Patent Description:
The background of the invention is that air supported vessels are an important part of future shipping as an alternative to achieve the strict emissions requirements that are coming. Air supported hulls have a significantly reduced hydrodynamic resistance compared to conventional comparable hulls. By further developing air supported hulls to reduce air loss from the air supported chamber, increase directional stability and reduce hydrodynamic turning resistance moment(s), it will help bringing air supported vessels to become an even more interesting option within the market for environmentally friendly shipping.

Most of the air supported vessels on the market today are what are also called air cushion boats or "Hovercraft" and many of them can move on land and in water. They often have an inflatable skirt around the hull which is internally filled with air and creates a boundary for the air supported chamber which, with the help of an excess pressure, lifts the vessel, but there are also some designs of air cushion boats with fixed hulls also called Surface Effect Ship (SES) or " Sidewall Hovercraft". Such types of vessels have both an air cushion, like a hovercraft, and a hull like a conventional vessel. When the air cushion is in use, only a small part of the hull protrudes into the sea.

<CIT> patent from <NUM> deals with a soft, stable multi-chambered hull, which has a number of high-pressure chambers around the periphery. The hull has further included a valve slot which provides a means for emptying the continuously charged high pressure chamber. The high-pressure chambers under the boat provide soft support with the air cushion and low friction. A disadvantage of such a hull, where there is so little buoyancy in the side walls of the high-pressure chambers, is that the vessel will lose stability as soon as the pressure in the air supported chambers drops or the fans for blowing in high-pressure air are switched off. The buoyancy elements are not in the keel itself, so the hull will also sink deeper into the water as soon as the high-pressure air is turned off. Another disadvantage of such a hull, where there is a deep longitudinal keel on starboard and port all the way from the stern and almost to the bow, is a high hydrodynamic turning resistance moment and great drag due to the length of the keel in the sea. There will also be a disadvantage with air discharge, in that high-pressure air is required and it will also require much more energy to lift the hull out of the water.

In <CIT> patent from <NUM>, the air cushion fan is also used as a propulsion fan for the vessel. This will require much energy, both to lift the vessel and also to have enough thrust to propel the vessel forward. This patent is for a vessel that should be able to move both on water and on ice, like a sled by turning some longitudinal skirts <NUM> degrees, so they are lower than the keels. This invention will require too much energy to effectively move forward economically in relation to fuel consumption and thus indirectly in relation to today's environmental requirements.

<CIT> patent from <NUM> describes an air-cushioned vessel with a planing hull in the aft part and a front part which is delimited in whole or in part by a skirt. The aft part is delimited by two keel sections and the forward part is delimited by the flexible skirt.

<CIT>, <CIT>, <CIT>, <CIT> disclose other examples of vessels.

The present invention generally aims to solve at least one, but preferably several, of the problems that exist from the prior art.

An advantage of the invention on an air supported vessel where the lower part of the air supported chamber's starboard and port side walls are arranged with a longitudinal keel step on the starboard and port side respectively, is reduced air leakage from the air supported chamber under the keel step thresholds. The same advantage also applies to the V-shaped bow with the side wall of the air supported chamber bow with the bow step and the bow step threshold, which is reduced air leakage.

Another advantage of the invention on an air supported vessel where the V-shaped bow lies with reduced or very little water influence in operation, is that the V-shaped hull gets a better load distribution aft, which in turn gives a more advantageous ratio between lifting force and resistance on the keel parts of the V-shaped hull, on the starboard and port side, respectively Furthermore, it is an advantage of the invention that the two straight longitudinal keel parts on the starboard and port side, respectively, which extend from the stern to slightly past the rear part of the V-shaped bow and with a greater draft than the V-shaped bow, provides good directional stability on the V-shaped hull, especially when waves slant in from the front or waves slant in from behind.

Preferred embodiments of the invention will be described in more detail below with reference to the accompanying figures, in which:.

The present invention bring about an air supported vessel comprising the features as given in claim <NUM>.

In one embodiment of the invention may the starboard keel part <NUM>. S comprises a starboard longitudinal keel step <NUM>. S and a starboard keel step threshold <NUM>. S, which forms a lower starboard lateral delimitation of the air supported chamber's starboard side wall <NUM>. S, to reduce air leakage below a starboard keel line KL. S, and the port keel part <NUM>. B comprises a port longitudinal keel step <NUM>. B and a port keel step threshold <NUM>. B, which forms a lower port lateral delimitation of the air supported chamber's port side wall <NUM>. B, to reduce air leakage below a port keel line KL.

