FIELD

The present disclosure relates to a watercraft system.

In particular it relates to a submarine or a submersible comprising a number of modules that may be assembled and disassembled.

BACKGROUND

Submarine vessels typically comprise a pressure hull, casing and appendages. One of these appendages is often a bridge fin which extends away from the pressure hull. The pressure hull and the casing can be collectively referred to as the hull form. Although the bridge fin extends away from the hull form, it is an intrinsic part of the superstructure of the submarine, typically comprising a support structure made of members welded together, which extend from, and are carried by, the pressure hull , and to which is attached a shell to form a hydrodynamic surface that, in use, will form part of the outer skin of the submarine.

If it is required to alter the configuration of bridge fin, for example to upgrade the equipment it houses or implement an advantageous design change, the metal work of the bridge fin must be at least in part removed by cutting the shell and support members, then attach new support members by welding, and apply a new shell shape. Such activity is labour intensive, threatens the integrity of the existing vessel, and requires a significant amount of time and hence cost.

As such significant work happens rarely in the life of a large vessel, conventional methods are entirely adequate. However, where testing of different variants of a watercraft, or frequent changes in operational requirements of a watercraft arise, conventional reconfiguration methods mean that a vessel can only be adapted a small number of times before its configuration cannot be significantly further adjusted, and an alternative vessel must be used.

In order to provide a submarine structure with the required properties, additional features such as tiles are often applied to the exterior of the hull, which means the tiles are exposed to harsh environments, become weathered, damaged and/or fall off. The presence of absence of the tiles can only be determined visibly, which cannot be done while the submarine is operational. The tiles can only be replaced by working on the outside of the hull, possibly underwater at sea, and hence in harsh conditions, or in a facility with a dry dock, which is a time consuming, inconvenient and expensive procedure. Access constraints during and after assembly mean that, conventionally, they cannot be applied to the inner surface of the hull. During a reconfiguration of the hull shape, tiles may need to be removed and re-attached, adding to the complexity of the build process to ensure the hull is adequately covered.

Hence a watercraft system with a bridge fin structure which allows for easy re-configuration is highly desirable.

SUMMARY

According to the present disclosure there is provided an apparatus and methods as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

Hence there may be provided a watercraft system (10), wherein the watercraft system (10) is a submarine or a submersible configured to be submerged in water. The watercraft system (10) may comprise a pressure hull module (100) having a longitudinal axis (114) which extends between an aft end (116) and a forward end (118) of the watercraft system (10), and which defines a first interface element (112). The watercraft system (10) may further comprise a bridge fin module system (200) which extends from the pressure hull module (100) in a direction away from the longitudinal axis (114). The bridge fin module system (200) may comprise a first bridge fin sub-module (210) which defines a second interface element (222) configured to be coupled and uncoupled from the first interface element (1 12). The first bridge fin sub-module (210) may extend from the second interface element (222) to terminate at a third interface element (232). The bridge fin module system (200) may comprise a second bridge fin sub-module (220) which defines a fourth interface element (242) configured to be coupled and uncoupled from the third interface element (232).

The bridge fin module system (200) may comprise a third bridge fin submodule (230) which defines a fifth interface element (252) configured to be coupled and uncoupled from the third interface element (232) such that the watercraft system (10) is operable with either the second bridge fin submodule (220) or the third bridge fin sub-module (230) forming part of the bridge fin module system (200).

The bridge fin module system (200) may further comprise a fourth bridge fin sub-module (240) which defines a sixth interface element (262) configured to be coupled and uncoupled from the first interface element (112) of the pressure hull module (100). The fourth bridge fin sub-module (240) may extend from the sixth interface element (262) to terminate at a seventh interface element (272). The fourth interface element (242) of the second bridge fin sub-module (220) may be configured to be coupled and uncoupled from the seventh interface element (272). The fifth interface element (252) of the third bridge fin submodule (230) may be configured to be coupled and uncoupled from the seventh interface element (272). The watercraft system (10) may be operable with either the first bridge fin sub-module (210) or fourth bridge fin sub-module (240) forming part of the bridge fin module system (200).

