The invention relates to a tanker with a double bottom and vertical cylindrical cargo tanks. The invention also relates to a method for providing tankers having double bottoms and cylindrical cargo tanks.

The invention is especially intended for use in connection with tankers of all sizes for chemicals/products. The inventive concept concerns engineering and arrangement of the cargo tank area on such vessels.

A common structure and a common arrangement of the cargo tan area consists of a tank arrangement with a double bottom fo IMO class II cargo and also a double skin (hull side), longitudinal and transverse bulkheads of plane steel plate with stlffeners and frames, or corrugated steel plate without stlffeners, but with frame stiffening, and decks (o top of the tanks) with stlffeners and frames, eithe externally on the deck or internally in the tops of th tanks.

Also, tankers with spherical tanks are known, which tanks ar designed to be integrated with the hull, or to be separat elements. Tankers with cylindrical tanks are known, in whic the tanks sit in foundations in the cargo tank area, possibl with vertical tanks in the cargo tank area. Tankers are als known with horizontal cylindrical tanks which are integrate with the ship's hull. Structurally, such tankers may b considered to be a kind of double-walled tubes. The tank are, thus, very large and occupy most of the cross sectiona space of the hull. Internal division is provided with plan or rounded bulkheads.

It is an object of the invention to provide a tanker in whic a large number of separate tank spaces will be available

all of which are preferably smooth inside to facilitate cleaning. The tanks should also form integrated elements of the ship's structure.

It is a special object of the invention to propose a tanker design which may be implemented in an advantageous manner with an older vessel, e.g. a so called 0B0 vessel, bulk ships and conventional tankers.

According to the invention a tanker with a double bottom and vertical cylindrical cargo tanks in the space between tank top and deck is, thus, proposed, which tanker is charact¬ erized by the fact that the cargo tanks have a circular cross section or a cross section forming part of a circle, and that respective cargo tank bottoms and tops are flat constituting integrated parts of the tank top, and deck respectively, without stlffeners below the deck.

With such a tanker an advantageous division into a plurality of comparatively small tanks is achieved, which is especially advantageous in connection with so called parcel cargo of varying specific weight. The tanks will also have plane or *» smooth internal faces so that cleaning will be much facilita¬ ted. Also the suitable properties of the circular cylinder shape permitting a higher specific weight of the cargo in the cylindrical tanks, are utilized in an advantageous manner. As regards structure and dimensions improved economics are achieved due to more favourable thickness of material and the absence of stlffeners, as well as due to highly reduced welding operations.

In an advantageous embodiment the tanks may be connected by bulkheads without stlffeners. Utilizable external tank areas are, thus, provided between the cylindrical tanks. Said tank areas may either be empty when the ship has a cargo, or they may be used for more light-weight cargo with a specific weight of less than 1.00, and they will also facilitate cleaning.

The external tank area between the circular cylindrical tanks may, advantageously, be made of ordinary steel, whereas e.g. so called clad steel or so called coated steel may be use for the cylindrical tanks if that is deemed satisfactory. B using, e.g. clad steel and coated steel, there will be minimized transition zones between the steel grades and, thus, reduced galvanic corrosion between various steel grades. Galvanic corrosion is an undesirable proble occurring with time in connection with operation and maint enance.

As mentioned, the tanks will facilitate cleaning. This is du to the fact that the tank area is devoid of all kinds o stiffener means. A minimum coat-area is achieved, resultin in minimized maintenance cost. Furthermore, a simple an central positioning of tank cleaning machines is permitte as well as a rational and economic structure and operation o cargo handling and tank maintenance. The tank spaces betwee said circular cylindrical tanks are prismatic and will, thus also be suited for a central positioning of cleanin machinery, so that said tanks also facilitate cleaning.

Due to the special structure with vertical circular cylind rical tanks or tanks forming part of a circular cylinder preferably connected by plane bulkheads, the cargo tanks ma be embodied in a modular system, so that the members use will be practically identical and economical in productio and mounting. The arrangement of tanks may also be varied t form a desired pattern in plan view.

It is essential that the bottom and top of each tank is fla and forms an integrated member of the tank top and deck respectively. A flat top, and bottom, respectively, should b understood to indicate that they are adapted to the shape o the tank tops, or deck, respectively (camber, inclination etc.). The tank mantles will extend substantially at righ

angles with the top and bottom and it is butt welded to the latter. Overlapping should be avoided. It would, thus, be a disadvantageous arrangement If a tank with an associated bottom were placed on top of a tank top with welding around. A deficiency of the weld (crack or the like) would cause an airspace between the bottom of a tank and the top of a tank (possibly between the top of a tank and the deck), and a leakage of cargo in such an airspace, which is not permitted.

It is also essential that no stlffeners are present or provided below the deck, since a special object is to avoid hard crossing points and crack indications between structural elements. The tank top is a "pure" deck surface with all stlffeners provided in the double bottom. Just beneath the deck the problem of stlffeners may be solved by either arranging a double deck or by placing stlffeners above said deck.

