US3369515A - Submersible barge - Google Patents

Description

Feb. 20, 1968 MICHIMASA ENDO SUBMERS IBLE BARGE 2 Sheets-Sheet 1 Filed May 20, 1966 \m J h & mm

MM QQ l Q 6 QmTQ mm mm 63 CQ INVENTOR- M/CHIMASA ENDO BY M" A 7702MB) MICHIMASA ENDO Feb. 20, 1968 SUBMERSIBLE BARGE Filed May 20, 1966 2 Sheets-Sheet 2 I NVENTOR. MICHIMASA ENDO A TTO QA/EY 3,369,5l Patented Feb. 2t], 1958 3,369,515 SUBMERIBLE BARGE Michimasa Endo, Nishinomiya-shi, Suma-ku, Kobe-sin, Japan, assignor to Continental Oil Company, Ponca City, Okla, a corporation of Delaware Filed May 20, 1966, Ser. No. 551,779 Claims priority, application Japan, Jan. 31, 1966, 41/ 5,476 4 Claims. (Cl. 114-74) ABSTRACT OF THE DISCLOSURE Apparatus for effecting underwater transportation of liquid cargo which provides relief as to variations in cargo volume while underway, the apparatus consisting of a submersible barge partitioned into balanced cargo spaces each having a system of expansion and collection tanks which provide an intermediate space between the cargo tank interiors and the barge exterior in which cargo overflow or shortage resulting from volumetric expansion or contraction can be changeably retained.

This invention relates generally, as indicated, to a submersible barge; and more particularly, but not by way of limitation, to particular cargo hold spaces on board a submersible tow vessel for use in transporting crude oil.

The prior art reveals a few instances of teachings to the general concept of submarine towage but, prior to this invention, the problems attendant the cargo hold spaces, such as problems of access and stable storage, have not been dealt with.

It was found that transport by submersible barge could be desirable for moving large quantities of crude oil, especially if the same transport route is run at regular intervals. The submerged tow encounters much less resistance during its use than would any of the known types of surface transport barges. The first advantage is that the submerged barge encounters no sea resistance from surface turbulence, e.g., waves, wind, etc. This detriment can be very great and tends to reduce greatly the maximum tow-speed which can be achieved with surface hauling equipment. The surface barge can be towed at only a few knots, if given good sea conditions, while the submerged barge, as presented herein, can be hauled at speeds up to around sixteen knots. Further, even with this difference in tow speed, the towing force required of the hauling ship is still considerably less in the case of the submerged tow than it would be with a dredge-type barge of comparable size. Thus, the present invention enables a faster tow with less towing force.

The submerged barge concept is also attractive from the cost viewpoint, both in manpower and in maintenance. The submersible vessel of this invention is designed so that no manpower is required at any time during the voyage or when left to await loading or unloading. Also, the vessel enables savings in docking fees since it requires no port facilities while tied up or anchored out. In one planned usage, the unmanned, submersible barge can be fully loaded with cargo and then hauled at standard speed by a fully loaded tanker or cargo ship, as opposed to a sea going tug, to a first port of call. The barge can then be dropped off at the first port and the tanker or cargo ship can proceed to another destination with its remaining cargo.

The operation of a submersible barge for transporting liquid cargo requires special consideration as to the cargo hold spaces. It is necessary that the cargo be maintained as constant as possible both in weight and distribution relative to the center of gravity of the barge. Very little cargo shifting can be tolerated in the stabilized vessel.

Access to the cargo spaces is another important consideration since the partially submerged vessel must be serviced for loading and unloading of the cargo. With access space limited, especial importance attaches to the manner in which the loading is to be efiiciently carried out. Further, in submarine transport, the behavior of the cargo itself is a consideration. The barge may travel through water of varying temperatures which can change the temperature ofthe cargo and thus its volume in accordance with the expansion and contraction characteristics of the particular cargo. Suitable pressure alleviation equipment is necessary in order to maintain the barge stable while under tow.

