AU2007231696B2 - Vessel - Google Patents

Abstract

A water-going vessel (10) has a centre hull (14) configured to be disposed partly below the water level, a support structure (18) fixedly joined to the 5 centre hull, and a pair of outer hull portions (24) rotatably connected to the support structure to enable rotation between a lowered position and a raised position. Hydraulic rams (28) are provided for rotating the outer hull portions between the lowered and raised positions. Propellers (70) are provided for propelling the vessel and located in anti-cavitation nozzles (72). The centre 10 hull has an internal chamber (50) to accommodate occupants, and windows (54) through which the occupants can view underwater scenery outside the vessel. C-1 0 - 0 5,9 (N I r~J I ij I; I I I I j 1 I L.J I I~~l ~ 1 I ~-I'. ' 'I f~y# - 1 I Ii I tA I I~~f I I--i I---i I ~--.--4 ~~---1 --4 '-'"/,, ' N 'V ~' I~~J I- _ _I lii A' I III' £ I - i" I A 4 ~ ,~ I I -a U--' I I ~ I~ a,~ 0 \ I i 0

Description

AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Applicant: Barry May Actual Inventor: Barry May Address for Service: HODGKINSON McINNES PATENTS Patent & Trade Mark Attorneys Level 21, 201 Elizabeth Street Sydney NSW 2000 HMP Ref: P20746AU00 Invention Title: Vessel Details of Associated Provisional Application(s): Australian Patent Application No. 2006905994 dated 30 October 2006 The following statement is a full description of this invention, including the best method of performing it known to us: P1 IOKPAU 2 VESSEL FIELD OF THE INVENTION 5 This invention relates to a water-going vessel, and in particular a vessel adapted to enable underwater viewing by occupants of the vessel. BACKGROUND TO THE INVENTION 10 It is sometimes desirable or necessary for occupants in a water-going vessel to be able to view objects and sights below the water level. One common example pertains to the viewing of coral reef, which is particularly significant in the tourism industry. 15 There are certain known vessels adapted for this purpose. These typically include chambers which are or can be disposed below water level and which have windows allowing occupants of the chambers to view underwater scenery. 20 In particular, Australian Patent No. 554889 for Applicant's earlier invention discloses a water vessel in which the hull includes a viewing cabin for accommodating passengers, and has viewing windows to enable the passengers to view underwater scenery. The cabin and windows are adapted to be permanently below water level during normal operation. A 25 disadvantage of this vessel is that, as a result of the shape and dimensions of the hull, the vessel is not suitable for relatively high speed travel, and is thus not suited to travelling relatively large distances which may be required for transporting passengers, for example, from a harbour to an open-sea area where the desired scenery is located. 30 Australian Patent No. 569919 discloses a water craft having a main, central hull and two secondary, side hulls. Each of the side hulls is connected to the main hull by means of a pair of arm arrangements which are connected to a super-structure extending upwardly from the main hull. The arrangement of 3 arms is a parallelogram-like configuration. This configuration allows the main hull to be moved relative to the side hulls between a lowered and raised position. While the parallelogram-like configuration maintains a constant relative vertical orientation of the hulls to one another, it is a relatively 5 complex and hence potentially expensive structure, and essentially confines the occupants to the main hull. This is considered disadvantageous when the vessel is used for leisure purposes. Australian Patent No. 644152 discloses a water craft having a floating portion 10 which includes a pair of hulls, and a viewing cabin which is carried by the floating portion. The viewing cabin can be moved from a raised position in which it is at or above the water level to a lowered position in which it is at least partially submerged. A disadvantage of this craft is that the mechanism provided for raising and lowering the viewing cabin must be particularly 15 sturdy, and sufficiently powerful to exert the considerable force required to lift the full weight of the viewing cabin from its lowered position, and to overcome the full buoyancy of the viewing cabin when submerging it into its lowered position. In addition when the viewing cabin is in its raised position, it occupies a relatively large part of the floating portion, which leaves limited 20 space for passengers. Furthermore, when the viewing cabin is in the raised position, because the craft is effectively carrying the full weight of the viewing cabin clear of the water, it cannot attain relatively fast transit speeds without large motors being provided. These factors significantly add to the cost of such a craft, and render it unsuitable for being sail driven. 