Ballast-cargo grid system for tankers

A plurality of narrow ballast tanks arranged around the periphery of diaphragms. The peripheral ballast tanks facilitate the construction, installation, operation, and maintenance of the diaphragms that segregate the cargo oil from the ballast water in the oil tanker in which they are fitted. The peripheral ballast tanks in general are built along the longitudinal and transverse bulkheads and ship's sides, but they can also be arranged to sub-divide the lower portion of large cargo tanks, they, in effect, form a tank grid about the lower portion of the cargo tanks' space, with the cells in the grid being suitable for the reception of the diaphragms. The diaphragms each consist of three main parts: a vertically movable thin and flat partition, that can be buoyant in order that it may float on ballast water; a mating but fixed partition rim fitted outside of the movable partition; and elastomeric membrane sheet that is fitted between and attached to the movable partition in such a manner that the complete diaphragm forms an impervious barrier to oil or water attempting to pass from top to bottom or vice verse. A movable partition guide is also provided. By locating the fixed partition rim at mid-point of the movable partition travel on the sides of the peripheral ballast tanks, major savings of membrane material can be achieved.

BACKGROUND OF THE INVENTION 
International maritime agreements require that most new oil tankers have to 
be fitted with a system capable of keeping the cargo oil and ballast 
water, including their residues, physically apart at all times, i.e. a 
segregated ballast system must be fitted. 
The inventor's U.S. Pat. No. 4,117,796 "Double Sectioned Tank" discloses a 
means whereby segregation of the cargo oil and ballast water is achieved 
without most of the very substantial loss of cargo carrying capacity 
necessitated by the standard method of using entirely separate tanks to 
contain each of the two substances. 
The present invention relates generally to improvements to the aforesaid 
U.S. Patent. The improvements make unnecessary certain items in the patent 
and will facilitate the manufacture, installation, operation, and 
maintenance of the diaphragms disclosed in the patent, while also 
providing means whereby the hull girder strength may be improved. The 
provision of ballast tanks located low down in a tanker fitted with the 
improvements may also increase seakeeping and ship stability performance 
by reducing stiffness in the cargo loaded condition. 
It will be noted that a standard segregated ballast oil tanker will have to 
designate capacity equivalent to approximately one-third of it's cargo 
capacity to the carriage of segregated ballast. In the cargo loaded 
condition this space will be filed with air, i.e. the tanker will carry 
only approximately two-thirds of the cargo it would be capable of carrying 
if it were an ordinary non-segregated ballast tanker. 
A segregated ballast tanker that is fitted with the present invention will 
utilize a large proportion of the designated ballast space to carry 
revenue generating cargo. 
PRIOR ART 
U.S. Pat. No. 4,117,796 of Strain, describes a special type of tank that 
can be built into the cargo tanks of an oil tanker and which, by the use 
of movable semi-solid steel and reinforced elastomeric diaphragms, can 
allow for the carriage of cargo oil in portion of the empty ballast tanks, 
without any product cross-contamination, i.e. it provides fully segregated 
ballast space, while allowing for greater cargo carrying capability than 
an identical externally dimensioned standard ballast tanker. It also 
allows for the provision of protective segregated ballast double bottom 
space in the cargo loaded condition. 
U.S. Pat. No. 3,477,401 of Hayama illustrates a submarine fitted with a 
flexible bag or membrane to segregate oil from ballast water in the hull 
of the vessel. 
U.S. Pat. No. 2,696,185 of Snoddy discloses a horizontal membrane cargo oil 
segregation system. 
U.S. Pat. No. 3,943,873 of Hering and Schwartz depicts a vertical membrane 
cargo oil/ballast water segregation system for an oil tanker. 
U.S. Pat. No. 3,707,937 of Liles describes a collapsible container for 
segregating cargo oil and ballast water in an oiler tanker. 
U.S. Pat. No. 3,922,985 of Hamilton teaches a system whereby expansible 
bladders are used to contain cargo oil while an outer steel compartment is 
designed to carry segregated ballast water. 
U.S. Pat. No. 3,745,960 of Devine shows an oil tanker having a particular 
arrangement of bulkheads and tanks wherein there is a minimum of metal 
exposed to corrosive fluids. 
