The present invention relates to a waterborne vessel and relates particularly, but not exclusively, to a waterborne vessel that utilises a surface effect to carry large payloads at high speed.

The use of surface effect ships and boats is known for increasing the operating speed of the vessel. Such boats and ships are sometimes described as a cross between a hovercraft and a catamaran with front and rear skirts connecting the bowels and stern of the catamaran hulls to form an enclosure. Powerful fans blow air into this enclosed space increasing the air pressure in that space which partially lifts the hulls out of the water, thereby reducing the drag effect of the hulls in the water. An example of such a vessel is used by the Norwegian Navy and referred to as the Skjold.

Although such vessel are able to travel at high speeds in reasonably calm waters the inclusion of the skirts has a number of disadvantages. For example, the skirts are liable to damage and once damaged the fans, and therefore the surface effect, becomes ineffective and the vessel is unable to travel at high speed and is then slower than a standard vessel. Furthermore, such vessels struggle to operate effectively in anything that resembles rough weather conditions. This is in part due to the risk of damage to the skirts but also because rough waters reduce the effectiveness of the fans whenever the enclosure created by the hulls and the skirts is opened as a result of the more violent movement of the vessel.

A further example of a surface effect vessel is disclosed in the International Patent application published under the number WO 93/07046. In this example the drag effect of the water on the whole of the vessel is reduced in order to allow the vessel to travel at sufficient speed to enable the air travelling between the hulls at high speed to have the effect of lifting the vessel partially out of the water. However, the vessel described in this example is only partially successful in providing sufficient lift to reduce the drag effect of the water on the whole of the vessel and allow it to travel at high speeds .

Preferred embodiments of the present invention seek to overcome the above described disadvantages of the prior art. According to an aspect of the present invention there is provided a waterborne vessel comprising: - a hull including a plurality of hull portions extending along the length of the vessel and forming at least one channel therebetween, a portion of said hull portions shaped to cause a narrowing of said channel at least partially along its length; at least one propulsion means for driving said vessel forwards; and at least one vortex forming unit extending from said hull into at least one said channel. By providing a vortex forming units which extend from the hull into the channel, the advantage is provided that when the vessel is travelling at a sufficient velocity vortices are formed within the channel which provide additional lift to the vessel reducing the drag in the water. As a result, a high- speed vessel can be provided capable of carrying significant weights of cargo. This reduced drag is provided without the need for additional fans, as seen in other surface effect vessels and which require additional energy to create the lift. Furthermore, the above described vessel does not require skirts connecting the catamaran hulls across the front and rear to retain the air pressure created by the fans. This makes the vessel of the present invention significantly more robust and reduces the requirement for maintenance. Furthermore, because the lift is created without the use of skirts and fans, the vessel is able to travel at higher speeds in rougher waters than surface effect vessels of the prior art. In a preferred embodiment the hull comprises three hull portions and two channels therebetween.

For most sizes of vessel two channels provides the optimum lift and drag reduction.

In another preferred embodiment each channel is formed from a first wall of a first said hull portion, a second wall of a second said hull portion and a third wall joining said first and second walls.

In a further preferred embodiment the first and second walls are substantially vertical and said third wall is substantially horizontal.

The preferable shape for the cross-section of the channel is substantially rectangular and the three walls described above together with the surface of the water provide this shape.

The hull preferably comprises a forward portion and a rearward portion wherein a cross-section of said channel of said forward portion reduces in cross-sectional area from a front to a rear of the forward section and a cross-section of said channel of said rearward section remains substantially the same along the majority of said rearward section. By providing a forward portion of the vessel in which the cross-section of the channel reduces the advantage is provided that the forward portion acts as a funnel directing air into the channel, increasing the air pressure within the channel and causing lift. With the rearward section having a substantially consistent cross-section the advantage is provided that the vortices produced continue to provide lift. The or each vortex forming unit is preferably contained within said forward portion of said hulls.

The vortex forming units are only required in the forward portion of the channels as it is in this section that the vortices are created and they are able to maintain themselves along the length of the channel once created.

In a preferred embodiment the vortex forming unit comprises at least one first vortex forming member having at least one first surface extending into said channel substantially perpendicular to a portion of said hull from which said first vortex forming member extends .

In another preferred embodiment the vortex forming unit comprises at least one first vortex forming member having at least one first surface extending into said channel substantially perpendicular to a second surface of said first vortex forming member which extends from said hull at an acute angle very close to said hull.

In a further preferred embodiment the vortex forming unit comprises at least one first vortex forming member having at least one first surface extending into said channel substantially perpendicular to the direction of travel of the vessel .

It is the perpendicular edge of the first vortex forming members which create the initial turbulence the results of the formation of the vortices.

In another preferred embodiment vortex forming unit comprises at least one second vortex forming member extending from said hull portion substantially parallel to said direction of travel. Preferred embodiments of the present invention will now be described, by way of example only, and not and in any limitative sense with reference to the accompanying drawings in which :-

Figure 1 is a front view of a vessel of the present invention;

Figure 2 is a schematic plan view of the vessel of figure 1 ; and

Figure 3 is a schematic side sectional view of the vessel of figure 1 ; Figure 4 is a view of a portion of the vessel from underneath;

Figure 5 is a side view of the portion of the vessel shown in figure 4.

