EP0863835B1

EP0863835B1 - A method and arrangement for decreasing the risk for sinking of a ship

Info

Publication number: EP0863835B1
Application number: EP96935693A
Authority: EP
Inventors: Göran Tengwall
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-04-12
Filing date: 1996-10-11
Publication date: 2000-08-16
Anticipated expiration: 2016-10-11
Also published as: SE9501358L; EP0863835A1; DE69609859D1; ES2152047T3; SE9501358D0; AU7351396A; WO1997013680A1

Description

Technical Field

The present invention relates to a method and arrangement for decreasing the risk for sinking or loss of a ship, which due to harsh weather or a damaged ship lets in water from the surrounding sea.

Background of the Invention

The news often reaches us that a ship has collided with another one, one of the ships herewith having sunk, or that a ship is burning or that a ship has disappeared with its entire crew.

At a study of the circumstances at losses deficiencies in the design of the ships often can be found. Ships are normally not built to withstand more than certain strains according to regulations, which often are old. The size and speed of the ships have increased, and the design of the hulls have changed, but the regulations have not been changed to the same degree.

At the introduction of steam ships, i e the ships were propelled by steam produced by coal fired boilers, the ships were divided by transverse bulkheads for and aft of the two cargo spaces. The ships were strongly built, and the cargoes, often coal, coke and timber, were placed close to frames and board, which further reinforced the ships. Double bottoms were provided but were not entirely used for ballast water.

These ships were often not so severely damaged at collisions that they sunk. The speeds were moderate, and the hit ship moved sideways at collisions, which alleviated the damages. The stems were straight and accordingly hit the other ship in its side above the waterline. The boilers were protected by coal boxes.

Around the latest turn of the century the regulation was introduced that a passenger ship over a certain length should be divided into sections by transverse bulkheads between the tank roof (or double bottom) and the main deck. The sections were not to be longer than that a ship should be kept afloat with two waterfilled sections but not three. The cargo ships did not have such a division.

These regulations have in principle not been changed, and many ships have sunk with more than two waterfilled sections either after a collision or for some other reason.

The rule that a ship shall not sink with two waterfilled sections does not have any real relevance in later times, when the ships have grown in size and further been designed in such a way that they can damage each other below the waterline at collisions.

At about 1960 the habit was namely started to provide merchant vessels with a forwardly under the waterline extending part, which is called "bulb" and the purpose of which is to contribute to higher speed and lower fuel consumption.

Today practically all ships have bulbs. Bulbs act at collisions as an old fashioned ram. For this reason it has become more common that ships sink after collisions, because the bulb of the other ship damages the ship below the waterline.

Environmental activists long complained that ships transported sometimes bunker oil, sometimes ballast water in the same tank and at emptying of ballast water also emptied residual bunker oil into the sea. Many tanks were emptied in this way over the seas, and the quantities were of course large, especially near the bunker harbours. A prohibition against this method was introduced, but the designs of the ships were hardly changed.

Ever since the time of the sailing ships the ships have been built into halves starting from the keel. Ships of later times have become entirely plane in the bottom without any visible keel. Internally opposite the place where the keel was there is still a keelson, which in spite of the lack of a keel has retained its name.

A keelson in a modern ship is not exposed to the same type of load as in the time of the sailing ships, but the keelson is still made of extra thick plate and without through holes. The reason for the lack of holes in the keelson is the desire to tightly separate the two halves of a double bottom. By longitudinally dividing the double bottom in three, four or more parts instead of two the danger from ships provided with bulbs can be decreased, and there will be better possibilities to ballast the ship more economically providing more cargo carrying capability with the same draft. Segregated bottom tanks may accordingly be provided.

The keelson, which may remain, perhaps mostly for historical reasons, can be with or without through holes, and side keelsons can be placed at each side of the keelson at suitable distances therefrom. In this way central tanks and side tanks are created. Service tunnels for oil, steam, electricity and water with outlets in both ends and at least one exit to deck can be built between the different tanks in the double bottom. This disposition of the double bottom provides completely other possibilities than the present disposition of the tanks.

If the central tanks are used for bunker oil and the side tanks for ballast water, many advantages are obtained. The oil is for example protected against collision damages by the side tanks. The same is true in shallow waters, if the ship goes aground at passage of narrow sounds or the like. The risk for environmental damages decreases greatly.