SUMMARY OF THE INVENTION 
Special narrow ballast tanks are arranged around the periphery of the 
semi-solid diaphragms disclosed in the inventor's U.S. Pat. No. 4,117,796 
"Double Sectioned Tank". The narrow tanks will usually have a height equal 
to the maximum upper travel position of the diaphragm, plus the height of 
double bottom space required. By making the narrow tanks on the ship's 
side at least the required minimum width, they will provide "protective 
ballast space" for the cargo oil tanks, as will the double bottom tanks if 
they are at least the required minimum height. 
The narrow ballast tanks generally follow the contours of, and can be built 
as part of, an oil tanker's main longitudinal and transverse bulkheads, 
and the ship's sides. In cases where it is decided to sub-divide the main 
cargo tanks to facilitate installation of the diaphragms, the narrow tanks 
can be used as dividers. The lower portion of the narrow ballast tanks can 
extend to, or into, the "double bottom" ballast space and they can be made 
common with, or separated from, this space as desired. 
A diaphragm consists of three main parts, 
(a) a vertically movable thin flat solid or compartmentalized partition 
that may be of steel, or equivalent material; 
(b) a fixed thin flat solid partition rim that may also be of steel, or 
equivalent material; and 
(c) a thin flexible membrane sheet of reinforced elastomeric material the 
properties of which include resistance to abrasion and tearing and which 
is also compatible with sea water, hot and cold crude and other oils and 
chemicals. 
Fastenings, guide, and safety means are also provided as disclosed in U.S. 
Pat. No. 4,117,796, "Double Sectioned Tank". 
By using oiltight/watertight fastenings to join one end of a membrane to a 
movable diaphragm partition, and the other end of the membrane to a fixed 
partition rim, and attaching the latter, at the position of movable 
partition mid-travel, to the sides of a particular set of peripheral 
ballast tanks, a fully segregated cargo oil/ballast water system is 
obtained, while allowing that portion of cargo tank space through which 
the movable partition travels to carry, at a particular time, either cargo 
oil or ballast water without any cross-contamination between the substance 
occupying that space, and the residues and vapours from the substance that 
previously occupied that space. 
The following major advantages are commensurate with the invention as 
claimed: 
1. A tanker fitted with the invention will carry substantially more cargo 
than an identical externally dimensioned standard segregated ballast 
tanker. 
2. Only approximately half of the amount of membrane material (U.S. Pat. 
No. 4,117,796, Item No. 18 "fabric sheet") will be required - resulting in 
easier manufacture, handling, installation, and maintenance of the 
membranes, and also lowering their cost. 
3. The substantially smaller amount of membrane material required will 
result in a simpler and less complicated system for practical shipboard 
operation. 
4. The strips of elastic material or springs (U.S. Pat. No. 4,117,796, Item 
No. 20 "elastic material or springs") for guiding the membranes are made 
unnecessary in most cases. 
5. The straight sides of the peripheral ballast tanks will provide ideal 
support for the diaphragms and make diaphragm support plates (U.S. Pat. 
No. 4,117,796, Item No. 100 "fabric sheet support plates") unnecessary in 
most cases. 
6. Strength can be built into the peripheral ballast tanks to help 
compensate for the internal steelwork removed to allow space for the 
installation and operation of the diaphragms. 
7. The peripheral ballast tank grid system will provide extra longitudinal 
and transverse strength for the tanker's hull.

DETAILED DESCRIPTION OF THE INVENTION 
While the invention will be described in connection with example 
embodiments, it will be understood that it is not intended to limit the 
invention to those embodiments. On the contrary, it is intended to cover 
all alternatives, modifications, and equivalents, as may be included 
within the spirit and scope of the invention as defined by the appended 
claims. 
For reasons of clarity, emphasis throughout this detailed description will 
be placed on the invention as applied to oil tankers, but it will be 
understood that the invention, with slight and obvious modification is 
also suitable for use in chemical carriers, liquified gas carriers, other 
liquid carriers, and cargo ships, and for other uses outside the shipping 
industry. 
Also should the shipowner so wish, with slight and obvious modification a 
diaphragm can be placed in the side of a tank, i.e. with the movable 
partition 11 and attachments in a vertical positon. 
Cargo and ballast tank filling and emptying arrangements are conventional 
and are not depicted in the drawings. 
Referring to FIG. 1, this depicts an oil tanker 10 that is fitted with the 
present invention. Segregation diaphragms, the purpose of which is to 
segregate the cargo oil from the ballast water, are fitted in the cargo 
tanks of the oil tanker 10. Each segregation diaphragm consists of a 
movable partition 11, a partition rim 12 which is fixed, and a reinforced 
elastomeric membrane 13 that has its ends attached by suitable means, 
which may be clamp-bars and bolts 14, to the movable partiton 11 and the 
fixed partition rim 12. 
