DE GEETER, Pieter Jan (87 Rupert Street, Subiaco, Australian Capital Territory 6008, AU)
| The Claims Defining the Invention are as Follows 1. A container for transporting a liquid through sea water or fresh water, said container having a flexible tube like body, closed at a forward end by a flexible conical shaped nose portion (conical nose) which tends to a point at the most forward end of said body, and closed at a rearward end by a flexible conical shaped tail portion (conical tail) which tends to a point at the most rearward end of said body, said body being formed of impervious material, said conical shaped nose portion having towing means attached thereto for pulling said container from the forward end thereof, said body having an uppermost surface portion forming in use at least part of an upper half-cylindrical body and having a lowermost surface portion forming in use at least part of a lower half- cylindrical body, wherein said uppermost surface portion is longitudinally shorter when under tension than said lowermost surface portion when under equivalent tension, allowing said body to expand more underneath when filled with liquid, and so urging said points of said conical shaped nose portion and said conical shaped tail portion to the water surface. 2. A container as claimed in claim 1 wherein the water impervious material of the body is more buoyant than sea water. 3. A container as claimed in claim 1 or 2 wherein the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the horizontal plane, is from 20 degrees to 32.5 degrees when the container is filled and floating in water. 4. A container as claimed in claim 3 wherein the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the horizontal plane, is about 22.5 degrees when the container is filled and floating in water. 5. A container as claimed in any one of the preceding claims wherein the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the vertical plane is from 10 degrees to 22.5 degrees when the container is filled and floating in water. 6. A container as claimed in claim 5 wherein the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the vertical plane is about 15 degrees when the container is filled and floating in water. 7. A container as claimed in any one of the preceding claims wherein the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the horizontal plane, is from 20 degrees to 32.5 degrees when the container is filled and floating in water. 8. A container as claimed in claim 7 wherein the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the horizontal plane, is about 22.5 degrees when the container is filled and floating in water. 9. A container as claimed in any one of the preceding claims wherein the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the vertical plane is from 10 degrees to 22.5 degrees when the container is filled and floating in water. 10. A container as claimed in claim 9 wherein the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the vertical plane is about 15 degrees when the container is filled and floating in water. 11. A container as claimed in any one of the preceding claims wherein said conical nose has an uppermost surface portion forming in use at least part of an upper half-conical portion and has a lowermost surface portion forming in use at least part of a lower half-conical portion, wherein said conical nose uppermost surface portion is longitudinally shorter when under tension than said conical nose lowermost surface portion when under equivalent tension, and so assisting with urging said point of said conical shaped nose portion to the water surface when the container is filled and floating in water. 12. A container as claimed in claim 11 wherein said conical nose has an uppermost surface portion forming in use at least part of an upper half-conical portion and has a lowermost surface portion forming in use at least part of a lower half- conical portion, wherein said conical nose uppermost surface portion is longitudinally shorter than said conical nose lowermost surface portion, and so assisting with urging said point of said conical shaped nose portion to the water surface when the container is filled and floating in water. 13. A container as claimed in any one of the preceding claims wherein said conical tail has an uppermost surface portion forming in use at least part of an upper half-conical portion and has a lowermost surface portion forming in use at least part of a lower half-conical portion, wherein said conical tail uppermost surface portion is shorter than said conical tail lowermost surface portion when under tension, and so assisting with urging said point of said conical tail to the water surface when the container is filled and floating in water. 14. A container as claimed in claim 13 wherein said conical tail has an uppermost surface portion forming in use at least part of an upper half-conical portion and has a lowermost surface portion forming in use at least part of a lower half- conical portion, wherein said conical tail uppermost surface portion is shorter than said conical tail lowermost surface portion, and so assisting with urging said point of said conical tail to the water surface when the container is filled and floating in water. 15. A container as claimed in any one of the preceding claims wherein the upper half-cylindrical body forms less than half the circumference of the body, and the lower half-cylindrical body forms more than half the circumference of the body when the container is filled with liquid and floating in water. 16. A container as claimed in any one of the preceding claims wherein the upper half-cylindrical body and the lower half-cylindrical body are segmented, being formed of upper surface segments and lower surface segments respectively, where the sum of the maximum lengths of the lower surface segments along the longitudinal extent of the body, exceeds the sum of the lengths of the upper surface segments along the longitudinal extent of the body, by a maximum of from 1% to 3%. 17. A storage system for compacting the container as described above, after its emptying, said storage system comprising a spool onto which said container, when empty or during emptying, can be rolled, said spool being removably securable to a barge for support during spooling, and removable from said barge for transporting. 18. A storage system for compacting the container as described above, after its emptying, said storage system comprising a sleeve which may be stored in concertina fashion over a tube like applicator, said sleeve being deployed by passing said applicator around and along the length of said container when empty, encasing said container within said sleeve. 19. A transport system for transporting a liquid through sea water or fresh water, said transport system comprising a container as described above connected by its towing means via an inclined tow line to a towing vessel, said tow line being fed from an elevated position on said vessel at an angle sufficient to assist with maintaining the point of the most forward end of the container above the water surface, when the towing vessel is underway in a forward direction. 20. A transport system as claimed in claim 19 wherein said tow line is fed from a tensioning arrangement, arranged to feed in and out said tow line to maintain tension in said tow line between said towing vessel and said container within operational limits for said container and said tow line. 21. A transport system as claimed in claim 19 or 20 wherein said elevated position is adjustable in height in order to adjust the elevation angle of said tow line to said container, to assist in maintaining the most forward end of the container above the water surface, in more severe sea states when the towing vessel is underway in a forward direction. 22. A container for transporting a fresh water through sea or ocean, said container having a flexible cylindrical body, closed at each end by a slender tapering conical portion tapering to a point at each end, said body being formed of impervious material more buoyant than water, said container having towing means located depending from one or both of said points for pulling said container, said body having an uppermost longitudinal extent and a lowermost longitudinal extent, wherein said uppermost longitudinal extent is longitudinally shorter when under tension than said lowermost longitudinal extent, allowing said body to expand more underneath when filled with water, and so urging said points to the water surface while the entire uppermost longitudinal extent of said body floats above the sea or ocean surface. |
Field of the Invention
This invention relates to transport of fluids, and in particular to a container and system for transporting water. Background Art
The following discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.
