GB2075432A - Barge-carrying vessel - Google Patents

Abstract

A barge-carrying vessel S has a forepeak F an afterpeak A and a laterally open cargo deck D which, by filling ballast tanks sinks below water level so that loaded barges P1-P4 can be floated over the Deck D either for warping them out laterally for unloading or for winching them in for loading the vessel. In a modification, the deck D is open at the stern and the barges are warped out or winched in over the stern in a direction away from or towards the forepeak F. The vessel hull under the cargo deck has a substantially trapezoidal configuration in cross section in order to increase the stability of the vessel when submerged. The vessel bottom is formed by the shorter one of the two parallel sides of the trapezium. From the bottom the sides of the trapezoidal hull extend slopingly upwards to the cargo deck. When the vessel S is deballasted when under way, the deck D and the barges P1-P4 are above water level. The vessel can be a converted tanker and details are given of a method of conversion. <IMAGE>

Description

SPECIFICATION Barge-carrying vessel In the cargo freight shipping trade there has been for a long time a tendency to build larger and larger vessels in order to decrease transport operation and labour costs as far as possible. This tendency has however caused loading and unloading times of vessels in port to increase whilst port costs and manoeuvring costs in port have risen as vessel sizes have increased.

Another drawback with large vessels of several hundred thousand tons is that with increasing scarcity of freight orders, the large vessels are the first to undergo the risk of being laid up. In times of depression this has struck to a considerable extent against ore and tank tonnage particularly, where vessels of between 80,000 and 450,000 tons have been extremely prolific.

In recent times attention has been directed to those difficulties, there have been proposals inter alia, for collecting ocean-going barges into barge trains towed by ocean-going tugboats. Another proposal is concerned with cutting out large side panels in a tanker structure, these side panels being formed as load containers which by being fixed onto a skeleton part of the tankerform the outer hull shape of the vessel together with the carcase. In this iatter proposal, load containers of 250,000 tons per container are contemplated, with a total length of the skeleton part of the vessel of 600 metres.

Many ship design proposals are also known with which cargo-carrying barges are loaded on to ships with a recessed deck by submerging the deck of the mother ship under the water surface with the aid of ballast tanks so that the barges can float over the deck.

However, none of these proposals have been put into practice. This may be due to the fact that the problem of providing satisfactory stability of the mother ship during its sinking for loading or discharging and raising before continuing its voyage had not yet been satisfactorily solved.

An unsafe feature of most of the proposals is also that when the mother ship is under way the barges are positioned close to sea level or even partly submerged.

None of the proposals just mentioned are favourable from the seaworthiness aspect. The barge trains are naturally extremely sensitive to heavy seas, and this also applies to tankers made up from large load containers and a skeleton including fore and aft sections, or barge-carrying vessels with the barges carried close to the water level so that they are subjected to the effects of sea heaving. Stresses on the barge fixing arrangements and hydraulic locking devices on such vessels are enormous.

Barge-carrying ships or vessels have also been proposed where barges are floated in over a deck of the vessel, after the vessel has been ballasted to a suitable level, through ports opening in the bow of the vessel so that the barges are thus protected in heavy seas from the heaving action of the sea by means of the hull plating of the vessel. However, such bow ports are unmanageable and vulnerable, and have not constituted an ideal solution.

Further, such vessels are again not sufficiently stable when submerged during loading or discharging. This instability seems to be the most serious unsolved problem in all known proposals.

A measure of a vessel's stability is its metacentric height, i.e. the distance between the centre of gravity of the vessel and the intersection between the buoyancy resultant and the symmetry plane of the vessel when the vessel is heeled. This point, the vessel metacentre, has a practically unaltered position up to angles of heel of about 15 .

The metacentric height is, inter alia, dependent on the position of the centre of gravity of the vessel and the moment of inertia of the water line surface. So that a centre of gravity which is situated low down and a large moment of inertia give a large metacentric height which is dependent on the water density, so long as the water line surface intersects the side plating of the vessel, that is so long as the vessel is not totally submerged along part at least of its length.

A barge-carrying vessel, which has the major portion of the hull under the barge-carrying cargo deck filled with water during loading and unloading of the barge on to and off the vessel has hardly any stability other than that obtained from the fore and aft sections of the vessel. It has therefore been proposed to provide a longitudinal tank along each of the vessel chines, that is along the turns of the bilges, at the bottom of the vessel, to be used as air tanks. However, it is doubtful whether air tanks in this position greatly contribute to stability when the vessel has its cargo deck sunken.

