TECHNICAL FIELD

This invention relates to a ship according to the preamble of claim 1 .

In particular, the invention relates to an arrangement of the bulkheads of the ship.

BACKGROUND OF THE INVENTION

The design of ship is subject to various safety regulations. A ship that is subjected to a damage must meet certain criteria with regard to heeling/listing, height of freeboard, etc. This is mainly solved by designing the ship with internal watertight bulkheads at specific distances. The distances between these bulkheads are governed by Solas (Safety of Life at Sea, International Maritime Organization, IMO) requirements, in this case Solas 90 regulation II-1/B/8. In addition there is a special damage requirement for ro-ro (roll-on/roll-off) passenger ship, trading in European waters, EU directive 2003/25/EC. These requirements state that a ro-ro passenger ship can be subjected to water on the bulkhead deck. To meet both Solas and the EU directive a number of measures need to be taken.

Some of the terms used in this disclosure can be explained as follows:

B "Breadth (B) is the greatest moulded breadth of the ship at or below the deepest subdivision draught". In short, this is the greatest moulded breadth of the ship (without outer plates, shell plating etc.).

Bulkhead deck Freeboard deck on a passenger ship.

Bulkhead Internal walls on a ship.

Damage A damage to the ship. A ship is designed on the basis of a theoretical damage, the extent of which is defined in relevant standards, rules and regulations.

Double bottom Space between bottom plate/keel and tank top. Ls "Subdivision length (Ls) of the ship is the greatest projected moulded length of that part of the ship at or below deck or decks limiting the vertical extent of flooding with the ship at the deepest subdivision draught". The subdivision length is often approximately the same as the summer load line.

Shell plating Plates which form the external surface of the hull.

Tank top 'Roof of double bottom space. This level is normally referred to as Deck 1 .

The extent of a theoretical damage according to standard requirements is: Damage length (0.03 ^* L _S + 3) m or maximum 1 1 m, where L _s is the subdivision length.

Damage width > B/5 (i.e. the "depth" of the damage from the side of the ship towards the centre line of the ship).

Damage height The vertical extent of the theoretical damage is not restricted.

A ship is divided into a number of watertight compartments by means of bulkheads. These bulkheads are arranged to provide strength and safety to the ship, and the particular arrangement depends on the size and type of the ship. Typically the arrangement includes a number of transversal bulkheads extending from side to side across the space between the bottom and the bulkhead deck.

Apart from the obvious aim - to keep a ship afloat - the arrangement of the watertight bulkheads is based on stability calculations and studies to optimise the ship's behaviour should it be damaged. Depending on where a ship is damaged, different compartments and combinations of compartments will be flooded. Any one of these damage cases must not sink the ship entirely, nor cause it to list too much, let alone capsize. The latter is normally solved by cross-flooding, i.e. making sure that the loss of buoyancy is the same on both sides of the ship. This will cause the entire ship to sink a little deeper, but will minimize list.

A particular problem that sometimes arises, depending on the size and type of the ship, is related to the fitting of the ship engine(s) in the watertight compartments. A ship engine is relatively large and heavy, its length may be 10-20 m or even more, and so it requires a large compartment. For safety reasons, a single compartment is not allowed to have a too great volume as it might be filled with water, which can have a too large impact on the buoyance and stability of the ship. If the ship is provided with two (large) engines, these are often fitted in two separate watertight compartments. Conventionally, this is accomplished by means of two rectangular compartments arranged side by side, preferably at a central position of the ship.

However, in some cases the size of the engines (in relation to the size of the ship) is such that it becomes difficult to meet the regulations stated above for the separate compartments if they are arranged in the conventional manner as even the total volume of one of the individual compartments would be too great.

In the case of ro-ro ship a further difficulty often arises in that the location of the cargo space makes it necessary to place the engines more astern than in other types of ship.

This disclosure focuses on the problem of how to arrange the bulkheads so as to form compartments suitable for accommodating large elongated equipment, typically ship engines but also LNG (liquid natural gas) tanks or other equipment, while still complying with the regulations. SUMMARY OF THE INVENTION

An object of this invention is to provide a ship that exhibit improved capabilities of housing large elongated equipment in watertight compartments compared to conventional ships. This object is achieved by the ship defined by the technical features contained in independent claim 1 . The dependent claims contain advantageous embodiments, further developments and variants of the invention.

