WO2014199152A2

WO2014199152A2 - Watercraft hull

Info

Publication number: WO2014199152A2
Application number: PCT/GB2014/051794
Authority: WO
Inventors: Nicholas FALLA
Original assignee: Xocoatl Limited
Priority date: 2013-06-11
Filing date: 2014-06-11
Publication date: 2014-12-18
Also published as: GB201310337D0; WO2014199152A3; GB2515031A

Abstract

The present invention relates to watercraft hulls which, in use, are able to expel gas into water surrounding the hull to affect the hull's hydrodynamics. In a first aspect, the invention provides a hull (1), comprising a bow (2) and an elongate projection (3) projecting from the bow, wherein the elongate projection has at least one gas outlet (5) for expelling gas ahead of the bow below the waterline (4) during use. Also provided are vessels incorporating such hulls, moulds for making such hulls, and gas-expelling apparatus.

Description

WATERCRAFT HULL

FIELD OF THE INVENTION

The present invention relates to watercraft hulls, in particular, watercraft hulls that include apparatus to improve the hydrodynamics of the hull. INTRODUCTION

As a watercraft moves through water it is subject to a number of forms of resistance. For example, a moving watercraft experiences boundary layer skin friction, proportional to the area of its hull exposed to the water, and form drag, dependent upon the hull size and shape. The hull form also generates waves of different types. The movement of the watercraft causes formation of a bow wave as it pushes water out of its path. The hull form also creates dispersing and transverse waves dependent upon a large number of variables. Formation of waves requires energy, meaning that any reduction in the size and persistence of such waves generally leads to efficiency improvements.

These, and other, sources of resistance limit the efficiency with which a watercraft is able to move through the water. For motor powered watercraft, increasing resistance means that more fuel is required to reach and maintain a given speed. In addition, increasing resistance may mean that it is necessary to use higher specification equipment (e.g., a higher-power engine) to achieve a desired speed of travel.

In addition to limiting the efficiency of travelling through the water, these sources of resistance generally act to limit the velocity obtainable by a watercraft to the "hull speed". Although not strictly a theoretical "maximum" speed, the hull speed can usually be considered, for practical purposes, to be the maximum speed obtainable by a watercraft, because disproportionately more energy is required to increase the speed of the watercraft as it approaches this speed. In the case of a full-displacement watercraft the hull speed is approximately equal to 1.34 times the square root of the waterline length of the hull in feet.

Semi-planing or planing hulls are able to travel at speeds higher than the hull speed as they lift out of the water at increasing speeds. However, such hull designs are not practical for every type of watercraft, and are inefficient at slow speeds compared to full-displacement watercraft. Traditionally, designers have sought to improve the efficiency and hull speed of full- displacement watercraft by altering the form of the hull and the mass of the watercraft and its cargo. A good example of this is the provision of a bulbous bow - a bulb-shaped protrusion projecting from the bow below the waterline, which counteracts bow wave formation. Such bulbous bows have been shown to improve fuel efficiency by as much as 12% to 15%, and have the bonus effect of providing additional buoyancy which improves the pitching moment to some degree.

However, there remains a need to develop hulls and apparatus to improve the efficiency with which watercraft are able to travel through the water. Given the scale of the shipping industry and the large distances travelled by many vessels, even relatively modest improvements in efficiency (resulting in fuel efficiency) can be very important. In addition, there remains a need to develop hulls that are able to travel at, or above, their traditional hull speed.

SUMMARY OF THE INVENTION

At its most general, the present invention relates to hulls which, in use, are able to expel gas into water surrounding the hull to improve their hydrodynamics. In a first aspect, the present invention provides a hull, comprising a bow and an elongate projection projecting from the bow, wherein the elongate projection has at least one gas outlet for expelling gas ahead of the bow below the waterline during use.

The hull of the present invention allows gas in the form of, for example, bubbles or a gas sheet, to be injected into the water ahead of the hull. This results in a number of advantageous features.

Firstly, adding gas to water ahead of the bow reduces the density of the medium through which the hull is moving. Having a reduced density medium at the front of the hull reduces wave-making resistance, because the hull has to push aside less dense water as it travels forward. In addition, decreasing the density of the medium at the front of the hull compared to the back of the hull produces an area of low pressure which has the effect of "sucking" the hull forward.