The object of the present invention is to attempt to overcome the aforementioned difficulties in barge-carrying vessels and to this end, according to this invention, we provide a barge carrying vessel having a cargo deck, which is arranged to carry a plurality of barges and which is open laterally or at one end, the vessel having ballast tanks which when filled, cause the water level to rise above the cargo deck so that loaded barges can float over the deck either for warping out and winching in laterally for unloading and loading, or for warping out and winching in in a fore and aft direction, wherein the hull of the vessel under the cargo deck has a trapezoidal cross-sectional shape, the width of the bottom of the hull being equal to the length of the shorter parallel side of the trapezium, and the sides of the hull sloping upwards and outwards at least as far as the cargo deck.

Such a hull shape contributes to stability of the vessel when it is ballasted for floating barges on or off, as well as during emptying of the ballast tanks after loading or unloading barges.

Still further improved stability is gained by providing double-skin plating extending upwards from the sloping sides to the cargo deck on both sides of the vessel to form upright tanks at the sides of the cargo deck. The tanks may terminate with air tanks at their tops.

Alternatively, on either side of the trapezoidal hull, as seen in section, wing tanks of substantially triangular cross section may be provided along and directly below the cargo deck at both sides of the vessel, the wing tanks extending from the cargo deck to the chines to form the trapezoidal crosssection. These tanks also form air tanks.

Such a hull gives stability both during loading and unloading of barges as well as when the vessel is under way. Neither does the vessel require any barge entry ports which have to be sealed since the cargo deck is high above the sea surface out of contact with breaking seas when the vessel is deballasted and under way.

Loading and unloading of the barges may take place optionally with the aid of loading and unloading ports which are above water level when the vessel is deballasted, with the vessel in a bay or in other sheltered water close to a port. For this purpose the vessel is sunk sufficiently by filling ballast tanks so that the barges will float over the cargo deck for warping out or winching in during loading and unloading respectively. Subsequently the vessel is raised to normal freeboard heights, if required after loading new barges, by pumping water out of the ballast tanks.

The present invention stems from an exhaustive analysis of transport technique and loading and unloading techniques in port, particularly with regard to voluminous goods such as containers, trailers, automobiles and piece goods. The difficulties of getting large vessels into port and to wharfs as well as the requirement for sophisticated loading and unloading equipment has given the inventor the idea that the need is to have smaller vessels in port but during transport between the ports there is a need for as large and as seaworthy vessels as possible. These mutually incompatible requirements have given the inventor the concept that it is economic to be satisfied with very incomplete utilization of the cargo capacity of a large seaworthy vessel during transport provided that this makes it possible to simplify and accelerate load handling in port.

Investigation has established that even if only 2030% of a large vessel's cargo capacity is utilized in a vessel in accordance with the invention by distributing this capacity over a plurality of cargo barges disposed on the cargo deck of the vessel, then this brings about such a large saving in port fees, since the vessel does not need to go in to port, and in loading and unloading costs since loading and unloading take place from barge to port and vice versa, that the incompletely utilized load capacity of the vessel during the voyage is compensated to a large extent.

The invention also consists in accordance with another of its aspects of a method of building a vessel in accordance with the invention by converting an existing tanker. This method involves steps which will de described later.

Some examples of vessels, and an example of a method of building a vessel in accordance with the invention will now be described with reference to the accompanying drawings in which Figures 1, 2, and 4 are perspective views of one example of the vessel at different stages of operation; Figure 3 is a perspective view of a second example of the vessel; Figure 5 is a cross-section through the first example of the vessel along the line V-V of Figure 4; Figure 6 is a cross-section through the second example of the vessel along the line Vl-Vl of Figure 3, and Figure 7 is a cross-section showing a modification of the second example;; Figure 7 is a similar section of the modified embodiment according to Figure 3, where the vessel is provided with vertically arranged tanks on either side of the vessel, and formed by double sides.