Water or other liquids are usually conveyed across sea or ocean by means of tankers and often supertankers. In addition to this, conveyance by towage of "bags" of synthetic material containing the liquids has been utilised. Due to high drag resistance in the water, these conveyance methods require large propulsive power and suffer from consequent associated high fuel consumption. As a consequence, the cost of delivered liquid per kilolitre is becoming commercially uncompetitive.
Most existing bags, such as Spragg bags, are rounded at the ends, both in the horizontal and the vertical plane. This causes flow stagnation at the front and a large wake at the stern. As a consequence the form drag resistance of the bag is high in comparison to its skin drag resistance, substantially reducing its towage speed at a given towing force.
Nordic bags (operating in the Mediterranean) have minimised flow stagnation at the front by a more pointed shape with the bag's front extremity raised toward the water surface by means of an external float. Although reducing the form drag of the front section of the bag it has the disadvantage of overall towage resistance being increased by the wave resistance and current resistance of the float which is significant in percentage of total towage force. Furthermore, the rigid, non- stretchable connection utilised between the mass of the float and the mass of the water body inside the bag increases the risk that the connection will fail during severe sea states. The mass of the float also reduces the ability of the front section of the bag to follow the orbital motion of waves approaching head on. As a consequence the resistance force generated by wave action is relatively high, causing a substantial reduction in towage speed.
Retrieval of the emptied bag from the sea is a time consuming affair whilst the weight of the bag (stored on the towage vessel during the return trip to the point of origin) is substantial, increasing the vessel's draught and, as a consequence, reducing its towage speed through the water. Both effects substantially increase total round-trip time of a bag (which is inversely proportional to the total amount of water that can be conveyed per bag per year). It renders existing towage technology uneconomical over large towage distance (in excess of roughly 1000km) in comparison to other water supply solutions.
It is an object of the invention to provide an improved flexible bag-like container for the transporting of water, that substantially overcomes some of the problems in the prior art or at least provides an alternative arrangement to previously described arrangements.
It is also an object, in a system for transporting water in a flexible bag-like container, to provide an improved arrangement for retrieval.
Throughout the specification unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Throughout the specification unless the context requires otherwise, the word "include" or variations such as "includes" or "including", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Disclosure of the Invention
In accordance with one aspect of the invention there is provided a container for transporting a liquid through sea water or fresh water, said container having a flexible tube like body, closed at a forward end by a flexible conical shaped nose portion (conical nose) which tends to a point at the most forward end of said body, and closed at a rearward end by a flexible conical shaped tail portion (conical tail) which tends to a point at the most rearward end of said body, said body being formed of impervious material, said conical shaped nose portion having towing means attached thereto for pulling said container from the forward end thereof, said body having an uppermost surface portion forming in use at least part of an upper half-cylindrical body and having a lowermost surface portion forming in use at least part of a lower half-cylindrical body, wherein said uppermost surface portion is longitudinally shorter when under tension than said lowermost surface portion when under equivalent tension, allowing said body to expand more underneath when filled with liquid, and so urging said points of said conical shaped nose portion and said conical shaped tail portion to the water surface.
Preferably the entire body is made of the same material.
Preferably the water impervious material of the body is more buoyant than sea water.
Preferably the water impervious material of the body is more buoyant than fresh water.
Preferably the water impervious material resists fluid transfer under osmotic pressure.
Preferably the when the vessel is filled with fresh water, the body is sufficiently buoyant that its entire longitudinal uppermost surface portion locates above the surface of the sea or ocean.
Preferably the lengths of the conical shaped nose portion and the conical shaped tail portion are sufficient, in relation to the filled draught of said vessel when carrying fresh water in the sea or ocean, to ensure that the body rises with its entire longitudinal uppermost surface portion above the surface of the sea or ocean.
Preferably the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the horizontal plane, is from 20 degrees to 32.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of from 40 degrees to 65 degrees. Preferably the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the horizontal plane, is up to 30 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of up to 60 degrees.
Preferably the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the horizontal plane, is up to 27.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of up to 55 degrees.
Preferably the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the horizontal plane, is up to 25 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of up to 50 degrees.
Preferably the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the horizontal plane, is around 22.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of around 45 degrees.
Preferably the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the vertical plane is from 10 degrees to 22.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the vertical plane of from 20 degrees to 45 degrees.
Preferably the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the vertical plane is from 12.5 degrees to 20 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the vertical plane of from 25 degrees to 40 degrees.
Preferably the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the vertical plane is up to 17.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the vertical plane of up to 35 degrees.
Preferably the angle of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the vertical plane is around 15 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the vertical plane of around 30 degrees.
Preferably the angles of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the horizontal and vertical planes are about two thirds of that of the conical nose longitudinal surface relative to the longitudinal axis of the conical nose in the horizontal and vertical planes. Providing sharper angles in the conical tail assists in minimising drag from flow separation at the stern of the container..
Preferably the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the horizontal plane, is from 20 degrees to 32.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of from 40 degrees to 65 degrees.
Preferably the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the horizontal plane, is up to 30 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of up to 60 degrees.
Preferably the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the horizontal plane, is up to 27.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of up to 55 degrees.
Preferably the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the horizontal plane, is up to 25 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of up to 50 degrees.
Preferably the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the horizontal plane, is around 22.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the horizontal plane of around 45 degrees.
Preferably the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the vertical plane is from 10 degrees to 22.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the vertical plane of from 20 degrees to 45 degrees.
Preferably the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the vertical plane is from 12.5 degrees to 20 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the vertical plane of from 25 degrees to 40 degrees.
Preferably the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the vertical plane is up to 17.5 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the vertical plane of up to 35 degrees.
Preferably the angle of the conical tail longitudinal surface relative to the longitudinal axis of the conical tail in the vertical plane is around 15 degrees when the container is filled and floating in water. This would provide an angle between longitudinal surfaces (conical angle) in the vertical plane of around 30 degrees.