Secondly, the gas-enriched water will decrease the skin friction experienced by at least a portion of the hull, "lubricating" portions of the hull in contact with water by reducing the viscosity of the boundary layer. Thirdly, the provision of the elongate projection has several positive impacts on bow wave formation. The decreased density of the medium at the bow reduces the amount of water driven up in the bow wave which, in combination with gas leaving the water at the crest of the bow wave, reduces the bow wave and resultant wake. In addition, the elongate projection, and gas expelled from the elongate projection, will create a bow wave near the leading point of the elongate projection, which allows the overall bow wave to be sculpted and manipulated. This bow wave originating from the elongate projection can be used to destructively interfere with bow waves generated by other parts of the hull.

Fourthly, the elongate projection increases the length of the hull which should increase the effective hull speed, by increasing the effective waterline length of the hull. The increased length of the hull should also lead to an improvement in the pitching moment of the hull.

Taken together, these beneficial effects should result in at least one of the following advantages: (1) improved fuel efficiency, (2) increased hull speed, and (3) an improved pitching moment. The beneficial effects are more than just the sum of effects attributable to the elongate projection and effects attributable to gas delivery -the elongate projection and the gas delivery act synergistically to produce the above advantages.

The skilled reader will understand that terms used throughout this application are intended to be in-keeping with conventional nautical terminology, unless specified otherwise.

For example, the terms "bow" and "stern" are used in their conventional sense, to refer to the front and rear of the hull respectively. "Waterline" is also used in its conventional sense to mean the level on the hull which meets the surface of water, in use, and "prow" is used to refer to the part of the bow above the waterline. Relative directional terms such as "front", "back", "forward", "backward", "ahead", "behind", "higher", "lower", "topside", "underside", "above", and "below" etc. are used in the context of a hull as it would be when afloat, with the bow being considered forward of the stern.

The elongate projection of the present invention projects forward from (i.e., ahead of) the bow of the hull. That is, the elongate projection is angled relative to the vertical axis of the hull, such that the elongate projection projects forward of the bow of the hull. The elongate projection may be horizontal, or substantially horizontal. That is, the elongate projection may be parallel to, or substantially parallel to, the plane defined by the waterline of the hull.

Differently stated, the elongate projection may be oriented parallel to, approximately parallel to, or at a shallow angle (e.g., less than 10°, less than 20°, less than 30°, or less than 45°) relative to, the longitudinal axis of the hull - the longitudinal axis being an imaginary line running from the centre of the stern to the centre of the bow, parallel to the waterline.

Preferably, the elongate projection is oriented parallel to the longitudinal axis of the hull (i.e., perpendicular to the vertical axis of the hull). Orienting the elongate projection parallel to the longitudinal axis of the hull allows for the projection to be made streamlined, helping to minimise drag.

In embodiments the elongate projection may be the forward-most part of the hull. In other words, the elongate projection may extend further forward than the forward-most part of the prow of the hull (ignoring attachments such as bowsprits). Preferably, the elongate projection extends significantly further forward than the forward-most part of the prow of the hull. For example, the elongate projection may have at least 30% of its length ahead of the forward-most part of the prow, at least 50% of its length ahead of the forward-most part of the prow, at least 70% of its length ahead of the forward-most part of the prow, or at least 80% of its length ahead of the forward-most part of the prow. Preferably, the elongate projection has at least 50% of its length ahead of the forward-most part of the prow.

In embodiments of the present invention, the projection is "elongate". That is to say, the length of the projection is greater than its width. Preferably the length of the projection is significantly greater than its width. The elongate projection may have a length to width ratio of least 2:1 , at least 3: 1 , at least 4:1 , at least 5: 1 , at least 6:1 , at least 7: 1 , at least 10:1 , or at least 15:1.