The invention concerns a ship comprising a lower deck, such as a tank top, and an upper deck, such as a bulkhead deck, arranged above the lower deck, said lower and upper decks extending in a longitudinal direction of the ship, wherein the lower deck is provided with watertight walls (bulkheads) that extend vertically between the lower and the upper deck and define a plurality of separated watertight compartments distributed between the upper and lower decks, and wherein a first of said watertight walls (a first bulkhead) extends in a transversal manner from side to side of the ship so as to separate two longitudinally adjacent first and second compartments.

The invention is characterized in that the first watertight wall does not extend only in a transversal direction but also in the longitudinal direction so as to provide the first compartment with a first longitudinally extending portion that extends into the second compartment, wherein the first longitudinally extending portion is arranged at a first distance from a first side of the ship, and wherein the first distance is greater than a width or depth of a theoretical damage according to standard requirements for the type of ship concerned.

Such a design has the effect that a longitudinally extended space for an engine or other elongated equipment is provided in the first compartment without making the total volume of the same compartment unnecessarily or unallowably large. The size and shape of the longitudinally extending portion is preferably adapted to the particular elongated equipment to be arranged in the first compartment. The elongated equipment will typically occupy most of the space or at least most of the surface area of the longitudinally extending portion and protrude into the remaining part of the first compartment. To simplify manufacturing, the first watertight wall may be an assembly of straight wall sections connected together, where each of the sections may extend strictly in either a transversal or a longitudinal direction. However, the first watertight wall may include parts or section that are bent and/or that extend in a direction different from strictly transversal or strictly longitudinal.

While keeping the total volume at an acceptable level, the first compartment is at the same time still open from side to side of the ship, which means that if the first compartment is flooded in an accident the inflowing water can be distributed evenly over the breadth of the ship so as to minimize listing.

Further, the side space formed between the longitudinally extending portion and the side of the ship will form part of the second compartment, or a third compartment depending on the particular arrangement of bulkheads, and since this side space is sufficiently large (width-wise) to protect the extending portion and thus the first compartment from being damaged and flooded in the event of a (theoretical) damage (provided that the first watertight wall is not damaged in the region where it connects to the side of the ship), this can be used to reduce the number of compartments flooded if the ship is subject to a damage.

For instance, by arranging other bulkheads in suitable positions, including further bulkheads delimiting the second compartment and additional bulkheads below the lower deck, and in particular by arranging the other bulkheads in suitable longitudinal positions in relation to the first bulkhead/watertight wall to provide room for a damage longitudinally between the bulkheads in the region where the "safety space" is formed between the longitudinally extending portion and the side of the ship, the number of compartments flooded in the event of a damage can be reduced. The longitudinal distance between the bulkheads/walls should thus be greater than the theoretical damage length. Typically the width of the side space is at least B/5 where B is "greatest moulded breadth of the ship" as described above. The above design of the first compartment also provides for a corresponding arrangement of the second compartment, i.e. an arrangement where a longitudinally extending portion is provided also in the second compartment. This can done by arranging a section of the first watertight wall along a centerline of the ship and let this section act as a delimiting central wall of both the longitudinally extending portions. Alternatively, for instance if some other object is arranged at the centreline and prevents placing a bulkhead section at that position, the bulkhead section may be placed some distance at the side of the centreline or two central separate (but connected) bulkhead sections may be arranged on opposite sides of the centreline. In addition to the wall/bulkhead section(s) arranged in association with the centerline, further wall sections can be arranged to connect the central sections (if there are two central sections) and to define the remaining parts of the first watertight wall and thus of the adjacent parts of the first and second compartment.

Using such a delimiting central wall (or pair of central walls), two longitudinally extended spaces for two engines or other elongated equipment, one space in the first compartment and one in the second compartment, can be provided close to the centreline and symmetrically arranged around the centerline in the transversal direction. As the longitudinally extending portions are open in opposite longitudinal directions, i.e. the first one towards the first compartment (e.g. towards the bow) and the second one towards the second compartment (e.g. towards the stern), the equipment arranged in the two longitudinally extending portions will be longitudinally displaced in relation to each other (if the equipment is longer than the longitudinally extending portion and protrudes into the remaining part of the compartment). Such a displacement can normally be accepted. The maximum total length of the equipment is set by the longitudinal distance between the inner end part of the longitudinally extending portion and a further watertight wall that defines the opposite end of the compartment in question.