The present invention contemplates a submersible tow vessel containing cargo holds which are self-regulating as to maintaining their capacity volume through changes in cargo temperature, and which are constructed to provide maximum efliciency in the loading and off-loading phases of operation. In a more limited aspect, this invention contemplates a submersible hull member, having necessary ballast and trim tanks, which is compartmented in-to pressure-resistant cargo space of predetermined volume and nonpressure-resistant cargo space of predetermined volume; and wherein, the nonpressure-resistant cargo hold spaces are adapted to be filled to capacity, and they are further provided with a system of expansion and collec tion tanks which (i) maintain the capacity cargo volume while underway and (ii) serve to direct and regulate the cargo flow and sea water replacement during loading and off-loading of the liquid cargo.

It is an object of the present invention to provide a submersible barge for carrying a capacity volume of liquid cargo.

It is a further object of the invention to provide liquid cargo spaces which maintain capacity volume despite changes in the cargo temperature.

It is another object of the invention to provide a liquid cargo space for a submersible tow vessel which contains its capacity volume while alleviating pressure gradients arising between the inside and the outside of the cargo space walls.

It is still another object of the present invention to provide compartments within each cargo space which occupy a predetermined volume of the cargo space and which serve both to alleviate expansion and contraction of the cargo and to aid in the loading and off-loading of cargo.

Finally, it is an object of this invention to provide a submersible barge capable of fast, low cost crude oil transportation which allows quick and efficient cargo handling during all phases of operation.

Other objects and advantages of the invention will be evident from the following detailed description when read in conjunction with the accompanying drawings which illustrate the invention.

In the drawings:

FIG. 1 is a schematic side view of the preferred form of the barge in vertical section;

FIG. 2 is a section taken along line 22 of FIG. 1;

FIG. 3 is a section taken along line 33 of FIG. 1;

FIG. 4 is a section taken along line 44 of FIG. 1;

FIG. 5 is a section taken along line 5-5 of FIG. 1; and

FIG. 6 is a top plan view of the preferred form of the submersible barge.

General The invention of this disclosure has, in one instance, been specifically designed for use in transporting crude oil in the Mediterranean Sea; however, it should be under stood that the design parameters may be varied for any particular usage and/or area. The submersible barge, as described herein, has a principal function of transporting crude oil from a source port to a refinery and then the barge is returned to the source port to refill and repeat the run.

There are many obstacles to be overcome in construct ing a submersible barge which can be reliably towed with acceptable efficiency. Heretofore, the theoretical designs which have been recorded were very basic disclosures having neither the awareness of the problems to be encountered nor the scope of experimental findings which would enablea solution to the various problems. The design as set forth in this disclosure isthe result of wind tunnel and sea tests which have provided the empirical data and hardware knowledge which allow construction of a highly efficient transport vessel that is capable of moving cargo via the water subsurface at greatly increased speeds.

The submersible barge as disclosed herein has been designed with a specific shape and weight such that the best and most stable operating characteristics are achieved. The craft is balanced and baliasted so that it will have a known function of movement and it will travel in an equilibrium condition when under tow. That is, that given the proper amount of cargo, and when the craft is then properly ballastcd and trimmed, the towed submersible barge will travel in a desired pattern without any necessity for further direct control. The barge can then be controlled to a sufficient degree by the speed of tow and/or the length of the towline.

When the speed of the tow approaches about nine (9) knots, the barge will start to submerge and will continue to submerge as a function of the speed of tow and/or the length of the towline. The submergence force is a resultant of (1) drag due to frictional resistancee of the hull, (2) lift forces of wings and hull (a depressive force in this case), (3) tension of the towing wire at the connecting point to the barge, and (4) the reserve buoyancy of the barge. These same forces act about their respective moment centers and combine to an equilibrium condition of their resultants at a given tow speed and towline length.

In FIG. 1, the hull or skin 20 of the vessel is shaped as a streamlined body of revolution having a parallel midbody. A ballast keel 21 is formed on the underside of hull and is loaded with solid ballast of that desired weight which is necessary to secure stability of the barge. The barge is designed so that, when fully loaded with cargo and properly ballasted to have a predetermined reserve buoyancy, and when trimmed, the vessel 10 will float at the surface of the water with only the fair-water 22 and a small portion of freeboard extending above the surface.

