VESSEL HULL

Abstract: Hull design for vessels, such as ships and barges, with longitudinal and transverse bracing elements (11, 12, 13, 14, 16) that serve as a skeleton for hull plating (18). The hull plating (18) is attached to the longitudinal ribs or braces (14A-B, 16) and possibly to the keel, and extends mainly along the longitudinal axis of a vessel. The hull plating between at least some individual longitudinal braces that lie adjacently, is given concave curvature, so as to produce mainly tensile stresses in the plane of the plating.

Description: Vessel hull The present invention concerns a hull particularly for ships and similar marine structures of the type stated in the introduction to Claim 1. Background In a traditionally designed ship hull, the plating and bracing system is arranged so that the external pressure primarily is carried by bending stresses in the hull plating. Loads are led from the plating to the primary braces (usually longitudinal braces) then to the secondary braces (usually transverse frames) and finally to the ship ' s side/- longitudinal bulkhead for distribution along the "ship's beam". In smaller vessels the plating is often given a double curvature. In a double curved plate the external pressure will mainly be carried by compressive in-plane stresses (shell stresses). When a ship ' s hull is traditionally designed, it can be optimized for weight or production costs. A weight optimized structure is characterized by relatively thin hull plates and a dense framework of primary and secondary braces. This results in a complicated structure with high production costs. The complicated structure introduces several problems. It brings about a range of complicated connections between the various bracing components in steel and aluminium hulls, as well as in glassfibre hulls (GRP). This can easily lead to cracking because of fatigue or delamination in GRP hulls. All hull components are normally designed so that the stress level is below an accepted elastic stress level. When plate sections are exposed to excess loading there will be local deformation in the plates at the connection to the bracing and the stresses in the plates will gradually change from bending stress to tensile stress (membrane stress). The result will be permanent deformities in metal hulls and local cracking in glassfibre hulls (GRP-hulls). Objective The main objective of the present invention is to create a hull for ships, barges and other marine structures, that permits weight and cost reductions in the production of hulls made of steel, aluminium or composites. The invention also has the objective of reducing the number of structural details which are particularly exposed to damage. It is also an object to simplify the connections between the plating and the braces. A further objective of the invention is to find new methods of fabricating hulls that will help to reduce costs. Invention The invention is defined in Claim 1, and other advantageous features of the invention are given in the subsidiary claims. The invention is based on the use of what is known as membrane tension, i.e. a concave section of plating that supports external pressure by means of tensile membrane stress. The concave plates are placed between and fixed to longitudinal braces which are supported on transverse frames that in principle are not attached to the skin hull plates of the ship. In cases where the hull plating is connected to other members than the longitudinals, by for example a transverse bulkhead, this is achieved without any real forces being transferred directly from the hull plating to the transverse member. The use of membrane sections can be combined with parts of a hull where a traditional bracing system is used. The new proposed type of structure can be produced in a known manner. = There are numerous differences between a traditional structure and this new one. The use of a membrane section should bring about a considerable weight reduction. In addition, it will be much less expensive to produce a hull in accordance with the invention. In a metal hull the number of welded meters will be reduced and there will mainly be simple continuous welds. It will only be necessary to a minor extent to have bent or rolled transverse frames. The invention is particularly favourable where weight reductions are essential such as in high-speed vessels. When a membrane section is used, it is the maximum permitted tensile stress in a material that decides the load carrying capacity. This means that steel, aluminium and glassfibre can be loaded at about the same stress level. Thus the invention results in considerable weight savings when glassfibre or aluminium are used. In a glassfibre structure, the problems associated with the connection of internal bracing to the hull, will be reduced. Furthermore the problems related to cracking and redistribution of stresses will be almost avoided when a hull section is overloaded. The invention can be used for all types of ships hulls, hulls for barges and other marine structures. The only precondition is that the hull must generally only be exposed to external lateral pressure. This is particularly the case for high-speed vessels, either catamarans or single-hulled ships and naval vessels, for example. Example The invention will now be described in more detail by reference to the enclosed drawings, where: Fig. 1 shows a schematic cross-section of a small vessel, Fig. 2 shows a detail of a catamaran cross-section with a laminated skin, (sandwich construction). Figs. 3-5 show details of the hull in Fig. 2, with the bottom, side and transition of the deck/side respectively, in different variants of materials and design details, while Fig. 6 shows a cross-section from the hull of a larger vessel. Fig. 1 shows a design where the present invention is used on a single hull, in a small high-speed vessel such as a patrol craft. The figure shows a midship frame in the hull. The hull structure consists of a transverse frame 11 that is connected to a deck beam 12 and an internal brace 13, that if necessary can be used as a support for the interior deck. The transverse frames 11 are connected to the longitudinals 14. The example shows two longitudinal braces 14a and 14b on each side, and a V-shaped keel 16. The keel 16 is further braced by transverse plates 17 at each transverse frame. The membrane section 18, that is the concave plating section, is connected to the longitudinal 14 so that they extend from the bow to the stern. The membrane sections are welded in the longitudinals 14 and the keel 16 by continuous longitudinal welds. The hull plates form concave sections between the longitudinals. The plates have a radius of curvature that is