WO2022071813A1

WO2022071813A1 - Apparatus and system for introducing air below a boat hull

Info

Publication number: WO2022071813A1
Application number: PCT/NZ2021/050168
Authority: WO
Inventors: Graham Buchanan CAVE; Ian Kenneth CARTER
Original assignee: Venairjet Systems Limited; Carter, Simon
Priority date: 2020-09-30
Filing date: 2021-09-30
Publication date: 2022-04-07

Abstract

The idea of introducing a layer of air between the hull of a watercraft and the water that it is passing through has been around for some time, but the systems and methods used have not been efficient, or have required additional power sources to operate. The present invention provides an air introduction device that can be made as part of a boat hull, or 5 which can be fitted to a boat hull, and which creates a local venturi effect that draws air from an air source and releases the air behind the device to form a layer of air. The air introduction device has a low profile and is substantially wedge shaped, with a pointed end of the device facing the forward direction, and an air outlet is provided along a wide rear end of the device. 10

Description

Apparatus and System for Introducing Air below a Boat Hull

FIELD OF THE INVENTION

This invention relates to an apparatus and a system for introducing air below a moving boat hull. The apparatus and system can be used on a range of boats, for example, but not limited to, boats with planing hulls such as power boats, launches and motor yachts, and boats with displacement hulls such as sail boats and sailing yachts.

BACKGROUND

It has long been known that the friction between a boat hull and the water can be reduced by introducing air between the boat hull and the water. Air is significantly less dense than water, and in fact, at sea level, water is more than 750 times denser than air. And for this reason it is easier to move a boat hull through air than it is through water.

The most classic example of this is the hovercraft, which floats above the water on a cushion of air. However, hovercraft are notoriously difficult to handle, and require large engines and fans to produce enough airflow to sustain the cushion of air between the craft and the water. In addition, the fans create significant noise on the deck of a hovercraft.

A number of systems have been explored which inject air into the water immediately adjacent the hull of more conventional watercraft. Some of these systems create air pressure using a pump, or from ram air captured in a forward-facing scoop, and they direct the air through manifold systems to an array of injectors or outlets at the exterior of the hull.

Examples of prior art boats and systems incorporating air scoops and using air pressure produced by a ‘ram air’ effect are described in US patent 5,456,201, US 6,250,246 and US2001/0139542. Examples of prior art boats and systems incorporating pumps to produce air pressure are described in US patent 5,456,201.

The use of the venturi effect has also been explored also, where one or more venturi devices are used to draw air from the atmosphere, or a pressure reservoir, and into the water beneath the boat hull. Examples of these are described in US 7,997,221 and US 7,752,986. Some draw water into ducts and then using the venturi effect introduce air into the water which is then released below the water line to produce some level of friction reduction.

The systems that require a compressor are clearly inconvenient because they require a significant amount of additional equipment including an engine and fuel source. This equipment takes up room which is often required for other things within a typical boat hull, adds weight which has a negative effect on the boats’ performance, creates more noise, and creates more maintenance and reliability issues for the boat owner.

The use of ram air requires significant modifications to the hull, or scoops that extend out from, or above the hull. Such modifications are not usually convenient or are unsightly, and in any case, the effectiveness of systems using ram air is highly questionable since it requires very high speeds to produce even small amounts of ram air pressure.

The use of the venturi effect would seem to be the most promising. Some of these systems include internal passageways in which the venturi effect is harnessed. However, systems that require internal passageways for water flows are less convenient, they are more complex and will result in significant efficiency losses.

There is also another venturi system which incorporates relatively long lateral slots in the hull - refer to US 7,752,986. However, these systems can cause significant discontinuities in the structure of the hull. And since many boats have monocoque hulls, or semi-monocoque hulls, the lateral slots in the structure can significantly weaken the structure.

What is needed is a more efficient system that does not introduce large amounts of new equipment, or require major modifications to the hull, or require power to operate, or create significant additional maintenance issues and/or noise.

In this specification unless the contrary is expressly stated, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned.