The barge is then taken down to its cruising depth by the force of the forward towing movement as exerted by the low line 24, a suitable cable. As the vessel 16 approaches about nine (9) knots, the increasing water drag along the bottom of the hull 2t] acting with the force of forward tow about the center of the reserve buoyancy, tends to tilt the vessel 10 forward and it submerges. The lift force or depression from how wings 26 is also instrumental in the accelerating or diving condition and tends to aid the submerging resultants. The vessel 10 will then come to an equilibrium condition at a predetermined depth which is a function of the vessels speed and towing angle (length of towline). The vertical fin 23 and the stern wings 25 provide stability to the craft after it reaches the equilibrium condition; that is, the proper depth, speed and attitude for standard speed towing.

The proper volume of the vessel It), which is a function to be considered relative. to the physical size of the vessel and the towing requirements, must be such that a definite desired amount of buoyancy results when the yes sel 10 is completely loaded. The cargo tanks 27 and 28,

after and forward, respectively, are built to be nonpressure-resistant and the central cargo tank 30 is of pressureresistant design. Complete loading is of great importance so that there can be little or no shifting of weight within the vessel 10 at any time when it is underway. Therefore, each of the nonpressure-resistant cargo holds or tanks 27 and 23 and the pressure-resistant cargo hold or tank 30 must be of a proportionate total volume in order to interact with other buoyancy and gravity forces of the vessel 19 to allow the attaining of equilibrium conditions. Also, the various ballast and trim tanks (to be described) must be of proper volume as dictated by the operational requirements.

A further parameter controlling the size of cargo tanks 27, 28 and 30' is the specific gravity of the cargo and the mean sea water. The barge must be designed to enable the proper reserve buoyancy, as required by considerations of the size and dead weight of the vessel and the chosen towing characteristics (speed, cablelength and depth), when the cargo tanks 27, 28 and 30 are totally filled and the necessary ballast and trimming conditions are met, Further, the volume of the cargo tanks is adjusted to provide a balanceable relationship as follows. On the loaded (cargo) voyage, the three cargo tanks 27, 28 and 30 will be completely filled with crude oil of a predetermined specific gravity to thereby adhere to design conditions and enable the proper reserve buoyancy to be imparted to the vessel. On the return voyage, the tank volumes are apportioned so that when the nonpressure- resistant tanks 27 and 28 are completely filled with sea water, having the greater specific gravity, and the pressure-resistant tank 30 is maintained void (filled only with air at sub: stantially atmospheric pressure), the vessel 10 will still have the same buoyancy and will respond to towing in the same manner.

Description of the invention Referring again to FIG. 1, there is shown a preferred design of the vessel 10, the design having compartmentation which adheres to the dimensions and weights referred to in this specification. As previously indicated, the vessel It is formed with a hull (skin) 20, a streamlined body of revolution, and the appertinent external stabilizing and controlling members. The hull 20 is compartmented to provide the three watertight and oiltight cargo holds or tanks cargo tanks 27 and 28, respectively, contain the expansion and collection tanks as will be described. The midships cargo tank 34) is pressure-resistant (shown as a double line) as formed in hull 20 between the transverse bulkheads 34and 42 and above a deckplate 46. The pressureresistant tank 30 is airtight and it is strengthened by a plurality of transverse web members 48 which also extend below and serve to minimize ballast motion in the underlying auxiliary tank 50 as will be shown in connection with FIG. 3. The main longitudinals 51 and 53 support the transverse members 38 in the cargo tank spaces 27 and 28..

Ballast tanks are locatedfore, aft and amidships in the vessel 10 and each tanks capacity is designed in keeping with the overall size and buoyancy which is necessary to enable the desired tow characteristics. The forward main ballast tank 52 (also see FIG. 2) is formed in the hull 20 between transverse bulkhead members 40 and54 and the deckplate 56. The longitudinal member 58 serves to strengthen the tank. Beneath the deckplate 56 is the forward trim tank 60, a pressure-resistant space (double line) as bounded by hull 20, dcckplate 56 and the lower portions board) of the main ballast tank 52. The holes serve for entry and exit of sea water during the ballast venting and ballast blowing control functions. The trim tank capacity is controlled by dockside pumping facilities and therefore no provision is specified for flood control.

An auxiliary or midships trim tank 50 is provided beneath the pressure-resistant cargo tank 30 and centered on the ballast keel 21. FIG. 3 shows the midships tanks in cross-section as taken at 3-3 of FIG. 1. The hull 20 supported by the transverse webs 48 defines the pressureresistant (double line) shell with the bent deckplate 46 forming an oiltight separation between cargo tank 30 and midships trim tank 50. A longitudinal stiffener 68 is placed in the center of trim tank 50 and is provided with holes 70 (see FIG. 1) for water passage bet-ween the port and starboard sections of the tank.