sufficient to give pure tensile stress. The longitudinal frames 14 are placed so they follow the lines of the hull. The transverse frames 11 can be welded only to the longitudinals 14. Thus the transverse frames 11 will only be exposed to compressive forces under normal load conditions. In this example metal plates are used as the membrane sections 18. A similar type of structure can be used for hulls with glassfibre hull plates. The plating or the membrane sections 18 must here be laid continuously over the longitudinals 14. The fibres in such a glassfibre membrane are to be laid in the direction that gives the optimal utilization of the tensile strength of the material. In a hull that has membrane sections designed in accordance with the invention, the forces that are transferred from the plating to the braces will mainly be forces acting perpendicularly to the hull surface. Thus the strength reguirements on the connection between the hull plating (membrane sections) and the longitudinal braces are not high. Fig. 2 shows a catamaran hull with a laminated outer hull plating (sandwich plates). The hull consists of a transverse bulkhead 20 that acts as a support for a deck beam 21 and outer transverse frames 24 and inner transverse frames 25 that extend down towards the keel area. In the ship's side, the deck beams 21 are attached to a longitudinal 26. Similar longitudinals 27 and 28 are located one under the other along each side of the ship. In the transition to the keel area there is a longitudinal 29 on each side. The deck 30 is built in a traditional manner. From the deck next to frame 26 and down towards the keel area (longitudinal 29) the hull plates are laid as membrane sections 31. Traditional means of construction are used by the keel 33 and the longitudinal frames are connected to a local web 33 in the keel region. From the longitudinal 29B close to the keel membrane sections 32 cover the hull up to the centre line 22. Longitudinal braces 27B and 28B are found as indicated in Fig. 2. In the central part of the hull (wet deck) the hull plates are attached to the transverse bulkhead 20. Fig. 3 shows the details of the area that are close to the keel region. The transverse brace 24 in this example has a quadratic section, and can be made of glassfibre for example. The hull plate 31 has a sandwich construction with covering layers of glassfibre-reinforced plastic and with foam as the core material. Fig. 4 shows the equivalent details as Fig. 3 for the attachment of the hull plates 31 at the transition to the deck. Here, the transverse frames are alsomade of glassfibre profiles 24, with longitudinals 26 and 27 built into the transverse frame structure. Fig. 5 shows the arrangement of a longitudinal 27 used in a modified hybrid design where an aluminium transverse frame 25 is used. Here the longitudinal 28A is attached with two aluminium brackets 49 that are welded to the transverse frame 24. In this example, laminated single hull plates 31 are used, These could be made of glassfibre. In both these examples the hull plates will have pure tensile stresses, apart from in the area where the hull plates lie against the transverse frames. The tensile stresses result in lateral forces that are carried by the longitudinals 26, 27, 28 and 29. Fig. 6 shows a section through a tanker designed in accordance with the invention. The hull has a transverse frame 34 that is divided into sections with intermediate longitudinals 35. The transverse frame sections 34A-E support the bottom plates 36, that form the inside base of the tank 37. The longitudinal frames 35A-F that support the concave skin plates 38 are welded to the transverse frames. At the transition between the bottom and the ship's side, the transverse frame 34F has closely spaced longitudinal braces 351 using known methods, and is covered by an extension of the hull plates 38. The ship's sides have two sections 34G and 34H with a transverse frame and interior walls 39 in a known manner. The outer part of the longitudinals 35G-J is welded to the hull plates 40. The hull plates are formed so that a concave arched membrane section 41 is formed in an equivalent manner as at the bottom. The topside of the vessel is designed by known means, with a transverse frame 42, longitudinal braces 43 and plates 44 midship. In addition, there are membrane sections 45 and 46 at the sides of the midship plates 44 and a traditional braced plate section 47 in the upper part of the ship ' s side, between the outer membrane section 46 and membrane section 41. With the alternative design of a tanker as in Fig. 6, the bottom plates 36 can be shaped as membrane sections, with or without connection to the transverse frames. Also the interior wall, or parts of this can be shaped as membrane sections, with or without connection towards the transverse frames along the sides of the ship. This gives the same advantages as when a membrane section is used for the outer hull plating. The invention will provide a basis for a simplified production that will in turn give considerable reductions in cost. If the frames are correctly positioned it is possible for example to lay the hull plates out by being unwound from a plate spool. Further, the invention enables more rational assembly of machinery, equipment and the like before the hull plates are attached. The invention can be combined with parts of hulls that are designed by traditional means.

Claims: CLAIMS : 1. Hull design for vessels, such as ships, barges and other vessels, where there are longitudinal and transverse bracing elements (11, 12, 13, 14, 16) that serve as a skeleton for hull plating (18) that is attached to the longitudinal bracing elements, and that will carry the external water pressure, static as well as dynamic, c h a r a c t e r i z e d by the hull plating (18) being attached to support ribs or braces (14A-B, 16) and possibly to the keel, that extends mainly along the longitudinal axis of a vessel, and that the hull plating between at least some individual longitudinal braces that lie adjacently, is given concave curvature, so as to produce mainly tensile stresses in the plating plane. 2. Device as claimed in Claim 1, c h a r a c t e r i z e d by the longitudinal braces (14A-B, 16) being situated in a known manner on transverse braces or transverse frames (11). 3. Device as claimed in Claims 1 or 2, c h a r a c t e r i z e d by the hull plates (18) being attached on the outer edge of longitudinal ribs (14A-B, 16), such that the tensile stresses in the skin plates are mainly transferred as inward forces on the longitudinal frames.

Inventors: SYVERTSEN KAARE, SYVERTSEN, KAARE
Applicants: SINVENT AS
Application year: 1990
Main classification: B63B3
IPC codes: B63B3