The second bridge fin sub-module (220) may have a different configuration to the third bridge fin sub-module (230).

The first bridge fin sub-module (210) may have a different configuration to the fourth bridge fin sub-module (240).

Adjacent interface elements may be coupled by a fixing means (400).

The fixing means (400) may have a first configuration in which the adjacent interface elements are coupled with one another. The fixing means (400) may have a second configuration in which the adjacent interface elements are operable to be un-coupled from one another.

The fixing means (400) may comprise a threaded nut and threaded bolt, and/or the or each fixing means (400) may comprise an assembly of a threaded bolt, a reaction nut and a tension nut.

The bridge fin module system (200) may be configured to house an equipment module (500).

The sub-modules (210, 220, 230, 240) of the bridge fin module system (200) may be defined by a shell (600) having an outer surface (602) which, in use defines a hydrodynamic surface of the bridge fin module system (200) and an inner surface (604). A plurality of walls (606) may extend from the inner surface (604), each (or at least some) of the walls (606) intersecting with at least one other wall (606). An intersection node (610) may be defined where two walls (606) meet. A cavity (630) may be defined in regions delimited by edges (654) of the walls (606) to thereby define a lattice structure (608) on the inner surface of the shell (600).

A polymer-based material (640) may be provided in a least one cavity (630) to thereby form a coating on the inner surface (604) of the shell (600).

The polymer-based material may be configured to absorb energy.

The outer surface (602) of the shell may define a continuous surface which defines an external control surface of the watercraft system (10).

The shell (600) and walls (606) may be integrally formed.

The nodes (610) may define connection features (620) configured to attach internal structures. The nodes (610) may define connection features (620) configured to support, anchor and/or carry internal structures.

There may be provided a watercraft system (10), wherein the watercraft system (10) is a submarine or a submersible configured to be submerged in water. The watercraft system (10) may comprise a pressure hull module (100) which defines a first interface element (112) and a bridge fin module system (200) which extends from the pressure hull module (100). The bridge fin module system (200) may comprise a first bridge fin sub-module (210) which defines a second interface element (222) configured to be coupled and uncoupled from the first interface element (112), the first bridge fin sub-module (210) extending from the second interface element (222) to terminate at a third interface element (232). The bridge fin module system (200) may further comprise a second bridge fin sub-module (220) which defines a fourth interface element (242) configured to be coupled and uncoupled from the third interface element (232). The submodules (210, 220) of the bridge fin module system (200) may be defined by a shell (600) having an outer surface (602) which, in use, defines a hydrodynamic surface of the bridge fin module system (200) and an inner surface (604). A plurality of walls (606) may extend from the inner surface (604), each (or at least some) of the walls (606) intersecting with at least one other wall (606). An intersection node (610) may be defined where two walls (606) meet. A cavity (630) may be defined in regions delimited by edges (654) of the walls (606) to thereby define a lattice structure (608) on the inner surface of the shell (600).

There may be provided a method of manufacture of a watercraft system (10), wherein the watercraft system (10) is a submarine or a submersible configured to be submerged in water. The watercraft system (10) may comprise a pressure hull module (100) and a bridge fin module system (200) which extends from the pressure hull module (100). The bridge fin module system (200) may comprise a first bridge fin sub-module (210) and a second bridge fin sub-module (220) configured to be coupled to one another. The sub-modules (210, 220, 230, 240) of the bridge fin module system (200) may be defined by a shell (600) having an outer surface (602) which, in use defines a hydrodynamic surface of the bridge fin module system (200) and an inner surface (604). The method may comprise providing a plurality of walls (606) to extend from the inner surface (604), each (or at least some) of the walls (606) intersecting with at least one other wall (606). An intersection node (650) may be provided where two walls (606) meet. A cavity (630) may be provided in regions delimited by edges (654) of the walls (606) to thereby define a lattice structure (608) on the inner surface of the shell (600). The shell (600) and walls (606) may be integrally formed using additive layer manufacturing to provide the walls (606) on the shell (600).