OBJECT

It is therefore an object of the present invention to provide an apparatus and system for introducing air below a boat hull which will at least go some way towards overcoming one or more of the above-mentioned problems, or at least provide the public with a useful choice.

STATEMENTS OF THE INVENTION

Accordingly, in a first aspect, the invention may broadly be said to consist in an air introduction device for use on a boat hull, the air introduction device having; a body with a forward end and a rear end, a first face which extends from the forward end to the rear end and which is configured to pass through water when in use, an air inlet situated between the forward end and the rear end and which does not pass through the first face, and an air outlet situated at or adjacent the rear end of the body; and the device is formed as a protrusion which extends outwardly from the lines of a hull, or is formed as a discrete part that can be fitted to the exterior of a hull; and the body is configured to produce a venturi effect when passing through water and thereby to cause air to be drawn in through the air inlet and out of the air outlet.

Preferably the device is manufactured as a discrete part and has a second surface that is configured to be adhered to the outer surface of the hull of a boat.

Preferably the device is substantially wedge shaped when viewed looking toward the first face. Preferably the device is widest at its rear end.

Preferably the device is narrowest at its forward end.

Preferably the device has a rounded, or bull nosed, front end.

Preferably the device has a substantially Vee shaped leading edge.

Preferably the device has a substantially straight trailing edge.

Preferably the first face has longitudinal grooves extending substantially from the leading edge of the body to the trailing edge.

Preferably the grooves taper out, or finish before they reach the trailing edge.

Preferably an air passage or wide groove links the air inlet to the air outlet.

Preferably the air passage is a relatively shallow and wide passage which is open to the second face.

Preferably the air outlet is an elongate slot extending along a greater portion of the rear end.

Preferably an inner surface of the air outlet is substantially aligned with a local surface of the hull of a boat when the device is formed as a part of the hull, or is fixed to the hull of a boat.

Preferably the air outlet takes up a greater part of the area of a rear face of the device.

Preferably a transition from the first face to the rear face a substantially sharp transition, that is, a transition having a radius of less than one millimetre.

Preferably a forward end of the air passage communicates with, or is, a hole through the hull of the boat.

Preferably the hole through the hull of the boat is a circular hole. Preferably the thickness of the device, or the distance that the device protrudes from the lines of the hull, is less than a quarter of a width of the device at its widest point.

In a second aspect, the invention may broadly be said to consist in apparatus for introducing air below a boat hull, the apparatus including one or more air introduction devices substantially as specified herein.

In a third aspect, the invention may broadly be said to consist in an air introduction system incorporating at least one apparatus for introducing air below a boat hull substantially as specified herein.

Preferably the air introduction system includes an array of air introduction devices.

Preferably the air introduction system includes one or more manifolds which supply air to the or each air introduction device.

Preferably the or each manifold includes one or more air inlet ports situated above a waterline of the hull.

Preferably the or each manifold is attachable to the hull of a boat.

Preferably the or each manifold is attachable to the hull of a boat using removable fasteners.

Preferably the or each manifold is attachable to an exterior of the hull of a boat.

Preferably the or each manifold that is attachable to an exterior of the hull of a boat has a cross sectional profde which is designed to minimise hydrodynamic resistance when moving through water.

Optionally the or each manifold is attachable to an interior of the hull of a boat.

Preferably the or each manifold that is attachable to an interior of the hull of a boat includes a channel in the form of a top hat section that is fixable to an inside surface of the hull. In a fourth aspect, the invention may broadly be said to consist in a boat incorporating at least one apparatus for introducing air below a boat hull, and/or at least one air introduction system for introducing air below a boat hull, substantially as specified herein.

Preferably the boat includes at least one air reservoir adjacent to the area of the hull of the boat which is on contact with water when the boat is underway or is planing.

Preferably the air reservoir is open to the atmosphere above a waterline of the boat.

Optionally the air reservoir includes an opening to atmosphere that is below the waterline of the boat when the boat is at rest and is above the waterline adjacent to the opening when the boat is underway or planing.