In an example of the invention, each of the first and second compartments has the general shape of an F, where one of the F's is upside down and facing in the opposite direction in relation to the other F as seen from above (i.e. one of the F's is rotated 180° in the horizontal plane) and where the lower horizontal bar of each F is placed in between the two horizontal bars of the other F. The first watertight wall forms a single delimiting wall that separates the two F-shaped compartments. Two additional and separate watertight walls define the vertical bars of the two F's. The upper horizontal bar of each F corresponds to a part of the corresponding compartment that extends along the side of the ship (one at each side of the ship). The lower horizontal bar of each F corresponds to the longitudinally extending portion of each compartment. The top and bottom portion of each F is delimited by the first and second sides of the ship.

In a variant of this example, a further watertight wall section is arranged in a substantially transversal direction at each side of the ship so as to partly or fully enclose the part of the corresponding compartment that extends along the side of the ship, i.e. the upper horizontal bar of each F. This way each enclosed part of the upper horizontal bar of each F-shaped compartment forms a buoyancy compartment laterally delimited by the further watertight wall section, the side of the ship, and (a part of) the first watertight wall. Provided that these delimiting components are not damaged, these buoyancy compartments will not be flooded even if the first or second compartments get flooded when the ship is subjected to a damage. This reduces the total volume flooded, which is an advantage with regard to a damage buoyancy and stability perspective. In case only a buoyancy compartment is damaged and flooded, but not the first or second main compartment, the arrangement with buoyancy compartment is of course also an advantage in that flooding of the main compartments is avoided. In an embodiment of the invention the first watertight wall is arranged to provide the second compartment with a corresponding second longitudinally extending portion that extends into the first compartment, wherein the second longitudinally extending portion is arranged at a second distance from a second side of the ship, and wherein also the second distance is greater than the width or depth of the theoretical damage according to standard requirements for the type of ship concerned.

In an embodiment of the invention the ship comprises a space below the lower deck, such as a double bottom between a tank top and a bottom plate/keel of the ship, wherein said space is provided with further watertight walls that extend vertically in said space and define a further set of separated watertight compartments including at least a first and a second void tank, wherein the first and second void tanks are arranged below the first and second compartments and extend at least along the first side of the ship over a longitudinal distance that intersects with the vertically projected position of a section of the first watertight wall that extends from the first side of the ship, wherein the width of the first and second void tanks along the first side of the ship is at least equal to the width or depth of the theoretical damage according to standard requirements for the type of ship concerned, wherein the first and second void tanks are longitudinally separated at the first side of the ship by a void wall section that extends in a transverse direction from the first side of the ship, and wherein the longitudinal distance between the void wall section and the section of the first watertight wall that extends from the first side of the ship is greater than a length of a theoretical damage according to standard requirements for the type of ship concerned. This way it can be avoided that all four compartments and tanks, i.e. the first and second compartments plus the first and second void tanks, get flooded if subjected to a theoretical damage. In an embodiment of the invention the first watertight wall comprises a plurality of wall sections including first and second longitudinally extending sections and a first transversally extending connecting section that connects the first and second longitudinally extending sections, wherein the first and second longitudinally extending sections and the first transversally extending connecting section form the first longitudinally extending portion of the first compartment.

In an embodiment of the invention the transversally extending connecting section is arranged at end portions of the first and second longitudinally extending sections.

In an embodiment of the invention the first longitudinally extending section extends along the side of the ship at said distance from the side of the ship. In an embodiment of the invention the second longitudinally extending section extends along a centreline of the ship.

In an embodiment of the invention the first watertight wall comprises a first transversally extending outer section that connects the first longitudinally extending section with the first side of the ship.

In an embodiment of the invention the first watertight wall comprises a third longitudinally extending section and a second transversally extending connecting section that connects the third longitudinally extending section with a further longitudinally extending section of the wall, wherein the third and the further longitudinally extending sections and the second transversally extending connecting section form the second longitudinally extending portion of the second compartment.

In an embodiment of the invention the first watertight wall comprises a second transversally extending outer section that connects the third longitudinally extending section with the second side of the ship.

In an embodiment of the invention the first and second compartments extend transversally over the width of the ship.

In an embodiment of the invention the first watertight wall extends transversally over the width of the ship.

In an embodiment of the invention the ship comprises further watertight walls that, besides the first watertight wall, define an additional transversal delimitation of each of the first and second compartments.

In an embodiment of the invention the wall sections are connected to each other at end portions thereof.

In an embodiment of the invention the width or depth of the theoretical damage is one fifth of a greatest moulded breadth of the ship according to standard regulations Solas 90. In an embodiment of the invention a length of a theoretical damage is (0.03 ^* l_s + 3) m or maximum 1 1 m, where L _s is the subdivision length according to standard regulations Solas 90.