The method may further comprise providing a polymer-based material (640) in at least one cavity (630) to thereby form a coating on the inner surface (604) of the shell (600), wherein the polymer-based material is configured to absorb energy.

There may be provided a watercraft system (10), wherein the watercraft system (10) is a submarine or a submersible configured to be submerged in water. The watercraft system (10) may comprise a pressure hull module (100) having a longitudinal axis (114) which extends between an aft end (116) and a forward end (118) of the watercraft system (10), and which defines a first interface element (112). The watercraft system (10) may further comprise a bridge fin module system (200) which extends away from the pressure hull module (100) in a direction away from the longitudinal axis (14). The watercraft system (10) may further comprise a bridge fin module system (200) which extends from the pressure hull module (100) in a direction perpendicular to the longitudinal axis (14). The bridge fin module system (200) may comprise a first bridge fin submodule (210) which defines a second interface element (222) configured to be coupled and uncoupled from the first interface element (112). The first bridge fin sub-module (210) may extend from the second interface element (222) to terminate at a third interface element (232). The bridge fin module system (200) may further comprise a second bridge fin sub-module (220) which defines a fourth interface element (242) configured to be coupled and uncoupled from the third interface element (232). The bridge fin module system (200) may further comprise a third bridge fin sub-module (230) which defines a fifth interface element (252) configured to be coupled and uncoupled from the third interface element (232). The method may comprise at least one of the steps of: coupling the first bridge fin sub-module (210) and second bridge fin sub-module (220); uncoupling the first bridge fin sub-module (210) and second bridge fin submodule (220); and/or coupling the first bridge fin sub-module (210) and third bridge fin sub-module (230).

Hence there may be provided a submarine bridge fin with a modular design such that a top end of the bridge fin may be removed from and reattached to the lower bridge fin section or a new top section attached for the purposes of performance changes and or transportation.

The system may comprise hull sections with an embedded geodesic lattice structure on the interior surface for structural strength, which may be manufactured through an Additive Manufacturing process. A polymer based material is cast into the recesses of the lattice to provide additional beneficial properties to the structure.

BRIEF DESCRIPTION OF THE FIGURES

Examples of the present disclosure will now be described with reference to the accompanying drawings, in which:

Figure 1 shows an assembled watercraft system of the present disclosure; Figure 2 shows an exploded view of a first example of a bridge fin module assembly of the present disclosure;

Figure 3 shows an exploded view of a second example of a bridge fin module assembly of the present disclosure;

Figure 4 shows a sub-module a bridge fin module assembly of the present disclosure;

Figure 5 shows a sub-module a bridge fin module assembly of the present disclosure;

Figure 6 shows an additional sub-module a bridge fin module assembly of the present disclosure; and

Figure 7 shows a section of an inner surface of a hull section with a configuration of the present disclosure; and

Figure 8 shows a sectional view of an inner surface of the hull section shown in figure 7.

DETAILED DESCRIPTION

Aspects of the watercraft system 10 are shown in figures 1 to 8. The watercraft system 10 of the present disclosure may be, as illustrated, a submarine (e.g. a submersible configured to be submerged in water). The present disclosure also relates to a method of manufacture which enables benefits of the watercraft system 10 to be realised. The present disclosure also relates to a method of operation of the watercraft system 10, in particular how it may be assembled.

As shown in figure 1 , the watercraft system 10 may comprise a pressure hull module 100, or hull form, which defines/com prises a pressure hull 110 (e.g. a pressure vessel) having a longitudinal axis 114 which extends between an aft end 116 and a forward end 118 of the watercraft system 10. The pressure hull module 100 defines a first interface element 112.

The pressure hull module 100, or hull form, may further comprise a casing (not shown) around the pressure hull 110.

In some examples, the pressure hull 110 may provide most or all of the structure of the pressure hull module 100. In some examples, the terms “pressure hull 110” and “pressure hull module 100” may be used interchangeably to describe features having a common, equivalent and/or combined function (for example, in structures in which no outer casing is provided).