In a fifth aspect, the invention may broadly be said to consist in a kit of parts for forming an apparatus or air introduction system for introducing air below a boat hull substantially as specified herein when assembled, said kit including at least a plurality of air introduction devices.

Preferably the kit includes a suitable adhesive for fixing the air introduction devices to the exterior of a hull of a boat.

Preferably the kit includes one or more manifolds substantially as specified herein.

The invention may also broadly be said to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of the parts, elements or features, and where specific integers are mentioned herein which have known equivalents, such equivalents are incorporated herein as if they were individually set forth.

DESCRIPTION

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: FIGURE 1 is a perspective view of an outside surface of an air introduction device according to the present invention,

FIGURE 2 is a perspective view of an inside surface of the air introduction device,

FIGURE 3 is a plan view of the air introduction device in which cross-sectional planes AA, BB and CC are defined,

FIGURE 4 is the cross-sectional view AA,

FIGURE 5 is the cross-sectional view BB,

FIGURE 6 is the cross-sectional view CC,

FIGURE 7 is a perspective view showing a section of an array of air introduction devices,

FIGURE 8 is a plan view of the section of an array of air introduction devices,

FIGURE 9 is a cross sectional view showing airflow through one of the air introduction devices,

FIGURE 10 is a perspective view of a boat hull fitted with two arrays of the air introduction devices,

FIGURE 11 is a close-up perspective view of the boat hull,

FIGURE 12 is a top plan view of the boat hull showing a manifold system for delivering air to the arrays of air introduction devices,

FIGURE 13 is a cross sectional view showing the manifold system in greater detail, and

FIGURE 14 is a perspective view showing a removable panel which contains one of the arrays of the air introduction devices. With reference to Figures 1 to 14, an air introduction device (11) according to the present invention will now be described. The air introduction device (11) is intended for use with apparatus or systems for introducing air below a boat hull to reduce the friction when a boat hull travels through water, particularly at speed. When a boat is fitted with one or more of the air introduction devices (11), and is travelling through the water, each air introduction device (11) creates a venturi effect which draws air from within the hull, or from an air supply manifold, and out through a passage and into the water below the boat hull.

An array of air introduction devices (11) is used to effectively create a cushion of air under the hull which will significantly reduce the friction between the boat hull and the water, when a boat is travelling through the water, and will reduce the power requirements and fuel bum to achieve the same speed through the water, or will increase the boat’s speed without increasing the power requirements.

With reference to Figure 1 to 6, the details of each individual air introduction device (11) will be described. While it is envisaged that the air introduction devices (11) could be formed integrally when the hull is formed, in this example each air introduction device (11) is formed as a discrete part. Each air introduction device (11) has a body (13) with a forward end (15) and a rear end (17).

The device (11) has a first face (19) which in use is an outer face, and which extends from the forward end (15) to the rear end (17). The first face (19) is generally the lower face when installed and is configured to contact and to pass through water. A second and opposite face, or a mounting face (21), of the device (11) is configured to be fixed to the underside or exterior of a hull of a boat, for example by gluing the second face (21) directly to a prepared section on the hull. Figure 4 shows a layer of adhesive (22) that is used to fasten each air introduction device (11) to the hull, or to a panel that can be fastened to the hull.

The air introduction device (11) has an air inlet (23) situated between the forward end (15) and the rear end (17). The air inlet (23) passes through the second face (21) but not through the first face (19). An air outlet (25) is situated at or adjacent the rear end (17) of the body (13).

The body (13) is configured to produce a venturi effect when passing through water. It is the venturi effect that produces a localised drop in pressure in the water at the rear end (17) of the body (13). And when the speed of the boat is sufficient, the pressure drops to a level that is below the local atmospheric pressure, and for this reason air is then caused to to be drawn into the air inlet (23) and out of the air outlet (25).

It can be seen in the figures that the device (11) is substantially wedge shaped when viewed looking toward the first face (19). The device is widest at its rear end (17) and is narrowest at its forward end (15). The device (11) has a rounded, or bull nosed, front end (15), and has a substantially Vee shaped leading edge (27). The first face (19) culminates in a trailing edge (29) at the rear end of the first face (19).

