WO2008153413A1

WO2008153413A1 - Deck structural system for a multihull vessel

Info

Publication number: WO2008153413A1
Application number: PCT/NO2008/000212
Authority: WO
Inventors: Pål G. BERGAN
Original assignee: Det Norske Veritas As
Priority date: 2007-06-12
Filing date: 2008-06-12
Publication date: 2008-12-18
Also published as: GB0711358D0

Abstract

The present invention relates to a catamaran vessel comprising at least two hulls (3) interconnected by a structural deck structure (2) in parallel spaced relationship, where the deck structure comprise a multiple of cell, layers (14, 15), each cell layer being divided into at least two cells rigidly connected to one another, the cells further spanning between the longitudinal broadsides of the catamaran vessel and whose cells provide sheltered space for various types of usage such as for cargo storage. A method for manufacturing the cellular deck.structure is also disclosed, where parts of or entire walls and decks of the cellular structure are assembled from prefabricated panels that are joined together by welding, bolting or other appropriated types of joining techniques consistent with the materials used and where the deck structure may be placed on top of the hulls by way of lifting or skidding as a whole or by parts.

Description

DECK STRUCTURAL SYSTEM FOR A MULTIHULL VESSEL

The present invention relates to a catamaran type marine vessel comprising two hulls arranged spaced apart and parallel to each other. The hulls extend in the direc- tion of travel and are connected to each other by way of a connecting deck structure, which carries connecting forces as well as various types of loads on the deck structure. In particular the invention relates to a deck structure for catamaran vessels that has necessary structural stiffness and strength to allow for large vessels with the two hulls to be widely separated.

Vessels equipped with more than one hull, i.e. catamarans, have long been known, and present a number of advantages compared with the conventional type of vessel. Thus, the catamarans typically have a larger loading area for a given displacement than vessels equipped with conventional hulls, they have a better resistance to roll- ing motion and are capable of higher speeds for a given engine power. Furthermore, increased stability is obtained with vessels of the catamaran type, since the hulls of the vessel can be arranged at a relatively large distance from each other.

However, certain problems of design and construction are encountered in this type of vessel, which are primarily associated with difficulties in obtaining a sufficiently strong and stiff joining structure between the different hulls of the vessel by way of the deck structure joining the said hulls. Another disadvantage by these vessels is the limitation of speed in rough sea in order to avoid severe wave impacts against the lower side of the deck structure. There is also a need of assuring for the vessel to have a good longitudinal motion performance in order to reduce heave and pitching which typically worsen the problem of wave impacts. Thus, the overall accelerations and relative motions between the vessel and the waves are important in relation to the operational performance of the vessel. Accelerations determine loads on cargo, equipment and the vessel itself and are important in relation to the comfort of people onboard.

When waves build up between the hulls of the vessel there is risk of waves hitting the lower side of the catamaran deck (slamming). These impact forces are normally dealt with by way of shaping the lower side of the deck structure as a wedge (keel) such that the waves to some extent will be forced to the side rather than giving a direct hit. Moreover, the deck structure also has to be strengthened in order to sustain such impact forces. This type of wedge design of the deck structure has the disadvantage that it generally reduces the air gap between sea and deck itself, and it is also impractical in terms of the possibilities for effective utilization of the hull space because of internal beams and various types of stiffening elements. The complexity and cost of such designs implies that catamarans have normally not been made with a large distance between the two hulls. In the light of the above the catamaran vessels will be subjected to large bending and torsion stresses and also to large deformation forces when in motion. This will result in that larger catamaran vessels must be built with a more complex and heav- ier construction, which will increase the expenses considerably.

Accordingly, one object of the invention is to provide in multi-hull vessels of the aforesaid a deck construction which achieves a reduction in the stresses and the deformation forces acting on the vessel.