For the purposes of measuring the dimensions of the elongate projection, the "width" is taken to be its maximum thickness, and the "length" is taken to be the distance from the base of the projection to the end of the projection - its "tip". In embodiments where the elongate projection is separate apparatus, the "base" is the part of the elongate projection which is attached to or attachable to the bow. In embodiments where the elongate projection is integrally formed with the hull, the "base" is considered to be the part of the bow which starts to project forward to form the elongate projection. For example, if the elongate projection extends from a bow which sweeps back towards the stern, the base of the elongate projection is taken to be the narrowest cross-section of the bow which includes the location on the hull, nearest to and below the waterline, where the bow starts to project forward to form the elongate projection.

Advantageously, an elongate projection has a streamlined shape, and allows

commencement of the bow wave to be shifted forward of, and gas to be delivered ahead of, the bow, whilst minimising the impact of skin friction from the projection.

Suitably, the elongate projection is a pipe. Preferably, the pipe has a hollow interior in fluid communication with the at least one gas outlet. Preferably, the elongate projection tapers towards the end of the projection (the "tip" of the projection). At least the final 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the length of the elongate projection may be tapered towards the tip (i.e. narrow towards the tip). Preferably at least the final 40%, most preferably at least the final 50% of the elongate projection is tapered towards the tip. Most preferably, the elongate projection tapers along the majority of its length towards its tip, e.g., the projection is an elongate cone. A tapered elongate projection is particularly well streamlined, helping to minimise drag. In addition, a tapered elongate projection is structurally robust, and has a minimal wetted surface area in use, which minimises resistance caused by skin friction. Where the elongate projection tapers towards its tip the elongate projection can be described as a "lance". Preferably such a lance tapers for the majority of its length. A lance shape which tapers for the majority of its length provides a particularly robust structure, with good streamlining and minimal wetted surface area.

In preferred embodiments the elongate projection includes a bulbous portion and a relatively narrower portion, wherein the bulbous portion is closer to the bow than the narrower portion. Advantageously, this allows the hull to benefit from the bow wave disruptive effect of a bulbous bow, coupled with the above-described advantages of the elongate projection. The ratio of the length of the bulbous portion to the length of the narrower portion may be, for example, 1 :1 , 1 :2, 1 :3, 1 :4, 1 :5, 1 :7, or 1 :10. In embodiments of the present invention, at least a portion of the elongate projection is below the waterline of the hull, to permit gas to be expelled into the water in use. In other words, the elongate projection is at least partially submerged, in use. For example, at least 10%, at least 25%, at least 50%, at least 70%, at least 80%, at least 90% or approximately 100% of the elongate projection may be below the waterline of the hull. Preferably, at least 80%, more preferably at least 90%, of the elongate projection is below the waterline of the hull.

In embodiments of the present invention, the length of the elongate projection may be adjustable. For example, the elongate projection may be retractable/extendable. In other words, the elongate projection may be movable to alter the length that it projects ahead of the bow. In some embodiments the adjustable elongate projection is telescopic. In some embodiments, the adjustable elongate projection is retractable into the hull.

Being able to adjust the length of the elongate projection has a number of advantages. Firstly, the adjustable elongate projection can be retracted or extended to suit conditions. For example, the length of the adjustable projection may be adjusted according to the speed of the watercraft during use, e.g., increasing length with increasing speed. Additionally or alternatively, the length may be adjusted to take account of currents, wave conditions, and leeway. Secondly, the adjustable elongate projection can be retracted to prevent damage. For example, when mooring up the projection can be retracted to a stowed configuration to prevent damage to the projection, the hull in general, and/or the mooring.

The gas outlet of the present invention expels gas through an opening.

In one embodiment of the present invention, the elongate projection has only one gas outlet. This gas outlet may be positioned at, for example, the tip of the elongate projection.

In preferred embodiments, the elongate projection has a plurality of gas outlets for expelling gas ahead of the bow below the waterline during use. Advantageously, a plurality of gas outlets allows excellent control over the volume of gas delivered by the elongate projection.

For example, it is easier to provide a large volume of gas from a plurality of gas outlets compared to a single gas outlet. To increase the volume of gas delivered from a single outlet, it is necessary to increase the gas pressure in the system, or to increase the size of the outlet. Increasing the pressure in the system will increase the velocity of bubbles expelled from the gas outlet. Increasing the size of the gas outlet can have an adverse effect on the streamlining of the elongate projection and will affect the shape of expelled gas, e.g., the size of gas bubbles. However, a plurality of smaller gas outlets is likely to be more streamlined than a single, larger gas outlet delivering an equivalent amount of gas. In addition, a plurality of gas outlets means that a larger volume of gas can be delivered without compromising the shape of the expelled gas, e.g., the size of gas bubbles.