An interface element may be provided as a flange or other joining interface feature. Hence on the pressure hull module 100, the first interface element 112 may define, bound and/or extend around an opening in the pressure hull module 100. That is to say, the pressure hull module 100 may have a module opening, for example for a user to pass through, which is bounded by the first interface element 112.

The watercraft system 100 further comprises a bridge fin module system 200, which may define a water tight or freely flooded zone 250. When assembled, the bridge fin module system 200 forms a bridge fin. The assembled bridge fin extends away from the pressure hull module 100. The bridge fin may extend from the pressure hull 110. The assembled bridge fin may extend away from the pressure hull module 100 in a direction perpendicular to the longitudinal axis 114. The bridge fin has a leading edge 280 and a trailing edge 282 for hydrodynamic performance.

In examples in which a casing is provided around the pressure hull 110, the bridge fin extends from the pressure hull 110 and through the casing.

The bridge fin module system 200 is configured to house equipment (i.e. an equipment module 500).

As indicated in figures 1 to 6, the bridge fin is an external hydrodynamic feature configured as part of the watercraft system 10. The primary function of the bridge fin may be for the stowage of equipment 500, as represented by a dashed line in figure 1. The equipment module 500 may comprise masts and/or periscopes which can be raised and lowered as required. Hence the bridge fin may be provided as a hydro-dynamically optimised structure around the equipment 500 to enable the equipment module 500 to be provided in this location. Additionally, the bridge fin may also provide a location to navigate the submarine from when on the surface.

As shown in figures 1 to 6, the bridge fin module system 200 may comprise a number of bridge fin sub-modules 210, 220, 230, 240. The sub-modules 210, 220, 230, 240 of the bridge fin module system 200 are each defined by a shell 600 (e.g. a thin material and/or sheet like material) having an outer surface 602 which, in use defines the external hydrodynamic surface of the bridge fin module system 200 (i.e. the surface visible from outside of the watercraft system 10). The outer surface 602 of the shell defines a continuous surface which defines an external hydro-dynamic surface of the watercraft system 10. The shell 600 of thin material also has an inner surface 604.

Figure 2 shows an exploded view of the sub-modules of a first configuration (e.g. a first example) of the bridge fin module system 200. Figure 3 shows an exploded view of the sub-modules which make up a second and/or third configuration (e.g. a second or third example).

In the example of figure 2, the bridge fin module system 200 comprises a first bridge fin sub-module 210 which defines a second interface element 222 configured to be coupled and uncoupled from the first interface element 112 of the pressure hull module 100.

The first bridge fin sub-module 210 extends from the second interface element 222 to terminate at a third interface element 232. Hence the third interface element 232 is spaced apart from the second interface element 222 by the height of the shell 600 of the first bridge fin sub-module 210. That is to say, the second interface element 222 defines one end of the first bridge fin submodule 210, and the third interface element 232 defines the opposing end of the first bridge fin sub-module 210 with the shell 600 extending therebetween. The shell 600 of the first bridge fin sub-module 210 defines a hollow chamber, with an opening at an end defined by the second interface element 222 and an opening at its opposite end defined by the third interface element 232.

There is also provided a second bridge fin sub-module 220 which defines a fourth interface element 242 configured to be coupled and uncoupled from the third interface element 232. Hence, when coupled to the first bridge fin submodule 210, the second bridge fin sub-module 220 is spaced apart from the pressure hull module 100 by the first bridge fin sub-module 210. That is to say, the pressure hull module 100, first bridge fin sub-module 210 and second bridge fin sub-module 220 are provided in series. As shown in figure 3, the bridge fin module system 200 comprises a third bridge fin sub-module 230 which defines a fifth interface element 252 configured to be coupled and uncoupled from the third interface element 232. Hence when coupled to the first bridge fin sub-module 210, the third bridge fin sub-module 230 is spaced apart from the pressure hull module 100 by the first bridge fin submodule 210. That is to say, the pressure hull module 100, first bridge fin submodule 210 and third bridge fin sub-module 230 are provided in series.

