IE781247L

IE781247L - Tanker.

Info

Publication number: IE781247L
Application number: IE781247A
Authority: IE
Original assignee: Conway Charles S
Priority date: 1977-06-23
Filing date: 1978-06-21
Publication date: 1978-12-23
Also published as: DE2827716A1; NO146943C; SE7807095L; NO782156L; JPS5433486A; IT7824932A0; NL7806811A; CA1099996A; DK278778A; IT1158861B; PT68205A; GB2000474B; ES471038A1; NO146943B; GR64880B; GB2000474A; IE46940B1; FI781965A7

Abstract

To reduce leakage in the event of hull rupture of a tank vessel for the transportation of liquid cargo having a specific gravity which is less than that of water and which comprises at least one watertight cargo compartment, a water- tight horizontal deck 17 is disposed within the compartment above the load waterline of the tank vessel and at a distance above the hull bottom which is less than or equal to H(Sw/Sc), where H represents the vertical height of the waterline of the vessel above the hull bottom, Sw represents the specific gravity of water, and Sc represents the specific gravity of the liquid cargo. As described, the vessel's cargo space is divided by longitudinal and transverse bulkheads and the horizontal deck 17 into separate upper and lower water- tight liquid-receiving tanks 19, 20 arranged above and below the waterline of the vessel and the upper tanks 19 have a vertical height which is less than that of the lower tanks 20. Details are given of a loading and discharge arrangement for the tanks. <IMAGE> [GB2000474A]

Description

469 40 The present invention relates generally to tanks in a fluid, and in particular to an improved liquid cargo tank construction for tanker vessels.

Tanker vessels for the transportation in bulk 5 of liquid cargo are known in the art. See, for example, U.S. Patent No. 2,918,032. Such tanker vessels generally comprise a plurality of liquid-tight transverse bulkheads and one or more liquid-tight longitudinal bulkheads which subdivide the tanker vessel into a plurality of liquid-10 tight storage compartments. If the bottom or a side of the hull of such a tanker vessel is ruptured by grounding or some other accident, the affected cargo tanks will leak until the "pressure head" of the liquid cargo in each tank, i.e., approximately the portion of the liquid 15 cargo disposed above the waterline of the vessel, flows out of the tanker vessel. Such leakage is a significant potential problem in so-called nSWBT* and "double-bottom" ;4 69 40 ;v. ;tanker vessels, which have greater freeboard than conventional tanker vessels, and, hence, a greater cargo pressure head. ;In recent years, pollution by oil tankers as 5 a result of a hull rupture caused by grounding or other major catastrophe has become of increasing concern. As a result, various anti-pollution tanker constructions have been proposed. One of these is the so-called 10 "double-bottom" tanker design which essentially comprises a tanker vessel having two spaced-apart hull bottoms. The purpose of this design is to prevent leakage from the tanker's cargo tanks if the outer hull bottom is ruptured by, for example, grounding. Such a design may 15 not prevent leakage, however, where major damage is caused by grounding or some other accident since such damage may also cause the inner hull bottom to rupture in addition to Lhe outer one. Moreover, besides the additional expenses involved in manufacturing such a tank-20 er, the space between the Inner and outer hull bottoms is unusable for the transportation and storage of cargo and,, as a result, such a design increases the expenses ;'V ;of operati.i The advantages of the foregoing embodiments of the invention are that the upper cargo tanks can be ful-25 ly utilized for cargo and/or ballast. This feature permits the tank vessel to be smaller in size, and thus less expensive to operate, compared to "double-bottom" or 8 469 40 "SVfflT" tankers. The upper cargo tanks can also be loaded as one tank and the liquid cargo can be discharged through the valve means by gravity to the lower cargo tanks by opening the valve means. Alternatively, 5 any or all of the upper cargo tanks can be utilized for the transportation and storage of multi-grade cargoes since the additional charging and discharging means interconnects the upper cargo tanks. Moreover, since the cargo carried by the vessel has a specific gravity which 10 is less than that of water, the liquid cargo in the lower cargo tanks will have a positive upward pressure when the bulkhead is disposed below the neutral pressure height. Thus, by opening a valve to an upper cargo tank, the liquid cargo is transferred from the lower cargo tank 15 to the upper cargo tank where it can be readily discharged or transferred using either the charging and discharging means or the additional charging and discharging means of the tank vessel. Thus, a tank vessel constructed according to the invention should not require salvage 20 cargo removal assistance, which is a very expensive and time-consuming operation.