25 Australian Patent No. 728042 discloses a monohull watercraft with a viewing pod that can be moved by hydraulic rams, from a raised position, downwards through an opening in the hull, to a lowered viewing position under the water. In its raised position, the pod is disposed within the hull and the 30 opening is closed in a watertight manner. This craft suffers from a disadvantage in common with that described above in relation to Patent No. 644152, in that relatively high forces are required to be applied by the rams to cause the pod to move to the lowered position, due to the buoyancy of the 4 pod. In addition, the single-hull nature of the craft renders it relatively unstable, particularly when the pod is in the lowered position. It is an object of this invention to overcome or ameliorate disadvantages 5 of the prior art, or to provide an alternative thereto. In this specification, any discussion of prior art is not intended to, and does not, constitute an admission, implication or suggestion, that the prior art forms part of the common general knowledge in Australia or 10 anywhere else. SUMMARY OF THE INVENTION According to the invention, there is provided a water-going vessel for use 15 in a body of water, the vessel including a centre hull configured to be disposed at least partly below the water level of the body of water and providing buoyancy for the vessel when the vessel is in an upright operational position, the centre hull defining an internal space for accommodating occupants, and including 20 windows; a support structure fixedly joined to the centre hull so as to be substantially non-movable relative thereto; a pair of outer hull portions disposed on opposite sides of the centre hull, each outer hull portion being configured to be disposed at 25 least partly below the water level and to provide buoyancy to the vessel, and being rotatably connected to the support structure to enable rotation of the outer hull portion relative to the centre hull between a first, lowered position and a second raised position; a drive means configured for rotating each outer hull portion 30 between said first and second positions; and at least two ballast tanks, fixed in relation to, and disposed on opposite sides of, the centre hull wherein the vessel is configured, when it is floatingly supported in the upr eight position in the body of water for the centre hull to be caused 35 to move, 5 to a lowered operational condition on raising of the outer hull portions from their first positions to their second positions, and filling of the ballast tanks with water, in which the windows are in a lowered position at least partly disposed below the water level to enable underwater viewing 5 therethrough by said occupants, from the lowered condition to a raised condition on lowering of the outer hull portions from their second positions to their first positions and emptying of the ballast tanks, in which the window are raised relative to their lowered condition such that the windows are at least partly raised 10 relative to their lowered positions. In a preferred embodiment, the vessel is configured to enable movement of the outer hull portions from their first positions towards their second positions simultaneously with filling of the ballast 15 tanks with water, and movement of the outer hull portions from their second positions towards their first positions simultaneously with emptying of the ballast tanks. 20 In a preferred embodiment, each of the outer hull portions, when in its second position, extends laterally further from the centre hull than when the outer hull portion is in its first position. Preferably, each outer hull portion is rotatably connected to the support 25 structure by at least one hinge connection having an axis of rotation which is substantially horizontal; whereby rotation of the outer hull portion between the first and second positions is via an arc of rotation which is in a substantially vertical plane. 30 Each o ter hull portion, when in the first position, preferably extends downwards from the support structure, and when in the second position preferably extends sideways from the support structure, 6 Preferably, the angle between the position of each outer hull portion when in its first position and its position when in its second position is substantially 90 degrees. 5 In a preferred embodiment, the drive means includes at least a pair of telescopic double-acting hydraulic rams, each ram being joined at one end to the support structure and at an opposite end to a respective one of the outer hull portions. 10 Preferably, each ram is connected to the support structure and the respec ive outer hull portion at connection positions such that when the ram is in an extended condition the outer hull portion is in the first position and when the ram is in a shortened condition the outer hull portion is in the second position. 15 In a preferred embodiment, the vessel includes at least three ballast tanks fixed in relation to, and disposed on each side of, the centre hull. In a preferred embodiment, the vessel includes a respective propeller 20 attached to each outer hull portion. Preferably, each propeller is disposed on the respective outer hull portion so as to be at an inner, lower edge of the outer hull portion when it is in its first position, and at an outer, lower edge of the outer hull portion 25 when it is in its second position. The vessel is preferably configured such that the depth at which each propeller is adapted to be disposed in the body of water when the outer hull to which it is attached is in its first position is substantially the same 30 as the depth when that outer hull is in its second position. In a preferred embodiment, each propeller is of a type adapted to be operated as a surface piercing propeller.