In addition, providing a plurality of gas outlets allows the distribution of expelled gas to be controlled, e.g., shaped. The flow from the gas outlets can be used to "sculpt" a low pressure region ahead of the bow, and deliver air precisely to the bow. In particular, the combination of a plurality of gas outlets on the elongate projection of the present invention means that gas can be delivered precisely, e.g., to a relatively small cross-section of the bow. In other words, the gas can be focussed to a specific part of the hull as it moves forward.

In embodiments in which the elongate projection has a plurality of gas outlets, the gas outlets may be distributed along the length of the elongate projection.

Advantageously, as mentioned above, distributing a plurality of gas outlets along the length of the elongate projection provides excellent control and shaping over the distribution of the expelled gas. The plurality of gas outlets may be evenly spaced along the length of the elongate projection. Alternatively, the plurality of gas outlets may be distributed along specific sections of the length of the elongate projection only. For example, the gas outlets may be distributed along the first 50% of the length of the elongate projection only (i.e., positioned towards the bow, away from the tip), or along the final 50% of the length of the elongate projection only (i.e., positioned towards the tip).

Preferably, the elongate projection is the forward-most part of the hull, and at least one of the plurality of gas outlets is positioned further forward than the forward-most part of the prow of the hull. For example, in such embodiments at least one of the plurality of gas outlets may be positioned at the tip of the elongate projection. Most preferably, more than one of the plurality of gas outlets is positioned further forward than the forward-most part of the prow of the hull.

In embodiments in which the elongate projection has a plurality of gas outlets, the plurality of gas outlets may be distributed around the perimeter of the elongate projection. In this instance the plurality of gas outlets being distributed "around the perimeter" means that the gas outlets "encircle" the elongate projection. That is, they are positioned about the width of the elongate projection, e.g., on the topside, the sides, and the underside of the elongate projection.

The plurality of gas outlets may be evenly spaced around the perimeter of the elongate projection. Alternatively, the plurality of gas outlets may be distributed on specific sections of the perimeter of the elongate projection only. For example, the plurality of gas outlets may be distributed on the lower half of the elongate projection only, or the upper half of the elongate projection only. Alternatively, the plurality of gas outlets may be on the underside of the elongate projection only, on one or both sides of the elongate projection only, or on the topside of the elongate projection only. The positioning of the gas outlets around the perimeter of the elongate projection allows excellent control over the distribution of gas expelled from the elongate projection.

In preferred embodiments, the plurality of gas outlets is distributed along the length and around the perimeter of the elongate projection. The plurality of gas outlets may form a regular array on the elongate projection. Such an array may take the form of, for example, a square lattice, a rectangular lattice, or a hexagonal lattice. In embodiments having a plurality of gas outlets, the gas outlet density (i.e., the number of gas outlets per unit surface area of the elongate projection) may be the same along the length of the elongate projection. In other embodiments, the gas outlet density may vary along the length of the elongate projection. In some embodiments, the elongate projection has a plurality of gas outlets, wherein each of the gas outlets has an opening, and each of the openings is the same size (e.g., the same diameter opening).

However, it is preferred that the elongate projection has a plurality of gas outlets having different size openings, i.e., gas outlets having one size of opening and gas outlets having a relatively larger size opening. The size of a gas outlet's opening determines, amongst other things, the shape and velocity of gas expelled from the opening. Thus, providing a plurality of gas outlets with different size openings allows the distribution of expelled gas to be shaped and controlled.

In particular, where gas is delivered in the form of bubbles, providing a plurality of gas outlets with different size openings allows excellent control over the size of bubbles expelled from the elongate projection. The size of a bubble will determine, amongst other things the velocity with which the bubble rises. In addition, the size of a bubble will increase as it rises in the water. Thus, providing a plurality of gas outlets having different size openings provides good control over bubble size, and allows the development of bubble size with time to be taken into account.