Aside from the foregoing, there are numerous other advantages provided by a tank vessel constructed in accordance with the invention. For example, bottom 25 damage repair costs following grounding are greatly reduced compared to vessels with double bottoms. Also, the safety of the vessel is considerably enhanced com 4 ti 9 4 0 pared to other types of ships following major accident or grounding damage in cargo tank areas since the vessel will practically maintain its normal trim and draft when all of the lower cargo tanks are full no matter which 5 cargo tanks are ruptured. As a result, a tank vessel constructed according to the invention is virtually un-sinkable, regardless the extent of the damage to the hull bottom, as long as longitudinal structural integrity of the vessel still exists. A tank vessel constructed ac-10 cording to the invention will also have little or no change in buoyancy after grounding unlike double-bottom tanker vessels which, upon grounding, will lose buoyancy rapidly. Finally, butterworth clewing and gasfreeing of the upper and lower cargo tanks can be carried out 15 simultaneously from the main deck of the vessel much more rapidly than in double-bottom tanker vessels. Typically, one set of upper and lower cargo tanks in a tank vessel constructed according to the invention will require about three to five hours for butterworth cleaning and 20 gasfreeing, whereas the same amount of deeming would require one day or more for one set of tanks in a double-bottom tanker vessel.

It should be noted that a tank vessel according to the invention may have various configurations and may 25 comprise, for example, an oil tanker, a barge, or an oil storage tank disposed in water in offshore drilling areas. If the vessel is a tanker, it should be noted that cer 469 40 tain of the upper cargo tanks may also be used as dry cargo, or storage holds, in which case hatch coamings and covers, or access trunks would be installed.

Examples of the invention will now be 5 described with reference to the accompanying drawings in which: Figure 1 is a partial, longitudinal, cross-sectional profile view of one embodiment of an improved liquid cargo tank construction for a tanker vessel con-10 structed according to the present invention; Figure 2 is a transverse cross-sectional view of the liquid cargo tank construction taken along section 2-2 of Figure 1; Figure 3 is another transverse cross-sectional 15 view of the liquid cargo tank construction illustrating side and bottom hull ruptures caused by grounding and/or hull side damage; Figure 4 is a top plan view of another embodiment of an improved liquid cargo tank construction lor 20 a tanker vessel constructed according to the present invention showing the additional charging and discharging means for the upper cargo tanks of the vessel; and Figure 5 is another partial, enlarged cross-sectional profile view of the liquid cargo tank con-25 struction illustrated in Figure 4 showing the additional charging and discharging means within an upper cargo tank.

Referring now to the drawings, in particular to 11 469 40 Figures 1 and 2, there is shown a tanker vessel, generally identified by reference numeral 10, which includes a hull comprising a bottom 11 and sides 12. The vessel includes a top deck 13 and a plurality of longitudinal 5 and transverse bulkheads 14 and 15 respectively which are disposed within the hull of the vessel and form a plurality of watertight cargo compartments 16 between top deck 13 and hull bottom 11 of the vessel. Watertight horizontal bulkhead 17 is disposed within the hull between top 10 deck 13 and hull bottom 11 above the waterline 18 of the vessel and forms separate upper watertight cargo tanks 19 and lower watertight cargo tanks 20 within at least one of the cargo compartments, and in the illustrated embodiment of the invention in a plurality of the cargo 15 compartments 16, above and below waterline 18 of vessel 10, so that the upper tanks have a vertical height which is less them that of the lower tanks. It should be noted that the horizontal bulkhead may form one upper cargo tank or a plurality of upper cargo temks in the forward, 20 aft, center or side sections of the tanker vessel, as desired, and that the vessel may include only a transverse bulkhead or may have one or more longitudinal bulkheads and transverse bulkheads forming the cargo compartments. 25 The horizontal bulkhead 17 is located above the waterline of the vessel, as previously stated, and also at a vertical distance h above the hull bottom of the 12 469 40 vessel which is less than or equal to the neutral pressure height in the cargo compartments, which is also located above the vessel waterline. The latter height is the maximum vertical height at which the cargo carried 5 by the vessel will be supported by the water in which the vessel is disposed and is given by the equation U(SW/SC), where H represents the vertical height of the waterline of the vessel above the hull bottom, i.e., the vessel draught, Sw represents the specific gravity of water, 10 and S represents the specific gravity of the cargo car-c riedby the vessel. With respect to the waterline of the vessel, the bulkhead is located at a vertical distance above the waterline which is less than or equal to Sc -1). The bulkhead is preferably located below, speci-15 fically approximately one foot below the neutral pressure height to allow for variations in the specific gravities of the cargo and the water due to changes in temperature, and vessel trim, which could cause a positive, i.e., downward, pressure to exist in the lower cargo tanks and 20 thereby permit cargo to leak from the vessel in the event of a hull rupture when the bulkhead is located at the neutral pressure location in the cargo compartments.