In an embodiment of the invention the ship is a roll-on/roll-off (ro-ro) ship or a ro-ro passenger ship. In an embodiment of the invention a watertight wall section is arranged in a substantially transversal direction at the first side of the ship, said watertight wall section being configured to connect to said side of the ship and to the first watertight wall so as to partly or fully enclose a part of the second compartment that extends along the first side of the ship between the first side and the first longitudinally extending portion of the first compartment.

BRIEF DESCRIPTION OF DRAWINGS

In the description of the invention given below reference is made to the following figure, in which:

Figure 1 shows, in a schematic and partly sectional side view, an embodiment of a ship according to the invention.

Figure 2 shows a top view of the arrangement of bulkheads/watertight walls between an upper deck (bulkhead deck) and a lower deck (tank top) according to a first embodiment.

Figure 3 shows a top view of the arrangement of bulkheads/watertight walls below the lower deck (tank top) according to the embodiment shown in figure 2.

Figure 4 shows a magnified view of a part of figure 2.

Figure 5 shows a magnified view of a part of figure 3.

Figure 6 shows the magnified view of figure 4 with the bulkhead arrangement below the lower deck indicated with dashed lines. Figure 7 shows a magnified view corresponding to figure 4 but relating to a second embodiment.

Figure 8 shows a magnified view corresponding to figure 5 but relating to a second embodiment.

Figure 9 shows the magnified view of figure 7 with the bulkhead arrangement below the lower deck indicated with dashed lines. Figure 10 shows a sectional view A-A according to figures 2-9. DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Figure 1 shows, in a schematic and partly sectional side view, an embodiment of a ship 1 according to the invention. The ship 1 is a roll-on/roll- off (ro-ro) passenger ship and has a bow/stem 2 and a stern 3. The term longitudinal direction refers to the longitudinal axis of the ship 1 that extends between the bow 2 and the stern 3. The term transversal direction refers to the width of the ship 1 (a direction perpendicular to the plane of figure 1 ).

The ship 1 is provided a lower deck, a tank top 4, and an upper deck, a bulkhead deck 5, arranged above the tank top 4. These decks 4, 5 extend mainly in the longitudinal direction of the ship 1 but, of course, also in the transversal direction.

The tank top 4 is provided with watertight walls (bulkheads) 6 that extend vertically between the lower and the upper deck 4, 5 and define a plurality of separated watertight compartments 7 distributed between the upper and lower decks 4, 5.

A bottom plate/keel 9 is arranged below the tank top 4. The space formed between the bottom 9 and the tank top 4 is denoted double bottom. This space is also provided with bulkheads/watertight walls that define various empty (air filled) void tanks and other tanks or compartments.

The ship 1 is further provided with, for instance, additional decks 8.

Figure 2 shows a top view of the arrangement of bulkheads/watertight walls 6 between then upper deck (bulkhead deck) 5 and the lower deck (tank top) 4 according to a first embodiment. Figure 2 thus shows the tank top 4 as seen from above with a centreline 19.

A particular bulkhead, a first watertight wall (bulkhead) 10, extends in general transversally between first and second sides 15, 16 of the shipl and the tank top 4. As will be described more in detail below, the wall 10 comprises a number of sections, some of which extending in a transversal direction and some in a longitudinal direction. However, in general the wall extends transversally across the breadth of the ship 1 .

Together with additional watertight walls 6a and 6b (that in this example extend in the conventional manner, i.e. strictly transversally across the ship 1 ), the first wall 10 defines and separates a first and a second watertight compartment 1 1 , 12. The first and second watertight compartments 1 1 , 12 are arranged adjacent each other in the longitudinal direction with the first compartment 1 1 located closer to the stern 3 of the ship 1 .

Figure 2 also shows further bulkheads 6c that, for instance, define a cargo space 17. Propellers 18 are also shown in figure 2.

Figure 3 shows a top view of the arrangement of bulkheads/watertight walls below the lower deck (tank top) 4 according to the embodiment shown in figure 2. Figure 3 thus shows the bottom 9 as seen from above with the centreline 19.

Watertight walls 21 , 22, 23, 26a, 26b define first and second void tanks 24, 25 and another tank 27, which tanks are located below the first and second compartments 1 1 , 12 located above the tank top 4. The details of this arrangement are described further below.

Figure 3 shows also the propellers 18 and further walls 6d that define further tanks or compartments.