As will be seen from Figure 1, a barge-carrying vessel S has a forepeak or forecastle F and an afterpeak or poop A. About a fifth of the hull volume is cut away along a well or cargo deck between the forepeak F and afterpeak A and the cargo deck is divided into four elongate parts carrying barges P 1, P2, P3 and P4. These barges together with the cargo therein are carried by the deck D of the vessel which is sunken when the vessel is ballasted but has sufficient freeboard when the vessel is not ballasted. The hull has wing tanks V of the type shown in Figure 5.

The procedure for unloading the barges is such that the part at least of the vessel hull under the deck D which is provided with tanks formed by longitudinal and transverse bulkheads is filled with water. Fore and aft ballast tanks are also filled so that the whole vessel is sunk to the level of the deck D.

There is still freeboard at the forepeak F and the afterpeak A above the water level at the fore and aft part of the vessel which is assumed to be at the level of the barge deck D. More water is filled into the fore and after ballast tanks until the barges are afloat can can be warped out laterally from the deck D.

For this purpose tugboats may be used, which have already towed out new loaded barges from a nearby port, ready to replace the barges which are removed. In this way the mother vessel S can unload part at least of its cargo and take on new cargo in a faw hours and continue to its next destination, while the barges which have been discharged from the vessel are towed into port for unloading in the usual manner at a wharf.

In conjunction with a practical embodiment of the invention, the seaworthiness of such a vessel will be demonstrated with figures. Such an embodiment is illustrated in Figure 2.

The vessel illustrated in Figure 2 has a length of 330 m and a beam 40 m and a templated depth of 25 m providing a total intended cargo volume of 3330000 m3 (330,000 m3). If the welldeck-between the forepeak and the afterpeak or poop is lowered by 6 m to a template depth of 1 9 m relative to the forepeak and the after peak, the cargo volume is reduced by about 600 000 m3 (60,000 m3) to 270,000 m3. Of these 35 000 m3 are required for carrying the weight of the vessel which is 35 000 tons. For carrying the four barges and for ballast purposes 235 000 m3 remains.

In order for the barges to float in over the deck D, the vessel must be sunk further to 25 m draught, whereby the following displacement must be overcome. In the forepeak and afterpeak: 80 x 30 x 6 = 14,400 tons For fore and aft beds: 34 4 x 10 x 6 x-=4O8Otons.

2 Added to this volume is the volume of centre and side tanks 250 x (4 x 6 + 6 x 6) m3 = 1 5.000 tons, Giving a total of 33,480 tons.

These 33,480 tons could be obtained in the following way: 15.000 tons could be pig iron ballast, for example, and the rest water ballast.

As soon as the new barges have been winched in over the deck D and have been secured, the water ballast is pumped out and the barges will come to rest on the deck D. After the ballast has been emptied out of the latest filled tanks, the water ballast is pumped out of the remaining tanks until a draught of 11 m has been reached, for example.

There is then the following situations: The vessel is loaded with about 15.000 tons of pig iron ballast and with four barges together weighing 60.000 tons. Furthermore there is a ballast load in the tanks of about 60.000 tons. To this there can be added 8.000 tons of bunker oil. This adds up to 143.000 tons.

The same denotations have been used in Figure 2 as in Figure 1. The barges have been provided with superstructures and again have the designations P1, P2, P3, P4. The barge P3 is just about to be winched in over the vessel deck D.

In this embodiment which is basically the same as the example of Figure 1, but a little less diagrammatic, there is a longitudinal centre tank C arranged on deck D, extending between the forepeak and the afterpeak and which thus forms a longitudinal combined box girder and central tank 6 x 4 m in cross section, and a transverse tankT and beam also having the dimension 6 x 4 m crosses the centre tank. Both towards the tank T and towards the forepeak and the afterpeak, the deck slopes upwards to adjust the fore and aft slope of the sides, bow and stern, of the barges. Similarly, the four deck portions slope upwards towards the centre tank C so that the barge sides which for the sake of stability suitably slope at an angle of 450 shall gently come against this tank.

The sides of the vessel also have wing tanks of the type illustrated in Figure 5.

Each of the four barges has a displacement of about 1 5.000 tons, a length of about 125 m and a beam of 20 m with a draught of about 5 m and can take about 8,000 tons of cargo. A total of between 30.000 and 35.000 tons of cargo is thus transported altogether. A dead weight with the barges of 60.000 tons is transported by means of a vessel of 200.000 tons deadweight with relatively little draught.