The division of the double bottom in this way provides greater possibility with as little ballast water as possible to trim the ship or to remove a slight heeling and accordingly to increase the effective cargo. The risk for decreased stability due to a non-filled tank decreases, because the tank is smaller than at a double bottom divided into two. The risk for a total loss after collision with a ship provided with a bulb decreases considerably, because the damaged tank is much smaller than the corresponding tank at a bottom divided into two.

If the division of the double bottom is followed up with a division of the ship between the tank roof and the main deck, a ship, which furthermore is divided in sections with transverse bulkheads, is virtually unsinkable.

Such a division of the ship can be made with longitudinal bulkheads between the tank roof and the main deck or above that.

Bulk and container ships usually lack intermediate decks and are therefore called ships with open cargo spaces (in spite of the container fittings). These ships should be provided with longitudinal bulkheads in the cargo spaces between the tank roof and at the level of the main deck. At construction the ships should also be provided with a double bottom divided into three or four compartments. By the addition of longitudinal bulkheads the ships will be heavier and be able to carry less cargo, but on the other hand they will be safer, so that a larger cargo can be permitted. Longitudinal bulkheads can also be introduced in older ships.

Tank and ore ships (as well as combined ships) are usually provided with longitudinal bulkheads, and no change in the area between the tank roof and the main deck is thus required. Tank ships should have double boards, if such are lacking. The ship type should at construction be provided with a divided double bottom for environmental reasons but also for a more effective ballast.

Passenger ships should be equipped with longitudinal bulkheads between the tank roof and the main deck, for example two longitudinal bulkheads, dividing the ship in three longitudinal sections. Longitudinal bulkheads are complementary to transverse bulkheads within the same area. This will make the ships virtually unsinkable at collision with another ship or at grounding. New ships should be provided with a double bottom divided into three or four compartments like other ship types. No ways down, such as stairs and elevators, can be permitted directly from the main deck. This should instead be built in to a height of about 2.5 m. Stairs and elevators are used from the deck above.

Known lost ships, such as Titanic and Andrea Doria, lacked longitudinal bulkheads and divided double bottoms.

Among Ro-Ro ships are ships for transporting cars and paper. They have a main deck, which is positioned comparatively high and sometimes lacks transverse bulkheads. Below the main deck there are sometimes fixed transverse bulkheads down to the tank roof.

Such ships should instead be provided with fixed longitudinal bulkheads between the main deck and the lowermost cargo deck. Fixed or sideways movable but tight longitudinal bulkheads should be placed on the main deck along the whole deck. The height should be at least the same as that of the cargo, and stanchions to the deck above can be provided.

Combi-ferries are combined cargo and passenger ships (ferries). They are very special with their main decks at a low position; the main deck is a car deck, which sometimes extends over the entire length and width of the ship. Longitudinal bulkheads, which can take care of water flowing in, are often lacking, in spite of the fact that the ship has cargo ports at both ends. At a damage of the stem port or a collision considerable amounts of water are let in, which at rolling easily can cause capsizing. If the water is not taken care of fastly, the ship can capsize. After the loss of Estonia many proposals for solving the problem with water on the car deck have been put forward. Most people agree that their shall be provided a division by longitudinal partition with for example one or two longitudinal bulkheads along the length of the entire deck. No ways down, such as stairs and elevators, can be permitted directly from the main deck. They should instead be built-in to a height of about 2.5 m. Comfortable stairs provide passage to and from the deck.

If there are cargo decks under the main deck the same methods with longitudinal and transverse bulkheads are utilized as at Ro-Ro ships.

According to DE-A-44 38 431 water can be pumped out from a collecting tank in the bottom of a ship. A ship may according to GB-A-2 230 745 have openings in the side boards for letting out water.

The Invention

The object of the present invention is to decrease the risk for loss of a ship, which due to harsh weather or a damaged ship lets in water from the surrounding sea. The invention shall be a supplement to the measures described above relating to the division of the ship into smaller sections.

The method according to the invention is characterized in that the water let in at a certain level over the bottom of the ship, for example on its main deck, is transported down in the ship, preferably to tanks in the double bottom of the ship, and from their up and out to the sea through a system of emptying tubes and outlet tubes by means of the pressure generated by the height difference of the water in the system.