Towards the ship's side (skin) tanks forming part of a circle, preferably semicircular tanks are placed, so that the vertical tank mantle edges extend at substantially right angles towards the ship's side and are welded to the skin or adjacent frame by pure butt welds. Here, it may be permitted to let the skin form part of the tank wall, but in most cases it will be desirable or necessary to use a separate vertical tank wall, parallel with the skin, which wall is made from common steel, and it will be most suitable to design the ship's hull with a double skin, the tank walls then forming an integrated part (welded into) of the inner skin. In this manner a clean and smooth inner wall is achieved in the sector shaped tanks as well, and obviously, in the tank spaces between the circular tanks or tank shaped like parts of a circle.

By the present invention it will also be possible to build the hull proper separately, with equipment and prefabricated tanks being mounted later. Building costs for the ship may,

thus, be cut down, at the same time as the highest standard of quality is maintained, which is most important, e.g. in tankers for chemicals. The hull proper may, thus, be built in countries having low building costs, and it may then be moved to a more soflsticated shipyard to be equipped and provided with tanks. The inventive concept may also be realized in connection with reconstruction of existing tankers or bulk ships into a more soflsticated tanker for chemicals/products.

According to the Invention a method is, thus proposed to provide a tanker with a double bottom and cylindrical cargo tanks, which Is characterized in that the ship's hull is completed with a double skin and decks, and that prefabric ated tank mantles with a circular or partly circular cros section and with reduced height relative to the height of th hold are then Introduced into the hold of the hull, ar placed in desirable locations on the double bottom, and ar then raised into contact with the deck and fastened to th latter, whereupon a prefabricated lower adapting member i inserted between the tank mantle and the tank top and i attached to the tank mantle and the tank top to finish th tank.

In an especially advantageous manner plates intended to b tank bottom plates are welded into respective openings of th top of the tanks before the above mentioned insertion.

Openings are made in the inner deck or the deck and the pre fabricated tank mantles are provided with an attached to plate of corresponding dimensions which Is welded into respective opening which Is part of the deck or inner deck.

The invention is disclosed in more detail below wit reference to the drawing, in which

Figure 1 shows a possible localization plan of a carg tank area on board a ship,

Figure 2 shows another possible arrangement of a cargo tank area, Figure 3 is a section through a double skin with an opening made for introducing tanks, Figure 4 shows a section in perspective of a tanker according to the invention, Figure 5 shows a section corresponding to that of Figure

4, but with a modified design of the tank top, Figure 6 is a diagrammatical ^" longitudinal section of the tanker, with a loose tank which is introduced to be mounted, Figure 7 shows a section like that of Figure 6, but with the tank in place immediately beneath the inner deck in the cargo tank area, Figure 8 shows a section like that of Figure 6, but with the tank mounted in place, Figure 9 shows the same section as Figure 3, but with the openings in the double skin closed and a sector- shaped tank mounted in place against the inner skin, and Figure 10 is a diagrammatical cross section of a convent¬ ional tanker, Figure 11 is a diagrammatical cross section of the ship as shown in Figure 10 after reconstruction and ready for vertical circular/partly circular tanks to be mounted, Figure 12 is a diagrammatical cross section of an 0B0- ship, and Figure 13 shows a corresponding section of the ship of

Figure 12 after reconstruction and ready for tanks to be mounted.

In Figure 1 a cargo tank area 1 on bord a tanker is shown. It is a top plan view and the tanker is shown to be provided with a double skin 2 ^' , 3 and 4, 5.

In cargo tank area 1 vertical circular cylindrical tanks 6, 7, and 8, as well as vertical tanks 9-16 which form part of a circular cylinder are placed. The separate tanks 6-16 are connected and stiffened relative to each other by the aid of plane bulkheads 17-28.

Figure 2 shows a cargo tank area 29 on board a ship which is provided with a double skin 30, 31, and 32, 33, respectively. There are three vertical circular cylindrical tanks 34, 35, and 36. Additionally, there is a number of semicircular cylindrical tanks 37-46. Between the tanks there are plane stiffening bulkheads 47-62.

It will be obvious to those skilled in the art than man other arrangements will be possible. In building the ne tanker it will be advantageous first to build the hull proper with a double bottom, a double skin, and double decks, an provide the tanks afterwards. Such a hull is shown in Figur 4 (see also Figure 5). The section shown in Figure 4 represents a hull 63 with a double bottom 64, double skins 6 and 66, and a double deck 67. An opening 68, see also Figur 3, is made in double skin 65. As shown, double skin 65 i designed with an outer skin 69 and an inner skin 70. Betwee said skins watertight frames 71, 72 are provided. Opening 6 is dimensioned to permit tanks 73 to be introduced throug said opening, as indicated by a dashed line in Figure 3.

In Figure 4 the hull is presumedly built from common steel In Figure 5, the same hull as In Figure 4, for that matter is modified in that the tank top 74 is provided with circula and areas where and areas of partly circular shape, wher stainless steel plates 75, 76 are welded in place. Sai plates may, e.g. be so called clad steel plates, i.e. stee plates with a different steel grade rolled on with due regar to the cargo which the cylinder tanks are intended to hold Correspondingly, circular openings and openings shaped lik parts of circles 78 are made in inner deck 77, see Figure 6.