6a In another preferred embodiment, the vessel includes a pair of anti cavitation nozzles, each propeller being disposed in a respective one of the anti-cavitation nozzles. 5 BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will now be described, by way of example only,.with reference to the accompanying drawings in which: 10 Figure 1 is a schematic side view of a vessel according to a first embodiment of the invention, with its outer hull portions in a lowered position; Figure 2 is a schematic side view of the vessel of Figure 1, with its outer hull portions in a raised position; 15 (continues on page 7) 7 Figure 3 is a schematic section view of a side half of the vessel as shown in Figure 1, viewed along the line III-III; Figure 4 is a schematic section view of a side half of the vessel as shown in Figure 2, viewed along the line IV-IV; 5 Figure 5 is a detailed view of part of the side half of the vessel as shown in Figure 3; Figure 6 is a detailed view corresponding to Figure 5, but with the outer hull portion in partially raised position; Figure 7 is a schematic plan view of the vessel of Figure 1, with one of 10 its hull portions being in a raised position and another in a lowered position; Figure 8 is a schematic side view of a vessel according to another embodiment of the invention, with its outer hull portions in a lowered position; Figure 9 is a schematic side view of the vessel of Figure 8, with its 15 outer hull portions in a raised position; Figure 10 is a schematic section view of a side half of the vessel as shown in Figure 8, viewed along the line X-X; Figure 11 is a schematic section view of a side half of the vessel as shown in Figure 9, viewed along the line XI-XI; and 20 Figure 12 is a schematic plan view of the vessel of Figure 1, with one of its hull portions being in a raised position and another in a lowered position. DETAILED DESCRIPTION 25 Referring to Figures 1 to 7, there is shown a water-going vessel 10 for use in a body of water 12, such as the ocean or a river. The vessel 10 is of a "trimaran" type, that is, having three hulls - a centre 30 hull 14, and two side hulls 16 disposed on opposite sides of the centre hull (only one side hull being shown). Each of the hulls 14 and 16 is of a long, narrow shape.

8 There is provided a support structure 18 which includes portions fixedly joined to the centre hull 14 and extending in opposite side directions from the centre hull (only one of the portions being shown). The support structure 18 is substantially non-movable relative to the centre hull 14. 5 As best illustrated in Figures 1 and 2, each side hull 16 includes a fore outer hull portion 20, an aft outer hull portion 22, which in a preferred embodiment includes an engine room, and a middle outer hull portion 24 between the fore and aft outer hull portions. Each of the fore and aft outer 10 hull portions 20, 22 are fixedly (immovably) joined to the support structure 18 on the relevant side of the vessel 10. By contrast, each of the middle hull portions 24 are rotatably connected to the support structure 18 on the relevant side of the vessel 10 by hinge connections 26 as best seen in Figures 3 to 6. 15 The hinge connections 26 enable rotation of the hull portions 24 relative to the support structure 18, through an angle of substantially 90 degrees, between a first, lowered position as shown in Figures 3 and 5, and a second, raised position as shown in Figures 4 and 6. 20 Drive means in the form of telescopic, double acting hydraulic rams 28 are provided at each side of the vessel 10, for rotating each hull portion 24 between the lowered and raised positions. Each ram 28 has an inner cylinder 30 and an outer cylinder 32 into which the inner cylinder can slide. The rams 25 28 are configured to be actuated so as to move from a fully extended condition, in which the inner cylinder 30 extends to a maximum extent from the outer cylinder 32, to a shortened condition in which the inner cylinder is substantially fully drawn into the outer cylinder, and from the shortened condition to the extended condition. The actuating force of the rams 28 is 30 provided by a suitable liquid such as oil, in a manner that would be understood by those skilled in the art.