The first face (19) has longitudinal grooves (31) extending substantially from the leading edges of the body to the trailing edge. The longitudinal grooves (31) are substantially parallel with a longitudinal axis (33) of the device (11). The grooves (31) taper out, or finish, before they reach the trailing edge (29). The termination of the grooves (31) is in the form of a radiused slope (35) extending from a base (37) of the grooves to the trailing edge (29).

The trailing edge (29) is a line connecting the rear end of a crest (39) of each of the grooves (31). The trailing edge (29) is at right angles to the longitudinal axis (33) and is straight where it intersects the first face (19), and is curved at each end where it intersects the leading edges (27).

An air passage (41) or wide groove links the air inlet (23) to the air outlet (25). The air passage (41) is a relatively shallow and wide passage which is open to the second face (21). An inner surface (47) of the air outlet (25) is substantially aligned with a local surface of the hull of a boat when the device is fixed to the hull of a boat.

The air outlet (25) is an elongate slot (43) extending along a greater portion of the width of the rear end (17). The elongate slot (43) is a slot formed where the rear end of the air passage (41) reaches a rear face (45) of the device (11). The rear face (45) is a face that is that is substantially at right angles to the second face (21) and is also at right angles to the longitudinal axis (33). The elongate slot (43) has an upper edge only when the device (11) is fitted to a hull of a boat, and then the lower surface of the hull defines the upper edge of the elongate slot (43). The air outlet (25), or the elongate slot (43), takes up a greater part of the area of the rear face (45).

The elongate slot (43) is considered advantageous since it allows a continuous shallow plume of air to exit each device.

The transition from the first face (19) to the rear face (45) is a substantially sharp transition, that is, a transition having a radius of less than one millimetre. By comparison, the leading edge (27) has a radius in the region of seven to twelve millimetres.

Initial testing indicates that the water does not flow around the sharp transition from the first face (19) to the rear face (45), but rather the entire rear face (45) defines the cross section of a plume of air (46) that trails behind each device.

With reference to Figures 7 to 9 the way in which the individual air introduction devices (11) interact with the hull of a boat is explained in further detail. A forward end of the air passage (41) communicates with a hole (49) through a hull (51) of the boat to which the device (11) is fitted. The hole (49) is a circular hole having a diameter preferably in the region of ten to twenty millimetres. Air is able to flow from within the hull and into the air passage (41) through the hole (49).

Figure 8 is a plan view which shows an example of a flow of water (53) relative to the air introduction devices (11). The forward end (15) of the air introduction devices (11) faces directly into the flow of water (53). Figure 9 is a side elevation which shows schematically how the flow of water (53) passes over each air introduction device (11), creating a low-pressure region or area at the rear end (17) of each one, and how a flow of air (57) is drawn down through each hole (49) and out the air outlet (25) at the rear end (17) of each air introduction device (11). A feature of the device (11) is its thickness, it has a very low profile. The distance that the device (11) protrudes from the lines of the hull, that is its thickness, is ideally in the region of six to eleven millimetres, or about a third to a quarter of the width of the device (11) at its widest point. The width of the device (11) at its widest point corresponds to the length of the rear face (45).

It is also worth noting that the device (11) has a relatively constant thickness over much of the body (13) of the device (11). This feature is helpful in minimising pressure points when getting a boat fitted with the devices onto or off a boat trailer.

With reference to Figures 10 to 14 the location and the layout of the air introduction devices (11) will be explained in greater detail. Figure 10 shows an ideal location for fitting the devices (11) to the underside of a boat hull, and the layout of a suitable array of the devices (11) which spans across the width of the lower surface of the hull.

The devices (11) are ideally fitted in a band or an array (55) that is situated at or near a forward end of the part of the hull that remains underwater when the boat hull is moving at speed or is planing. The entire under surface of the hull behind the front edge of the band (55) remains wetted when the boat is underway or is planing.

While a number of layouts could be used, it is envisaged that a staggered array, as shown in Figures 7 and 8, with the air plume (46) from one device (11) slightly overlapping the air plume from an adjacent device (11) is ideal.