Hence the first configuration of the watercraft system 10 (as shown in figure 2) may be assembled by coupling the first bridge fin sub-module 210 to the pressure hull module 100, and coupling the second bridge fin sub-module 220 to the first bridge fin sub-module 210. This may be followed, at some later point in time, by uncoupling the second bridge fin sub-module 220 from the first bridge fin sub-module 210. The third bridge fin sub-module 230 may then be coupled to the first bridge fin sub-module 210 to provide a second configuration of the watercraft system 10.

That is to say, the first configuration of the watercraft system 10 (shown in figure 2) may be assembled by coupling the second interface element 222 of the first bridge fin sub-module 210 to the first interface element 112 of the pressure hull module 100, and coupling the fourth interface element 242 of the second bridge fin sub-module 220 to the third interface element 232 of the first bridge fin sub-module 210. This may be followed, at some later point in time, by uncoupling the fourth interface element 242 of the second bridge fin sub-module 220 from the third interface element 232 of the first bridge fin sub-module 210. The fifth interface element 252 of the third bridge fin sub-module 230 may then be coupled to the third interface element 232 of the first bridge fin sub-module 210 to provide a second configuration of the watercraft system 10 as indicated in figure 3.

As represented by a dashed line in figure 3, the bridge fin module system 200 may further comprise a fourth bridge fin sub-module 240 which defines a sixth interface element 262 configured to be coupled and uncoupled from the first interface element 112 of the pressure hull module 100. The shell of the fourth bridge fin sub-module 240 extends from the sixth interface element 262 to terminate at a seventh interface element 272. Hence the sixth interface element 262 is spaced apart from the seventh interface element 272 by the height of the shell of fourth bridge fin sub-module 240.

The fourth interface element 242 of the second bridge fin sub-module 220 is configured to be coupled and uncoupled from the seventh interface element 272. The fifth interface element 252 of the third bridge fin sub-module 230 is configured to be coupled and uncoupled from the seventh interface element 272. The watercraft system 10 is operable with either the first bridge fin submodule 210 or fourth bridge fin sub-module 240 forming part of the bridge fin module system 200. The watercraft system 10 is operable with either the first bridge fin sub-module 210 or fourth bridge fin sub-module 240 coupled to the pressure hull module 100.

Hence a third configuration of the watercraft system 10 may be assembled by coupling the fourth bridge fin sub-module 240 to the pressure hull module 100, and coupling the second bridge fin sub-module 220 to the fourth bridge fin submodule 240. This may be followed, at some later point in time, by uncoupling the second bridge fin sub-module 220 from the fourth bridge fin sub-module 240. The third bridge fin sub-module 230 may then be coupled to the fourth bridge fin submodule 240 to provide a fourth configuration of the watercraft system 10.

That is to say, the third configuration of the watercraft system 10 may be assembled by coupling the sixth interface element 262 of the fourth bridge fin sub-module 240 to the first interface element 112 of the pressure hull module 100, and coupling the fourth interface element 242 of the second bridge fin submodule 220 to the seventh interface element 272 of the fourth bridge fin submodule 240. This may be followed, at some later point in time, by uncoupling the fourth interface element 242 of the second bridge fin sub-module 220 from the seventh interface element 272 of the fourth bridge fin sub-module 240. The fifth interface element 252 of the third bridge fin sub-module 230 may then be coupled to the seventh interface element 272 of the fourth bridge fin sub-module 240 to provide a fourth configuration of the watercraft system 10.

The watercraft system 10 is operable with either the second bridge fin submodule 220 or the third bridge fin sub-module 230 forming part of the bridge fin module system 200. The second bridge fin sub-module 220 or third bridge fin sub-module 230 may be coupled to the pressure hull module 100 via the first bridge fin sub-module 210 or the fourth bridge fin sub-module 240.