9 Each ram 28 has one end 34, being a free end of the outer cylinder 32, which is rotatably joined to the support structure 18 at the relevant side of the vessel 10, and an opposite end 36, being a free end of the inner cylinder 30, which is rotatably joined to the hull portion 24 at that side of the vessel. 5 It will be noted that the end 36 of each ram 28 is connected to the relevant hull portion 24 at a location which is adjacent to the top of the hull portion when it is in its raised position. In addition, the hinge connections 26 are positioned so as to be approximately midway up the height of each hull 10 portion 24 when it is in the raised position. As a result, when the rams 28 are in their extended positions as shown in Figure 5, the hull portions 24 are in their lowered positions. As the rams 28 are actuated to move to their shortened conditions, this causes them to draw 15 the hull portions 24 to their raised positions as shown in Figures 1 and 4. In Figure 7 one of the hull portions 24 (being the upper one as viewed in the figure) is shown in its lowered position, while the other hull portion (being the lower one as viewed in the figure) is shown in its raised position. 20 The hinge connections 26 have axes of rotation 38 which are substantially horizontally orientated, so that the rotation of the hull portions 24 from their lowered positions to their raised positions causes them to move through an arc of rotation 40 which is in a substantially vertical plane, as shown in Figure 6. 25 Each of the side portions of the support structure 18 includes ballast tanks 42. In a preferred embodiment, there are three or more ballast tanks 42 on each side of the centre hull 14. The upper surface 44 of each of the side portions of the support structure 18 is level and continuous with the upper 30 surface 46 of the centre hull 14, and these surfaces, together, serve as a deck for the vessel 10, the deck being generally designated 48.

10 Within the centre hull 14, there is an internal chamber 50 for accommodating occupants. The entrance to the chamber 50 (not shown) includes a stairway near the aft end of the chamber, the stairway extending into the chamber from an aft area of the deck 48. In a preferred embodiment, another 5 stairway or emergency ladder (not shown) is also provided, which leads from the deck 48 to a position near the centre of the chamber 50. The sides 52 of the centre hull 14 include windows 54, which enable occupants of the chamber 50 to look outside the centre hull. 10 In different embodiments, the vessel 10 is propelled by sails or motors. In one preferred embodiment, the vessel 10 is equipped with both a sail 56 and motors (not shown) and is capable of being driven by both propulsion means simultaneously. 15 In use, when the hull portions 24 are in their lowered positions, the configuration of the vessel 10 is as a trimaran, that is, a three-hulled vessel. The combined buoyancy of the centre hull 14 and hull portions 24 causes the vessel 10 to float in the water 12 so that the water level, in relation to the 20 vessel, is at the position 58 shown in phantom lines in Figures 1, 3 and 5, with portions 60 of the hulls being disposed below the level of the water. The windows 54 are then disposed substantially above the level of the water 12. In this configuration, and due to the long, narrow shape of the hulls 14 and 25 16, the vessel 10 is adapted for relatively high speed travel, for example up to 15 knots. Such speeds are suitable for traversing relatively large distances, say from a port or dock to a remote location where underwater viewing is to occur, such as a coral reef. 30 The shallow draft of the vessel 10 in this configuration enables it to operate in shallow harbours, areas of shallow reef, and shoal areas.