Figure 4 shows a magnified view of a part of figure 2. In particular, figure shows the first and second compartments 1 1 , 12 and the first watertight wall 10. Figure 4 shows, for instance, that the first wall 10 in this example is made up of seven wall sections 10a-10g. It is also shown that, in this example, each compartment 1 1 , 12 has a general shape of an F. The first and second compartments 1 1 , 12 are unsymmetrical.

Figure 5 shows a magnified view of a part of figure 3. In particular, figure 5 shows the watertight walls 21 , 22, 23, 26a, 26b, the first and second void tanks 24, 25 and the other tank 27.

Figure 6 shows the magnified view of figure 4 with the bulkhead arrangement below the lower deck 4 indicated with dashed lines. In other words, figure 6 shows the same things as shown in figure 4, but in addition, the walls 21 , 22, 23 located below the top tank 4. In this example, the walls 26a and 26b on the double bottom are located right below the walls 6a and 6b and so the former walls cannot be seen in figure 6. The function and advantages of the above arrangement will now be described mainly with reference to figures 4-6.

The first watertight wall 10 does not extend only in a transversal direction but also in the longitudinal direction and provides the first compartment 1 1 with a first longitudinally extending portion 1 1 a that extends into the second compartment 12. The first longitudinally extending portion 1 1 a is arranged at a first distance from a first side 16 of the ship 1 . This first distance corresponds to the (transversal) length of the wall section 10g and the longitudinal wall section 10 f is thus located at least this distance from the side 16 of the ship 1 (see figure 4). This first distance is greater than a width or depth of a theoretical damage according to standard requirements for the type of ship concerned, which in this case is one fifth of a greatest moulded breadth of the ship 1 , i.e. B/5 (according to standard regulations Solas 90). This means that the first longitudinally extending portion 1 1 a will not be directly affected by a theoretical damage. The first watertight wall 10 is arranged to provide a corresponding arrangement with regard to the second compartment 12: a second longitudinally extending portion 12a is provided that that extends into the first compartment 1 1 . The second longitudinally extending portion 12a (i.e. the wall section 10b, see figure 4) is arranged at a second distance (transversal length of wall section 10a, which in this case is the same as the length of section 10g) from a second side 15 of the ship 1 . As to the width of a theoretical damage, what is said about the first compartment 1 1 above applies also to the second compartment 12.

Elongated equipment (not shown in the figures), such as a ship engine, can be arranged in each of the compartments 1 1 , 12 by letting it partly be arranged in the longitudinally extending portion 1 1 a, 12a and letting the remaining part protrude longitudinally into the remaining space of the corresponding compartment 1 1 , 12.

At least within a distance from the side 15, 16 of ship 1 subject to the width of a theoretical damage, the longitudinal distance between the different bulkheads, i.e. the distance between the rear bulkhead 6a and the wall sections 10a and 10g, respectively, as well as the distance between the front bulkhead 6b and the wall sections 10a and 10g, respectively (see figure 4), is greater than the damage length of a theoretical damage, which in this case is (0.03 ^* l_s + 3) m or maximum 1 1 m, where L _s is the subdivision length according to standard regulations Solas 90.

This means that only one, or none, of the bulkheads 6a, 10a/10g and 6b will be affected by a theoretical damage (see figure 4).

As an example, it can be assumed that the first side 16 of the ship 1 (i.e. the lower side in figure 4) is subject to a theoretical damage: A) If the damage occurs close to the rear wall 6a, the first compartment 1 1 will be flooded (as well as a compartment to the left of the first compartment 1 1 ). B) If the damage occurs in the middle between the rear wall 6a and the wall section 10g, no bulkhead will be affected and only the first compartment 1 1 will be flooded.

C) If the damage occurs close to the wall section 10g, the first and second compartments 1 1 , 12 will be flooded.

D) If the damage occurs in the middle between the wall section 10g and the front wall 6b, no bulkhead will be affected and only the second compartment 12 will be flooded.

E) If the damage occurs close to the front wall 6b, the second compartment 12 will be flooded (as well as a compartment in front of the second compartment 12). Accordingly, in all cases zero or one bulkhead/wall will be affected, not two. For symmetry reasons, the same applies if the second side 15 is subjected to the damage.

Since the first and second compartments 1 1 , 12 are reasonably small, it can be accepted that one of the above bulkheads arranged on the tank top 4 is affected by the damage.

The first compartment 1 1 (as well as the left compartment 12) extends transversally to the opposite side 15 of the ship 1 . Incoming water will thus be more or less evenly distributed over the breadth of the ship 1 so that listing will not be severe. The first and second compartments 1 1 , 12 are somewhat asymmetric around the centreline 19 but the asymmetry is sufficiently small to be acceptable with regard to listing.