The gas outlets having larger openings may be interspersed with gas outlets having smaller openings. For example, gas outlets with larger openings and gas outlets with smaller openings may alternate along the length and/or around the perimeter of the elongate projection. Alternatively, the gas outlets having different size openings may be positioned on different sections of the elongate projection. For example, gas outlets with larger openings may be positioned on the first 50% of the length of the elongate projection (i.e., positioned towards the bow, away from the tip) and smaller gas outlets on the final 50% of the length of the elongate projection only (i.e., positioned towards the tip), or vice versa. In some

embodiments, the size of the gas outlets may decrease with distance from the tip. In other embodiments, the size of the gas outlets may increase with distance from the tip.

The at least one gas outlet may be, for example, a pore/hole. However, in preferred embodiments, the at least one gas outlet is a nozzle. In embodiments having a plurality of gas outlets, the gas outlets may comprise nozzles in conjunction with some other form of gas outlet, such as a pore. However, it is preferred that each gas outlet of the plurality of gas outlets is a nozzle.

By "nozzle" we mean a gas outlet, having a spout and an opening, which can be used to control the flow of gas. Advantageously, a nozzle can be used to control the flow

characteristics of gas expelled from the elongate projection. For example, the nozzle's spout can be angled so that gas is expelled from the elongate projection at a specific angle, advantageously allowing greater control over the distribution of gas expelled from the elongate projection. Preferably, the hull includes a valve to control the flow of gas to at least one gas outlet. The valve allows adjustment of the flow of gas to the at least one gas outlet. Suitably, the valve is adjustable between an open configuration, in which gas can flow to the at least one gas outlet, and a closed configuration, in which gas cannot flow to the at least one gas outlet.

Being able to open and close the valve to control the supply of gas to at least one gas outlet has a number of advantages. For example, the valve can be closed when gas is not being supplied to the at least one gas outlet, preventing water from entering the hull and/or gas supply. Additionally or alternatively, a controller (e.g., a person or a computer) can choose when to open the valve to start the expulsion of gas from the at least one gas outlet. For example, the controller may choose for gas to be expelled from the at least one gas outlet under certain conditions only, e.g., when the hull reaches a certain speed.

Preferably, the valve can be partially opened. Such a valve may be continuously adjustable from its closed to its open configuration. Alternatively, the valve may be adjustable between the closed configuration, one or more discrete partially opened configurations, and the open configuration. A valve which is switchable between a closed configuration, a partially opened configuration, and an open configuration allows excellent control over the flow of gas to the gas outlets. For example, the configuration of the valve can be adjusted dependent on the conditions, such as the speed of the hull. For example, the amount that the valve is opened may increase with the speed of the hull. In embodiments where there is a plurality of gas outlets, there may be a valve to control the flow of gas to all of the gas outlets. Additionally or alternatively, there may be a valve to control the flow of gas to a subset of the gas outlets. For example, in embodiments having different size gas outlets, the subsets may correspond to gas outlets of different sizes e.g., a first valve controlling flow to gas outlets of one size and a second valve controlling flow to gas outlets of another size.

In embodiments where the gas outlets are distributed along the length of the elongate projection, the subsets may correspond to gas outlets at different lengths along the elongate projection. For example, there may be a first valve controlling flow to gas outlets along the first 50% of the length of the elongate projection, and a second valve controlling flow to gas outlets along the final 50% of the elongate projection.

In embodiments where the gas outlets are distributed around the perimeter of the elongate projection, the subsets may correspond to gas outlets at different parts of the perimeter. For example, there may be a first valve controlling flow to gas outlets on the upper half of the elongate projection, and a second valve controlling flow to gas outlets on the lower half of the elongate projection. Alternatively, there may be separate valves controlling flow to gas outlets on the topside, and/or the sides and/or the underside of the elongate projection. Advantageously, having valves associated with all, or a subset, of the gas outlets provides excellent control over the distribution of gas expelled from the elongate projection. This is especially the case when the valves are adjustable between a closed configuration, a partially opened configuration, and an open configuration.

In one embodiment the hull comprises a plurality of gas outlets, each of which has a valve to control the flow of gas, i.e., one valve per gas outlet.