It will be appreciated with this discussion of angles in the horizontal and vertical planes, due to the constraining nature of the material forming the container with respect to the load being contained thereby, and the buoyancy of the container and/or load being carried, the container will take on a flattened configuration when floating in the ocean, resulting in the angle viewed in the vertical plane being sharper than the angle in the horizontal plane.
Preferably said conical nose has an uppermost surface portion forming in use at least part of an upper half-conical portion and has a lowermost surface portion forming in use at least part of a lower half-conical portion, wherein said conical nose uppermost surface portion is longitudinally shorter when under tension than said conical nose lowermost surface portion when under equivalent tension, and so assisting with urging said point of said conical shaped nose portion to the water surface when the container is filled and floating in water.
Alternatively or additionally, preferably said conical nose has an uppermost surface portion forming in use at least part of an upper half-conical portion and has a lowermost surface portion forming in use at least part of a lower half-conical portion, wherein said conical nose uppermost surface portion is longitudinally shorter than said conical nose lowermost surface portion, and so assisting with urging said point of said conical shaped nose portion to the water surface when the container is filled and floating in water.
Preferably said conical tail has an uppermost surface portion forming in use at least part of an upper half-conical portion and has a lowermost surface portion forming in use at least part of a lower half-conical portion, wherein said conical tail uppermost surface portion is shorter than said conical tail lowermost surface portion when under tension, and so assisting with urging said point of said conical tail to the water surface when the container is filled and floating in water.
Alternatively or additionally, preferably said conical tail has an uppermost surface portion forming in use at least part of an upper half-conical portion and has a lowermost surface portion forming in use at least part of a lower half-conical portion, wherein said conical tail uppermost surface portion is shorter than said conical tail lowermost surface portion, and so assisting with urging said point of said conical tail to the water surface when the container is filled and floating in water.
Preferably the body when filled, has a narrowing tapering diameter towards said forward end and said rearward end.
Most preferably there is, when filled, a smooth surface transition along the surface of the body from the point at the conical nose to the point at the conical tail. This will minimise flow separation along the surface of the container during towing, and as a consequence, will also minimise the drag form of the container during towage.
Preferably the container is fabricated in the shape of a flat two dimensional profile, symmetrical about its longitudinal axis in top plan and bottom plan view, and symmetrical about its transverse central axis, at any point along the longitudinal extent of the body. Preferably the water impervious material of the body has a relatively high elasticity and a relatively low shear deformation resistance, so that the container when floating in sea water will adopt a symmetrical profile, and wave induced longitudinal deformation during towing of said container will assist in keeping said conical shaped nose portion and conical shaped tail portion at the surface of the water body in which the container is immersed. The result of this, and other measures inherent in the design of the container that maintain the conical shaped nose portion and conical shaped tail portion points at the water body surface during towing, virtually eliminate over pressure at the conical shaped nose portion and underpressure "suction" at the conical shaped tail portion, reducing total drag form to a level far lower than in the case of currently operational bag systems.
At sufficient length of the conical shaped nose portion and conical shaped tail portion sections (sharpness of conical angle), the nose and tail of the container will have a greater tendency to rise to the surface of the water body. Furthermore, with greater length of the conical shaped nose portion and conical shaped tail portion sections, there will be reduced flow separation during towing, reduced drag, and minimal bow wave and wake. These advantages should be achievable with a conical angle of 60 degrees, although sharper angles would be expected to provide greater advantages.
That said, there is a trade off between sharpness of angle in the conical shaped nose portion and conical shaped tail portion, and capacity of the container. In practice, a conical angle of 45 degrees in the horizontal plane and 30 degrees in the vertical plane provides a container with the best compromise between reduced drag and maximised liquid carrying capacity.
An additional advantage that is achieved through the sharpness of the conical shaped nose portion and its flexibility is that incoming ocean waves are not reflected by the container, but rather travel through the container, without substantially reducing its tow speed through the water.
Preferably the upper half-cylindrical body forms less than half the circumference of the body body, and the lower half cylindrical body forms more than half the circumference of the body when the container is filled with liquid. Preferably the lowermost surface portion has a smaller modulus of elasticity than the uppermost surface portion, to the extent that the lowermost surface portion has up to 10% greater stretch than the uppermost surface portion.
Preferably the lowermost surface portion has from 1 % to 10% greater stretch than the uppermost surface portion.
Preferably the lowermost surface portion has from 2% to 5% greater stretch than the uppermost surface portion.
Preferably the lowermost longitudinal extent of the container has from 1% to 5% greater length than the uppermost longitudinal extent of the container.
Preferably the lowermost longitudinal extent of the container has from 2% to 5% greater length than the uppermost longitudinal extent of the container.
The longer the container is, the lower will be the percentage difference in length between the lowermost longitudinal extent and the uppermost longitudinal extent, but most preferably the lowermost longitudinal extent of the container has about 2% greater stretch or length than the uppermost longitudinal extent of the container.
Preferably, in order to minimise peak forces in stress levels in the material of the body of the container during severe sea states, the material of the body has elasticity in transverse (hoop) direction at least as high as the elasticity of the material in the longitudinal direction. Preferably the material of the body is capable of withstanding a required stretch before failure in the order of 15% to 20% of the unloaded length.
Preferably the upper half-cylindrical body and the lower half-cylindrical body are segmented, being formed of upper surface segments and lower surface segments respectively, where the sum of the maximum lengths of the lower surface segments along the longitudinal extent of the body, exceeds the sum of the lengths of the upper surface segments along the longitudinal extent of the body, by a maximum of 10%. This can be achieved by fabricating the lower surface segments on a three dimensional formwork. Preferably the sum of the maximum lengths. of the lower surface segments along the longitudinal extent of the body exceeds the sum of the lengths of the upper surface segments along the longitudinal extent of the body, by a maximum of 8%.
Preferably the sum of the maximum lengths of the lower surface segments along the longitudinal extent of the body exceeds the sum of the lengths of the upper surface segments along the longitudinal extent of the body, by a maximum of 6%.
Preferably the sum of the maximum lengths of the lower surface segments along the longitudinal extent of the body exceeds the sum of the lengths of the upper surface segments along the longitudinal extent of the body, of from 1% to about 4%.