One further aim with the present invention is to provide a new deck structural system that has the necessary structural stiffness and strength to allow the hulls to be widely separated. The simplicity and flat shape of the deck structural system is also such that it will be possible to achieve a large air gap between the water surface and the deck structure and thereby greatly reduce the threat of damage from slamming of waves.

It is a further aim with the present invention to provide a structural system that will allow for great flexibility in the use of the space within the connecting structure, where the open, unobstructed cells within the deck structure are an important part of this. The deck structure itself may thus be efficiently used as cargo space, cabins, power generating machinery, fuel tanks, equipment etc., or other types of space needed onboard the ship.

Yet another object of the present invention is to provide a deck design with a repetitive geometry thus reducing fabrication costs. The key to this is the repetitive geometric nature of the current design concept.

Another object of the connecting deck structure is to provide strength for both force transfer between the two hulls and, if so desired, for carrying large loads within deck hold and on top of the deck. The proposed concept is highly efficient with regard to both these aims.

It is a further aim of the present invention to provide a manufacturing method for a deck structural system and a catamaran vessel, where the fabrication costs are reduced. The mentioned repetitive nature of the deck structure lends itself to prefabri- cation and efficient assemblage of components.

According to the present invention the catamaran vessel will represent a major im- provement compared with current catamaran designs with respect to providing a ^■ wide deck structure with large capability for storage of loads, reduced costs and time for manufacturing, enhanced structural strength and stiffness, improved sea keeping performance and reduction of slamming problems, and provide great flexibility for adaptations to desired, specific usage in terms of cargo, passengers and operational functions.

A final aim, which is related to the rolling stability of wide catamarans and is made possible by the current invention, is that it may be feasible to operate the current type of catamarans without use of ballast water to stabilise the vessel. Ballast water in ships constitutes a major environmental problem because of organisms and pollutants transported from one port to another by way of the ship.

These objectives are achieved with a structure and a manufacturing method according to the invention as defined in the enclosed independent claims, where embodiments of the invention are given in dependent claims.

The present invention is intended to enable a catamaran vessel to be utilized to a greater extent, and comprises a vessel having at least two hulls arranged in a spaced relationship, which hulls extend essentially parallel with each other and a structural deck system that is adapted to join and to transfer the forces between the hulls.

The structural deck system comprises one or more layers or decks. Each of the layers or decks comprises at least two cells, where each of the cells is formed of at least three walls connected along a longitudinal axis of the cell. The cells are preferably completely open at their ends, but may also be closed by end covering faces.

The cells in each layer or deck are further rigidly connected, thereby forming a structural deck system that is cellular, where the cells are orientated such that the longitudinal axis of a cell extends in a direction traverse of a normal headway direction of the vessel. The structural deck system preferably spans fully between longitudinally broadsides of the vessel.

The cell walls of the structural deck system preferably coincide with a traverse bulkhead or stiffening frame system within each hull.

In one embodiment the cells that are forming the structural deck system may have a rectangular cross section, but as a skilled person will understand, other cross sections may be applicable for the task to be carried out. The interconnected cells can further form a deck structural system consisting of at least two interconnecting layers.

The cells may partly or wholly be made by different materials, for instance of welded, stiffened steel plates, of prefabricated steel sandwich plates with internal stiffeners or corrugated cores, open or closed welded aluminium beam sections, steel concrete sandwich elements, stiffened steel plates with lightweight concrete between etc.

In one preferred embodiment the (cellular) structural deck system is assembled from prefabricated panels that are joined together by welding, but one may also for instance apply bolting or other joining techniques consistent with the materials used.

In accordance with one embodiment the transversally oriented cells in the deck structure provide a unique storage space that is accessible from both sides for loading and/or unloading. In particular, almost any type of wheeled cargo, such as cars, trucks, wheeled containers etc. can easily be transported in and out of the cells. Also cargo without wheels can easily be transported in and out of the cells by way of fork lifts, trucks and/or lifting, rolling, or skidding arrangements within the cells. Easy access to and from the cells can be obtained by way of ramps along the quay.

