VESSEL HAVING AN IMPROVED HULL SHAPE

Abstract

This relates to vessels in general, but in particular to vessel designed to be exposed from low to medium to high waves. Both for comfort of persons, animals or fragile goods, steady sailing is preferred, without causing the waves slamming in on the vessel hull or excessive pitching of the vessel. This is also the case for service and supply vessels performing operations in relation to offshore or subsea installations. To obtain a solution to the aforementioned issues the present invention provides a vessel, wherein a stern of the vessel extend below a design waterline (Tdwl), and wherein opposite side faces of the stern, when seen in an opposite direction of the vessels primary sailing direction, form an acute angle under and above the design waterline (Tdwl) to decrease the vessels displacement in the rear end and are adjoined along at a line of symmetry forming a stern centerline.

Claims

1. A displacement type vessel comprising a rear end arrangement for reducing wave impact loads on the vessel, which rear end consists of the part of the vessel backwards from the vessel's midship mark, when seen in the vessels primary sailing direction, and which vessel has a transversely symmetrical hull shape about its center line (CL), wherein a stern (11) of the vessel extend below a design waterline (Tdwl), and wherein opposite side faces (14, 15) of the stern (11), when seen in an opposite direction of the vessels primary sailing direction, form an acute angle under and above the design waterline (Tdwl) to decrease the vessels displacement in the rear end and are adjoined along at a line of symmetry forming a stern centerline (16), wherein the stern centerline of the vessel above the design water line (Tdwl) has a non-concave shape and is sloped forwards in the vessels primary sailing direction, and wherein a vessel bottom (17) of the rear end arrangement conforms to an engine driven propulsion system (18).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0021] The vessel according to the present invention will now be described in more detail with reference to the accompanying figures. The accompanying figures illustrates examples of embodiments of the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0022] FIG. 1 illustrates a side view of an example of embodiment of the present invention.

[0023] FIG. 2 illustrates a perspective view of an example of embodiment of the present invention.

[0024] FIG. 3 illustrates a frame line view of a rear part of an example of embodiment of the present invention.

[0025] FIG. 4 illustrates a frame line side view of an example of embodiment of the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

[0026] FIG. 1 illustrates a side view of an example of a vessel design according to the present invention. The illustrated vessel is a displacement type of vessel comprising a rear end arrangement or stern 11 and a bow 10. With reference to FIG. 4 a more detailed illustration of the rear end arrangement 11 is outlined. The rear end arrangement or stern is symmetrically shaped around a center line (CL). A bulb arrangement 12 is arranged on a bottom surface of the stern providing an outlet position on the hull of the vessel for a propeller shaft (not illustrated). In FIG. 4 there is also illustrated an opening 13 wherein the propeller shaft may extend out from the hull into free water below the vessels bottom surface 17. As indicated in FIG. 4, the stern may extend below a design water line (Tdwl) and the bottom surface conforms to an engine driven propulsion system 18 below the rear end of a below water vessel bottom 17, when in use.

[0027] In FIG. 4 the shape of the stern centerline above the design water line (Tdwl) is convex-like shape. The center line may also incorporate straight sections as shown in FIGS. 1 and 2. FIG. 4 further shows how frame lines 21 of the stern are outwardly sloping from the design water line (Tdwl) and how the frame lines 21 run upwards in a convex-like shape and gradually backwards towards the center line (CL) when the vessel is seen in cross-section.

[0028] An aspect of the present invention is to reduce the buoyancy of the stern compared to a more traditional design of sterns in the prior art. In the example illustrated in FIG. 2 it is illustrated how side surfaces 14, 15 are adjoined along a line of symmetry forming a stern centreline 16, wherein the side surfaces 14, 15 form an acute angle under and above the design waterline Tdwl thereby decreasing the vessels displacement volume in the rear end 11 compared to many prior art designs.