As illustrated by figure 2 and figure 3, the second bridge fin submodule 220 may have a different configuration to the third bridge fin submodule 230. That is to say, the second bridge fin sub-module 220 may have a different shape, size, geometry, combination of features and/or be made from a different material to the third bridge fin sub-module 230

As illustrated by figure 2 and figure 3, the first bridge fin sub-module 210 may have a different configuration to the fourth bridge fin sub-module 240. That is to say, the first bridge fin sub-module 210 may have a different shape, size, geometry, combination of features and/or be made from a different material to the fourth bridge fin sub-module 240.

Adjacent interface elements of the hull modules and/or sub-modules may be coupled (e.g. joined together) by a fixing means 400 which extend therebetween. The fixing means 400 may have a first configuration in which the adjacent interface elements are coupled (e.g. engaged) with one another. The fixing means 400 may have a second configuration in which the adjacent interface elements are operable to be un-coupled (e.g. dis-engaged) from one another. Hence the fixing means are configured to join and the hull modules (and submodules) together, and also configured and operable to be dis-engageable to allow the hull modules (and sub-modules) to be disconnected from one another.

The fixing means 400 may be provided as a nut and bolt (or stud), or other appropriate fixing which allows for engagement and disengagement. Hence the fixing means 400 may comprise a threaded nut and threaded bolt. The or each fixing means 400 may comprise an assembly of a threaded bolt, a reaction nut and a tension nut.

Alternatively, or additionally, interface elements of the hull modules and/or sub-modules may be coupled (e.g. joined together) by a bonding process, for example welding. Hence the hull modules (and sub-modules) may be welded together during assembly, and when disassembly is required the weld zone can be cut through and reworked to allow for another joining process. The modules and/or sub-modules may be configured and operable to couple/engage with each other to form a sealed joint, so that the modules and/or sub-modules form a completed bridge fin which is watertight and/or airtight.

Hence the modules and sub-modules of the watercraft 10 may be provided as a kit of parts for a submarine.

As shown in figures 4 to 8, a plurality of walls 606 extend from the inner surface 604 of the shell 600, each (or at least some) of the walls 606 intersecting with at least one other wall 606, and being spaced apart from an adjacent wall 606 where they do not intersect. An intersection node 610 is defined where two walls 606 meet.

A cavity 630 is defined in regions delimited by edges 654 of the walls 606 to thereby define a lattice structure 608 on the inner surface of the shell 600. That is to say a lattice structure 608 is formed by walls 606 on the inner surface of the shell 600, cavities 630 being defined in regions delimited by edges/sides 654 of the intersecting walls 606. Hence at least two walls 606 may extend at an angle to another two walls 606. That is to say, a cavity 630 is defined in regions delimited by edges/sides 654 of intersecting walls 606 to thereby define a lattice structure 608 on the inner surface of the shell 600.

The shell 600 and walls 606 may be integrally formed. The shell 600 and walls 606 may be formed by using additive layer manufacturing methods.

Both the shell 600 and walls 606 may be formed using non-metallic or metallic additive manufacturing techniques to additively construct the shell 600 and lattice structure 608 in a common manufacturing process (e.g. to form the shell 600 with the lattice structure 608 onto the interior surface of the shell). Hence the shell 600 and walls 606 may be integrally formed from the same material. That is to say, the shell 600 and walls 606 may be integrally formed from a common material by the same manufacturing technique.

The common material may be chosen from a list comprising metals (for example titanium), metal alloys (for example titanium alloys) and composite materials comprising, but not limited to, polymers. The composite material may comprise carbon fibre in a polymer matrix. The nodes 610 may define connection features 620 configured to attach to internal structures, for example floors and machinery. The nodes 610 may define connection features 620 configured to support, anchor and/or carry such internal structures.

The lattice structure 608, including nodes 610 and edges 654, may be configured to provide structural support to the shape formed by the shell 600. That is the nodes 610 and edges 654 are provided in positions on the shell 600 which optimise the structural strength of the bridge fin module system 200. The lattice structure 608 may be geodesic, where “geodesic” is taken to mean relating to or denoting the shortest possible line between two points on a sphere or other curved surface.