Traditional boat design is based upon a simple mandate, and does not offer many dynamic solutions to cope with differing operating speeds, draughts, environmental conditions and other factors (for example, depth of water). By controlling gas being expelled from an elongate projection, by using a valve to control the flow of gas to at least one gas outlet (which valve can adjust the size of the gas outlet, and the volume or velocity of flow through the gas outlet), it is possible to provide a dynamic solution to optimise the size and shape of the bow wave created by the hull (particularly in embodiments where there is a plurality of gas outlets controlled by one or more valves). This means that, in use, the bow wave can be adapted to suit external conditions which the vessel is encountering. In use, gas expelled from the gas outlet of the elongate projection is provided with gas from a gas source.

In one embodiment, the gas source is a stored gas source. The stored gas source may be a container containing a gas, e.g., a gas cylinder. Alternatively, the stored gas source may be a container containing a liquid or a solid. The liquid may generate gas by vaporisation, or through a chemical reaction. Similarly, the solid may generate gas by sublimation, by melting followed by vaporisation, or by a chemical reaction.

In preferred embodiments, the gas source is atmospheric gas. In some embodiments atmospheric gas is captured and stored for use. However, in preferred embodiments the atmospheric gas is taken from the atmosphere as required, without being stored.

In a preferred embodiment, the gas is air. The use of air has a number of advantages over other gases. For example, air has a very low density compared to water, is freely and plentifully available, is easy to handle, and is non-polluting. In some embodiments gas is generated from the gas source at pressure, and thus may not require pumping. However, it is preferred that gas from the gas source is pumped to the at least one gas outlet by a pump.

In a preferred embodiment atmospheric air is pumped directly to the at least one gas outlet by a pump. Advantageously, this method of delivering air to the at least one gas outlet does not require storage facilities, which would add to the weight of a watercraft incorporating a hull of the present invention.

In use, the gas expelled from the at least one gas outlet may be a mixture of gas and liquid, e.g., gas and water, such as air and water. For example, the gas source may be a mixture of gas and liquid, or gas from a gas source may be mixed with a liquid (e.g., ambient water) before being expelled from the at least one gas outlet.

The gas outlet of the elongate projection and gas source are in fluid communication with one another. The skilled person will understand ways of delivering gas from the gas source to the gas outlet, such as conventional tubing.

The elongate projection may be an integral part of the bow. Alternatively, the elongate projection may be separate apparatus which is attached to the hull (e.g., retrofitted to the hull).

When the elongate projection is separate apparatus attached to the hull, the elongate projection has an attachment portion which is attached to the hull. The attachment portion may be, for example, a bracket or plate attached to the bow by, for example, welding, rivets, bolts, screws, glue, or resin.

The hull may have one or more sponsons (e.g., a stabilising projection from the side of the hull). Advantageously, providing one or more sponsons compensates for loss of buoyancy which may result from providing gas to the bottom of the boat, and thus gives additional stability. In embodiments where the hull has one or more sponsons, it is preferred that the hull is a cathedral hull - a V-bottom hull with sponsons either side of the "V".

Advantageously, such a hull shape is particularly buoyant. The full length of the hull, measured parallel to the waterline, is known as the length overall (LOA). The lower limit of the length overall (LOA) for hulls of the present invention may be, for example, 2 metres, 3 metres, 4 metres, 5 metres, 6 metres, 7 metres, 8 metres, 9 metres, 10 metres, 12 metres, 15 metres, 20 metres, 25 metres, 30 metres, 50 metres, 75 metres, 100 metres, or 200 metres. The upper limit of the length overall for hulls of the present invention is not particularly limited but may be, for example, 10 metres, 20 metres, 25 metres, 30 metres, 50 metres, 75 metres, 100 metres, 200 metres, 300 metres, 400 metres, or 500 metres.

It will be appreciated that the lower and upper limits for the release rate can be combined together to form ranges, such as 2 metres to 20 metres and 50 metres to 500 metres, and the present invention is intended to cover all such combinations.

In a second aspect, the present invention provides a watercraft comprising a hull of the first aspect.

By "watercraft" we mean a vessel which travels through the water - a marine vessel. For example, the watercraft may be a boat, such as a motor boat or a sailing boat, or a ship, such as a tanker, a container ship or an aircraft carrier.