Peripheral ballast tanks 15 are located around the outside of the 
segregation diaphragms, and the partition rims 12 are fitted, usually by 
welding, to those sides of the peripheral ballast tanks 15 that face the 
movable partitions 11, and generally at the position of movable partition 
11 mid-travel. The peripheral ballast tanks 15 depicted are built on 
either side of the transverse bulkheads 16, which they help to strengthen, 
and by means of holes cut in the bulkheads can be made common, or kept 
separated, to the shipowner's requirements. The longitudinal ballast tanks 
15 are not shown in this drawing for reasons of clarity. 
A guide cylinder 17, or other guide means, is fitted to each movable 
partition 11, and a guide bearing 18 and bearing beam 19, are fitted to 
constrain the movable partition 11 to movement in a vertical direction 
only. This movable partition 11 movement is confined to the space between 
the bearing beam 19 and the bottom frames 20 or the internal structure of 
the oil tanker 10. The ship's bottom 21 may need to be reinforced to help 
compensate for steelwork removed in order to make space for the 
diaphragms. 
The ship's main deck 22, cofferdams 23, fore peak 24, machinery space 25, 
bridge 26, and accommodation 27, are conventional. 
A diaphragm, together with its fittings and peripheral ballast tanks 15, 
forms an impermeable barrier to oil and water, and transforms a tank in 
which it is fitted into four distinct spaces, each with its own function, 
namely; 
(a) peripheral ballast tanks 15 space, dedicated to segregated ballast; 
(b) dedicated cargo oil space 28, located above the maximum height of 
travel of the movable partition 11; 
(c) dedicated segregated ballast space 29, or double bottom space, located 
above the hull bottom plating 21 and below the minimum height of travel of 
the movable partition 11; and 
(d) diaphragm space 30, located between the peripheral ballast tanks 15, 
with its height extending from the tops of the bottom frames 20, i.e. 
lowest position of movable partition 11 travel, to the maximum height of 
the peripheral ballast tanks 15, i.e. highest position of movable 
partition 11 travel, and, depending on which mode the tanker is 
functioning in at a particular time, it will either contain cargo oil or 
clean ballast water, as decided by the position of the diaphragm, i.e. 
with the movable partition 11 in the lower position it will contain cargo 
oil, and with the movable partition 11 in the raised position it will 
contain clean ballast water, without any cross-contamination of the two 
substances, their residues or vapours. 
It will be noted that all cargo oil carried in the diaphragm spaces 30, is 
additional to that which may be carried in a conventional segregated 
ballast tanker with identical external dimensions. 
Referring to FIG. 2, this shows a large diaphragm fitted in a centre cargo 
tank 35 of the oil tanker 10 of FIG. 1. Smaller diaphragms are fitted in 
the port wing tank 36 and the starboard cargo wing tank 37. Peripheral 
ballast tanks 15 are built along the tanker's port side 31, port 
longitudinal bulkhead 32, starboard longitudinal bulkhead 33, and 
starboard ship'side 34. The transverse peripheral ballast tanks 15 are not 
shown in this Figure. 
The port wing tank diaphragm is depicted in the raised, i.e. ballast 
position, and the centre tank and wing tank diaphragms are shown in the 
lowered, i.e. cargo loaded position. When the diaphragms are in the raised 
position, the peripheral ballast tanks 15, are also filled with ballast 
water. These tanks are empty when the diaphragms are in the lowered 
position and the cargo is on board. 
The additional guide cylinder 17 fitted to the centre movable partition 11, 
provides extra guide means to help cope with the large weight of movable 
partition 11 material involved. 
The longitudinal and transverse peripheral ballast tanks 15, can, according 
to the shipowner's requirements, be designed for internal fluid 
communication with one another and also with bottom frame space 29, 
including diaphragm space 30 when the tanker is in the ballast mode of 
operation. 
Referring to FIG. 3, this is a plan view of the peripheral ballast tanks 15 
in a V.L.C.C. similar to but larger than the tanker depicted in FIGS. 1 
and 2. To further sub-divide the cargo tank spaces, and to provide extra 
hull strength, an additional longitudinal bulkhead, the centre 
longitudinal bulkhead 38, is fitted. 