Thus, the preferred bulkhead height h above the hull bottom of the vessel is given by the equation h «= 25 H(S /S )-l, where H represents the vertical height in w c feet of the waterline of the vessel above the vessel hull bottom, and h represents the vertical height in 13 46 9 40 feet of the bulkhead above the hull bottom.

It should be noted that the term waterline as used herein refers to the load line of the vessel which is required to be used during its operation, for example, 5 the vessel's summer draught, and that as known to those persons skilled in the art, the location of the water-line may vary slightly with respect to its height above the vessel's hull bottom according to the load line utilized. 10 For example, assuming that the vessel waterline used for determining maximum loading of the vessel is located 45 ft. above the hull bottom of the vessel and that the specific gravity of the water in which the vessel is disposed is 1.0269 (which is the specific gravity 15 of sea water), the horizontal bulkhead is preferably located at a vertical height of 45.2753 ft. above the hull bottom (or 0.2753 ft. above the waterline) when Boscan heavy crude oil (specific gravity 0.9986} is carried by the vessel, 46.8419 ft. above the vessel hull bottom 20 (1.8419 ft. above the waterline) when heavy fuel oil (specific gravity 0.9659) is carried by the vessel, and 51.7396 ft. above the hull bottom (6.7396 ft. above the waterline) when diesel fuel (specific gravity 0.8762) is carried by the vessel. 25 Figure 3 illustrates the operation of the li quid cargo tanks of the invention upon the occurrence of (a) minor grounding damage to hull bottom 11, illu- 14 46940 strated by rupture 21 in hull bottom 11, (b) heavy grounding damage to the hull bottom, illustrated by rupture 22, and (c) side hull rupture 23 resulting from docking, barge, tug or similar damage. In the case of 5 rupture 21, a negligible amount of cargo, illustrated by the shaded area 24, is lost since the horizontal bulkhead 17 isolates and contains the fluid pressure head of the liquid cargo in upper cargo tank 19 above lower cargo tank 20 affected by the rupture. Since the liquid 10 cargo in the cargo compartment has a specific gravity which is less than that of water, outflow of the pressure head of the liquid cargo in the affected cargo compartment is prevented. In the case of rupture 22, again only the liquid cargo illustrated by shaded area 25 in 15 Figure 3 is lost due to the lesser specific gravity of the liquid cargo compared to that of the water. In the case of side hull rupture 23, a larger amount of liquid cargo, illustrated by shaded area 26, is lost, namely, that portion of the cargo which extends up to the height 20 of the rupture in the hull. However, due to the containment of the pressure head by horizontal bulkhead 17 in the affected cargo compartment by the upper cargo tank 19, leakage of the liquid cargo from the lower cargo tank is relatively slow. This may permit some of the liquid car-25 go to be transferred from the affected lower cargo tank to another cargo tank of the vessel. Such a cargo transfer is achieved as a result of the negative pressure 15 4 69 4 0 created in lower cargo tanks 20 by the location of the horizontal bulkhead.

Figures 4 and 5 illustrate another embodiment of a liquid cargo tank constructed according to the in-5 vention. In this embodiment of the invention, valves 27 are disposed in sumps 28 provided in each of the upper cargo tanks 19 of the tanker vessel. The sumps collect liquid cargo in the upper cargo tanks and the valves, which are disposed between and couple each of the 10 upper and lower cargo tanks in the vessel, permit transfer of the liquid cargo from upper tanks 19 to lower tanks 20 and vice-versa. The tanker vessel also includes an additional liquid cargo charging and discharging system for charging and discharging the upper cargo tanks 15 which is redundant and is provided in addition to the main liquid cargo charging and discharging system (not shown) coupled to the upper and lower cargo tcinks of the tanker vessel. The additional charging and discharging means includes suction means, which may comprise a rootor-20 driven pump 29, such as a centrifugal pump or a rotary pump which is suitable for use with the tanker vessel's emergency diesel generator output, coupled to a first pipe 30 extending longitudinally within the upper cargo tanks 19 and a plurality of transversely-disposed second 25 pipes 33. coupled to pipe 30 which interconnect the! upper cargo tanks. A discharge outlet 33 is coupled to the pump and a charging inlet 34 is coupled to pipe 30 for 16 4 0940 loading and unloading the upper cargo tanks. The additional charging and discharging means may, as previously mentioned, be used for cargo salvage, for charging and discharging multi-grade cargoes, and for the transfer of 5 liquid cargo from one of the upper cargo tanks to another of the tanks, either upper or lower, in the vessel. Both the valves 27 and the second pipes 31 of the additional liquid cargo charging and discharging system are controlled by hand wheels 32 which extend vertically upwardly 10 above the top deck 13 of the vessel. The valves and the hand wheels are located at the aft end of the upper cargo tank. 17 460 40