With regard to the space provided below the lower deck/tank top 4, i.e. the double bottom between the tank top 4and the bottom plate/keel 9 of the ship, it was mentioned above that watertight walls 21 , 22, 23, 26a, 26b define first and second void tanks 24, 25 and another tank 27, which tanks are located below the first and second compartments 1 1 , 12 located above the tank top 4.

The void tanks 24, 25 are simply empty and have a function of providing buoyancy to the ship 1 . The other tank 27 can be used for various purposes.

As can be best seen in figures 5 and 6, the first and second void tanks 24, 25 are arranged below the first and second compartments 1 1 , 12 and extend at least along the first side 16 of the ship over a longitudinal distance that intersects with the vertically projected position of a section 10g of the first watertight wall 10 that extends from the first side 16 of the ship 1 . This means that the first and second void tanks 24, 25 are located at least in an area along the first side 16 of the ship and that at least one of the void tanks 24, 25 is located straight below the first wall 10, and more precisely straight below a part thereof where it extends from the side of 16 of the ship, i.e. below wall section 10g (see figures 5-6). As can be seen in figures 5 and 6, the first and second void tanks 24, 25 extend in this example in a transversal direction along (in front of and at the rear of) the other tank 27 and extend in a corresponding way also along the opposite side 15 of the ship 1 under the wall section 10a. The transversal extension of each of the void tanks 24, 25 is important for stability reasons in case a void tank is subject to damage and gets flooded (the flooding water can be transversally distributed). A purpose of the other tank 27, besides offering a storage or tank volume inside, is to limit the total volume of the void tanks 24, 25. The tank 27 is arranged at a distance at least B/5 from each of the sides 15, 16 of the ship 1 and is therefore not affected by a theoretical damage.

The width of the first and second void tanks 24, 25 along the first side 16 of the ship 1 (and in this case also along the second side 15) is at least equal to the width or depth of the theoretical damage according to standard requirements for the type of ship concerned, i.e. in this case B/5. As explained above and shown in figure 6, this is the same as for the first and second longitudinally extending portions 1 1 a, 12a.

Further, the first and second void tanks 24, 25 are longitudinally separated at the first side 16 (and in this case also at the second side 15) of the ship 1 by a void wall section 22 that extends in a transverse direction from the first side 16 of the ship 1 (and in this example a further void wall section 21 that extends in a transverse direction from the second side 15, see figure 5).

Further, the longitudinal distance between the void wall section 22 and the section of the first watertight wall 10 that extends from the first side 16 of the ship, i.e. the wall section 10g, is greater than a length of a theoretical damage according to standard requirements for the type of ship concerned, which in this case is (0.03 ^* L _S + 3) m or maximum 1 1 m, where L _s is the subdivision length according to standard regulations Solas 90.

Correspondingly, the longitudinal distance between the further void wall section 21 and the section of the first watertight wall 10 that extends from the second side 15 of the ship, i.e. the wall section 10a (see figure 6), is also greater than the length of a theoretical damage.

The advantage of the particular arrangement of the void tanks 24, 25 is the following: The vertical extent of the theoretical damage is not restricted. This means that if the ship is subject to a theoretical damage, the whole side of the ship will be affected, from the bottom 9 and upwards. To meet the requirements (and, of course, to reduce the effects of a real damage), too many compartments, a too large volume of the ship, cannot be allowed to be flooded, and the bulkheads in the double bottom should therefore preferably interact in an advantageous way with the bulkheads arranged between the top tank 4 and the bulkhead deck 5.

Above has been described how the first and second compartments 1 1 , 12 are affected depending on the longitudinal position of the theoretical damage. As can be understood from in particular figure 6, by providing a longitudinal distance between the first wall 10 and the void wall section at the side 15, 16 of the ship 1 (within the width of a theoretical damage), i.e. between the walls 21 and 10a and between the walls 10g and 22 in figure 6, it can be avoided that more than three of the four compartments/tanks (i.e. the first and second compartments 1 1 , 12 plus the first and second void tanks 24, 25) are flooded if the ship 1 is subjected to a theoretical damage.

With reference to the examples A-E above, and to figure 6, the following will be the effects:

A) Damage occurs close to the rear wall 6a.

- First compartment 1 1 and first void tank 24 will be flooded (as well as a compartment to the left of the first compartment 1 1 ).

B) Damage occurs in the middle between the rear wall 6a and the wall section 10g.

- First compartment 1 1 and first void tank 24 will be flooded.