The spacing of the walls 606 from one another may vary, such that the cavities 630 may vary in surface area around the inner surface of the shell 600. Hence in regions where greater strength is required, the lattice structure may be more dense (e.g. walls closer together, cavities are smaller) and in regions in which less strength is required the lattice structure may be less dense (e.g. walls further apart, cavities are larger). Hence the lattice enables strength to be provided where needed, and not provided where not needed, which saves on weight and materials.

The lattice density (e.g. cavity 630 size) may vary between in different locations, especially in regions of high curvature. Lattice density (e.g. cavity 630 size) may be uniform in size and spacing. The cavities 630 may be polyhedral, for example diamond and/or or hexagonal.

Walls 606 may be formed with a double curvature (i.e. curving in three dimensions) to pass around the curved shape of the shell 600. The walls 606 may be three to four times thicker than the skin 600.

The interface elements may define flanges, wherein the flanges are configured to abut so they may be joined to couple the modules and/or submodules together.

As shown in figures 5, 6 the nodes 610 may define mounting structures.

For example, the nodes may define pyramid shaped structures. These may be drilled and tapped into for holding equipment, or for attaching a structure and/or equipment to inside of the shell 600.

A polymer-based material 640 may be provided in a least one cavity 630 to thereby form a coating on the inner surface 604 of the shell 600. The polymer- based material 640 may comprise carbon fibre.

The polymer material 640 may be cast and set in at least one cavity 630. That is to say, the polymer material may be provided in a cavity 630 of the lattice structure 608 after the lattice structure has been completed.

Alternatively, the polymer material 640 may be integrally formed with the shell 600 and walls 606 by an additive manufacturing process. That is to say, the polymer material may be provided in a cavity 630 of the lattice structure in the same manufacturing process in which the shell 600 and walls 606 are formed.

Edges 654 and nodes 610 are arranged to form the cavities 630. The cavities may be closed polyhedral areas. These act as moulds for the injection or casting of the polymer-based material. Once set, the polymer material can improve the mechanical and/or operational properties of the bridge fin structure.

Hence a method of manufacture of a watercraft system 10 according to the present disclosure may comprise providing a polymer-based material 64 in at least one cavity 630 to thereby form a coating on the inner surface 604 of the shell 600.

The polymer-based material may be configured to absorb energy. For example, it may be configured to absorb vibration, act as an electromagnetic insulator and/or acoustic insulator.

Hence there is provided a watercraft system 10 comprising modular and/or sub-modular hull sections which may be coupled and uncoupled when required, many times, to provide different configurations and/or functionality. For example, sub-modules may house different equipment and/or have different external geometries, and thus can be assembled with the pressure hull 110 as required to optimise the functionality of the resultant watercraft 10 assembly.

Hence a bridge fin assembly 260 can be built up using sub-modules, each of which can be swapped for another, and each sub-module can be swapped independently of another sub-module. Having a modular bridge fin assembly 260 built up using sub-modules also provides the advantage that the watercraft 10 can be dis-assembled for transportation (for example in an aircraft or larger water vessel) and then re-assembled after delivery.

The combination of shell 600 and lattice structure 608 made of walls 606 enable sub-modules of the bridge fin to have the required individual stiffness and/or strength such that they are free standing (i.e. do not need a separate support structure).

In examples in which the bridge fin defines a free flood area 250, watertight integrity of the module and/or sub-module interface elements where the modules and/or sub- modules are joined is not required. Hence the sub-modules can be a relatively light construction as do not need to withstand any pressure forces.

The use of additive layer manufacturing methods to provide the shell 600 and walls 606 mean the walls 606 can be provided any desirable pattern on the internal surface of the shell 600.

The provision of support by the nodes 610 for internal structures (e.g. equipment, ladders, floors) means that no additional structure is required inside the shell 600, which maximises the space available for inside the bridge fin.

Providing the polymer-based material 640 on the internal surface of the shell 600, in the cavities 630 formed of the lattice means that the polymer-based material 640 is shielded from harsh environments elements (i.e. sea water) and also less likely to become damaged, fall off and/or need replacing.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.