Preferably the watercraft is powered by a propeller assembly, and the propeller of the propeller assembly is positioned further below the waterline of the hull than the or each gas outlet. In other words, the location of the part of the propeller nearest to the waterline is lower than the or each gas outlet. Positioning the propeller below the or each gas outlet means that the propeller operates in deeper, denser water, away from the gas-enriched water created by the gas outlets. This means that the gas-enriched water does not cause a reduction in the power provided by the propeller assembly.

In a third aspect, the present invention provides a mould for forming the hull of the first aspect. The mould can be used to create a hull of the first aspect out of, for example, fibreglass.

In a fourth aspect, the present invention provides apparatus for expelling gas ahead of the bow of a hull below the waterline, comprising an elongate member having an attachment portion, for attaching to the bow of a hull, wherein the elongate member has at least one gas outlet for positioning ahead of the bow of the hull.

The elongate projection may have any of the optional and preferred features mentioned above. In a fifth aspect, the present invention provides a mould for forming the apparatus of the fourth aspect. The mould can be used to create apparatus of the fourth aspect out of, for example, fibreglass.

In a sixth aspect, the present invention provides a kit of parts comprising apparatus of the fourth aspect and attachment means, for attaching the attachment portion of the apparatus to a hull. For example, the attachment means may be rivets, or bolts.

In a seventh aspect, the present invention provides a hull comprising a bow, the hull having at least one gas outlet for expelling gas ahead of the bow below the waterline during use, and a propeller assembly attachment point, wherein the propeller assembly attachment point is configured to attach to a propeller assembly so that the propeller of the propeller assembly is further below the waterline of the hull than the or each gas outlet. The propeller assembly attachment point may be, for example, a bracket or plate.

Providing gas from one or more gas outlets decreases skin friction on the hull in use, and thus "lubricates" the bottom of the hull. However, aerating the water leads to a decrease in the density of the medium through which the hull is travelling, which can reduce the power provided by the propeller assembly. Positioning the propeller of the propeller assembly below each gas outlet means that the propeller operates in deeper, denser water, away from the gas-enriched water created by the gas outlets. This means that the gas-enriched water does not cause a reduction in the power provided by the propeller assembly.

The gas outlet may have the optional or preferred features described above for the first aspect of the present invention.

In an eighth aspect, the present invention provides a watercraft comprising a hull of the sixth aspect and a propeller assembly attached to the propeller assembly attachment point.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a side view of a prior art hull with a bulbous bow; Figure 2 is a side view of a hull of the present invention, having an air-expelling lance; Figure 3 is a top view of the hull of Figure 2;

Figure 4 is a side view of the hull of Figures 2 and 3, showing the air-expelling lance in use as the hull moves forward through the water; Figure 5 is a side view of a hull of the present invention, in which the air-expelling lance is riveted to the bow of the hull;

Figure 6 is a side view of a hull of the present invention, in which the air-expelling lance has a bulbous portion close to the bow of the hull;

Figure 7 is a top view of the hull of Figure 6; Figure 8 is a close-up side view of an air-expelling lance of the present invention, showing how the width and length of the lance are determined.

Figures 9 and 10 are close-up side views of an air-expelling lance of the present invention, having a plurality of nozzles.

Figure 11 shows a side view of a vessel according to the eighth aspect of the present invention, incorporating a hull of the eighth aspect of the present invention.

DETAILED DESCRIPTION

Figure 1 shows a prior art hull 101 with a bulbous bow. The bow 102 of the hull has a bulbous portion 103 which sits below the waterline 104 and disrupts formation of the bow wave as the hull 101 travels through the water. This bow wave disruption causes an improvement in fuel efficiency.

Figures 2 and 3 show a hull 1 according to the present invention. The hull 1 has a bow 2 with a lance 3, submerged below the waterline 4, projecting forward from the bow and extending beyond the prow of the hull 1. The lance 3 continuously tapers towards its tip, to give good streamlining as the hull 1 travels forward through the water. The lance 3 is oriented at an angle A relative to the vertical axis Z of the hull, and adopts a relatively shallow angle relative to the longitudinal axis X.

