AU696808B2

AU696808B2 - Stabilising method

Info

Publication number: AU696808B2
Application number: AU45862/96A
Authority: AU
Inventors: Ralph Downham
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-03-06
Filing date: 1996-03-01
Publication date: 1998-09-17
Anticipated expiration: 2016-03-01
Also published as: GB2298629B; GB9504406D0; GB2298629A; AU4586296A; GB9604761D0

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

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Name of Applicant: Actual Inventor: *5

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RALPH DOWNHAM and ALVIN DAVID TOMS Ralph DOWNHAM SHELSTON WATERS 60 MARGARET STREET SYDNEY NSW 2000 Address of Service: Invention Title: "STABILISING METHOD" The following statement is a full description of this invention, including the best method of performing it known to us:-

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-la- STABILISING METHOD This invention relates to loading and unloading at sea.

Not uncommonly material is transferred between a waterborne vessel and either another waterborne vessel or a ground based object. If even a moderate sea is running there will be relative movement of the two objects especially if a or the vessel is small.

The relative movement may cause difficulties. For example, if a crane is mounted on a fixed structure and is attempting to pick up material in the hold of a vessel there is a danger that the grab will strike the hatch coamings damaging the grab or coaming. The regulatory authorities will prevent a vessel with hatches that do not seal from sailing.

Assuming that the grab has negotiated the hatch it is then necessary to pick up material in hold space. If the vessel is moving upward relative to the crane the grab may strike the hull bottom damaging the grab or the hull. If the vessel falls away then material may not be picked up.

Where the crane is mounted on a vessel the problem is likely to be even more severe since the vessel being unloaded will float higher and higher in the water while the draft of the vessel being loaded will increase.

According to the invention there is provided a method of loading or unloading a first vessel, the method comprising the steps of: i. providing a second vessel having a) a positive metacentric height b) a load bearing surface for engaging the first vessel c) a plurality of floodable buoyancy columns upstanding from the SRA loadbearing surface the buoyancy columns having a discharge -111 1 -2d) a plurality of floodable buoyancy tanks, and e) transfer means, ii. flooding at least some of the buoyancy columns or buoyancy tanks so that the load bearing surface of the second vessel is submerged.

iii. positioning the second vessel with the load bearing surface under the first vessel and with the buoyancy columns flooded above the waterline of the second vessel, iv. discharging water from the buoyancy columns such that the load bearing surface engages the first vessel, and v. loading or unloading the first vessel with the transfer means.

Embodiments of the invention will be illustrated by way of non-limiting example only by reference to the accompanying figures of which: Fig. 1 is a plan view at main deck level of a vessel for use in the invention.

S:Fig. 2 is a plan view at the gantry level of the vessel of Fig. 1.

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Fig. 3 is a plan view of he accommodation deck of the vessel of Fig. 1.

Fig. 4 is a plan view of the bridge deck of the vessel of Fig. 1.

Fig. 5 is a side elevation of the vessel of Fig. 1 alongside a Panameax bulk carrier and supporting a barge.

Fig. 6 is an amidships section of the arrangement of Fig. Fig 7 is a top plan of the vessel, barge 3.,d bulk carrier.

Fig. 8 is a schematic cross section of the arrangement of Fig. 7.

The second vessel 1 of use in the method is semisubmersible. It is movable between a first position with the main de k below the waterline, referred to hereinafter as the "transfer position", and a second position in which the waterline is lower typically -3with the main deck 2 above the waterline. The vessel 1 comprises a hull 3 with a main deck 2. The hull is provided with floodable ballast tanks (not shown) to vary the draft of the vessel. Main deck 2 has a top surface corresponding with the underside of a herein a "first vessel" barge to be received on it. Preferably, the barge bottom and main deck are flat-bottomed. The barge could however have a curved bottom and be received on a curved deck or on curved supports carried on the deck. A plurality of buoyancy columns are provided. A buoyancy column comprises a tank upstanding firom the second vessel that is capable of being filled to above the equilibrium water line of the second vessel transfer water line emptied. In general at least three buoyancy columns will be provided.

In the illustrated embodiment four buoyancy columns are provided. The cross-sectional area of the buoyancy columns is small.

o• The precise cross-sectional area is not of the essence of the invention. It is important however that the vessel should have a positive metacentric height. The e• buoyancy columns are desirably as small as possible while still providing a small positive metacentric height with all tanks fully flooded.