The centre tank also serves as a walkway between the forepeak and the afterpeak and to mount winches and mooring bollards etc.

In Figure 3 there is illustrated a barge-carrying vessel formed with hull plating sloping outwards giving a hull which is trapezoidal in section. In this case a heavy centre tank C is provided extending from the forepeak along the whole length of the vessel to is transom. The centre tank is formed as a heavy structure stiffening the whole vessel and it also accommodates a funnel leading down to the machinery space. The same reference letters have been used in this case as in the previous example.

However, the hull side plates extend slopingly upwards past the deck D, and the barges are warped or winched in and out from the stern of the vessel and not from the sides. This barge-carrying vessel otherwise functions in the same way as that previously described. There is thus a ballasted position provided by water ballast in which the water level extends about 6 m above the deck D, thereby enabling the barges to be pulled into the water channels formed above the deck, and also a level corresponding to the sailing position in which the vessel has about 8-1 0 m freeboard.

Substantial advantages are achieved by the barge-carrying vessel and the barges which it is adapted to carry.

In the first place a considerable saving in freight costs is gained since the consumption of fuel oil is insignificantly greater than what would have been consumed for a vessel having a cargo capacity corresponding to the barge's cargo capacity, and this also applies to a large extent for the crew costs as well.

In the second place a gain is made in shortened loading and unloading time for the vessel as well as for port costs, since the vessel does not need to go in to port but can unload the barges in a sheltered bay in the vicinity of the destination port.

In the third place, storage problems occur in most ports due to the increase in the shipping of containers, trailers and vehicles. These problems can partially be solved by using the vessel and its barges, which can float up to a wharf and be loaded directly with the cargo as the cargo arrives at the port. The barges can be used as storage places in this way.

In the fourth place the barges can be loaded and discharged at places where the depth is insufficient for larger ships.

In the fifth -place obtaining cargo for a return voyage is facilitated.

In the sixth place it is possible to load different cargos into different barges thus making the whole transport system more flexible.

In the seventh place, loading and unloading can be done during the day time, thus enabling a more even working rate for the stevedores.

In the eighth place, there will be less damage to cargo, since loading and unloading takes place during the daytime and without hurry.

Apart from the new construction of barge-carrying vessels, the invention also relates to a particularly advantageous method of building such vessels.

It is known that ore and tanker tonnage is extremely sensitive to trends in the world economic situation. During the present downward, trend, tanker tonnage has been very heavily hit, and hundreds of tankers of sizes from 80,000 to 350,000 tons are at present laid up. The total amount laid up attains the figure of 48 million tons. Vessels in sizes of between 200,000 and 300,000 tons are especially badly hit. The number of vessels of these sizes which are laid up is calculated at the moment to well over 100. By means of the method in accordance with the present invention, a larger number of vessels of about 250,000 tons can be utilised.

The method in accordance with the invention of building barge-carrying vessels by converting a tanker includes the following steps: a) lowering the tanker skin plating between the fore peak and after peak by from 20 to 30% of the moulded depth of the tanker either by bending out the side plating to the required extent, or by lowering the deck of the hull between the fore peak and the after peak by removing a part of the ships structure and by forming air tanks of triangular cross-section on both sides of the hull between the new lowered deck and the chines of the hull, thus obtaining a hull of trapezoidal cross-sectional shape.

b) rebuilding a portion of the original deck between the forepeak and the after peak into a supporting box girder containing central tanks, the girder having a width of substantially 10% of the deck width; c) building new deck sections and closing tanks affected by lowering of the deck, so that deck wells of channels for accommodating barges are formed on both sides of the central beam; and, d) optionally also providing the central beam with tanks which are triangular shaped in cross section along both its longitudinal sides, these triangular sectional tanks serving as balance tanks when the vessel is ballasted with the deck below water level and also serving as further stiffening of the vessel in a fore and aft direction.

The side wings are also preferably provided fore and aft with protection against breaking seas, and the forepeak is preferably provided with protection running transversely.

A tanker of 330,000 m3 and 255,000 tons dead weight converted in this way is illustrated in Figure 5. The reference letters are the same as those in the Figures already described. From the existing deck of the tanker there has been left a longitudinal beam C and a cross beam T at right angles thereto.