According to one embodiment of the invention, a transition between the starboard longitudinal keel step <NUM>. S and the starboard aft part of the bow step <NUM>. S may be a starboard discontinuous transition <NUM>. S, while being a transition between the port longitudinal keel step <NUM>. B and port aft part of the bow step <NUM>. B is a port discontinuous transition <NUM>.

The term "discontinuous transition" is used to describe that the forward part of the relatively sharp keel lines of the keel steps <NUM>. B does not run over into the bow step <NUM>, but extends forward and past the aft parts of the bow steps <NUM>. B, see especially <FIG>, <FIG> and <FIG>.

The advantages of having a transverse starboard and port step <NUM>. B, is to make the bow base line BBL to have a reduced draft in relation to the longitudinal keel steps on the starboard and port side <NUM>. B respectively, so that drag and wave resistance are reduced. Another advantage is that the hydrodynamic turning resistance moment is reduced by having a bow baseline BBL that has little draft.

In another embodiment of the invention, the V-shaped bow <NUM> may have a bow base line BBL with a slight fall forward calculated from a transition between the bow step <NUM>, respectively the starboard longitudinal keel step <NUM>. S or the port longitudinal keel step <NUM>.

Such a design may help to increase buoyancy in the V-shaped bow <NUM>, so that the vessel obtain better stability and may have a more flexible weight distribution on the main deck. Another advantage is that the bow base line BBL will be approximately horizontal when the vessel has an aft trim or when the vessel's bow rises in the sea during thrust, and will thus contribute to reduce the risk of air discharge below the bow threshold <NUM>.

According to one embodiment of the invention, the starboard keel part <NUM>. S may be parallel to the V-shaped hull's <NUM> centerline CL and where the port keel portion <NUM>. B may be parallel to the V-shaped hull's <NUM> centerline CL.

By having two parallel keel parts, on the starboard and port side <NUM>. B respectively, around the V-shaped hull's <NUM> center line CL, the directional stability will be improved compared to the directional stability of a conventional V-hull, and especially against waves coming slanted in from the front or back. Lateral stability will also increase, the GZ curve, compared to a conventional V-hull.

In another embodiment of the invention, the side wall bow <NUM> of the air supported chamber may be completely or partially, outwardly inclined.

In a further embodiment of the invention, the longitudinal keel steps, respectively on the starboard and port side, <NUM>. B and the bow step <NUM> may be substantially vertical steps.

The entirely or partially air supported chamber side walls, respectively on the starboard and port side, <NUM>. B help to give the V-shaped hull <NUM> buoyancy and stability when the vessel is at rest and there is no supply of air to the air supported chamber <NUM>. The vertical longitudinal keel steps, respectively on the starboard and port side, <NUM>. B and the bow step, which sits on the lower edge of the air supported chamber side walls <NUM>. B, <NUM>, are an obstacle for air to escape below the threshold on the vertical longitudinal keel steps, respectively on the starboard and port side, <NUM>. B and the threshold on the bow step <NUM>.

In an embodiment of the invention, the V-shaped bow <NUM>, comprising the bow step <NUM>, may extend aft to the aft starboard, and respectively the aft port, transition point <NUM>. B which is located near the middle <NUM> x CWL of a construction water line KVL. By pulling the V-shaped bow section in CWL <NUM> close to the middle of the construction waterline CWL, there is less hydrodynamic turning resistance moment(s).

<FIG> show one or more embodiments of a hovercraft according to the present invention.

In <FIG> there is a profile only illustrated, elevation, which shows a longitudinal section of an embodiment of the basically V-shaped hull <NUM>, which is the same hull as shown in <FIG>, where the surfaces are now tinted with a gray color , so that the V-shaped bow <NUM> comes forward, both of these Figures shown are seen from the outside towards the starboard side of the hull.

<FIG> shows an embodiment of the basically V-shaped hull <NUM> with a more general elevation of the longitudinal section, which can either be viewed towards the starboard or port side, as the basically V-shaped hull <NUM> is symmetrical about the centerline CL. Details such as starboard or port, the keel part <NUM>. B, the V-shaped bow <NUM>, the bow base line BBL, starboard or port, the keel line KL. B, starboard or port, are marked on the figure. discontinuous transition <NUM>. B, the construction waterline KVL, the aft starboard, or port, transition point <NUM>. B, the forward starboard or port point <NUM>. B and the V-shaped bow section in KVL <NUM>, to illustrate where they are located on the basically V-shaped hull <NUM>.