C) Damage occurs close to the wall section 10g. - First compartment 1 1 , second compartment 12 and first void tank 24 will be flooded.

D1 ) Damage occurs in the middle between the wall section 10g and the void wall section 22.

- Second compartment 12 and first void tank 24 will be flooded.

D2) Damage occurs close to void wall section 22.

- Second compartment 12, first void tank 24 and second void tank 25 will be flooded.

D3) Damage occurs in the middle between the void wall section 22 and the front wall 6b.

- Second compartment 12 and second void tank 25 will be flooded.

E) Damage occurs close to the front wall 6b.

- Second compartment 12 and second void tank 25 will be flooded (as well as a compartment in front of the second compartment 12). Accordingly, in all cases two or three compartments/tanks, out of the four discussed here, will be affected and flooded, not all four. One of the four compartments/tanks will thus stay watertight and provide buoyance to the ship 1 . For symmetry reasons, the same applies if the second side 15 is subjected to the damage.

With reference to the figures, the arrangement of bulkheads etc. can be additionally described as follows.

The first watertight wall 10 comprises a plurality of wall sections 10a-10g including first and second longitudinally extending sections 10d, 10f and a first transversally extending connecting section 10e that connects the first and second longitudinally extending sections 10d, 10f, wherein the first and second longitudinally extending sections 10d, 10f and the first transversally extending connecting section 10e form the first longitudinally extending portion 1 1 a of the first compartment 1 1 . The transversally extending connecting section 10e is arranged at end portions of the first and second longitudinally extending sections 10d, 10f.

The first longitudinally extending section 10f extends along the side 16 of the ship at said distance (at least the width of a theoretical damage) from the side 16 of the ship 1 .

The second longitudinally extending section 10d extends along or in parallel to a centreline 19 of the ship 1 . The first watertight wall 10 comprises a first transversally extending outer section 10g that connects the first longitudinally extending section 10f with the first side 16 of the ship 1 .

The first watertight wall 10 comprises a third longitudinally extending section 10b and a second transversally extending connecting section 10c that connects the third longitudinally extending section 10b with a further longitudinally extending section of the wall 10 (in this example 10d), wherein the third and the further longitudinally extending sections and the second transversally extending connecting section 10b form the second longitudinally extending portion 12a of the second compartment 12.

As an alternative to what is shown in the figures, the first wall 10 may comprise two centrally arranged longitudinal sections instead of the single section 10d as exemplified here. A reason might be that here is another object arranged at the centreline. Two (typically parallel) central wall sections may be arranged on opposite sides of such an object. Further wall sections can be arranged to connect these two sections and the other sections. The first watertight wall 10 comprises a second transversally extending outer section 10a that connects the third longitudinally extending section 10b with the second side 15 of the ship 1 .

The first and second compartments 1 1 , 12 extend transversally over the width of the ship, from the first side 16 to the second side 15.

The first watertight wall 10 extends transversally over the width of the ship 1.

The ship 1 comprises further watertight walls 6a, 6b, that, besides the first watertight wall 10, define an additional transversal delimitation of each of the first and second compartments 1 1 , 12. The wall sections 10a-1 Og of the first wall 10 are connected to each other at end portions thereof.

Figures 7-9 relate to another embodiment, or rather a variant of the embodiment described above. Most parts of the two embodiments are similar so the same drawing references are used for similar parts and focus is set below on the differences.

Figure 7 shows a magnified view corresponding to figure 4 but relating to the second embodiment.

Figure 8 shows a magnified view corresponding to figure 5 but relating to the second embodiment.

Figure 9 shows the magnified view of figure 7 with the bulkhead arrangement below the lower deck indicated with dashed lines. In this second embodiment, a further watertight wall section 31 , 32 is arranged in a substantially transversal direction at each side 15, 16 of the ship 1 so as to partly or fully enclose the part of the corresponding compartment that extends along the side of the ship, i.e. in this case the upper horizontal bar of each F-shaped compartment. This way each enclosed part of the upper horizontal bar of each F-shaped compartment forms a buoyancy compartment 33, 34 laterally delimited by the further watertight wall section (31 or 32), the side of the ship (15 or 16), and (a part of) the first watertight wall (10b or 10f). Provided that these delimiting components are not damaged, these buoyancy compartments 33, 34 will not be flooded even if the first or second compartments 1 1 , 12 gets flooded when the ship 1 is subjected to a damage. This reduces the total volume flooded. In case only a buoyancy compartment 33, 34 is damaged and flooded, but not the first or second main compartment 1 1 1 , 12, the arrangement with buoyancy compartments 33, 34 is of course also an advantage in that flooding of the main compartments 1 1 , 12 is avoided.

