signal to said control means upon the substantial equivalence of said first and second signals.

9. Apparatus as claimed in claim 8, wherein said valve means is closed thereby maintaining the amount of liquid in said tank when said comparator means produces said third signal.

References Cited UNITED STATES PATENTS 24,751,921 '6/1956 Baldwin et al 73-65 X 3,128,375 4/1964 Grimncs 7365 X MILTON BUCHLER, Primary Examiner. T. M. BLIX, Assistant Examiner.

Claims

1. A METHOD FOR ESTABLISHING AND MAINTAINING THE DRAFT AND TRIM OF A VESSEL, COMPRISING THE STEPS OF VARYING AN AMOUNT OF LIQUID IN EACH OF AT LEAST TWO TANKS DISPOSED SEPARATELY IN THE HULL OF SAID VESSEL, SIMULTANEOUSLY ESTABLISHING THE LEVEL OF LIQUID IN EACH OF SAID TANKS, COMPARING THE INSTANTANEOUS VALUES OF MIDSHIP DRAFT AND TRIM AGAINST PREDETERMINED VALUES THEREOF, CONTROLLING THE