The cell openings may be closed by using hatches, hinged doors or other types of covering devices, whereby the cargo will be fully protected against the weather conditions. In addition to providing cover for the cells, such covering devices may also be the part of a loading and unloading ramp system. The covering devices are attached to the cells in appropriate ways and may also comprise sealing arrangements. However, these covering elements are not structural elements of the cells. Of course, as the covering devices are a part of the whole system, they will be subjected to minor loads acting on the vessel, but they will not imbibe the major forces that the cells are exposed to. The cells may of course also be used as open cells provided this is consistent with the overall safety of the vessel.

Within cells one may provide rolling and or sliding arrangements for moving of goods without wheels, for instance standard containers. Further, one may also di- vide the cells in their horizontal or vertical directions by use of lightweight decks and walls. Such arrangement may also be made movable or detachable to obtain greater flexibility with respect to adaptations to various types of cargo and to specific stacking procedures. For instance, one may store several layers of cars on top of each other within one cell by way of mounting internal decks within the same cell.

The cells also provide well protected internal rooms within the vessel when the invention is used for other types of ships than cargo vessels. The cells can be used as covered space for many types of machinery and equipment. Moreover, the cells can serve as a shell for installing cabins of crew and passengers. Upper side of the cells forms a large, planar and essentially unobstructed upper deck with great flexibility in terms of use. By this almost any type and size of cargo can be placed on the upper deck. Special access ramps on the quay and possibly also integrated or positioned on the vessel, may be used for moving cargo on and off. Various lifting devices may further be used for movement of goods and equipment.

For other types of applications than cargo and container vessels the upper deck may be used for many other purposes depending on the functions of the vessel. For instance the deck may be equipped for different types of work functions such as lift- ing, laying of pipe lines or cables, placing of machinery for power generation and so on. The deck structure may also be used as a foundation for placing various types of superstructures on top of it; for instance, superstructures for catamaran passenger vessels.

The hulls and the cellular deck structure of the catamaran may be constructed in a conventional manner by assemblage of modules in a dry dock. However, the invention also lends itself to non-conventional construction methods. For instance, the hulls may be constructed separately at one location and the deck structure at another location possibly different from the first one, whereafter the hulls and the deck structure are brought together to a common location where the parts will be put together by lifting or skidding the deck on top of the hulls (mating). This may be done in one single operation or in several steps where the cellular deck is assembled from several parts.

The present invention seeks to provide a catamaran type vessel which, even for very wide catamarans, has a particularly strong and stiff connecting structure capable of carrying all forces occurring due to movement of the sea, in particular bending, shear, warping, and torsion forces, and whose connecting structure, which in addition to its function as a crucial structural element for the entire vessel, provide unique possibilities for storage and provide protected space for other types of functions or usage for the vessel.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred non-limiting embodiments of the invention, as illustrated in the accompanying drawings:

Fig. 1 A illustrates main forces acting on a traverse cross-section of a catamaran vessel,

Fig. 1 B illustrates main forces acting in the longitudinal direction of the catamaran vessel,

Fig. 1 C illustrates resulting main differential force components from waves acting on the catamaran vessel, Fig. 2 shows a cross-section of a double layer of cells of the catamaran vessel,

Fig. 3 shows storage of cargo in deck cells, and

Fig. 4 shows one type of sideways loading and unloading of cargo in deck cells.

Figures 1 A-C shown some major load cases that catamaran vessel hulls 3 and a connecting structural deck system 2 are exposed to and therefore have to be designed to withstand. The catamaran vessel's 1 own weight, cargo loads and wave forces will try to deform the catamaran vessel 1 and exert forces both in the transverse and the longitudinal direction of the catamaran connecting structural deck sys- tern 2.