11 Once the vessel 10 has reached its destination, the rams 28 can be actuated to cause the hull portions 24 to move from their lowered positions to their raised positions. The buoyancy forces exerted by the water 12 on the hull portions 24 are thus diminished, and this causes the centre hull 14 to be 5 immersed to a greater depth in the water. It will be appreciated that the centre hull 14 can be immersed in the water 12 to differing depths by varying the position of the hull portions 24 between the fully lowered and fully raised positions. Such an intermediate position of 10 one of the hull portions 24 is shown in dashed lines in Figure 6, with this hull portion being designated 24.1. The water level, in relation to the vessel 10, when hull portions 24 are in the position of the hull portion 24.1 in Figure 6, is at the position 61 shown in 15 Phantom lines. To achieve the maximum depth of immersion of the centre hull 14 in the water 12, as shown in Figures 2 and 4, as the hull portions are being rotated from their lowered positions to their raised positions, water from the body of 20 water 12 is pumped into the ballast tanks 42 by pumps (not shown). In this position, the water level, in relation to the vessel 10, is at the position 62. The level of water in the various ballast tanks 42 can be adjusted to control the fore and aft trim of the vessel 10. This can also assist in limiting "free 25 surface" movement of water in the ballast tanks 42. When the centre hull 14 is in the maximum immersed position, the windows 54 are substantially fully immersed in the water 12. This enables occupants of the chamber 50 to easily view scenes under the water, such as coral reef, 30 from within the chamber. In this position of the centre hull 14, as the hull portions 24 are in their fully raised positions, they are not adapted for rapid travel through the water 12, and the vessel 10 is thus only capable of 12 moving relative slowly, which is suitable for the viewing of underwater scenery. It will be appreciated that the windows 54 are positioned to face at a 5 downward angle as shown in Figures 3 to 6. This allows an unobstructed view to occupants of the chamber 50 of underwater scenery, regardless of whether the hull portions 24 are in their raised or lowered positions or any position in between. 10 When the hull portions 24 are in their raised positions, they have upper surfaces 64 which are substantially continuous with the upper surface 44 of the support structure 18, and thus serve as extensions of the deck 48. In this position, the hull portions 24 also extend, laterally, further from the centre hull 14 than when in their lowered positions. They thus also provide 15 additional lateral stability to the vessel 10. Different relationships between mobility and underwater visibility through the windows 54 can be achieved by varying the depth of immersion of the centre hull 14 in the water 12; this in turn, is achieved by varying the location of 20 the hull portions 24 between the fully lowered and fully raised positions. The configuration of the hull portions 24, and their ability to be rotated between their fully lowered and fully raised positions, results in the vessel 10 being easily adaptable between a fast-speed, non-viewing mode and a slow 25 speed, viewing mode. The fast-speed, non-viewing mode is suitable for transporting passengers over a large distance to an underwater scenery location but not for allowing the viewing of underwater scenery through the windows 54. The slow-speed, viewing mode, while not being suitable for high speed travel, does enable viewing of underwater scenery through the 30 windows 54. In addition, when the vessel is in the non-viewing mode - that is, with the hull portions 24 in their lowered positions and the windows 54 above the 13 water level, the windows can be kept clean and free of marine growth which eliminates the need for applying anti-fouling substances to the windows. Reference is now made to Figures 8 to 12 in which a vessel 10.2, according 5 to a different embodiment to that described in relation to Figures 1 to 7, is shown. Parts of the vessel 10.2 having corresponding parts in the vessel 10 are designated by similar reference numerals, except that they have the suffix ".2". 10 The configuration of the vessel 10.2 is substantially the same as that of the vessel 10, except as described below and as illustrated in the drawings. In particular, while, in the vessel 10, the fore and aft outer hull portions 20 and 22 on each side of the vessel are immovably joined to the support 15 structure 18, with only the middle hull portions 24 being rotatably connected to the support structure, in the vessel 10.2 the whole of each of the outer hull portions, designated 24.2, is rotatably connected to the support structure 18.2. 20 It will be noted, especially with reference to Figures 7 and 12, that the forward parts of the outer hull 24.2 of the vessel 10.2 are offset laterally outwards when compared with the fore hull portions 20 of the vessel 10. This allows for more unobstructed viewing by occupants through the forward 25 and rear windows 54.2. In addition, when these outer hull portions 24.2 are in their raised positions, the forward and rear portions of the outer hulls are clear of the water which results in less drag on, and greater manoeuvrability of, the vessel 10.2 when compared with the vessel 10. 30 As the aft outer hull portion 22 is movable relative to the support structure 18.2, the aft outer hull portion is not used to house an engine room as in the vessel 10. with this engine room being located inboard of the outer hull portions 24.2.

14 Mounted at the rear of each outer hull portion 24.2 is a propeller assembly 66 having a drive mechanism 68 and a propeller 70 connected to the drive mechanism. The drive mechanism 68, in turn, is connected to the engine by a "Z"-drive leg connection (not shown). These "Z"-drive leg connections 5 enable the propeller assemblies 66 to be connected to the engine at any rotational position of the outer hull portions 24.2 relative to the support structures 18.2. The power for driving the propellers 70 is preferably supplied by hydraulic or 10 electric motors (not shown) which can operate at different angles. In another embodiment, a diesel engine may be provided for this purpose, and if required, it can be adapted to operate at angles of 45 degrees allowing the diesel engine to provide direct power to the propellers 70. 15 The propeller assemblies 66 are configured to operate with the propellers 70 being disposed at a very shallow depth. To minimise cavitation of the propellers 70, each assembly 66 includes an anti-cavitation nozzle 72 in which the propeller is disposed. 20 Each of the propellers 70 is located at a lower inner edge of the respective outer hull portion 24.2 when the hull portion is in its lowered position as shown in Figure 11, with the drive mechanisms 68 extending towards the centre of the vessel 10.2 at substantially 45 degrees to the vertical. As a result, when the outer hull portions 24.2 are moved to their raised positions 25 as shown in Figure 12, the drive mechanisms 68 extending away from the centre of the vessel 10.2 at substantially 45 degrees to the vertical. This arrangement allows each propeller 70 and its anti-cavitation nozzle 72 to be positioned at substantially the same depth in the water whether the outer hull portions 24.2 are in their raised or lowered positions. 30 While preferred embodiments of the invention have been described above, it will be understood by those skilled in the art that the invention is not limited to those embodiments, but may be embodied in many other forms.