<FIG> shows an embodiment of the profile of the bottom of an embodiment of the basically V-shaped hull <NUM> and where an embodiment of the recess in the basically V-shaped hull <NUM> is also shown, which in turn forms the air supported chamber <NUM> and where we see the air supported chamber ceiling <NUM>. The figure also shows that the initially V-shaped hull <NUM> seen against the bottom in gray tones so that the contours of the hull come out more clearly.

<FIG> shows an embodiment of a sketch/drawing of the bottom of an embodiment of the basically V-shaped hull <NUM>, where the basically V-shaped hull <NUM> is marked with lines and reference numbers to name the parts of the basically V-shaped hull <NUM>. It appears from the Figure that the keel parts, respectively on the starboard and port side, <NUM>. B, extend from the transom <NUM> up to the V-shaped bow <NUM>. At the transom <NUM> and between the starboard and port keel parts <NUM>. B there is a closing device <NUM> with a stern threshold <NUM>. Furthermore, the Figure shows the air supported chamber <NUM> with the air supported chamber ceiling <NUM> and the air supported chamber side walls, respectively on the starboard and port side, <NUM>. It is further shown that the air supported chamber side walls <NUM>. B each comprise a longitudinal keel step, on the starboard and port side respectively, <NUM>. B, and where the edge from the air supported chamber side walls <NUM>. B over to the keel parts <NUM>. B are respectively starboard and port longitudinal keel rise threshold <NUM>. The figure further shows the front part of the bottom of the basically V-shaped hull <NUM> where there is an air intake <NUM>, and that the V-shaped bow <NUM> also has the air supported chamber ceiling <NUM> and the air supported chamber side wall bow <NUM>. It is further shown that the air supported chamber's side wall bow <NUM> comprises bow step <NUM> with a lower edge as defined as bow step <NUM>. Incidentally, a center line CL is also shown, which divides the hull symmetrically into two parts, a starboard and a port part. The bow and stern are not defined as starboard and port.

<FIG> and <FIG> show an embodiment of the profile of a cross-section of the middle, a midships section, of the basically V-shaped hull <NUM> seen aft towards the transom <NUM>. <FIG> is in shades of gray which gives a better visual illustration of the curvature of the keel parts, respectively on the starboard side and port side, <NUM>. B, while <FIG> is a profile view/sketch. The figures show the partly or completely outward sloping air supported chamber side walls <NUM>. B and how the lower part of the air supported chamber side walls <NUM>. B is a longitudinal vertical keel step, on the starboard and port side respectively, <NUM>. The figures also show the lower edge of the keel parts <NUM>. B which is also the keel line threshold, on the starboard and port side respectively, <NUM>. B and which is also in this figure the keel line, on the starboard and port side respectively, KL.

<FIG> and <FIG> show the profile of a cross-section of the middle, a midships section, of the basically V-shaped hull <NUM> seen forward towards the V-shaped bow <NUM>. <FIG> is in shades of gray which gives a better visual illustration of the curvature of the V-shaped bow section <NUM>, while <FIG> is a profile view/sketch. The figures show the air intake <NUM> at the front and the partly or completely outwardly sloping air supported chamber side wall bow <NUM> and how the lower part of the air supported chamber side wall bow <NUM> is a bow step <NUM>. The figures also show the lower edge of the air supported chamber's side wall bow <NUM> here as a bow base line BBL. <FIG> also shows the difference in the draft between the starboard and port keel lines KL. S and the bow base line BBL.

<FIG> shows a sketch of a section at the longitudinal starboard, or port, keel sill <NUM>. B in an embodiment of the basically V-shaped hull <NUM>. The figure shows the keel lines, respectively on the starboard and port side, KL. B and the bow base line BBL, as well as the difference between the keel line, on the starboard and port side respectively, and the bow base line BBL, which is a transverse starboard keel step <NUM>. S and a transverse port keel step <NUM>. The figure shows here that the bow base line BBL follows the bow step <NUM>, and that the keel lines, on the starboard and port side respectively, KL. B follow the longitudinal keel step lines, on the starboard and port side respectively, right up to the decline in the discontinuous transition, on respectively starboard and port side, <NUM>. The figure further shows with a dashed line a recess area as the air supported chamber <NUM>, and where the front part is the air supported chamber's air intake <NUM> and the aft part is delimited by a closing device <NUM> with an aft threshold <NUM>. Two cross-sections are also marked with arrows, one aft with an A and one forward with a B. The cross-sections appear again in <FIG>.