The after main ballast tank 72 and after trim tank 74 are formed by the transverse bulkheads 32 and 76, the hull 20 and the reinforced deckplate 78. The after trim tank '74 is also made pressure resistant; hence, it should be apparent that any interior space which may be rendered filled or partially filled with air or void during submerged voyage conditions is formed to be airtight and press-resistant up to the largest rated operating pressures plus a percentage for safety factor. In one embodiment of this invention, this has been specified as the pressure at sixty (60) meters of sea depth. FIG. 4 shows the after tanks in section as taken at lines 44 of FIG. 1. The after main ballast tank 72 is provided with transverse webs 80 to support the outer skin or hull 20. Flood holes 82 are provided on the port and starboard lower sides of ballast tank 72 for sea water control, i.e., flooding and blowing of the ballast tanks. Suitable longitudinal stifieners 84 are provided to reinforce the ballast enclosure. The downwardly bent deckplate 78, of pressure-resistant construction, separates off the volume of the after trim tank 74. A longitudinal member 86 having water passage holes 88 (FIG. 1) supports and strengthens along the center line of the trim tank 74.

Spaces 36 and 44 near the middle of the vessel (FIG. 1) each comprise a pair of tanks, a collection and an expan sion tank, which are contained in and work in conjunction with the respective nonpressure- resistant cargo tanks 27 and 28. In the stability equation for the vessel, the volume of spaces 36 and 44 must be considered as part of the volume of cargo tanks 27 and 28 since each respective pair is in liquid communication. For transporting crude oil under one set of specific conditions, the expansion tank volume constituted for percent of the volume of its respective nonpressure-resistant cargo tank and the associated collection tank was about three percent of the volume of the same cargo tank. The after space 36 is formed between the hull 20, bulkhead 34, a vertical transverse plate 90 and the horizontal plate 92 within the after cargo tank 27. In the forward cargo tank 28, the hull 20, bulkhead 42, vertical plate 93 and horizontal plate 94 form the similar enclosure 44. The expansion and collection tanks are com partmented within the spaces 35 and 44 as hereafter described.

The respective fore and aft expansion and collection tanks are arranged in side-by-side relationship as shown in FIG. 5, a section from lines 5 of FIG. 1 through the forward cargo tank 28. The hull 20 is braced by the transverse stiffening member 94, a horizontal plate, which also serves as the lower panel of expansion tank 96 and collection tank 98. A vertical panel member 100 completes the bounds of the expansion tank 96 so that it is watertight from both the cargo tank 28 and the collection tank 98 with the exception of a pipe 102 which opens at the top-most part of the expansion tank 96 and extends down to the bottom of cargo tank 28. A suitable strainer or rosebox 104 is placed on the bottom end of pipe 102. The collection tank 98 is bounded by hull 20, transverse plate 94 and a rising panel 106 which is open at the top; hence, the collection tank 98 is in direct communication with the cargo tank 28 through suitable openings at point 108 in the transverse plate 94.

A flow direction panel 110 is affixed at the top of hull 20 and placed parallel to the rising panel 106, thus, forming a flow trap for liquids flowing between the collection tank 98 and the cargo tank 28 such that, effectively, liquid communication is between the topmost region of cargo tank 28 and the bottom of collection tank 98.

A bidirectional flow line 112, for hook-up to dockside facilities, communicates through a stop-valve 114 to an opening 116 at the top of the collection tank 98 and serves as an oil flow line for either loading or unloading, as will be explained later. A second coupler line 118, controlled by a stop-valve 120 extends down to a bell mouth suction head 122 which is placed near the bottom panel 94 of the expansion tank 96. The line 118 is a sea water line and is also bidirectional depending upon the phase of operation, i.e., loading or unloading of crude oil cargo. The valves 114 and 120 and control access are disposed within the fairwater 22 as illustrated. Reference to FIG. 6 will reveal the manner in which the after expansion and collection tanks 124 and 125, respectively, are similarly situated in the after cargo tank 27. v

The expansion and collection tanks find their first function in the cargo loading and unloading process as will be described in the operation section of the specification. Then, when the vessel is loaded and underway, the expansion tank supplies a reservoir wherein, in the event of a degree of expansion in the bulk of the crude oil cargo, due to temperature change, etc., the pressure is relieved by forcing crude oil into the expansion tank with the consequent displacement of sea water to the'exterior through the valve 120 which is left partially open during 'the sea voyage and acts as a relief outlet. Hence, the pressures are equalized and no crude oil is lost into the surrounding sea.