A catamaran vessel 1 in figure IA comprises two hulls 3 connected together by a deck 14. For the sake of simplicity only one deck is shown, but it should be understood that the structural deck system could comprise a plurality of decks 14. The hulls 3 may be of any design, according to the purpose for which the catamaran vessel has been built, independently of the invention.

The transverse vertical shear condition in figure IA will be associated by own weight and dead load on the deck structure 2 as well as differential hydrodynamic load on the hulls 3. Axial and shear loads in the transverse direction can be caused by wave forces on the side of the catamaran vessel 1. The figure further shows horizontal shear acting in the transverse direction. Such forces will typically be induced from dead weight, cargo loads on the deck structure 2 as well as hydrodynamic forces acting on the hulls 3.

Figure IB shows forces acting in the longitudinal direction of the catamaran vessel 1 , where these forces will try to bend the vessel 1. This is normally due to wave action, ballasting of the vessel as well as loads on the deck. structure 2. Longitudinal axial inertia forces acting on the catamaran vessel 1 are mainly caused by head wave forces or by accidental loads such as grounding and collisions.

A particular important load case for wide catamarans 1 is so-called "warping", a kind of twisting or torsion action. The warping case is a serious challenge for wide catamarans 1, and is typically caused by inclined, incidental waves acting with a phase difference on the two hulls 3. This can typically be explained (see also figure 1C) with that one of the hulls 3 wants to lift the bow and lower the aft part of one hull 3 due to the wave condition, whereas the other hull 3 would like to do the opposite. The turning of hulls 3 opposite ways (warping) is prevented by the strength and stiffness of the connecting deck structure 2, in particular the so-called torsional and warping rigidity of connected cells 4. A structural deck system 2 according to present invention is shown in figure 2, where the structural deck system 2 comprises a structure of connected cells 4 oriented in the traverse direction of the catamaran vessel 1. The cells 4 are constituted of a lower deck plate 5 and upper deck plate 6, which plates 5, 6 are connected to vertical wall plates 7 over the entire length of the cells 4. Two horizontal neighbouring cells 4 can be formed as independent cells 4, where they when connected to each other thereby will have double vertical wall plates 7, or they can share one vertical plate 7. Correspondingly, this will also be applicable for two vertical neighbouring cells 4 with common horizontal deck plates 5, 6. A number of horizontally connected cells 4 form a continuous layer or deck 14, 15 of the catamaran vessel 1. According to the present invention, the structural deck system 2 will then comprise at least two layers or decks 14, 15 of horizontal, continuously arranged cells 4, the layers or decks 14, 15 being aligned on top of each other, where two vertically neighbouring cells 4 in addition are arranged directly opposite each other.

By arranging the structural deck system in this way, over the entire longitudinal length of the catamaran vessel 1 , the torsion shear stresses in the vertical wall plates 7 tends to cancel each other out because of inverse stresses. Moreover, as the longi- tudinal axis of the cells 4 in the structural deck system 2 extend in a traverse direction of the forward direction of the catamaran vessel 1, the cells 4 will lock each other against warping.

The cells 4 can be manufactured by any suitable material and method; for instance the deck plates 5, 6 and walls 7 of a cell 4 can be made from extruded aluminium beams being welded together. The plates that make up the decks 5, 6 and the walls 7 in the cells 4 can be made from extruded H or "double H" aluminium beams that are welded together. Large plate sections can furthermore be prefabricated by for instance using different welding techniques.

One another possibility is to make the deck structure from steel. Sandwich type steel plates with corrugated core can be used for such purpose. Another possibility is to make the deck plates 5, 6 and walls 7 by way of conventionally welded, stiffened plates.

In figure 3 are further shown that fore and after cells 10 have a triangular geometry; this in order to provide additional structural stiffness and strength in the interaction with the two hulls 3 that are connected with the structural deck system 2. The fore and aft cells 10 can of course have other suitable geometries as long as they provide the stiffness and strength needed. As can be seen in the figure, the structural deck system 2 provides easily accessible, covered space for storage and goods. Wheeled cargo or trucks 8 are stored inside the cells 4. Such cargo 8 may also be stored in several layers within each cell 4 by providing fixed or movable light decks (not shown in the drawings) inside each cell 4.