A typical installation or system will include one or more internal air manifolds (61) which supply air from the surrounding atmosphere to each of the air introduction devices (11) via the holes (49) . Figure 13 in particular shows a manifold system (61 ) in which air from an inlet grill (63) on either side of the boat hull (51), and well above the waterline, is supplied via dropper ducts (65) to shallow rectangular cross sectioned ducts (67) which distributes the air to the holes (49) above each of the individual air introduction devices (11). The use of shallow rectangular cross sectioned ducts (67) minimises the space taken up by the manifold system (61) within the hull. In this example there are two shallow rectangular cross sectioned ducts (67), each one being supplied from a dropper duct on its side of the boat hull, and the two ducts (67) are each angled forward as they extend toward the centreline of the hull (51). In this way the ducts (67) are positioned directly above the two arrays of air introduction devices (11) which are similarly angled forward as they extend toward the centreline of the hull (51).

Figure 14 shows that each of the arrays of air introduction devices (11) are in fact fitted to a removable panel (71) which forms a part of the exterior of the hull (51). Each removal panel (71) can be fastened to the hull using screws or another suitable fastening system, and can be removed from time to time for maintenance purposes to allow any fowling that may occur over time to be cleaned out of the air manifolds (61), the holes (49) and the interior of each of the air introduction devices (11).

It is envisaged that the system could be sold as a kit of parts for forming a system for introducing air below a boat hull, for example, the kit could include a number of air introduction devices (11) and a quantity of a suitable adhesive for fixing the air introduction devices to the exterior of a hull of a boat. A layout for an array of the devices could be marked out on the hull, and holes (49) would then be drilled in the hull at the location of each air introduction device (11), prior to gluing the devices (11) to the hull.

VARIATIONS

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.

The example described herein shows the air introduction devices (11) fitted to a planing hull. It is envisaged that similar efficiencies could be gained by applying the devices (11) to a displacement hull.

In the example described herein, the device (11) is in the form of a discrete part that is formed and then fixed to a hull. However, in an alternative embodiment, the device (11) could be formed integrally during the manufacture of the hull and as a protrusion which extends outwardly from the lines of a hull.

As an alternative to the manifold system shown and described herein, it is envisaged that manifolds made up of channels in the form of a top hat section can be fixed to an inside surface of the hull, and can be used to supply air from an inlet port situated above the waterline of the hull to the devices (11).

A further alternative configuration can supply the devices (11) directly from an air reservoir adjacent to the area of the hull of the boat where the devices (11) are fitted. The air reservoir will normally be open to the atmosphere above a waterline of the boat to avoid water flowing back through the devices (11) when the boat is stationary.

However, it is envisaged that the air reservoir could alternatively include an opening that is below the waterline of the boat when the boat is at rest and is above the waterline adjacent to the opening when the boat is underway or is planing. For example, the air reservoir could be open to atmosphere at the stem of the boat, with the opening being below the waterline when the boat is at rest, and with the opening being above the local waterline at the stem of the boat when the boat is underway or is planing.

This configuration (with an opening below the waterline) is considered advantageous in that the air reservoir can fill up with water when the boat is stationary, for improved stability, and yet the reservoir can quickly drain when the boat begins planing, and at that time the reservoir can be filled with air at atmospheric pressure and can directly supply the devices (11) via the holes (49) in the bottom of the hull while the boat is planing.

As a further alternative to internally positioned manifolds, external manifolds could be used. For example, manifolds that are fitted to an exterior of the hull of a boat using removable fasteners. In such a case the manifolds would ideally have a cross sectional profile which is designed to minimise hydrodynamic resistance when moving through water. That is a manifold having a slender ‘D’ shaped profile in which the flat side of the ‘D’ profile is mated against the exterior surface of the hull, and countersunk screws are used to attach the edges of the profile to the hull, by engaging the screws with threaded inserts that are embedded into, or are fitted to, the hull. In the example described herein, the body (13) has a wedge shape, however, it is envisaged that alternative body shapes could be used, for example having curved leading edges similar to the shape or profile of a NACA duct, that is the inlet duct shape designed by the US National Advisory Committee for Aeronautics (NACA) for use on aircrrear fuselage skins for air inlets.