Referring again to FIG. 1, the bow and stern comprise non-watertight compartments 126 and 128. Each of these compartments is formed by the hull 20 and bulkheads 54 and 76 and each has suitable structural strengthening members, transverse and longitudinal, which is characteristic of the design type.

The bow wings 26 and stern wings 25 are suitably mounted on the hull and provided with adjusting mechanism. The adjusting mechanism may be a suitable manually controlled hydraulic device since the wing adjustments are made in port, before towing is underway, for the entire voyage. Each bow wing 26 has a connecting linkage 130 which extends through cargo tank 28 and hull 20 to a space in the fairwater 22 wherein the adjustment mechanism 132 is located. Each stern wing 25 is controllable through a linkage 134 from an adjusting mechanism 136, located high up in the vertical fin 23. The location of the adjusting mechanism 136 is easily accessible when the vessel 10 is at rest in a port or mooring facility. After the wing members 25 and 26 have been set previous to getting underway, they may be left at that setting for the entire voyage or a series of voyages.

The fairwater 22 encloses the necessary air pressure sources 140. This is a figurative showing and actually a bank of many of such compressed air containers is secured in the fairwater 22. Also, in the fairwater 22, there is a pressureresistant container 142 which houses and protects batteries in section 144, radio control equipment in section 146, and electromagnetic valves for blowing and venting ballast are contained in compartment 148.

The vessel has provision for radio control of certain functions as will be described. The electromagnetic valves in compartment 148 can be actuated eitherby radio when the vessel 10 is on the surface or by a pressure switch safety mechanism (at a predetermined maximum allowed depth) to blow the ballast and cause the vessel to rise A suitable antenna 149 in conventional submarine mounting is located on the faiiwvater 22 and in electrical connection with the radio equipment in section 146. It is also planned that the radio equipment space 146 contain further electronic equipment such as; a transmitter for surface indication, indicators for sea water and oil level, and radio controlled towline release equipment.

The iping and valving of the vessel, control of which is located in fairwater 22, is quite extensive and it is not shown since the particular layout and control is not part of the present invention. The nonpressure- resistant tanks 27 and 28 are adapted with piping and control equipment for distribution of sea water and crude oil, the type and direction of flow depending upon the phase of operations. This will be described below in the operation section.

With the midships cargo tank 30, the procedure for loading and otlloading must be different. The tank 30, a pressure-resistant tank, will contain crude oil on the payload trip but it must be maintained void on the return. Hence, when loading, the crude oil is pumped directly into the tank 30 and it is provided with a suitable pressure relief at the top. In unloading, a conventional suction mouth pipe (not shown) is connected to draw crude oil from the bottom of the cargo tank 30. At the same time a boster supply of air pressure is introduced at the top of tank 30. This booster air pressure is of medium-high pressure, about 1.5 kg./cm.

During in-port operations, such as loading and unloading, the cargo tank 30, as well as the cargo tanks 27 and 28, are supplied with suitable venting means which provide gas or fume escape through a conventional flame-arresting relief head (not shown).

The main ballast tanks 52 and 72 are filled and evacuated by conventional pneumatic control. When filling, the air within the ballast tanks is vented to allow sea water to come in through the flood holes 65 and 82. See FIGS. 2 and 4 showing sections of the forward and after ballast tanks, respectively. The ballast tanks are filled for both the payload and the return voyage. A high pressure compressed air source, 30 kg./cm. is utilized for evacuation by introducing the air in the top area of the ballast tank and forcing the sea water out through the floodholes. A pressure responsive safety device (not shown) is utilized for initiating the automatic blow off or evacuation of ballast when the vessel exceeds a preset subnormal depth.