It will be noted that the peripheral ballast tanks 15, together with the 
cofferdams 23, and other tanks such as bunker or small water tanks that 
may be incorporated, form a tank grid with cells suitably located to 
facilitate the installation and operation of the cargo oil/ballast water 
segregation diaphragms, by providing solid smooth flat support surfaces 
for the reinforced elastomeric membranes 13 (FIG. 2). 
Those peripheral ballast tanks 15, that are located at the tanker's 10 
sides, if of suitable width, will also provide protective ballast space 
for the adjacent loaded cargo tanks. The double bottom space 29 (FIG. 4), 
if of sufficient height, will also fulfill a similar function for its 
adjacent cargo oil tanks. 
Referring to FIG. 4, this shows various constructional details of the 
diaphragms and of the peripheral ballast tanks 15. Two different methods 
for locating the fixed partition rim 12 on the sides of the peripheral 
ballast tanks 15 are depicted. 
On the starboard ship's side peripheral ballast tanks 15, the partition rim 
12 is attached, usually by welding, to the straight inner side plating 39 
of the tank at movable partition 11 mid-travel position. The top plating 
40 of the side tank is extended, by an amount greater than the width of 
the partition rim 12, towards the movable partition 11, and forms an 
overlap of the tank side 39 to allow a mating fit between the movable 
partition 11 in its raised (ballast) position and the peripheral tank top 
40, this will help to prevent ballast water sloshing with possible 
membrane 13 damage and will also facilitate movable partition 11 securing 
means. 
On the peripheral ballast tank 15 that is attached to the starboard 
longitudinal bulkhead 33, a recess 41 is made in the inner side plating 39 
that is facing the movable partition 11, and the fixed partition rim 12 is 
fitted in the recess 41. This will allow the side of the movable partition 
11 to be located nearer to the side plating 39 of the peripheral ballast 
tank 15, with only a small, or no overlap by top plating 40, thereby 
attaining the same advantages as the first method described above of the 
partiton rim 12 attachment. 
For light movable partitions 11, guide and securing means may be waived, as 
depicted in this Figure, but for heavier movable partitions 11, guide and 
securing means, as disclosed in U.S. Pat. No. 4,117,796 "Double Sectioned 
Tank", are essential. 
Referring to FIG. 5, wherein different methods of construction and 
arrangement of the peripheral ballast tanks 15 are depicted. In the 
arrangement as shown the lower portion of a large cargo oil tank is 
divided into smaller portions for convenience in diaphragm manufacture, 
installation, operation and maintenance. 
The inner peripheral ballast tank 15 is built against the side of the port 
longitudinal bulkhead 32. The centre peripheral ballast tank 15 rests on 
and is attached to the bottom frames 20, and has its own integral bottom 
plating 42, instead of the ship's bottom plating 21. The outer peripheral 
ballast tank 15, that is built against the ship's port side 31 has a 
similar integral bottom. An intercostal 43 is fitted to divide the double 
bottom space 29 and to provide peripheral ballast tank 15 support and 
extra hull strength. 
The inner partition rim 12 is attached directly to the port longitudinal 
bulkhead 32. 
The port side frames 44 are conventional. The diaphragms, other than the 
fixed partition rims 12, and the transverse peripheral ballast tanks are 
not shown in this drawing. 
Referring to FIG. 6, wherein the lower portion of a large cargo oil tank is 
divided into four diaphragm spaces (or cells) 30 by the peripheral ballast 
tank 15, which follows the contours of the main longitudinal 16 and 
transverse 32 bulkheads and acts as a division of the space between the 
bulkheads and the ship's port side 31. 
In this drawing the peripheral ballast tank arrangement is depicted as one 
continuous ballast tank, but it will be understood that in practice this 
tank can be divided to suit the shipowner's ship stability and operational 
requirements. Also by suitable peripheral ballast tank arrangement, more, 
or less, than four diaphragm spaces 30 can be provided in each cargo tank 
to the shipowner's requirements. 
While certain novel features of my invention have been shown and described 
and are pointed out in the appended claims, it will be understood that 
various substitutions, omissions and changes in the forms and details of 
the device illustrated and in its operation can be made by those skilled 
in the art without departing from the spirit of the invention. Therefore 
what has been set forth is intended to describe and/or illustrate such 
concept and is not for limiting protection to any herein particularly 
described embodiment thereof.