Claims (15)

1. A water-going vessel for use in a body of water, the vessel including; 5 a centre hull configured to be disposed at least partly below the water level of the body of water and providing buoyancy for the vessel when the vessel is in an upright operational position, the centre hull defining an internal space for accommodating occupants, and including windows; 10 a support structure fixedly joined to the centre hull so as to be substantially non-movable relative thereto; a pair of outer hull portions disposed on opposite sides of the centre hull, each outer hull portion being configured to be disposed at least partly below the water level and to provide buoyancy to the vessel, 15 and being rotatably connected to the support structure to enable rotation of the outer hull portion relative to the centre hull between a first, lowered position and a second raised position; a drive means configured for rotating each outer hull portion between said first and second positions; and 20 at least two ballast tanks, fixed in relation to, and disposed on opposite sides of, the centre hull, wherein the vessel is configured, when it is floatingly supported in the upright position in the body of water for the centre hull to be caused to move, 25 to a lowered operational condition on raising of the outer hull portions from their first positions to their second positions, and filling of the ballast tanks with water, in which the windows are in a lowered position at least partly disposed below the water level to enable underwater viewing therethrough by said occupants, and 30 from the lowered condition to a raised condition on lowering of the outer hull portions from their second positions to their first positions and emptying of the ballast tanks, in which the windows are raised relative to their lowered condition such that the windows are at least partly raised relative to their lowered positions. 35 16

2. A vessel according to claim 1 configured to enable movement of the outer hull portions from their first positions towards their second positions simultaneously with filling of the ballast tanks with water, and 5 movement of the outer hull portions from their second positions towards their first positions simultaneously with emptying of the ballast tanks.

3. A vessel according to claim 1 or claim 2 wherein each of the outer 10 hull portions, when in its second position, extends laterally further from the centre hull than when the outer hull portion is in its first position.

4. A vessel according to claim 3 wherein, each outer hull portion is rotatably connected to the support structure by at least one hinge 15 connection having an axis of rotation which is substantially horizontal, whereby rotation of the outer hull portion between the first and second positions is via an arc of rotation which is in a substantially vertical plane.

5. A vessel according to claim 4 wherein each outer hull portion, 20 when in the first position, extends downwards from the support structure, and when in the second position extends sideways from the support structure.

6. A vessel according to claim 4 wherein the angle between the 25 position of each outer hull portion when in its first position and its position when in its second position is substantially 90 degrees.

7. A vessel according to any one of the preceding claims wherein the drive m ans includes at least a pair of telescopic double-acting hydraulic 30 rams, each ram being joined at one end to the support structure and at an opposite end to a respective one of the outer hull portions.

8. A vessel according to claim 7 wherein each ram is connected to the support structure and the respective outer hull portion at connection 35 positions such that when the ram is in an extended condition the outer 17 hull portion is in the first position and when the ram is in a shortened condition the outer hull portion is in the second position.

9. A vessel according to any one of the preceding claims, including S at least three ballast tanks fixed in relation to, and disposed on each side of, the centre hull.

10. A vessel according to any one of the preceding claims, including a respective propeller attached to each outer hull portion. 10

11. A vessel according to claim 10 wherein each propeller is disposed on the respective outer hull portion so as to be at an inner, lower edge of the outer hull portion when it is in its first position, and at an outer, lower edge of the outer hull portion when it is in its second position. 15

12. A vessel according to claim 11, configured such that the depth at which each propeller is adapted to be disposed in the body of water when the outer hull to which it is attached is in its first position is substantially the sarr e as the depth when that outer hull is in its second position. 20

13. A vessel according to any one of claims 10 to 12 wherein each propeller is of a type adapted to be operated as a surface piercing propeller. 25

14. A vessel according to any one of claims 10 to 12, including a pair of anti-cavitation nozzles, each propeller being disposed in a respective one of the anti-cavitation nozzles.

15. A vessel substantially as herein described with reference to any 30 one of the accompanying drawings.