Preferably the sum of the maximum lengths of the lower surface segments along the longitudinal extent of the body exceeds the sum of the lengths of the upper surface segments along the longitudinal extent of the body, of about 2%.
Joining segments of the body can be through sewing and thermally bonding, gluing or chemical welding, or other means that are known in the art.
The arrangement of the conical shaped nose portion and the conical shaped tail portion with the body effectively provides streamlining by "fishtailing.
Preferably the towing means comprises a plurality of lines attached in a substantially horizontal/flat plane along the conical shaped nose portion, being attached at multiple points to minimise point loadings on said conical shaped nose portion.
Preferably the towing means comprises a plurality of cords welded or bonded along the conical shaped nose portion, being attached at multiple points in a single plane along a horizontal longitudinal extent of said conical shaped nose portion to minimise point loadings on said conical shaped nose portion. Connecting along a horizontal longitudinal extent of said conical shaped nose portion, which may preferably be along the join or seam between the upper half conical portion and the lower half conical portion of said conical shaped nose portion, maintains flexibility in said conical shaped nose portion, which gives the required properties of being able to absorb and transfer wave energy incident on the conical shaped nose portion. Preferably said cords are circular and are braised or flattened out into flat straps close to their connection points to the container body.
Preferably the cords fan out in a horizontal or flat plane from a connector to which a further towing line may be attached to a towing vessel, to their connection points to the container body.
Preferably said flat straps are bonded along the surface of said conical shaped nose portion at the interface between the upper half conical portion and the lower half conical portion, and at the other end the cords merge at a connector to which a further towing line may be attached to a towing vessel.
Preferably said flat straps are bonded along the surface of said conical shaped nose portion at the interface between the upper half conical portion and the lower half conical portion, and bonded to each other, and at the other end the cords merge at a connector to which a further towing line may be attached to a towing vessel. The bonding along the surface increases the strength of the attachment of the conical shaped nose portion to the towing line, and maximises streamlining, and so minimises drag resistance.
Preferably the container includes a fluid transfer port located on or proximal to said conical shaped nose portion. The fluid transfer port may have any number fluid ports for receiving nozzles connected to pipes for filling and emptying, as required to suit the application and capacity of the container.
Also in accordance with the invention there is provided a container for transporting a fresh water through sea or ocean, said container having a flexible cylindrical body, closed at each end by a slender tapering conical portion tapering to a point at each end, said body being formed of impervious material more buoyant than water, said container having towing means located depending from one or both of said points for pulling said container, said body having an uppermost longitudinal extent and a lowermost longitudinal extent, wherein said uppermost longitudinal extent is longitudinally shorter when under tension than said lowermost longitudinal extent, allowing said body to expand more underneath when filled with water, and so urging said points to the water surface while the entire upper longitudinal extent of said body floats above the sea or ocean surface. Also in accordance with the invention there is provided a storage system for compacting the container as described above, after its emptying, said storage system comprising a spool onto which said container, when empty or during emptying, can be rolled, said spool being removably securable to a barge for support during spooling, and removable from said barge for transporting.
Preferably the barge is dynamically positioned to keep the rotational axis of the spool at right angles to the longitudinal axis of the container.
Also in accordance with the invention there is provided a storage system for compacting the container as described above, after its emptying, said storage system comprising a sleeve which may be stored in concertina fashion over a tube like applicator, said sleeve being deployed by passing said applicator around and along the length of said container when empty, encasing said container within said sleeve.
Preferably said sleeve is sealable and inflatable.
In accordance with a further aspect of the invention there is provided a transport system for transporting a liquid through sea water or fresh water, said transport system comprising a container as described above connected by its towing means via an inclined tow line to a towing vessel, said tow line being fed from an elevated position at an angle to said container sufficient to assist with maintaining the point of the most forward end of the container above the water surface, when the towing vessel is underway in a forward direction.
Preferably the elevated position is located along a column.
Preferably said column is pivotally mounted to said vessel.
Preferably said tow line is fed from a tensioning arrangement, arranged to feed in and out said tow line to maintain tension in said tow line between said towing vessel and said container within operational limits for said container and said tow line. This provides vessel movement pitch compensation in addition to compensation for positional variations brought about by the towing vessel and the container riding seas and swell, which will invariably translate to distance variations between the towing vessel and the container. Preferably said tow line is sufficiently stretchable to minimise peak forces at said container during severe sea states.
Preferably said elevated position is adjustable in height in order to adjust the elevation angle of said tow line to said container, to assist in maintaining the most forward end of the container above the water surface, in more severe sea states when the towing vessel is underway in a forward direction. It is important to prevent the nose of the container diving under the surface, as this would increase the drag force on the towing line to potentially unacceptable levels.
Preferably the elevated position is adjustable in height by a vertical heave compensator located on said towing vessel.
Preferably the elevation angle of the tow line is adjustable in the range of 10 degrees to 35 degrees.
Preferably the elevation angle of the tow line is adjustable in the range of 10 degrees to 30 degrees.
Preferably the elevated position is adjustable in the transverse direction in order to provide vessel movement roll compensation.
Preferably the elevated position is adjustable in the transverse direction by means of a dynamically controlled ram adjusting the transverse angle of said column.
In accordance with a further aspect of the invention there is provided a method of transporting a liquid through sea water or fresh water, said method comprising providing a container as described above connected by its towing means via an inclined tow line to a towing vessel, said tow line being fed from an elevated position at an angle sufficient to assist with maintaining the point of the most forward end of the container above the water surface, when the towing vessel is underway in a forward direction.
Preferably said tow line is fed from a tensioning arrangement, arranged to spool in and out said tow line to maintain tension in said tow line between said towing vessel and said container within operational limits for said container and said tow line. This provides vessel movement pitch compensation in addition to compensation for positional variations brought about by the towing vessel and the container riding seas and swell, which will invariably translate to distance variations between the towing vessel and the container.
Preferably said tow line is sufficiently stretchable to minimise peak forces at said container during severe sea states.