The beam C forms a central tank between the forepeak and afterpeak of the tanker and the beam T also forms ballast tanks as well as serving to stiffen the vessel. Deck wells are also formed for the four barges P1, P2, P3 and P4, of which P2 and P3 are not shown on the figure, and the barges can be winched into these wells when the vessel has been ballasted so that the level of its original deck is at water level. The wing tanks (of which only the port wing tank is shown in Figure 4) are denoted by V and are more clearly shown in cross section in Figure 5. As will be seen, the wing tanks contribute to stability in the ballasted position of the vessel when the water level is the one illustrated uppermost in Figure 5 and denoted by ON. When the vessel is under way, the lower water level NN is applicable and the wing tanks are then intended to protect the deck and barges against breaking seas. The provision of the wing tanks V makes the upper part of the hull of trapezoidal cross-section.

A displacement calculation for the conversion of the tanker illustrated in Figures 4 and 5 will be given below.

Between the forepeak and the afterpeak, the deck has been lowered by 6 m from 26 m to 20 m, the volume of the cargo tanks thus being diminished from 330.000 m3 to 255.000 m3.

For a draught of 20 m, 255.000 ton can be disposed in the following way: bunker oil 5.000 tons forepeak and afterpeak 8.000 tons ballast and vessel weight 242.000 tons dead weight total 255.000 tons The central tanks in the centre plane have not been used in the buoyancy calculation and the sludge tanks of a volume of 9.000 m3 have also been retained as a reserve. On the other hand, remaining ballast tanks of 13.000 m3 have been reckoned with.

When the vessel is ballasted to 26 m draught for unloading, the following extra displacement is obtained: forepeak and afterpeak about 80 x 30 x 6 = 14.400 tons central bulkheads about 250 x (4 x 6 + 6 x 6) = 15.000 tons fore and aft beds about 4 x 10 x 6 x 50/3 = 4.000 tons deck wings about 4 x 3 x 250 = 3.000 tons Total about 36.400 tons The following 36.400 tons can be obtained in the following way: old steel about 3.400 tons extra steel, pig iron ballast possibly partly steel from the old deck 22.000 tons (-3000 m3) about 20.000 tons ballast tank as above about 13.000 tons Total about 36.400 tons The following figures are obtained for sailing under load:: extra steel 22.000 tons barge load 60.000 tons water ballast 60.000 tons bunker oil 8.000 tons Total about 150.000 tons The barges have a weight of their own of 1500 to 2000 tons and can take a cargo load of 9000 to 10000 tons, and the barge-carrying vessel thus signifies that there is a voluminous cargo of 60.000 tons (including the weight of the barges) and that a vessel of 250.000 tons can be propelled with comparatively small power since the draught is about 12 m as against the draught as a tanker of 20 m.

It is indicated in Figure 6 how the conversion of the same vessel as just dealt with to the barge carrying vessel illustrated in Figure 3 can take place with a hull which is trapezoidal in section. The deck is lowered, instead of cutting off the side plating by cutting it free from the deck frames and bending the sides out.

In Figure 7 there is illustrated a section of a barge-carrying vessel of the kind illustrated in Figure 3 with hull side plates sloping outwards so that it is trapezoidal in section. In this case however, the central tank C has been replaced by tanks ST forming the upper side plating of the vessel, which joins up with the lower side plating S which is outwardly sloping with a trapezoidal configuration in section, and also joins up with the loading deck D. The lower parts of the inner skin plating of the tanks ST slopes towards the deck parallel to the outwardly sloping side plating S of the lower part of the hull for adapting to the side slope of the barge hull sides. In a similar way, the deck D slopes up towards the fore and aft bulkhead L for adapting to the corresponding slope of the other sides of the barge hulls.

Transport channels are thus formed in the longitudinal direction of the vessel for the barges P 1, P2, P3 and P4. The barges can be winched into these channels when the vessel is in the ballasted position ON.

Claims (14)

1. A barge-carrying vessel having a cargo deck, which is arranged to carry a plurality of barges and which is open laterally or at one end, the vessel having ballast tanks which when filled, cause the water level to rise above the cargo deck so that loaded barges can float over the deck either for warping out and winching in laterally for unloading and loading, or for warping out and winching in in a fore and aft direction, wherein the hull of the vessel under the cargo deck has a trapezoidal cross-sectional shape, the width of the bottom of the hull being equal to the length of the shorter parallel side of the trapezium, and the sides of the hull sloping upwards and outwards at least as far as the cargo deck.