<FIG> shows two half cross-sections, one aft A and one forward B taken from <FIG>, of an embodiment of the basically V-shaped hull <NUM>. The figure shows a composite cross-section of A and B about the center line CL, as the basically V-shaped hull <NUM> is symmetrical about the center line CL. Cross section A is an embodiment of the air supported chamber's starboard side wall <NUM>. S, here slightly sloping outwards, and comprising the starboard longitudinal keel step <NUM>. S, here vertical, and with a starboard longitudinal keel step threshold <NUM>. Cross section B is an embodiment of the side wall of the air supported chamber bow <NUM>, here very slightly sloping outwards, and comprising a bow step <NUM> with a bow step threshold <NUM>. Furthermore, the Figure shows the starboard keel line KL. S, which here hits the starboard longitudinal keel step <NUM>. S, and the bow base line BBL, which here hits the bow threshold <NUM>, and the difference between them, also called transverse starboard keel step <NUM>.

<FIG> shows an embodiment of frame sections in a port discontinuous transition <NUM>. B, also called the discontinuous transition area, seen obliquely from the bow towards the longitudinal port keel part <NUM>. The figure shows the recess area for the air supported chamber <NUM> with air supported chamber ceiling <NUM> which extends to the air supported chamber's port side wall <NUM>. B, here shown slightly sloping outwards. In the discontinuous transition <NUM>. B as shown in <FIG>, there are both bow steps <NUM> and port longitudinal keel steps <NUM>. B which are decreasing <NUM>. The figure also shows how the frames in the discontinuous transition from the V-shaped bow to the port longitudinal keel part with a port transverse step <NUM>. It is also apparent from the figure that the straight phasing of the longitudinal port keel part <NUM>. The hull is symmetrical and has a corresponding starboard design.

<FIG> and <FIG> show an embodiment of frame sections in a port discontinuous transition <NUM>. B, also called the discontinuous transition area, seen obliquely from above from the bow towards the port longitudinal keel part <NUM>. The hull is symmetrical and has a corresponding starboard design. The figures show the recess area for the air supported chamber <NUM> with air supported chamber ceiling <NUM> which extends to the air supported chamber's port side wall <NUM>. B, here shown slightly sloping outwards. <FIG> shows forward port point <NUM>. B, which is the forward termination of port discontinuous transition <NUM>. B or termination point for port keel part, and aft port transition point <NUM>. B, which is the aft termination of port discontinuous transition <NUM>. B (the transition point). From the forward port point <NUM>. B and to the aft port transition point <NUM>. B, lies, among other things, as shown in <FIG> and <FIG>:.

<FIG> shows how these geometric surfaces of the decreasing port keel step <NUM>. B, the outward sloping port keel surface <NUM>. B, the aft part of the port bow step <NUM>. B and the backward tapering port phasing part <NUM>. B are fitted together with relatively sharp angles, which fit well together when making hulls in aluminium, steel or other weldable materials, but can also be cast in carbon, plastic or fiberglass. Such a design as shown in <FIG> and <FIG> will also help to reinforce, stiffen, the hull in the discontinuous transition <NUM>.

<FIG> and <FIG> show an embodiment of frame sections in a port discontinuous transition <NUM>. B, also called the discontinuous transition area, seen from the center line and directly towards the forward part of the port longitudinal keel part <NUM>. The hull is symmetrical and has a corresponding starboard design. The figures show the port discontinuous transition <NUM>. B from an aft port transition point <NUM>. B to a forward port point <NUM>. B and where you have a port longitudinal keel step <NUM>. B on the frame at the aft port transition point <NUM>. B and where you have a bow step <NUM> on the frame at the forward port point <NUM>. In between these points, the forward port point <NUM>. B and to the aft port transition point <NUM>. B, there is a decreasing port keel step <NUM>. B, which extends from the aft port transition point <NUM>. B and straight forward and up outside its aft part of the port bow step <NUM>. B and ends in the forward port point <NUM>. B in the outer bow bearing surface <NUM>. The figures also show how the aft part of the port bow step <NUM>. B has a constant height/draft through the port discontinuous transition <NUM>. B before it is joined with the port longitudinal keel step <NUM>. B in the aft port transition point <NUM>. The figures also show that the port keel line KL. B does not follow the port longitudinal keel step <NUM>. B after the aft port transition point <NUM>. B and that there is a vertical step up to the bow base line BBL from the port keel line KL.