Preferably said elevated position is adjustable in height in order to adjust the elevation angle of said tow line to said container, to assist in maintaining the most forward end of the container above the water surface, in more severe sea states when the towing vessel is underway in a forward direction. It is important to prevent the nose of the container diving under the surface, as this would increase the drag force on the towing line to potentially unacceptable levels.
Preferably the elevated position is adjustable in height by a vertical heave compensator located on said towing vessel.
Preferably the elevation angle of the tow line is adjustable in the range of 10 degrees to 35 degrees.
Preferably the elevation angle of the tow line is adjustable in the range of 10 degrees to 30 degrees.
Preferably the elevated position is adjustable in the transverse direction in order to provide vessel movement roll compensation.
Alternatively, the elevated position is provided by a floating hull with elevating sheaves for the tow line, located closely to said container to provide the required elevation.
Brief Description of the Drawings A preferred embodiment of the invention will now be described in the following description or a water transport container made with reference to the drawings in which:
Figure 1 is a lateral elevation of a water transport container according to the embodiment; Figure 2 is a top plan view of the water transport container of figure 1 ;
Figure 3 is a transverse cross section of the water transport container through the body thereof, in a largely emptied state;
Figure 4 is a transverse cross section of the water transport container through the body thereof, in a filled state;
Figure 5 is a plan view of a fluid transfer port apparatus utilised with the water transport container;
Figure 6 is a plan view of a fluid transfer port apparatus utilised with the water transport container;
Figure 7 is a vertical cross-section through the fluid transfer port and apparatus shown in figure 5; Figure 8 is a plan view of a segment of the lower half cylindrical body of the water transport container, with a segment of the upper half cylindrical body of the water transport container shown in dotted outline for comparison;
Figure 9 is a side elevation showing assembly of the body of the water transport container, and illustrating an assembly jig for joining segments of the lower half cylindrical body and the upper half cylindrical body of the water transport container;.
Figure 10 is a side elevation of parts of the water transport container showing joined segments of the lower half cylindrical body and the upper half cylindrical body, and showing the segmented structure in the conical shaped nose portion and conical shaped tail portion of the water transport container;
Figure 11 is a plan elevation showing retrieval of a water transport container being emptied whist being wound onto a floating drum secured to a barge;
Figure 12 is a plan elevation of the barge and the floating drum shown in figure 11 ; Figure 13 is a side elevation of the barge and the floating drum shown in figure 11 ;
Figure 14 is a plan elevation showing retrieval of an emptied water transport container according to an alternative sleeving method;
Figure 15 is a plan elevation showing retrieval of the emptied water transport container according to the alternative sleeving method; and
Figure 16 is a cross section view of the sleeved emptied water transport container readied for transport;
Figure 17 is a lateral elevation of a towage vessel in use towing the water transport container of the embodiment; Figure 18 is a transverse view through part of the towage vessel shown in figure 17;
Figure 19 is a lateral elevation of an alternative towage vessel and arrangement, in use towing the water transport container of the embodiment; and Figure 20 is a transverse view through part of the towage vessel arrangement shown in figure 19.
Best WΙode(s) for Carrying Out the Invention
The embodiment is a streamlined water transport container 11 for transporting water across large distances. The water transport container 11 is a flexible bag like container, which is, in use, directly floated in the ocean (or other body of water), and towed across the surface of the ocean to transport water to water deficient regions. Upon arrival, the transported water in the container can be unloaded, treated if necessary, and then introduced into the water supply for any population centre in the water deficient region.
The container 11 has a resiliently flexible tube like body 13 which is closed at a forward end or nose 15 by a resiliently flexible conical shaped nose portion 17 which gradually tends to a point 19 at the most forward end 21 of the container 1 1. The body 13 is closed at a rearward end or tail 23 by a resiϋently flexible conical shaped tail portion 25 (conical tail) which also gradually tends to a point 27 at the most rearward end 29 of the container 11.
The body 13 (and the conical nose 17, and the conical tail 25) is made of water impervious material which is a marine grade loopmatting polypropylene woven fabric, and is made waterproof by a coating which provides sufficient durability in sea water and resists ultraviolet degradation at least for a useful serviceable life of the container. The coated fabric is nominally 3mm to 4mm thick, and is buoyant in water. The coated fabric is engineered to withstand 50kN/m2 pressure differential across the interface between the fresh water inside and salt water outside the largely submersed. This is roughly ten times the actual pressure differential that could occur during severe sea states, and is designed to ensure that the container will withstand rough sea states, in use.
The container 11 has towing means in the form of a towing tether 31 attached to the conical shaped nose portion 17, which may be secured to a hitch ring 33 and tow line 35 for a towing vessel 37 to tow the said container 11. The body 13 has a longitudinal uppermost surface portion 41 extending along the length at the top of the body forming in use at least part of an upper half-cylindrical body 43 and having a longitudinal lowermost surface portion 47 extending along the length at the bottom of the body forming in use at least part of a lower half-cylindrical body 49. The uppermost surface portion 41 is longitudinally shorter when under tension than the lowermost surface portion 47 when under equivalent tension, which results in the body 13 swelling more in the lower half of the body (located below the waterline 51 ) when filled with water, and consequently urges the points 19 and 27 of the conical nose 17 and the conical tail 25 to rise to the water surface 51. This urging, in combination with the buoyancy of the fabric, results in the angle of the conical shaped nose portion longitudinal surface relative to the longitudinal axis of the conical shaped nose portion being nominally about 22 degrees in the horizontal plane and nominally about 15 degrees in the vertical plane when the container 11 is filled with water. This equates to an angle between longitudinal surfaces (conical angle) of nominally about 45 degrees in the horizontal plane and nominally about 30 degrees in the vertical plane when the container 11 is filled with water. The conical tail 25 is constructed in the same manner, so the angles observed in the conical tail 25 will be the same as described above for the conical nose 17. In addition, since the material of the body is more buoyant than water, the entire uppermost surface portion from point 19 to point 27 will lie above the surface of the water, and especially when the container 11 is filled with fresh water and resting in sea water.