For example in the illustrated embodiment the waterplane area of the vessel where the main deck is above the waterplane is about 620 m 2 and the metacentric height 50 m with the tanks empty. In the fully flooded position the waterplane is about 100 m 2 and the metacentric height about 2m.

The vessel is ballasted to float with the main deck beneath the keel of the barge t'o be stabilised. Water is then pumped or drained from the buoyancy columns Because the columns are quite small a relatively large change in water level is obtained by a relatively small change in buoyancy of the vessel. Since the total area of -lb.

-3athe buoyancy columns in the illustrated embodiment is 100 m 2 a change in buoyancy of 100t requires the water level in the columns to empty by 1 m. This upward force is sufficient to "fix" the vessel quite firmly to the underside of the barge without undue stress.

If a 0.5 m above the main water plane wave sweeps past the vessel immersing two columns an extra 0.5 m and a corresponding 0.5 m trough exposes 0.5 extra of the remaining columns there will be a increase in buoyancy at the submerged side of and a decrease in buoyancy at the exposed side of 25t. The change is thus sufficiently small to neither damage the barge nor "unstick" the vessel fiomn the underside of the barge In practice waves with a peak to trough height of around 2 mn will usually be S.enough to halt loading and unloading on other grounds and so a considerable safety o 0 margin will be present.

Since the second vessel is "stuck" to the bottom of the barge there will be little or no relative movement. Transfer means can then be provided on the second vessel for loading and unloading the barge. As will be seen from the plan views herein the hatches of bulk carriers are large compared to the size of the loading barges which means that there is quite a low chance of damaging the bulk carrier hatch cover while loading the bulk carrier. Similarly discharge to land can be from a feed head positioned say 1.5m above any components with little danger of damage. As the barge is unloaded it will tend to rise, and more slowly, the bulk carrier will tend to sink.

This does not matter greatly since the second vessel will

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remain in contact with the barge If necessary the vessel could be deballasted or the barge ballasted to ensure that the barge and vessel remain in contact.

Where as in the illustrated embodiment the buoyancy columns are filled above the waterline of the vessel when at its greatest draught, changes of ballasting of the vessel may not be necessary as the barge is unloaded. As hereinbefore described the vessel is positioned under the barge and deballasted to give a moderate up thrust. The seacocks to the buoyancy columns are left open. As the barge is unloaded it rises in the water. The vessel rises under it and water drains from buoyancy columns giving a substantially constant upward force. It may be desirable however to provide fenders (10) for example of Yokohama type between the bulk carrier and the barge/vessel combination since the barge will tend to rise and the bulk carrier will tend to sink.

.9 The precise discharge method employed is not of the essence of the S' 15 invention. For example a simple grab crane could be mounted on the vessel. In other embodiments an Archimedes screw can be employed. This is particularly desirable for grain. Other methods included bottom unloading and loading.

In a preferred embodiment of the invention at least one bucket chain S• unloader (11) is provided. In the illustrated embodiment a single bucket chain 20 unloader (11) is mounted on a gantry (12) on linear bearings. The unloader (11) can traverse the barge deck (13) and is adjusted to be just proud of the deck (13).

The unloader (11) can transverse the barge from side to side and then be moved end-to-end relative to the barge Alternatively the unloader (11) can traverse from end-to-end and then side to side. Rel 'ive movement can be achieved by pulling the barge through the vessel as described hereinafter or the gantry and unloader can slide relative to the vessel.

In a preferred embodiment two bucket chain unloaders can be ganged together side by side. The initial traverse is through the centre line of the pyramid of material, for example coal, carried on the barge. Much of the material is removed leaving two smaller lines of material. Each unloader can be run through a line removing the vast majority of material. In many cases the barge will be sent to receive a further load and so the remainder can be left. If desired it could for example be bulldozed into position and then removed.

Having lifted the material from the barge deck the next step is to transfer the material. Particulate material can only be efficiently transferred at moderate angles unless for example an airlift or Archimedes screw is used and therefore an indirect transfer is preferred to raise the material over the bulk carrier's rails.