DEFINITIONS

Throughout this specification the word "comprise" and variations of that word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.

ADVANTAGES

Thus, it can be seen that at least the preferred form of the invention provides a device, or apparatus and a system for introducing air below a boat hull which can;

• be incorporated into the design of a hull with minimal effect on the structural integrity of the hull since circular holes cause minimal stress concentrations, or

• be retrofitted onto an existing hull with minimal or zero structural modifications required and with relative ease since the required circular holes in the hull of the boat are easy to form using conventional tooling,

• provide a plume of air under the hull of a boat for the purpose of reducing friction as the hull passes over the water, and

• provide minimal inconvenience to the job of putting a boat onto, or off, a boat trailer.

Claims

1. An air introduction device for use on a boat hull, the air introduction device having;

• a body with a forward end and a rear end,

• a first face which extends from the forward end to the rear end and which is configured to pass through water when in use,

• an air inlet situated between the forward end and the rear end and which does not pass through the first face, and

• an air outlet situated at or adjacent the rear end of the body; and the device is formed as a protrusion which extends outwardly from the lines of a hull, or is formed as a discrete part that can be fitted to the exterior of a hull; and the body is configured to produce a venturi effect when passing through water and thereby to cause air to be drawn in through the air inlet and out of the air outlet.

2. The air introduction device as claimed in claim 1, wherein the device is manufactured as a discrete part and has a second surface that is configured to be adhered to the outer surface of the hull of a boat.

3. The air introduction device as claimed in claim 1 or claim 2, wherein the device is substantially wedge shaped when viewed looking toward the first face.

4. The air introduction device as claimed in any one of claims 1 to 3, wherein the device is widest at its rear end.

5. The air introduction device as claimed in any one of claims 1 to 4, wherein the device is narrowest at its forward end.

6. The air introduction device as claimed in any one of claims 1 to 5, wherein the device has a rounded, or bull nosed, front end. The air introduction device as claimed in any one of claims 1 to 6, wherein the device has a substantially Vee shaped leading edge. The air introduction device as claimed in any one of claims 1 to 7, wherein the device has a substantially straight trailing edge. The air introduction device as claimed in claim 7, wherein the first face has longitudinal grooves extending substantially from the leading edge of the body to the trailing edge. The air introduction device as claimed in claim 9, wherein the grooves taper out, or finish before they reach the trailing edge. The air introduction device as claimed in any one of claims 1 to 10, wherein an air passage or wide groove links the air inlet to the air outlet. The air introduction device as claimed in claim 11, wherein the air passage is a relatively shallow and wide passage which is open to the second face. The air introduction device as claimed in any one of claims 1 to 12, wherein the air outlet is an elongate slot extending along a greater portion of the rear end. The air introduction device as claimed in any one of claims 1 to 13, wherein an inner surface of the air outlet is substantially aligned with a local surface of the hull of a boat when the device is formed as a part of the hull, or is fixed to the hull of a boat. The air introduction device as claimed in any one of claims 1 to 14, wherein the air outlet takes up a greater part of the area of a rear face of the device. The air introduction device as claimed in claim 15, wherein a transition from the first face to the rear face a substantially sharp transition, that is, a transition having a radius of less than one millimetre. - 17 - The air introduction device as claimed in any one of claims 11 to 16, wherein a forward end of the air passage communicates with, or is, a hole through the hull of the boat. The air introduction device as claimed in any one of claims 1 to 17, wherein the thickness of the device, or the distance that the device protrudes from the lines of the hull, is less than a quarter of a width of the device at its widest point. An air introduction system incorporating at least one apparatus for introducing air below a boat hull, wherein the system includes an array of air introduction devices as claimed in any one of claims 1 to 18, and one or more manifolds which supply air to the or each air introduction device . The air introduction system as claimed in claim 19, wherein the or each manifold includes one or more air inlet ports situated above a waterline of the hull.