The conical shaped nose portion 17 and the conical shaped tail portion 25 each have an uppermost surface portion forming in use at least part of an upper half-conical portion and each have a lowermost surface portion forming in use at least part of a lower half-conical portion. The conical nose 17 and conical tail 25 uppermost surface portions are longitudinally shorter when under tension than the conical shaped nose portion lowermost surface portions when under equivalent tension (when the container 11 is filled with water), and so assist in forcing the end points 19 and 27 to the water surface 51. The differing lengths between the uppermost surface portions compared with the lowermost surface portions are achieved through the cross-section plane at the transition 53 between the conical nose 17 (and the conical tail 25) and the body 13 being at an acute angle 55 to a plane 57 normal to the longitudinal axis 59 of the conical nose 17 (and the conical tail 25). Note that the longitudinal axis of the conical nose 17 (or the conical tail 25) and the longitudinal axis or extent of the container 11 are not the same. In use the longitunal axis of the conical nose will be disposed at an obtuse angle relative to the longitudinal extent of the container, of perhaps up to 11.25 degrees (Refer to figure 1).
As can be seen in figure 1 , the body 13 when filled with water and floating in the sea, has a narrowing tapering diameter towards the nose 15 and the tail 23. There is a smooth surface transition between the surface of the body 13 and the surface of said conical shaped nose portion 17 and the surface of said conical shaped tail portion 25, which separation of the water flow from the body of the container, thus minimising its form drag in the water during towing, so reducing drag.
The container includes a fluid transfer port 61 located proximal to the conical shaped nose portion 17, at the forward end 15 of the body 13. Referring to figure 7 the transfer port 61 is shown in cross-section, mated with a nozzle connector. Referring to figures 6 and 7, the fluid transfer port has two closable apertures 63 into each of which are received a nozzle head 65 with highly permeable domed cage 67 which protrudes into the interior of the container 11 and is provided to prevent the inner surface of the fabric from blocking the outlet during emptying. The nozzle heads 65 are supported in a flotation body 69 which can sealingly mate with the material of the body along the uppermost surface portion 41 of the body 13 of the container 11. The nozzle heads form a manifold, which is connected via flanged connectors 71 to floating hoses 73, to convey the water from or to the container 11.
The flotation body 69 has sufficient flotation capacity whilst at the same time being heavy enough to press down with sufficient weight onto the uppermost surface portion 41 of the body 13 of the container 11 , in order to accomplish the required watertight sealing. The nozzle heads 65 are arranged to minimize pressure head loss by means of a gradually widening cross section in combination with a relatively large radius of curvature, to assist in maximising water conveying capacity.
Referring to figures 8 to 10 detail of the structure of and construction of the body 13 will now be discussed. As will be understood from the description which follows, the container 11 is fabricated in the shape of a flat two dimensional profile, symmetrical about its longitudinal axis in top plan or bottom plan view, and symmetrical about its transverse central avis, at any point along the longitudinal extent of the body 13. The upper half-cylindrical body 43 forms nearly half the circumference of the body 13, and the lower half cylindrical body 49 forms slightly over half the circumference of the body 13.
Referring to figure 10, the upper half-cylindrical body 43 and the lower half-cylindrical body 49 are segmented, being formed of upper surface segments 75 and lower surface segments 77 respectively. The sum of the maximum longitudinal lengths of the lower surface segments 77 exceeds the sum of the maximum longitudinal lengths of the upper surface segments 75 by about 2%.
The lower surface segments 77 have a nominal maximum width of 5 m and a length of 51m, (although up to 55 m might be possible) while the upper surface segments 75 have a nominal width of down to 4.9 m and a length of 50m. (It will be appreciated that the segments are not shown to scale in the drawings.) An upper surface segment 75 is laid flat on the ground, preferably a concrete floor in a factory, and a jig 79 (shown in cross-section in figure 9 (note that it is not to scale), figure 9 being a view through section C-C of figure 8) having a flat base 81 is laid over the upper surface segment 75, leaving all four edges exposed. A lower surface segment 77 is placed on the curved upper surface 83 of the jig 79 and the coincident longitudinal edges 85 of the lower surface segment 77 and the upper surface segment 75 are sewn together and then thermally bonded to seal the surfaces together. An upper surface segment 75 is illustrated in figure 8, overlying the jig 79. The underlying upper surface segment 75 has its transverse edges 87 shown in dotted outline, extending between opposite longitudinal edges 85.
Once the lower surface segment 77 and the upper surface segment 75 are joined, a new upper surface segment 75 is placed alongside the previous upper surface segment 75 with transverse edges 87 mating, which are then sewn and thermally bonded. The jig 79 is then slid onto the newly laid upper surface segment 75, and as this occurs the previously joined upper surface segment 75 will collapse onto the underlying lower surface segment 77 (shown as body 13 in figure 9). With the jig 79 repositioned, a new lower surface segment 77 is placed on the curved upper surface 83 of the jig 79 and the coincident longitudinal edges 85 of the lower surface segment 77 and the underlying upper surface segment 75 are sewn together and then thermally bonded to seal the surfaces together. The coincident transverse edges 89 of the adjacent lower surface segments 77 are sewn together and thermally bonded. Further segments are added in the same manner as construction of the body proceeds. The conical shaped nose portion 17 and conical shaped tail portion 25 are constructed in a similar manner to the body 15, and joined to the completed body 15. Referring to figure 5, the longitudinal edges 91 of segments 93 forming the conical shaped nose portion 17 have lines 95 attached along them, being attached at multiple points to minimise point loadings on the conical shaped nose portion 17.
The lines are in the form of flat cords 95 which are sewn and heat bonded along the longitudinal edges 91 of the segments 93 forming the conical shaped nose portion 17. The attachment of the cords 95 to the conical shaped nose portion 17 is in a single plane along a horizontal longitudinal extent of the conical shaped nose portion 17 (horizontal longitudinal extent of the conical shaped nose portion 17 when the conical shaped nose portion is filled). Connecting along a horizontal longitudinal extent of the conical shaped nose portion 17, which is not coincident with the longitudinal axis if the body 15, as the conical shaped nose portion in use will point upwards, maintains flexibility in the conical shaped nose portion, which gives the required properties of being able to absorb and transfer wave energy incident on the conical shaped nose portion.