Mounting of the separate tanks in a modified hull, like that of Figure 5, will be discussed in more detail below, with special reference to Figures 3, 5, 6, 7, 8, and 9.

The hull is presumed to be prepared, as shown in Figure 5, i.e. provided with a double bottom 64, double skins 65, 66, and a double deck 67, as well as provided with an opening 68. Circular plates and plates forming part of a circle 75, 76 of the same material as that used for the tanks are welded into the top 74 of the tank.

A tank mantle 79 is introduced through opening 68. Mantle 79 has reduced height as compared to the compartment height, i.e. the distance between the top 74 of the tank and the inner deck 77, and it is provied with a top 80 by welding. This shortened tank member 79 is conveyed to the desired location, e.g. on top of welded plate 76 in a suitable manner. In Figure 6 tank member 79 is shown to be placed on a carriage. 81, so that it can be rolled in a comparatively simple manner to its intended position on top of plate 76, as Indicated by the arrow in Figure 6.

On tank member 79 temporary brackets 82, 83 are mounted. When tank member 79 is placed above plate 76, jacks 84, 85 are placed on the top 74 of the tank. By the aid of said jacks 84, 85 tank member 79 is lifted from carriage 81, which is rolled off. By the aid of the jacks tank member 79 is lifted into the position as shown in Figure 7, and the top plate 80 of the tank Is welded into opening 78, as shown in Figure 7.

Jacks 84, 85 are removed, and an adapted ring 86 in placed between mantle 79 and tank top 74, 76. Ring 86 is welded to mantle 79 and to circular plate 76, which constitutes part of the top of the tank and will now form the bottom of the welded, vertical circle cylindrical tank 79.

In this manner all tanks are placed and welded to the hull Eventually, the last sector-shaped tank 87 is placed, a shown in Figure 9 and the double skin is closed by plates 88 89, as shown in Figure 9. The bottom of tank 87 consists o the sector-shaped plate 75 which Is welded into the top o the tank.

Between the vertical tanks bulkheads corresponding to thos shown in Figures 1 and 2 and in Figure 9 indicated b bulkheads 90 and 91 are welded in place. Localization an welding of bulkheads may, obviously, be made successively, i step with mounting of the tanks.

It may be of special interest to reconstruct existing tank o bulk ships into more soflsticated chemical/product tankers.

Examples of how this may be realized by use of the inventio are shown in Figures 10, 11, and 12, 13.

Figure 10 is a diagrammatical cross section through conventional tanker. The tanker has wing tanks 100 an central tanks 101. Wing tank and central tank are separate by a longitudinal bulkhead 102. Sturdy frames in wing tan and central tank are indicated by numeral 103, and 104 respectively, and longitudinal stlffeners 105 are Indicate on the inside of the hull side or skin 106 inside botto plates 107, on bulkhead 102, and below deck 108.

Figure 11 shows how the tanker of Figure 10 may be reco structed for mounting of vertical cylindrical tanks accordi to the invention. Portions of frames (the original shape i indicated by dashed lines in Figure 11) are burnt off - will often be a question of heavily corroded portions - and tank top 109, and an internal skin 110 with associat stlffeners 111 is provided. Directly underneath the de stlffeners 105 are removed and deck 108 is instead stiffen on the upper side by longitudinal stlffeners 112 and stur transversal stlffeners 113. In fact, a new ship's hull

provided which approximately corresponds to the ship's hull shown in Figures 4 and 5. In the same manner as disclosed above, the desired vertical cylindrical tankers can then be mounted.

A corresponding possible reconstruction of a bulk ship is shown in Figures 12 and 13. The bulk ship in Figure 12 has a tank top 114 and an inner skin 115. A loading hatch is indicated at 116.

In Figure 13 a cross sectional view of the reconstructed bulkship is shown. Inner skin 115 is here extended down to the double bottom 114 which is also extended outwards to the ship's side, the oblique wall 117 of the original cargo hold being removed. Hatch 116 is also removed and In stead a deck 118 is built, in fact corresponding to deck 108 of Figure 11. In this bulk ship the cargo hold has, thus, been stripped and the cross section was made more right angled, so that substantially the same cross section as that of Figure 11 and Figures 4 and 5 is achieved. Tanks may now be mounted here. In stead of introducing tank mantles and other tank comp¬ onents through the double skin, one or more of the hatches may, obviously, be used. Such hatches are then only closed upon mounting the tanks and fitting up the hold.

It was not shown or mentioned above, but it will be under¬ stood that the vertical cylindrical tanks may be made from suitable materials, whereas the ship's hull proper, i.e. the skin, double bottom and deck are made from ordinary steel used for ships. Suitable materials of the tanks are selected taking the intended cargo Into account. Much used materials in this connection are, as mentioned above, so called clad steel and coated steel, well known concepts within ship technology. Stainless steel is, obviously, a possible material as well.