Material is discharged from the bucket unloader (11) to a first conveyor The first conveyor (14) is generally substantially horizontal. The first conveyor (14) discharges onto a first transfer conveyor which in plan view is generally perpendicular to the first conveyor The first transfer conveyor (15) is inclined at up to about 150 to the horizontal. First transfer conveyor discharges onto a second transfer conveyor (16) generally antiparallel in plan view of the first conveyor Like the first transfer conveyor (15) the second transfer conveyor (16) is inclined at up to about 15° to the horizontal. These conveyors (14, 15, 16) convey the material around three sides of a rectangle allowing it to be elevated and brought alongside the bulk carrier The second transfer conveyor (16) discharges to a boom mounted, telescopic ship conveyor The ship

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S conveyor (17) discharges through the hatches of the bulk carrier As the ship conveyor (17) is telescopic when a first hold is full the boom can be extended to discharge into a further hold. This reduces the need to warp the barge and vessel combination along the side of the bulk carrier.

Positioning the vessel relative to the barge can require skill. The kinetic energy of a small barge weighing 5700t including cargo and moving a inms is about equal to the energy released by detonating about 0.75kg of TNT. To reduce the required skill and the likelihood of damage fenders may be provided. Preferred

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fenders are illustrated in the figures. Some buoyancy columns are provided with rubberised wheel fenders (20) mounted for rotational movement about a vertical axis.

Preferably at least some fenders (20) are mounted on arms (21) capable of being biased over the main deck for example by hydraulic rams. Preferably pairs of arm mounted fenders are joined by tiebars In use the arm mounted fenders are at least partially retracted to provide a moderately wide entry passage for the barge. If too small it will be difficult to receive the barge on the main deck and if too large the barge may acquire the significant kinetic energy during its movement and thus increase the likelihood of damage. When the barge is received over the main deck the arms are extended so as to gently but firmly press the barge against the opposing fenders. In a similar way the main deck may be provided with wheel fenders (24) although they will be generally rotatable 4e 4 about a horizontal axis. As illustrated a double line of wheel fenders runs down the S* centre of the main deck a single line runs to each side of the centre line. Preferably these fenders are resiliently mounted. It is preferred that at least some of the wheel fenders be powered for example by hydraulic motors this allows the barge to be accurately positioned and also to be moved under the unloader.

The vessel may be provided with accommodation and a wheelhouse. Since the main hull is submerged in the transfer position the accommodation and wheelhouse are conveniently situated elsewhere for example on top of a buoyancy column.

It will be apparent to the skilled worker that the invention is by no means restricted to the use hereinbefore described.

Claims

1. A method of loading or unloading a first vessel, the method comprising the steps of: i. providing a second vessel having a) a positive metacentric height b) a load bearing surface for engaging the first vessel c) a plurality of floodable buoyancy columns upstanding from the load bearing surface the buoyancy columns having a discharge d) a plurality of floodable buoyancy tanks, and e) transfer means, ii. flooding at least some of the buoyancy columns or buoyancy tanks so that the load bearing surface of the second vessel is submerged. iii. positioning the second vessel with the load bearing surface under the first vessel and with the buoyancy columns flooded above the waterline of the second 15 vessel, S" iv. discharging water from the buoyancy columns such that the load bearing surface engages the first vessel, and v. loading or unloading the first vessel with the transfer means.

2. A method as claimed in claim 1 wherein the transfer means comprises a bucket chain unloader.

3. A method as claimed in claim 1 wherein the transfer means comprise an Archimedes screw. M -8-

4. A method as claimed in any one of the preceding claims wherein the load bearing surface is provided with a plurality of rotatable wheel fenders.

A method as claimed in claim 1 wherein the buoyancy column is adjacent the load bearing surfaces and provided with rotatable wheel fenders.

6. A method as claimed in claim 4 or claim 5 wherein at least one of the wheel fend.,s are provided with a biasing means.

7. A method as claimed in claim 6 wherei, the biasing means comprises a hydraulic ram.

8. A method as claimed in any one of claims 4 to 7 wherein at least one of the wheel fenders is powered.

9. A method of loading or unloading a vessel substantially as described hereinbefore o by reference to any one cr more of the accompanying figures. DATED this RALPH DOWNHAM and ALVIN DAVID TOMS 15 Attorney: PETER R. HEATHCOTE Fellow Institute of Patent Attorneys of Australia Of BALDWIN SHELSTON WATERS *ll ABSTRACT The invention relates to a stabilising barges for loading and unloading in particular therein described a method of loading or loading a first vessel such as a barge comprising the steps of: i) positioning a second vessel having a positive metacentric height and a submerged load bearing surface under the vessel ii) deballasting the second vessel such that the lead bearing surface engages the first vessel without lifting the first vessel out of the water, iii) transferring the load by transfer means (11) mounted on the second vessel 0 *0* S 9* 99* 9