Referring to figures 3 and 4, an optional feature is illustrated which may be utilised in an alternative embodiment. The optional feature comprises providing the upper half- cylindrical body 43 of the body 13 with two double skin areas 101 along opposed longitudinal edges of the half-cylindrical body 43 of the body 15. This is shown in figures 3 and 4 in transverse cross-section through the body 15. The two double skin areas 101 form bladders 103 that may be inflated with air as is shown in figures 3 and 4. After inflation with air and filling of the body 15 of the container 11 with water, to full capacity as shown in figure 4, the bladders 103 enhance the rotational stability of the container 11.
Furthermore, the entrained air, by virtue of its high compressibility would have a significantly reducing effect on the peak hoop stress that would be generated in the body 15 of the container 11 by vertical 'squeezing' of its cross-sectional profile during severe wave action.
The water transport container 11 is filled with water at the port of origin, and then towed to the destination. Existing single point mooring (SPM) technology can be used to moor the container 11 for unloading. Unloading takes place as described above with reference to figures 6 and 7.
An operational control vessel 111 would be permanently stationed at a single point mooring (SPM) buoy 113 by means of telescopic connection means 115 which would preferably have a cradle end 117 with cushioning fenders 119 to prevent the operational control vessel 111 from swaying sideways into the SPM 113 at reversal of the tidal flow.
After the towing vessel has transferred the water transport container 11 by means of tow rope 121 to the operational control vessel it is moored at the tail of the water transport container 11 by means of a tail rope (not shown). At the turning of the tide the towing vessel would apply sufficient pull at the tail rope to keep the water transport container 11 fully stretched whilst the entire assembly swings around like a 'weathervane' through an arc of roughly 180 degrees.
Following 'docking' of the water transport container 11 , by attaching tow rope 121 to constant tension winch 123, nozzle heads 65 connected to the flotation body 69 are lowered, by means of a deck crane (not shown), onto the container's fluid transfer port 61 , after which unloading of the water transport container 11 would commence.
The container 11 could be towed back to its point of origin after most of its liquid content has been pumped out. Despite its greatly reduced draught, more than fifty percent of the skin of the container 11 would remain submerged. As a consequence the hydrodynamic towage resistance of the largely emptied container would not be much smaller than the towage resistance of the container 11 when filled, however this is seen as a disadvantage. Figures 11 to 16 illustrate two techniques for reducing sea water contact surface area of the container 11 , and consequently reduces the drag force during towage of the empty container 11.
Referring to figures 11 , 12, and 13, the container 11 is wound, during the emptying process, on a floating drum or spool 125 which is flexibly attached to a dynamically positioned barge 127. The rotation of the spool 125 squeezes the container 11 , increasing its internal water pressure, as the container 11 is wound onto the spool via a motor and gear box and belt drive arrangement 128. As a consequence the capacity of the discharging pump on the operational control vessel 111 is increased, resulting in a reduction in emptying time. Once the container 11 has been fully wound up on the spool 125, the spooled container 11 /spool unit 129 is unhitched from the barge 127, but it would not be taken on board of the towing vessel as this would increase its weight and draught and, as a consequence, reduce its speed through the water. Instead the unit 129 is towed with the spool axis aligned longitudinally, closely behind the towing vessel's stern, in order to minimise its protrusion beyond the vessel's stern wake boundary and, as a consequence, decrease the drag force on the spooled container 11/spool unit 129, enabling the towing vessel to approach its hull speed limit when under full power.
Referring to figures 14 to 16, a second technique is shown to reduce the fhctional contact area between the seawater and the container 11. Referring to figure 14, this entails squeezing the container 11 into a much smaller cross section. This is accomplished through encasement into an impervious fabric sleeve 131 which is stored in concertina fashion 133 on the outside of an applicator in the form of a rigid, trumpet shaped collar 135, and can be deployed off the narrow end of the collar 135. The impervious fabric sleeve 131 is gradually be released from the rigid, trumpet shaped collar 135, as the collar 135 is pulled over and along the container 11 tail 27 to front 19 by means of wires or ropes 137 after the end edge 139 of the fabric sleeve 131 has been tied to a tail rope 141 attached to the tail 27 of the container 11 , the tail rope 141 being connected to a stationary tender vessel 143. During the pulling of collar 135 from the tail of the container 11 to the nose of the container 11 , the container 11 is kept under longitudinal tension by means of pull force exerted by tender vessel 143 on the tail rope 141.
After the container 11 has been fully encased within the fabric sleeve 131 , the fabric sleeve is sealed at both ends. After removal and storage of the collar 135 onto the towing vessel 145 (see figure 15), the air pressure within fabric sleeve 131 is increased by means of air pump 147 which supplies air to the sleeve 131 by means of a hose 149. This has the effect of increasing the roundness of the sleeve's cross sectional profile from indicative profile 151 (in figure 16) to indicative profile 153 as shown in section A-A'. (the encased container 1 1 is not shown within the sleeve 131 in figure 16). As a consequence the sleeve's contact area with the seawater and its associated towage resistance are substantially reduced. In order to minimise time loss, towing could commence before the sleeve has been fully inflated. During the pressurization process and the associated, increasing roundness of the sleeve 131 , the towing vessel 145 would gradually gain speed until approaching its hull speed limit, if operating at full power. By providing the tail end or nose end of the container with a drainage hose 155 the above described pressurisation process would also have the beneficial effect of forcing all residual liquid from the container, minimising its mass and associated towing resistance.
As an alternative to pressurising the sleeve 131 , it is possible to subject the sleeve 131 to a vacuum via hose 149, sucking air out of the sleeve, and in that manner shrink the profile to a minimum, in order to reduce drad forces during towing.