At a supplementing method water can also be transported from the main deck or another deck through different kinds of drainage tubes, which extend from the deck near the board of the ship and obliquely downwards to the opposite board of the ship, where they open, but the water can also be transported through direct emptying tubes or short drainage tubes directly to the closest board.

An arrangement for carrying out the method according to the invention is characterized by emptying tubes, which extend from the deck down to tanks in the double bottom of the ship, and by outlet tubes, which extend from the tanks up to outlets in the board of the ship between the water line and the deck.

This system can be supplemented with different long drainage tubes, which extend from the deck near the board of the ship obliquely downwards to either board of the ship, where they open.

The inclination of the long drainage tubes is about 5 - 15°, preferably about 10°, whereas the inclination of the short drainage tubes can be greater or lesser.

Each such drainage tube is preferably provided with a non-return valve at its opening in the board. The deck opening of the drainage tube can also be provided with a non-return valve.

At a ship, which besides being provided with ordinary transverse bulkheads is provided with at least two longitudinal bulkheads, which extend generally all the way from the bottom of the ship at least past the deck, whereby at least three bottom tanks are formed, namely two side tanks and a central tank, emptying tubes extend in the vicinity of a longitudinal bulkhead from the deck down to a side tank, whereas outlet tubes in the vicinity of the board of the ship extend from the side tank up to the outlet. Each outlet tube is preferably provided with a non-return valve near its outlet.

In order to guarantee that all parts of the deck are emptied emptying tubes are arranged to take water from both sides of the longitudinal bulkhead, namely from a side portion of the deck and from a central portion of the deck.

In order to further improve the transport of water from the deck distributing tubes extend from the deck near the board to spaces under the deck, preferably past the different longitudinal bulkheads of the ship.

Summarizing, measures have been proposed above for improving the buoyancy of a ship after damages, among other things by dividing the ship in more sections than earlier. The proposals mean - with certain differencies depending on the type of ship - that the double bottoms are divided into sidetanks and central tanks and that longitudinal bulkheads are provided up to the preferred level of the main deck.

For Ro-Ro ships it is proposed that in the main deck and cargo decks thereunder there are provided distributing tubes and emptying tubes, which at a collision can take care of the water let in and transport this water down to all the three portions of the lowermost cargo deck and the ballast tanks. The purpose is to decrease the heeling and also to obtain a better stability for the ship. For combiships it is proposed that the main deck is emptied by means of some type of drainage tubes from the side edges of the deck to the board at either side. Furthermore it is proposed to arrange either vertical emptying tubes to the side tanks or horisontal emptying tubes to the closest board. The side tanks are rapidly filled, whereafter the water is pushed out through the outlet tubes at the same rate as it flows down into the tanks.

For example in Ro-Ro ships cargo decks, preferably the lowermost cargo deck, can be provided with foldable, liftable or pivotable transverse bulkheads, of which not all need to extend up to the roof. The division of the cargo deck in this way, which means that water is prevented from moving freely in the longitudinal direction, contributes to making the ship more stable and preventing greater trim adjustments, so that the manoueverability of the ship is maintained.

When absent, double boards are introduced on tankers and ore ships as protection against leakage at for example landing or excessive pressure by tug boats.

The Drawings

The invention will be further described below under reference to the attached drawings, in which Fig 1 is a section through a ship, preferably a so called combi-ferry, in the sea, Fig 2 is a section through the same ship, which here has been exposed to a damage on its port side, let in water and begun to heel over, Figs 3A - F in section and to a somewhat greater scale than Figs 1 and 2 show different subsystems of a device according to the invention, Fig 4 to an even greater scale and in a part-section shows a portion of the same ship with the different subsystems from Figs 3A - E combined, Fig 5 is a section through a part of a ship with a preferred embodiment of the subsystems according to Figs 3B and E and Figs 6 - 8 are cross sectional views along the lines VI-VI, VII-VII and VIII-VIII, respectively, in Fig 5.

Detailed Description of Preferred Embodiments

Fig 1 shows a section through a ship 1, preferably a so called combi-ferry. The ship is in a conventional way equipped with a double bottom, i e a tank roof 2 is arranged at a certain height over the bottom 3 of the ship. The ship has a main deck 4 over the normal water line. The ship can be provided with an upper deck 5 over the main deck 4.

The mentioned decks extend over the entire width of the ship 1, i e between its two sides or boards 6.

The ship 1 can - besides the mentioned decks - be provided with further decks, for example passenger decks below the main deck 4 and further decks over the upper deck 5.