The trim tanks, forward trim tank 60, after tank 74, and the auxiliary midships tank are each pressureresistant and are each filled with sea waterfront dockside lines. It is also contemplated to include intra-vessel pipes between the trim tanks for ballast adjusting purposes. Primarily, however, the trim tanks can each be filled to a proper ballasting volume from a dockside or other metered supply of sea water. Evacuation of the trim tanks requires booster air pressure coupled with sea water suction in the manner prescribed for the pressure-resistant cargo tank 30. I

Manholes 150 (FIGS. 1 and 6) are provided throughout the vessel for cleaning and access. Also, laddersand steps (not shown) are present in all interior spaces. The necessary mooring and handling facilities are located on the fairwater 22. The bollards 152 and closed fair leaders 154 provide fore and aft moring devices, and it should be understood that other devices for spring-line, or whatever mooring configuration, can be attached. A towing eye 156 is provided on the upper bow portion of the hull 20 to receive the tow-line 24. This is a towing point which can give good results but it should be stated that the point of tow can be anywhere from the exact bow point or center on back to about the beginning of tairwater 22, as long as the proper adjustment is made for the inclination of how wings 26.

FIG. 6, a top view of the vessel '19, shows several of the features to better advantage. in the fairwater 22, the compressed air containers 1% are aligned in parallel banks. Other suitable valving and pneumatic control devices (not shown) would be located in the fairwater. The electromagnetic valves which control the high pres sure, ballast tank air supply are located in compartment 148 within the pressure-resistant space 142, and suitable watertight venting means 158 are provided for the compartments 146 and 144 which contain the radio control gear and batteries respectively.v

Operation r The description of operation will proceed with reference to FIG. 1 unless otherwise noted. The vessel 10 is first loaded with crude oil. This entails either pumping or gravity fill of crude oil from dockside storage into the three cargo tanks. The loading of crude oil into the nonpressure- resistant tanks 27 and 28 will require simultaneous pumping out of sea water from the lower limit of the tanks 27 and 28 as will now be described with ref erence to cargo tank 28 and FIG. 5.

In the cargo unloaded condition, the cargo tank 28 will be full of sea water. To load crude oil, the line 112 is connected (at the dockside facility) to supply an.

input of crude oil through valve 114 and outlet 116 into the collection tank 93. The collection tank 98, having also been filled with sea water at the start, increases its crude oil content (from top to bottom), thereby forcing, first sea Water and then crude oil through the trap, over panel 106 and down through openings 198, into the main body of cargo tank 28. Simultaneous with this action, the dockside line 113 is withdrawing sea water from the bottom of expansion tank 96 which in turn draws replacing sea water, via the pipe .102 and rosebox 104, from the bottom of cargo tank .28. Since crude oil and sea water are immiscible liquids, the sea water can be efficiently withdrawn from the bottom while crude oil is supplied at the top.

When a predetermined amount of oil has been detected entering the expansion tanks 96 and 124 (see PEG. 6), the loading is ceased as the pro-per capacity has been reached; that is, the respective collection tanks 98 and I 124 and cargo tanks 28 and 27 will be filled to proper capacity with crude oil, and the expansion tanks 96 and 124 will contain some crude oil but also a sufiicient volume of sea water, This sufficient volume will adhere to the ballast stability equation of the vessel and will provide a small quantity of sea water for expelling from the tanks in response to any expansion of the crude oil cargo. If desired, a form of pressure relief device may be sup plied atop valve however, since the sea water in the expansion tanks 96 and 124 is in pressure equilibrium with the surrounding sea water, it will suffice to leave the sea water valves slightly open.

The midships cargo hold, pressure-resistant tank 30, also receive its full volume of crude oil from the dockside source and venting or air evacuation means is provided to allow filling of the pressure-resistant tank 30. This completes the cargo loading and each of the cargo tanks 27, 28 and 39 is completely filled with a predetermined volume of crude oil having a known specific gravity.