[0029] In another example of embodiment of the present invention the stern centerline 16 from the design water line Tdwl is sloped forward in the vessels primary sailing direction. This design contributes also to decrease the vessels displacement volume in the rear end 11. In addition, the sloping may also provide a changing buoyancy sine the sloping is providing a gradual decreasing of the displacement volume of the stern hull in upward direction from the design water line Tdwl.

[0030] In another example of embodiment of the present invention a shape of the stern hull is arranged to be outwardly sloping from the design water line Tdwl thereby providing that at least a lower portion of the stern hull is concave in shape, and wherein the hull shape of the stern hull runs upwardly in a convex-like hull shape, and is following gradually and upwardly back towards the center line (CL), so as to provide a decreasing buoyancy increase, in the upward direction of a major part of the stern, by a combination of the convex-like shape of the centerline of the stern and the shape of the stern.

[0031] In another example of embodiment of the present invention the centerline 16 of the stern 11 rises and has a substantially increasing curvature in the forward direction of the vessel in a lower part of the stern and in an upper part continues to rise with a substantially diminishing curvature. Examples of respective possible curvatures are illustrated in FIG. 4. The examples of angles are non-limiting values. In an example of embodiment the stern centerline curvature at an upper part of the stern increases upwardly from around 0 degrees to around 60 degrees relative to a vertical direction.

[0032] It is further possible to arrange one or more straight portions 19 of the stern centerline 16. It is also possible to add a spray board 20 on an uppermost part of the stern.

[0033] In another example of embodiment of the present invention an upper portion of the stern at an upper portion located above midway between the design waterline (Tdwl) and the top of the stern, the vessels have flare angles of the stern are in the range of 5-50 degrees relative to a vertical direction.

[0034] In another example of embodiment of the present invention, the hull below the design waterline (Tdwl) forms a bend or knuckle between a bottom of the hull and the stern, which bend or knuckle is of a smaller curvature than a lowest curvature of the centerline of the stern.

[0035] According to another example of embodiment of the present invention the vessel may comprise a foreship arrangement, which foreship consists of the part of the ship in front of the vessels midship mark, when seen in the vessels primary sailing direction, and which vessel has a transversely symmetrical hull shape about its center line (CL) and a substantially conventional form below its design water line (Tdwl), wherein a centerline of a bow of the vessel by the design water line (Tdwl) is curved backwards in the vessels primary sailing direction, and wherein a shape of the bow hull is outwardly sloping from the design water line (Tdwl) to provide at least a lower portion of the bow hull to be concave in shape, and wherein the shape of the bow hull runs upwardly in a curved shape, which gradually runs back towards the center line of the vessel (CL) thereby providing an upper portion, which is convex, so as to provide a decreasing buoyancy increase, in the upward direction of a major part of the bow, by a combination of the curvature of the centerline of the stern and the shape of the stern. It is also within the scope of the present invention that the bow hull of the vessel may comprise a bulbous bow below the design water line (Tdwl), and/or a knuckle or beak above the design water line Tdwl.

[0036] Embodiments of the present invention may be applied in all kinds of displacement type of vessels. Within this concept it is also important to note that the term displacement refers to situations where the stern is submerged into the water. This can also be the case with semi planning ship designs and is therefore within the scope of the present invention.

[0037] Embodiments of the present invention are beneficial to use in vessels engaged in service and supply operations of offshore facilities. This includes loading or offloading of items from the vessel to and from an offshore facility. Further, the use of embodiments of the present invention includes stationary subsea operations, during which the vessel is connected to a subsea facility or is involved in repair, maintenance or installation of a subsea facility. Embodiments of the present invention are further beneficial on vessels supporting helicopter platforms.

[0038] An aspect of the present invention, besides providing better sea going qualities of vessels in low to medium to high wave height, is that it is possible to manufacture vessels with lower sea to deck height when mitigating possible problems with high wave heights facing ocean going vessel designs.

[0039] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms comprising or comprises do not exclude other possible elements or steps. Also, the mentioning of references such as a or an etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.