In a traditional way the ship can be provided with a so called keelson 7, which extends centrally in the longitudinal direction of the ship between the bottom 3 and the tank roof 2. This keelson 7 is traditionally homogeneous, i e it separates a port tank from a starboard tank. If the ship is arranged in accordance with the present invention, it is if desirable possible to arrange break-throughs in the keelson 7 at equal distances, so that fluid can flow through the keelson.

In a traditional way the ship 1 is provided with a number of transverse bulkheads between the tank roof 2 and the main deck 4, which in the longitudinal direction divides the ship in sections separate from each other. The ship is however also provided with an optional number of longitudinal bulkheads within the same areas as the transverse bulkheads, in the shown case a port longitudinal bulkhead 8 and a starboard longitudinal bulkhead 9. These longitudinal bulkheads can extend from the bottom 3 of the ship upwards in certain cases past the upper deck 5, whereby the ship in the shown case is divided in three from each other generally separated sections in the transverse direction. The ship can if desired be provided with one or more longitudinal bulkheads above the main deck, and these bulkheads can be distributed in another way than in the shown case.

The longitudinal bulkheads 8 och 9 preferably extend all the way down to the bottom 3, whereby also the double bottom formed by the tank roof 2 is divided into separate tanks, i e a port sidetank 10, a central tank 11, comprising the keelson 7, and a starboard side tank 12. The portions of the

longitudinal bulkheads

8 and 9 which extend below the tank roof 2 can be called side keelsons. The central tank 11 can preferably be used for oil, whereas the

side tanks

10 and 12 can be used for salt water, for example for ballast and trim purposes. By its protected position the central tank 11 is environmentally especially suited for storage of oil.

The division of the ship both in longitudinal and transverse direction by means of transverse bulkheads as well as longitudinal bulkheads means that the ship is divided into a great number of smaller sections, leading to a very advantageous effect on the security and stability of the ship.

Fig 2 illustrates the process when for example a collision damage is caused in the port side slightly below the normal water line. The affected sections of the ship in vicinity of the damage are more or less rapidly filled with water depending on the size of the damage. Also neighbouring sections or volumes can gradually be filled with water, if the actual bulkheads have openings of some kind.

The ship begins to heel over more or less severely, as is illustrated in Fig 2. The division of the ship in more sections than usual means of course that the risk for a total loss is less than otherwise, but if the damage is large enough the ship can still sink, especially if neighbouring sections gradually are filled due to leaks in the different bulkheads or for other reasons.

It is thus extremely important to try and get rid of intruding water as soon as possible for preventing a total loss. This is the main purpose of the invention.

Figs 3A - F show a number of subsystems for transporting water away from above all the main deck 4. The sections according to Figs 3A - F correspond to the section according to Fig 1, and the same reference numerals are used in the different figures for the same details; for the sake of clarity Figs 3B - F are not provided with all reference numerals for parts that are shown in Fig 1 and Fig 3A.

Long drainage tubes 13 are shown in Fig 3A and short drainage tubes 13' in Fig 3E. Each such drainage tube 13, 13' extend from the main deck 4 in the vicinity of the board 6 obliquely downwards through the ship and opens through the board 6 of the ship, the long drainage tubes 13 opening on the opposite side and the short drainage tubes 13' on the same side. Non return valves can be arranged above all in the vicinity of the opening of the drainage tubes 13, 13' in the board, but there may also be reasons to arrange non return valves at the opening of the draining tubes 13, 13' in the main deck 4.

A number of such pairs of long drainage tubes 13 can be arranged along the length of the ship, for example one pair in each section of the ship divided by transverse bulkheads, whereas the short drainage tubes 13' can be arranged in pairs at for example each ten meters of the ship's length.

As long as the water pressure acting on the intake of each drainage tube 13, 13' at the main deck 4 exceeds the pressure at the outlet, which preferably opens in a recess 18 (Fig 3E) in the vicinity of the board 6, the drainage tube 13, 13' has the function to carry water away from the main deck 4.

The ship with the two mentioned decks, namely the main deck 4 and the upper deck 5, is shown in Figs 3A, E och F. In Figs 3B - D a further intermediate deck 15 is drawn between the main deck 4 and the tank roof 2 for illustrating that the intermediate space can be utilized for cargo.