Next the vessel 10 is properly-ballasted and trimmed t'or submarine travel. The fore and aft ballast tanks 52 and '72, respectively, are maintained to be filled with a volume of sea water. This is done by venting the air within the ballast tanks and allowing a required amount of sea water to flood the respective chambers of the ballast tanks 52 and 72. Next the vessel must be trimmed to maintain fore and aft balance and to compensate for overall weight and/ or buoyancy change of the vessel. The fore, aft and midships trim tanks 60, 74 and 50, respectively, are each connected to a dockside or other available source of compensating sea water. The compensating sea water is pumped into the pressure-resistant trim tanks, with simultaneous venting of air from the tanks, until the proper trimming of ballast is achieved; i.e., a reserve buoyancy of predetermined amount. In most cases the desired trimming will require a known volume of sea water (of particular specific gravity) in each trim tank and this can be determined by suitable flow meters measuring the input of compensating sea water to each of the trim tanks.

When proper trimming is achieved, the vessel will have the proper buoyancy and it will have the designated centers of both gravity and buoyancy, such that stable undersea towing can be carried out in accordance with the required parameters of the operation. When the loaded, ballasted and trimmed vessel sits dead in the water, the major portion of the vessel is underwater; only the fairwater 22 and the top of vertical fin 23 will be showing above the waters surface. As forward towing commences the vessel remains at the surface up to a speed of about nine (9) knots. Above nine (9) knots the vessel 10 will submerge and move deeper proportional to its speed of travel until it reaches the desired cruising depth. This crusing depth is regulated by a particular static setting of bow wings 26 (which are preset at a port facility and then left alone) as they function jointly with the length (angle) and speed of tow, the water resistance of the vessel, and the reserve buoyancy, so that the vessel will cruise stably at the proper depth. It is desirable to provide a towline of about 300 meters length and a towing speed of 14 /2 knots. This will then tow the vessel 10 at a depth of about 25 meters as measured from the water surface to the towpoint on the vessel (towing eye 156).

It has been found that changes in salinity, temperature and/or specific gravity can cause unusually large depth variations in submersible barges. The vessel of the present invention is designed to minimize these effects since it is positively ballasted to be at the surface when at rest, but in the event of great depth variation, automatic pressure switch means is provided to blow off all ballast at a predetermined depth, as decided by the depth rating factors of construction.

When entering port, or channels approaching thereto, the vessel automatically rises to a lesser cruising depth with reduction in speed. When the speed falls below about nine (9) knots, the vessel 10 surfaces and travels with the fairwater 22 exposed and it can then receive radio control signals from the tow ship via the antenna 149 which actuates the appropriate radio control and electromagnetic valves (not shown) located in spaces 146 and 148, to blow all ballast from tanks 52 and 72. This raises the vessel further out of the water and serves to enable better port maneuverability and servicing access.

When the vessel 10 has been maneuvered in and secured to a dockside facility at the receiving port, the cargo offloading can be effected. In emptying the nonpressureresistant cargo tanks 27 and 28, sea water is pumped in beneath the crude oil which is simultaneously pumped out from the top of the cargo tank. Referring again to FIG. 5, the pipes 112 and 118 are connected or valved at dockside for a function which is the reverse of their loading function. That is, sea water is pumped into the expansion tank 96, with consequent overflow from the top of tank 96 through pipe 102 to the bottom of cargo tank 28, while crude oil is being pumped out of the collection tank 98 via the outlet 116, valve 114 and pipe 112. The sea water floats the crude oil all the way to the top of collection tank 98 through passages 108, over the plate 106, and then down below the flow direction plate 110, until finally all crude oil has been floated to the area around the outlet of pipe 116. Remaining oil cargo floating above the level of horizontal plate 94 in the respective cargo tanks 27 and 28 may be floated or pumped out by conventional off-loading techniques, not specifically shown. Suitable detection means may be employed to signal the complete evacuation of the crude oil and pumping is stopped.

In this condition, the nonpressure-resistant tanks will be left completely full of sea water. This amount of sea water will be the proper volume for enabling precise ballasting of the vessel 10 on its return voyage, The stern cargo tank 27, also being of the nonpressure-resistant type, is loaded and unloaded in the same manner, and its respective expansion tank serves similarly to provide a reservoir of sea water for expulsion in response to pressure build-up within the cargo tank.