Claims

1. A vessel disposed in water and carrying a liquid having a specific gravity which is less than that of water, said vessel comprising a bottom, sides and a top forming at least one watertight compartment 5 between said top and said bottom for carrying said liquid, and a watertight horizontal bulkhead disposed within said vessel between said top and said bottom at a distance above the waterline of said vessel which is approximately equal to -1) where H represents the «>c vertical height of the waterline of the vessel above said bottom, 10 Sw represents the specific gravity of water, and Sc represents the specific gravity of said liquid, said horizontal bulkhead forming separate upper and lower watertight tanks within said compartment above and below said waterline of said vessel, said upper one of said tanks having a vertical height which is less than 15 that of said lower one of said tanks.

2. A vessel as claimed in claim 1, wherein said horizontal bulkhead is disposed within said vessel at a distance above the waterline of said vessel of about H(*^-l)-], where H represents the sc vertical height in feet of the waterline of said vessel above said 20 bottom, Sw represents the specific gravity of water, and Sc represents the specific gravity of said liquid.

3. A tank vessel carrying liquid cargo having a specific gravity which is less than that of water, said vessel including a hull comprising a bottom and sides, a top deck, at least one transverse 25 bulkhead disposed within said hull forming a plurality of watertight cargo compartments between said top deck and said hull bottom, and a watertight horizontal bulkhead disposed within said hull between said top deck and said hull bottom at a distance above the waterline of 18 46940 said vessel which is approximately equal to —1), where Sc H represents the vertical height of the waterline of the vessel above said hull bottom, Sw represents the specific gravity of water, and Sc represents the specific gravity of said liquid cargo, said horizontal 5 bulkhead forming separate upper and lower watertight cargo tanks within at least one of said cargo compartments above and below said waterline of said vessel, said upper tanks having a vertical height which is less than that of said lower tanks.

4. A vessel as claimed in claim 2, wherein said horizontal bulkhead 10 is disposed within said vessel at a distance above the waterline of said c vessel of about H(-^--l) —1, where H represents the vertical height in feet of the waterline of said vessel above said hull bottom,

5. Sw represents the specific gravity of water, and Sc represents the specific gravity of said liquid cargo. 15 5. A vessel as claimed in either claim 3 or claim 4, further comprising valve means disposed between and coupling said upper and lower cargo tanks for permitting transfer of said liquid cargo from said upper tank to said lower tank and from said lower tank to said upper tank. 20

6. A vessel as claimed in claim 5, wherein said tanker vessel includes a plurality of longitudinal and transverse bulkheads disposed within said hull, wherein said horizontal bulkhead forms separate upper and lower watertight cargo tanks in a plurality of said cargo compartments, and wherein said vessel includes main liquid cargo charging and discharging 25 means coupled to said upper and lower cargo tanks for charging and 19 4 694 0 discharging said upper and lower cargo tanks and additional liquid cargo charging and discharging means coupled to said upper cargo tanks for charging and discharging said upper cargo tanks.

7. A vessel as claimed in claim 6, wherein each of said upper cargo tanks further comprises sump means for collecting liquid cargo in said upper cargo tanks, said valve means in each of said upper cargo tanks being disposed in said sump means.

8. A vessel as claimed in claim 6, wherein said additional charging and discharging means includes suction means for removing said liquid cargo from said upper cargo tanks.

9. A vessel as claimed in claim 8, wherein said suction means comprises motor-driven pump means.

10. A vessel as claimed in claim 8, wherein said additional charging and discharging means comprises first pipe means coupled to said suction means, and second pipe means coupled to said first pipe means and said upper cargo tanks, said first and second pipe means interconnecting said upper cargo tanks.

11. A liquid cargo tank vessel substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 3 or Figures 4 and 5 of the accompanying drawings. Dated this 21st day of June 1978, (signed) DUBLIN 6 20