In Fig 3B there are shown wide emptying tubes 16, which at both sides are arranged in pairs between the main deck 4 and the tank roof 2 in the

sidetanks

10 and 12. The left emptying tube 16 in Fig 3B opens towards the port head deck section, while the emptying tube to the right opens towards the main deck central section. The purpose is to show that the emptying tubes 16 are arranged to drain water from all parts of the main deck, so that the deck is kept free from water independent of the heeling of the ship.

The emptying tubes 16 open in the two sidetanks 10 and 12. From these tanks outlet tubes 17 lead to openings in the board 6 between the main deck 4 and the water line. The outlet tubes 17 preferably open in recesses 18 in the board and are preferably there provided with non return valves.

Water carried down through an emptying tube 16 to the already

full sidetank

10 or 12 will be pushed out through the outlet tube 17 due to the pressure produced by the height difference of the water in the system, especially at a heeling of the ship.

Instead of emptying tubes 16 and outlet tubes 17 it is possible, as shown in Fig 3F, to arrange direct emptying tubes 16' from both sides of the

longitudinal bulkheads

8 and 9 at the main deck 4 to the nearest board 6, where they open in recesses 18 between the water line and the main deck 4.

The emptying tubes 16, 16' and the outlet tubes 17 can be generally equally distributed along the ship.

Narrower distributing

tubes

19, 20 and 21, which extend from the main deck 4 to the interior of the ship and decks 15 therebelow near the board 6, are shown in Fig 3C. The purpose of these distributing tubes 19 - 21 is to assist in carrying away water from these decks and to distribute down the water fairly uniformly in the ship in order to stabilize it. In the lower part of the ship the water carried down through the distributing tubes 19 - 21 can be taken care of by the system in the ship for this purpose, including bilge pumps. Distributing

tubes

19 and 21 thus extend from the main deck 4 and an intermediate deck 15, respectively, past the port longitudinal bulkhead 8 and open under the intermediate deck 15, whereas other distributing tubes 20 in a corresponding way extend all the way past the starboard longitudinal bulkhead 9 and open below the intermediate deck 15. For the sake of clarity only distributing tubes 19 - 21 from the port side are shown in Fig 3C, but corresponding tubes also extend from the starboard side of the ship in the direction to the left in Fig 3C.

Finally, air tubes 22, which extend from the two

side tanks

10 and 12 up past the upper deck 5, are shown in Fig 3D. The purpose of these air tubes 22 is to air the sidetanks.

The distributing tubes 19 - 21 and the air tubes 22 can be generally equally distributed along the ship.

In Fig 4 the left part of the ship is shown in section with the different subsystems brought together (with the exception of the air tubes 22). Thus, the drainage tubes 13, 13', the emptying tubes 16, the outlet tubes 17 and the distributing tubes 19 - 21 are shown here.

In later times the requirements on draining systems for ships have been discussed, for example that the water level on the car deck of a ferry shall be lowered by a third from a level of one meter in one minute. In order to take care of these very large water volumes it is possible to have an arrangement according to Fig 5 and Figs 6 - 8, which show sections from Fig 5.

The ship illustrated in Figs 5 - 8 has similar to the description above a tank roof 2, a bottom 3, a main deck 4, an upper deck 5, a board or side 6, a port longitudinal bulkhead 8, a side tank 10, a short drainage tube 13', an intermediate deck 15, emptying tubes 16 and outlet tubes 17.

The short drainage tubes 13' and the outlet tubes 17 can have the sections shown in Fig 6 and 7 and be attached to the inner side of the ships frame 6', on which the board 6 is attached.

The openings for the short drainage tubes 13' and the outlet tubes 17 in the board 6 over the water line can be provided with doors 23, which easily open at a water pressure from inside. Near the openings non-return valves can suitably be arranged.

In order to facilitate outward flow of water from the outlet tubes 17 these may be upwardly expanded, as is illustrated in Fig 5.

In order to accomplish an effective removal of water from the main deck 4 at both sides of the longitudinal bulkhead 8 the drainage tubes 16 can be given the form which above all appears from Fig 8. The inlets to the drainage tubes 16 can, if they open in the main deck 4 according to Fig 5, be provided with gratings. Alternatively, the emptying tubes 16 may extend somewhat up over the main deck 4, and the water may be admitted to the tubes through side openings provided with gratings or nets.

All the emptying tubes 16 on the port side shall open in the port side tank 10.