In the pressure-resistant tank 30, booster air is pumped in and the crude oil is suctioned out from the bottom of the tank. When the unloading operation is completed, the non-pressureresistant tanks 27 and 28 will be filled with sea water, and the pressure-resistant tank 30 will be void; the ballast tanks 52 and 72 can then be reflooded and the entire vessel will have the same reserve buoyancy and force moments of operation as in the cargo loaded condition. The return voyage can then be made under the same speed and tow conditions, and the submersible vessel 10 will have the same stability and operating parameters. Thus, by precisely proportioning the volumes of the cargo tanks in accordance with the specific gravities of crude oil and sea water, the same stability of operation is maintained on both the payload and return voyages.

It should be understood that the particular type of cargo space and its expansion and collection tanks can take various forms so long as the considerations of relative vertical placement are incorporated. It has been proposed that the nonpressure-resistant tanks of this invention could be located in numerous shapes and alignments relative to the pressure-resistant tank space as long as the weight distribution and buoyancy characteristics are properly designed. That is, the nonpressure-resistant tanks may be vertically aligned with the pressure-resistant tanks and alternately staggered along the length of the hull, or, the alignment may be horizontal with axially concentric placement of the tanks. Other design forms may be constructed in keeping with specific requirements as may be dictated by limitations due to port servicing, particular cargo, etc.

The specification has set forth a novel cargo tank space design for use in a submersible barge or a surface craft which, for some reason, may have strict requirements as to the loading and hauling of cargo. The cargo space as set forth herein provides a tank which can contain a liquid cargo while immersed in water, and which suffers no disadvantage when the surrounding water undergoes a change in mean temperature. The cargo space includes a small, known volume of space which is made to contain material for expulsion in response to temperature change, i.e., expansion of the cargo volume, without the loss of any cargo to the exterior. In like manner, the flow of cargo during loading and off-loading is directed and controlled between the cargo tank and its expansion and collection tanks such that complete and reliable handling of liquid cargo can always be effected. A cargo tank of the present type is actually an enabling factor in bringing about a practical submersible barge since it allows a large volume of cargo tank space which can be maintained constant (to a sufficient degree) as to weight and buoyancy.

Changes may be made in the combination and arrangement of elements as heretofore set forth in this specification and shown in the drawings; it being understood that changes may be made in the embodiment disclosed without departing from the spirit and scope of the invention as defined in the following claims.

What is claimed is: i 1. In a submersible barge for transporting crude oil,

cargo space comprising:

a hull of substantially circular cross-section;

a plate extending substantially horizontally across the hull forming a crude oil cargo tank below the plate, said plate having an opening in the medial portion thereof;

a first bulkhead extending vertically from said plate adjacent one side of said opening to the top of the hull, thus forming an expansion tank above the car go tank;

second bulkhead extending upwardly from said plate adjacent the opposite side of said opening into proximity with the top of the hull thus forming a collection tank above said cargo tank and providing communication between the collection tank and the cargo tank from above said second bulkhead, between said first and second bulkheads, and through said opening; and

a flow direction plate extending from the top of the hull downwardly into proximity with said plate within the collection tank and closely adjacent to said second bulkhead, thus forming a trap with said second bulkhead for liquid passing between the collection tank and the cargo tank.

2. A cargo space as set forth in claim 1 wherein:

said collection tank is formed to have a volume equal to about three percent of the total volume of said cargo, collection and expansion tanks.

3. In a submersible barge for transporting crude oil,

cargo space, comprising:

12 an expansion tank compartmented in a topmost region of each of said cargo tanks; a collection tank compartmented in a topmost region of each of said cargo tanks; 5 means in each of said cargo tanks providing liquid communication between the bottom of the cargo tank and the top of the expansion tank and, also, the bottom of the expansion tank and the exterior of the barge above the tank; and means in each of said cargo tanks providing liquid communication between the top of the cargo tank and the bottom of said collection tank and, also, the top of the collection tank and the exterior of the barge above the cargo tank. 15 4. Cargo space as set forth in claim 3 which is further characterized to include:

first valve means controlling liquid communication between the bottom of each expansion tank and the exterior of the barge; and

second valve means controlling liquid communication between the top of each collection tank and the exterior of the barge,

whereby the cargo tanks on-load cargo by simultaneously admitting crude oil at the second valve means and withdrawing sea water at the first valve means, and the tanks off-load. cargo by simultaneously admitting sea water at said first valve means and withdrawing crude oil at said second valve means.

References Cited UNITED STATES PATENTS 10/1916 Jack 1140.5 6/1966 Cannon 114-05

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