The cells 4 are preferably open at their ends, but they may also be equipped with covering devices, such as doors and/or hatches etc., which in a suitable manner can be connected to the cell openings. In addition to providing cover for the cells 4 such hatches may also be part of a loading and unloading ramp system 12 for the cargo or equipment 8 inside the cells 4. However, these covering devices are not structural elements of the cells, and even though they are subjected to minor loads acting on the vessel I₅ they will not be able to imbibe the major forces that the cells are exposed to.

A bridge and control room 9 shown in figure 3 is arranged on the deck structural system 2 foremost part, thereby giving a good view when navigating the catamaran vessel 1. The placing of the deck house may alternatively be in any other position on the upper deck depending on what is most suitable for the particular type of ship in question and on considerations regarding the comfort of the crew.

In figure 4 can be seen the unloading of the catamaran vessel 1 where the catamaran vessel 1 have moored to a quay 11 , and where hatches arranged on the cells 4 are a part of the loading and unloading ramp system 12. As will be apparent for the skilled person many other existing feasible arrangements for transfer of goods between port and the catamaran vessel 1 can be used.

Although it in the above description of the invention just have been made reference to a catamaran vessel 1 transporting people and/or goods it should be understood that the principles of the invention also are applicable for other types of multi-hull vessels, for instance pipe laying vessels, crane vessels, seismic vessels etc. as well for similar use for mono-hulls vessels.

The invention has now been explained with several embodiments. Only elements related to the invention is described and a skilled person will understand that the cells in the structural deck system can be formed from other materials than mentioned above, with other joining techniques, as prefabricated modules or elements or combinations of these, with different equipment for different type of vessels etc. The skilled person in the art will also understand that one may make several altera- tions and modifications to the described and shown embodiments that are within the scope of the invention as defined in the following claims.

Claims

1 Deck structural system (2) for a vessel (1) with at least two hulls (3), where the deck structural system (2) comprises a multiple of cell layers (14, 15), each cell (4) being formed of at least three walls (5, 6, 7) connected along a longitudinal axis of the cell (4), the deck structural system (2) being adapted to be connected to and to transfer forces between the hulls (3), charac t er - i z e d i n that the cell layers (14, 15) are aligned on top of each other, where two vertical neighboring cells (4) are arranged directly opposite each other, the cells (4) further being rigidly connected to each other along their longitudinal axis, each cell layer (14, 15) is further comprised of at least two open- ended cells (4) with the longitudinal axis of the cell (4) arranged in a trans- verse direction of a normal headway direction of the vessel (1).

2 System according to claim 1, characterize d in that the cells (4) form holds for different cargo and or loads (8).

3 System according to claim ^ c harac teri z e d i n that a fore and or an aft cell (10) relative the vessel (1) has triangular cross section.

4 System according to claim 1, characteriz ed in that one or more of the cell (4) comprise movable hatches and or doors.

5 System according to claim 8, c harac teri z e d i n that the hatches also are utilised as an access ramp system (11).

6 System according to claim 8, charact eri z e d i n that the cells (4) further comprise fixed and or movable interior decks.

7 System according to claim ^ c har acteri z e d i n that cells (4) are divided by internal bulkheads and or walls.

8 Manufacturing method for vessel ( 1 ) according to claim 1 c h arac t e ri z e d in that the hulls (3) and the deck structural system (2) are manufactured separately after which the deck (2) is lifted or skidded on top of the two hulls (3) in one or several pieces and thereafter connected to each other by appropriate connection means. Manufacturing method for deck characterized in that at least a part of the deck structural system (2) is assembled from prefabricated panels that are joined together by appropriate joining techniques.