Claims

A method of decreasing the risk for loss of a ship, which due to harsh weather or a damaged ship lets in water from the surrounding sea, characterized in that the water let in at a certain level over the bottom (3) of the ship, for example on its main deck (4), which is provided with dividing longitudinal bulkheads (8, 9), is directly transported either down in the ship (1), preferably to tanks (10, 12) in the double bottom of the ship, and from there up and out to the sea through a system of generally vertical emptying tubes (16) and outlet tubes (17) by means of the pressure generated by the height difference of the water in the system.
A method according to claim 1, characterized in that water can be transported from the main deck or another deck either through long drainage tubes (13) or short drainage tubes (13'), which extend from a deck (4) near the board (6) of the ship (1) and obliquely downwards, the long drainage tubes (13) extending to the opposite board (6) of the ship and the short drainage tubes (13') to the closest board, where they open.
A method according to claim 1, the ship being separated into smaller, water tight sections by means of longitudinal bulkheads and transverse bulkheads, characterized in that water basins are formed on a lowermost cargo deck by means of the longitudinal bulkheads, the sides of the ship and movable transverse bulkheads in order to obtain a stability for the ship and prevent greater trim changes, so that the operational ability of the ship is maintained.
An arrangement for decreasing the risk for loss of a ship (1), which due to harsh weather or a damaged ship lets water in from the surrounding sea at a certain critical level over the normal water level, for example on its main deck (4), characterized by generally vertical emptying tubes (16), which extend directly from the deck (4), which is provided with dividing longitudinal bulkheads (8, 9), down to tanks (10, 12) in the double bottom of the ship (1), and by outlet tubes (17), which extend from the tanks up to outlets in the board (6) of the ship between the water line and the deck.
An arrangement according to claim 4, characterized in that long or short drainage tubes (13, 13') extend from the deck (4) near the board (6) of the ship obliquely downwards, the long drainage tubes (13) extending to the opposite board (6) of the ship and the short drainage tubes (13') to the nearest board, where they open.
An arrangement according to claim 5, characterized in that the inclination of the long drainage tubes (13) is about 5 - 15°, preferably about 10°.
An arrangement according to claim 5, characterized in that each drainage tube (13, 13') is provided with a non-return valve preferably at its opening in the board (6).
An arrangement according to claim 4, the ship (1) being provided - besides the ordinary transverse bulkheads - with at least two longitudinal bulkheads (8, 9), which extend generally all the way through from the bottom (3) of the ship at least to the deck (4), at least three bottom tanks (10 - 12), namely two side tanks (10, 12), for example for ballast water, and a central tank (11) for example for oil, being formed, characterized in that emptying tubes (16) extend in the vicinity of a longitudinal bulkhead (8, 9) from the deck (4) down to a side tank (10, 12) and in that outlet tubes (17) extend in the vicinity of the board (6) of the ship from the side tank up to the outlet.
An arrangement according to claim 8, characterized in that each outlet tube (17) is provided with a non-return valve preferably in the vicinity of its outlet.
An arrangement according to claim 8, characterized in that each outlet tube (17) is expanded towards its outlet in order to facilitate effective outlet of water.
An arrangement according to claim (8), characterized in that an emptying tube (16) is arranged to let water in from either side of the longitudinal bulkhead (8, 9), namely from a side portion of the main deck (4) or from a central portion of the deck.
An arrangement according to claim 8, characterized in that distributing tubes (19 - 21) extend from the main deck (4) and decks (15) arranged thereunder near the board (6) to spaces under the decks arranged at the other side of the different longitudinal bulkheads (8, 9) of the ship.
An arrangement according to claim 8, characterized in that foldable, liftable or pivotable transverse bulkheads are arranged on cargo decks, preferably on the lowest cargo deck.
An arrangement according to claim 13, characterized in that the sides of the ship, the longitudinal bulkheads and vertically adjustable or pivotable water tight transverse bulkheads form basins for water for making the ship more stable and preventing greater trim adjustments, so that the manoeuvrability of the ship is maintained.
An arrangement according to claim 14, characterized in that only certain, for example each third, transverse bulkheads reach the deck above it, whereas the remainder of the bulkheads leave a certain space to this deck.
An arrangement according to claim 4, characterized in that the main deck (4) - except emptying tubes (16), outlet tubes (17) and the like - prevents passage of water from above as well as from below.