The further watertight wall sections 31 , 32 may be regarded to form part of the first watertight wall 10.

The buoyancy compartments 33, 34 may be provided with watertight doors and work as, for instance, storage rooms.

The arrangement of the void tanks 24, 25 is principally the same for the second embodiment as for the first embodiment. As can be seen in figure 8, together with figures 7 and 9, the void wall sections 21 , 22, which are denoted 21 a, and 22a in relation to the second embodiment, have both been moved in the longitudinal direction and are now arranged below the wall sections 10a and 10g. In principle, the void wall sections 21 a, 22a could be arranged as in figure 5, i.e. below the further watertight wall section 31 , 32, but the positioning shown in figure 8 provides for a more even distribution of water in the transversal direction in some damage cases. A comparison of the effects of the first and second embodiment (denoted 1 and 2 below) for the two levels of bulkheads (below and above the tank top 4) will now be given with reference to the examples A; B, C, D1 , D2, D3 and E given above (see also figures 7-9):

A) Damage occurs close to the rear wall 6a.

1 : First compartment 1 1 and first void tank 24 will be flooded (as well as a compartment to the left of the first compartment 1 1 ).

2: Same as for 1 , except that the part forming the second buoyancy compartment 34 will not be flooded.

B) Damage occurs in the middle between the rear wall 6a and the wall section 10g.

1 . First compartment 1 1 and first void tank 24 will be flooded.

2. Same as for 1 , except that the part forming the second buoyancy compartment 34 will not be flooded.

C) Damage occurs close to the wall section 10g.

1 . First compartment 1 1 , second compartment 12 and first void tank 24 will be flooded.

2. First compartment 1 1 (except for the second buoyancy compartment 34), first buoyancy compartment 33, first void tank 24 and second void tank 25 will be flooded.

D1 ) Damage occurs in the middle between the wall section 10g and the void wall section 22 (or the further wall section 31 ).

1 . Second compartment 12 and first void tank 24 will be flooded.

2. First buoyancy compartment 33 and second void tank 25 will be flooded.

D2) Damage occurs close to void wall section 22 (or the further wall section 31 ). 1 . Second compartment 12, first void tank 24 and second void tank 25 will be flooded.

2. First buoyancy compartment 33, (remaining parts of) second compartment 12 and second void tank 25 will be flooded.

D3) Damage occurs in the middle between the void wall section 22 (or the further wall section 31 ) and the front wall 6b.

1 . Second compartment 12 and second void tank 25 will be flooded.

2. Same as for 1 , except that the part forming the first buoyancy compartment 33 will not be flooded.

E) Damage occurs close to the front wall 6b.

1 . Second compartment 12 and second void tank 25 will be flooded (as well as a compartment in front of the second compartment 12).

2. Same as for 1 , except that the part forming the first buoyancy compartment 33 will not be flooded.

Accordingly, the second embodiment exhibits clear advantageous effects in most of the damage cases. For symmetry reasons, the same applies if the second side 15 is subjected to the damage.

Figure 10 shows a sectional view A-A according to figures 2-9. The structure of the bulkheads and the decks is the same for the two embodiments in the section A-A, but since wall sections have been added and moved some of the compartments defined by the bulkheads and decks shown in figure 10 differ between the two embodiments.

The arrangement of the voids in the double bottom under each large unsymmetrical compartment, should be such as to never allow all four (or more) spaces to be flooded in one damage case. For instance, if two engine compartments are flooded, only one void in the double bottom should be flooded. The voids in the double bottom shall, as in this case, generally be cross-flooded.

The buoyancy compartment should be arranged to the ship's shell plating. The optimal longitudinal location of the buoyancy compartment is adjacent to the bulkhead separating the two partially interleaved main compartments. The buoyancy compartment should be located on the most 'voluminous' side of each engine room. This principle also works for other types of compartments than engine rooms.

Preferred dimensions of each buoyancy compartment:

Transverse extent - (at least) S/5.

Longitudinal length - greater than damage length.

Height - from tank top up to Bulkhead deck.

The invention is not limited by the embodiments described above but can be modified in various ways within the scope of the claims. For instance, the above described bulkhead arrangement between the upper and lower deck (the bulkhead deck and the tanktop) is advantageous also for other arrangements (tanks etc.) below the lower deck. The lower deck may form the bottom plate/keel of the ship.