Referring to figures 1, 2 and 3, a waterborne vessel 10 is provided with a hull (generally indicated at 12) which is divided into a body 14 and a plurality (in this instance three) catamaran style hull portions 16, 18 and 20. In the embodiment shown, the hull portion 16 is the central and largest hull portion and the remaining hulls portions, 18 and 20, are located on either side of the central hull portion 16. Each of the hull portions 16, 18 and 20 is joined to its neighbour by the body 14. As a result, the internal surface 22 of hull portion 18 is connected to surface 24 of central hull portion 16 via the body surface 26. Likewise, the internal surface 28 of hull portion 20 is connected to surface 30 of central hull portion 16 via the body surface 32.

The three surfaces 22, 24 and 26 form a first channel 34 and when the vessel 10 is floating on the water this channel 34, in combination with the water surface on which the vessel is floating, forms a tunnel extending along the vessel from the bow of hulls 14 and 16 to their sterns. Likewise the three surfaces 28, 30 and 32 form a second channel 36 which forms a second tunnel with the water surface. All of the surfaces 22, 24, 26, 28, 30 and 32 are shaped so that a forward portion of the channels 34 and 36, and their respective tunnels, narrow along the vessel from bow to stern. That is, when the vessel 10 is placed on a perfectly still water surface, the cross-section of the tunnel, cut perpendicular to the direction of travel, has an area which decreases as you move towards the stern. This narrowing results from the convex curved shape of the hull surfaces 22, 24, 28 and 30 and also from the convex curved shape of the connecting surfaces 26 and 32.

The vessel is provided with a suitable means of propulsion and this is typically a water jet propulsion system familiar to those skilled in the art. However, any suitable means of propulsion can be used as long as it has sufficient power to propel the vessel at the high speeds required to create the surface effect set out below.

Attached to, or formed as part of, at least one of the surfaces 22, 24, 26, 28, 30 and 32 that form the channels 34 and 36 is at least one vortex forming unit which extends into the channel. The vortex forming unit can be divided into first vortex forming members 38, 44, 42 and 44 and second vortex forming members 46, 48, 50, 52, 54, 56, 58 and 60. Each channel has two first vortex forming members and four second vortex forming members such that the first channel 34 as first vortex forming members 38 and 40 and second vortex forming members 46, 48, 50 and 52 and second channel 36 as first vortex forming members 42 and 44 and second vortex forming members 54, 56, 58 and 60. With additional reference to figures 4 and 5, the first vortex forming members 38, 40, 42 and 44 are formed on the connecting surfaces 26 and 32 (which could be described as the roof of the tunnel) . The first vortex forming members include a vortex forming surface 62 which is deliberately angled to not smoothly transition from the connecting surfaces 26 and 32 so as to encourage the formation of vortices in the air that is travelling over that surface. This vortex forming surface 62 or 64 can be perpendicular to the direction of travel, perpendicular to the connecting surface 26 or 32 or can be perpendicular to the leading surface 66 or 68 of the first vortex forming member. As the vessel 10 moves in a forward direction air is able to travel over the leading surfaces 66 and 68. When these surfaces end, air turbulence is generated in the space immediately adjacent the vortex forming surfaces 60 and 64 and this turbulence leads to the formation of one or more air vortices .

The second vortex forming members 46, 48, 50, 52, 54, 56, 58 and 60 extend from the side wall surfaces 22, 24, 28 and 30 of the hull portions 16, 18 and 20. The second vortex forming members extend at least partially along the length of the surfaces and each has an upper surface 70 (indicated on second vortex forming member 46) and a lower surface 72. The upper surface 70 is typically substantially horizontal when the vessel is in use. The second vortex forming members are used in part to create the vortices but also to propagate the vortices created by the first vortex forming members.

Operation of the vessel 10 will now be described. When the vessel 10 is stationary and floating the water comes a significant distance up the hulls to approximately the line indicated at 74. As the vessel begins to move forward, in the direction F, air travelling into the tunnels created by channels 34 and 36 is forced inwards by the narrowing of the tunnels caused by the shape of the front portions of the surfaces 22, 24, 26, 28, 30 and 32. This results in an increase in the pressure of the air in the tunnels causing the vessel 10 to lift partially out of the water. As the velocity of the vessel increases the pressure, and therefore the lift, also increases. However, on its own this is not sufficient to lift the vessel far enough out of the water to reduce the drag of the hulls in the water enough to allow further increases in velocity. By the inclusion of the vortex forming units the air that is travelling fast over the surface of the channels 34 and 36 is disrupted resulting in the formation of vortices which result in additional lift to the vessel 10. These vortices further increase the air pressure within the tunnel causing the additional lift. Because the vessel is lifted further out of the water the drag of the water on the hulls, in particular the central hull 16, is further reduced allowing the vessel to travel faster .

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the protection which is defined by the appended claims. For example, the invention will in principle work using more or less channels / tunnels by including two or more hulls.