2. A vessel according to Claim 1, in which double-skin plating extends upwards from the sloping sides to the cargo deck on both sides of the vessel to form upright tanks at the sides of the cargo deck.

3. A vessel according to Claim 1 or Claim 2, in which wing tanks of substantially triangular section are provided along and directly below the cargo deck at both sides of the vessel, the wing tanks extending from the cargo deck to the chines to form the trapezoidal cross-section.

4. A vessel according to Claim 3, in which the hull below the cargo deck is divided into a plurality of ballast tanks by at least one longitudinal bulkhead.

5. A vessel according to any one of the preceding Claims in which a tank or tanks are provided along and extending upwards from the centre of the cargo deck by double-skinned plating extending upwards from the deck, the plating also enclosing a shaft which extends to a machinery space for containing ducting leading to a funnel.

6. A vessel according to any one of the preceding Claims in which the cargo deck has lowered portions with at least one raised portion between them the lowered portions being from 2030% of the templated depths of the hull below the raised portion, the lowered portions being arranged to accommodate two longitudinally extending rows of barges, the main decks of the barges extending substantially up to the level of the deck of the forepeak and the vessel being provided with ballast tanks and other ballast to enable the lowered portions to be ballasted below water level to enable the barges to be floated into position on the lowered portions and to provide adequate freeboard of the lowered portions, when unballasted for sailing.

7. A vessel according to Claim 6, in which one raised portion is formed by a heavy longitudinal box beam forming a central tank, the top of which is substantially level with the deck of the forepeak.

8. A vessel according to Claim 6, in which another raised portion is formed by a transverse box girder, substantially at the midpoint of the longitudinal box girder.

9. A vessel according to Claim 7 or Claim 8, in which the width of the box girder or box girders is substantially 10% of the width of the cargo deck, the upper surfaces of the girders being formed as walkways and being provided with winches and mooring means for handling and mooring the barges.

10. A vessel according to any one of Claims 7 to 9, wherein the lowered portions of.the cargo deck are connected to the sides of the box girder or girders and to a bulkhead of the forepeak by sloping bracing plates which form with the sides of the box girder or girders and with the bulkhead air tankswhich are triangular in section for balancing the vessel when it is ballasted with its cargo deck below water level.

11. A method of building a vessel in accordance with Claim 6 by converting a tanker, the method including the following steps: a) lowering the tanker skin plating between the fore peak and the after peak by from 20 to 30% of the moulded depth of the tanker either by bending out the side plating to the required extent, or by lowering the deck of the hull between the fore peak and the after peak by removing a part of the ships structure and by forming air tanks of triangular cross-section on both sides of the hull between the new lowered deck and the chines of the hull, thus obtaining a hull of trapezoidal cross-sectional shape; b) rebuilding a portion of the original deck plating between the fore peak and the after peak into a supporting box girder containing central tanks, the girder having a width of substantially 10% of the deck width; and c) building new deck sections and enclosing tanks affected by lowering the deck, so that deck shelves or deck channels are formed at both sides of the central girder for accommodating barges.

12. A method according to Claim 1 in which separate deck wells are formed in the cargo deck for accommodating barges by providing one or more transverse box girders across the deck.

1 3. A method according to Claim 11 or Claim 12, in which the central girder, and the transverse girder or girders when provided are provided along both their longitudinal sides with tanks which are triangular shaped in cross section, these tanks serving as balancing tanks when the vessel is ballasted with the cargo deck below water level and assisting in stiffening the box girders.

14. A method according to Claim 13, in which the side wing tanks are provided at the sides of the forepeak and afterpeak for protection against breaking seas, and the forepeak also being provided with similar protection in a transverse direction.

1 5. A method according to Claim 13 or Claim 14, in which the side wing tanks are provided with upwardly extending faces against which the barges can come into engagement to restrict lateral movement of the barges.

1 6. A vessel according to Claim 1 , substantially as described with reference to Figures 1 , 2, 4 and 5, or Figures 3 and 6 or Figure 7, of the accompanying drawings.

1 7. A method according to Claim 1 substantially as described with reference to Figures 3 and 6 or Figure 7 of the accompanying drawings.