Further arrangements are envisaged for return transport of the container 11 , which may include squeezing the empty container 11 into a fabric sleeve which would be unrolled like a sock or condom from the container's tail end over its full length after tail rope 141 would have been passed through an orifice in the anterior of the sleeve and re-attached to the point the container 11 was moored at. Whilst the container 11 is kept fully stretched by a moderate tow force applied by a towing vessel, the sleeve is pulled towards the front end of the container by means of wires or ropes which would be hauled in from the operational control vessel by means of winches. The applied pull force is indicated by the arrows. After the container has been fully encased, a toxic gas or liquid could be injected within the sleeve before it is sealed, for the purpose of exterminating marine growth. The wet cross section of the sleeved container is relatively small, minimizing its hydrodynamic towage resistance. This enables the towage vessel to reach a speed close to its hull speed limit when towing the sleeved container back to its point of origin.
Referring to figure 17, towage vessel 37 is shown connecting to the point 19 at the forward end 21 of the body 13 of the container 11 , by tow line 35. The towage vessel 37 has a column 161 which is pivotable transverely about a hinged connection 163. Roll compensation in the vessel 37 is provided by a hydraulic ram 165, as seen in figure 18 which is a transverse view through the vessel 37 through the column 161. The hydraulic ram 165 is controlled by control circuitry (not shown) to maintain the column 161 in an upright position, as near as vertical as possible.
The tow line 35 runs across circular sheaves 167, 169 to a horizontal surge compensator (sc) 171. While the horizontal surge compensator is shown as a ram arrangement, alternatively it may be in the form of a constant tension winch. The upper sheave 167 providing an elevated position, is connected by a steel cord 173 to a slide 175, which is slidable along the column 161 , controlled by control circuitry (not shown), in order to be able to alter tow angle a. The column 161 , with hinged connection 163 to the vessel's deck 177 is supported against falling towards the stern 179 of the vessel 37 by means of steel cord 181 , which connects to a connection point 183 located forwardly of the hinged connection 163.
The control circuitry (not shown), controls the roll compensator by adjusting the hydraulic ram 165, which extension is controlled by through the control circuitry being connected to a device that measures the roll angle of the vessel, ensuring that the column remains vertical at all times at any roll angle of the vessel. Longitudinal,
(forward or backward) motion of the column and hence the elevated position, as caused by pitching of the vessel is compensated by horizontal surge compensator 171.
Figure 19 is a view of an alternative towing vessel 37 which does not include a vertical column. Instead, the horizontal surge compensator 171 pays out tow line 35 as required, to maintain the required tension on the tow line 35. With a combination of sufficient 'stroke' of the surge compensator 171 , in combination with the stretch of the tow line 35 and stretch in the container 11 itself (because of its high stretchability in the longitudinal direction in combination with its great length, normally in excess of 500m), the container should be readily towable with long line towing, without failure occurring. In this embodiment, to avoid the roll compensation issue, the beneficial effect of the column is provided by a small streamlined float 185 having twin hulls 187, which is towed behind the towing vessel 37. The elevated position for the tow line 35 is provided by two pulleys 189 which are mounted above the hulls 187 on triangular framework 191 as shown in the figure 20
The water transport container 11 of the embodiment provides an arrangement where the drag resistance is minimised, through its bow and stern sections having a sufficiently small end angle, both in the horizontal plane and vertical plane, and a sufficiently large radius of curvature in the vertical plane (under water) and in the horizontal plane, preventing the main flow separating from the container and minimizing wave energy reflection.
The water transport container 1 1 is manufactured in such manner that the floating filled container will deform longitudinally in the vertical plane to the extent that the buoyancy of the fresh water inside the container lifts its end points to or close to the external water surface. This process can be aided and nose diving of the container can be prevented during severe sea states by upward force exerted at the bow end of the water transport container 11 by means of a tow rope or ropes array with positive tow angle, or by a towed float with an incorporated elevated pulley system through or over which the tow line can pass. At the stern, if necessary, this process can be aided by a suitably streamlined float which is attached to the rear of the water transport container 11. In addition this process is aided by the material from which the water transport container is constructed having a density lower than water.
It will be understood that the required deformation of the floating filled water transport container 11 can be established by ensuring that the water transport container skin material has sufficiently large elasticity in longitudinal direction, whereby, in- an alternative equally preferred embodiment, the elasticity of the lower layer is higher than the elasticity of the upper layer. Alternatively this can be achieved, as it is in the described embodiment, by using a concave template during construction of the segments forming the lower surface of the body of the container. The template should be concave in the vertical plane, in both directions (transverse and longitudinally).
It should also be understood that in order to minimize peak forces in the fabric during severe sea states the fabric's elasticity in transverse (hoop) direction should be at least as high as the elasticity of the container's skin material in the longitudinal direction.
In the transport system of the embodiment, the use of a traditional tug or specially designed towage vessel with a relatively long waterline and low drag resistance in the water is envisaged. The tug or powered vessel is connected to the water transport container 11 by means of an inclined tow rope in conjunction with an on-board stretching (or rope spooling) device in order to ensure that the peak force in the towing rope remains below an allowable limit during severe sea states.
The water transport container 11 of the embodiment is arranged to be compatible with the use of traditional single point mooring technology including an operational control vessel with (optionally) a shock absorber/cradle structure for emptying a filled water transport container by means of floating hose(s) with specially designed nozzle(s) head. These should have sufficient weight to provide a leakproof connection with the fluid transfer port 61 or 'blow hole' of the water transport container 11. The system of the embodiment also provides reduced towage resistance of an emptied water transport container 11 by means of reducing its wet contact area with the surrounding water through either squeezing the container lengthwise into a sleeve or collar, after which its wet circumferential area can (optionally) be further reduced by increasing or decreasing internal air pressure, or winding the largely emptied container 11 onto a floating drum or cylinder which is spooled with its axis at right angle to the container's longitudinal axis. The winding can be achieved by means of a dynamically positioned barge to which the floating drum or cylinder is flexibly connected. The winding takes place from the rear and results in the contents of the water transport container 11 being urged forwardly toward the fluid transfer port, through which they can be emptied. The squeezed or rolled container 11 can be towed closely behind the towing vessel in order to ensure that most of its cross sectional profile falls with the wake zone of the towing vessel, thus greatly reducing the required towage force.
It should be appreciated that the scope of the invention is not limited to the specific embodiment described herein, and that changes may be made without departing from the spirit and scope of the invention.
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