<FIG> shows an embodiment of frame sections in a port discontinuous transition <NUM>. B, also called the discontinuous transition area, seen from above straight down towards the forward part of the port longitudinal keel part <NUM>. The figure shows the frames in the air supported chamber ceiling <NUM> which extend towards the air supported chamber's port side wall <NUM>. B, which is slightly sloping outwards. The figure also shows the outwardly sloping port keel surface <NUM>. B and the backwards tapering port phasing part <NUM>. B, as these geometric parts have a horizontal design. The figure does not show the decreasing port keel step <NUM>. B nor the aft part of the port bow step <NUM>. B, as these geometric parts have a vertical design. The figure only shows the lines of the decreasing port keel step <NUM>. B and the aft part of the port bow step <NUM>. B, which are marked with thick black lines on the figure. It is clear from the Figure a straight decreasing port keel step <NUM>. B until it joins the outer bow bearing surface <NUM> and how the aft part of the port bow step <NUM>. B curves in and transitions to become bow step <NUM> in the V-shaped bow <NUM>.

<FIG> shows an embodiment of the frame sections in the discontinuous transition <NUM>. B in a plan sketch, seen from the center line CL towards the port side, and where a port step profile line <NUM>. B with a port step secant <NUM>. B, which is marked with a highlighted line , extends from an aft step point xB and a forward step point xB + lB, where the aft point xB is defined as the point where the port step profile line coincides with the port keel line KL. B and where the forward point xB + lB is defined as the point where the step profile line crosses the bow baseline BBL. The step profile line is defined as the hull line of the port keel step threshold on the decreasing port keel step <NUM>. B between the points xB and xB + lB.

The figure shows a definition of xy-coordinates, where the y-axis is defined as a function of x and the x-axis is the longitudinal direction of the hull. The average growth rate (here: the rise) between xB and xB + IB can thus be expressed mathematically as: <MAT>.

The derivative of the function f(x), i.e. f'(x), can be expressed as IB goes towards zero, then the secant approaches the tangent, because (xB + IB, f(xB + IB)) gets closer and closer to (xB , f(xB)). The gradient of the tangent becomes the gradient of the secant when lB approaches zero: <MAT>.

The figure shows that the port side riser edge <NUM>. B forms a secant angle αB, which is an acute angle with the port keel line KL. B, where the secant angle αB shows the pitch of the port side riser edge <NUM>. B between the points xB and xB + lB. The port sidestep profile line <NUM>. B can be curved, curved or similar, and need not in itself have a constant pitch between a rear step point xB and a forward step point xB + lB. The port sidestep <NUM>. B can therefore be used to define the relationship between the length and height of the port transverse step <NUM>. B in the form of the secant angle αB.

Further explanation to <FIG> for the discontinuous transition:.

The secant: a straight line which cuts through the profile line in at least two points and which here is delimited in the x direction by a length l, which is the distance between xB and xB + lB.

The rise of the secant may be written as, and is the average growth rate between xB and xB + lB: <MAT>.

The derivative of the function f(x), i.e. f'(x), can be expressed as l approaches zero, then the secant approaches the tangent, because (xB + lB, f(xB + lB)) gets closer and closer to (xB , f(xB)). The gradient of the tangent becomes the gradient of the secant as l approaches zero: <MAT>.

Claim 1:
An air supported vessel comprising the following features,
- a V-shaped hull (<NUM>)
- with a starboard keel part (<NUM>.S) and a port keel part (<NUM>.B), and
- with a V-shaped bow (<NUM>), comprising an outer bow bearing surface (<NUM>),
- where the V-shaped hull (<NUM>) has at least one air supported chamber (<NUM>) in a part of the V-shaped hull's (<NUM>) length below a waterline,
- the at least one air supported chamber (<NUM>) is delimited by an air supported chamber ceiling (<NUM>), air supported chamber starboard and port side walls (<NUM>.S, <NUM>.B) and with at least one aft closing device (<NUM>) with aft threshold (<NUM>) which forms an aft boundary of the at least one air supported chamber (<NUM>) and with at least one air support chamber air intake (<NUM>) which together with the side walls of the at least one air supported chamber in the bow (<NUM>) form a front boundary of the at least one air supported chamber (<NUM>),
wherein the V-shaped bow (<NUM>) further comprises a bow step (<NUM>) with a bow step threshold (<NUM>), which extends from a starboard longitudinal keel step (<NUM>.S) around the V-shaped bow ( <NUM>) to a port longitudinal keel step (<NUM>.B), and forms a lower boundary of the air supported chamber sidewalls in the bow (<NUM>), to reduce air leakage below a bow base line (BBL),
characterised by
- a transverse step at an aft part of the bow base line (BBL), comprising a starboard transverse step (<NUM>.S) and a port transverse step (<NUM>.B), where the starboard keel part (<NUM>.S ) with a starboard keel line (KL.S) and the port keel part (<NUM>.B) a the port keel line (KL.B) have greater draft than the V-shaped bow (<NUM>) with the bow base line (BBL) at the starboard transverse step (<NUM>.S) and the port transverse step (<NUM>.B).