In use, atmospheric air is pumped through a pipe (not shown) in the lance 3 and is expelled, in the form of bubbles, into the water surrounding the lance through a nozzle 5 positioned at the tip of the lance 3. The nozzle 5 has an adjustable valve (not shown) that can be used to shut the nozzle 5 and, more generally, to alter the flow rate of air through nozzle 5. As shown in Figure 4, as the hull 1 moves forward through the water the lance 3 causes a bow wave 6 to form forward of the prow, starting near to the tip of the lance 3.

Commencement of the bow wave 6 forward of the hull 1 effectively increases the waterline length of the hull 1 , which acts to increase the hull speed. The bow wave 6 formed by the lance 3 also interferes with bow wave formation at the prow of the hull 1 acting to decrease the overall height of the bow wave. In addition, bubbles 7 are pumped out of nozzle 5 which decreases the amount of water in the bow wave 6, and hence the bow wave's height. The bubbles 7 delivered from the lance 3 decrease the pressure in front of the hull 1 , leading to the hull being "sucked" forward. In addition, the bubbles 7 travel over the submerged hull, and act to decrease skin friction. Taken together, these effects lead to a reduction in resistance on the hull 1 , increasing the efficiency of travel, and resulting in an increased hull speed.

In Figures 2 to 4 the hull is made of fibreglass, and the lance 3 is integrally formed with the bow 2. Figure 5 shows a hull 21 similar to that in Figures 2 to 4, but in this case the lance 23 is a separate apparatus, having a flange 24 which is riveted to the bow 22.

Figures 6 and 7 show another embodiment of a hull 31 of the present invention. In this embodiment, the lance has a bulbous portion 33 followed by a narrower, tapered portion 34, with the bulbous portion 34 being closer to the bow 32. The bulbous portion 33, coupled with the narrower portion 34 help to disrupt bow wave formation, leading to improved efficiency. As in the embodiments described above, the lance has a nozzle 35 at its tip, for delivering air to the surrounding water.

Figure 8 shows the measurement of the length L and width W of a lance 43 according to the present invention which is integrally formed with the bow 42 of a hull. The length L is measured from the base of the lance 43 to its tip. In this case, the base is taken to be the smallest cross-section which includes the point 44 of the hull, nearest to and below the waterline 45, where the bow 42 starts to project forward to form the lance 43. In this instance, the width W is determined at the base of the lance 43, because the continuous taper of the lance 43 along its length means that the base is also the widest part of the lance 43. In this case, the ratio of the length of the lance 43 to its width is around 7:1. Figure 9 shows a close-up side view of a lance 53 according to the present invention. The lance 53 has a plurality of nozzles 55 evenly spaced along its length and spaced around its perimeter. In addition, the lance 53 has a hole 56 at its tip, through which air can also be expelled. Each nozzle 55 and the hole 56 are independently controlled by separate valves (not shown), meaning that the flow rate from each of the nozzles 55 and the hole 56 can be independently adjusted. This provides excellent control over the distribution of bubbles delivered from the lance 53. For example, the valves can be adjusted so that more air is delivered from the lower half of the lance 53 than the upper half of the lance 53.

Figure 10 is another close-up side view of a lance 63, which includes small nozzles 65 interspersed with larger nozzles 66, coupled with a hole 67 at the tip of the lance. The larger nozzles 66 only extend along the first half of the lance 63. In this case the lance 63 includes three valves (not shown) - a first valve controlling air flow to the small nozzles 65, a second valve controlling air flow to the larger nozzles 66, and a third valve controlling air flow to the hole 67. Figure 11 shows a vessel 71 according to the eighth aspect of the present invention. The vessel 71 includes nozzles 75 positioned in the hull of the bow 72 below the waterline 74, which expel air bubbles as the vessel moves through the water. Power is provided to the vessel 71 by a propeller 76, which is positioned further below the waterline 74 than the lowest of the nozzles 75. Air delivered from the nozzles 75 reduces skin friction on the submerged surface of the hull, but does not reach the propeller due to its deeper positioning in the water.

Claims

CLAIMS:

I . A hull, comprising a bow and an elongate projection projecting from the bow, wherein the elongate projection has at least one gas outlet for expelling gas ahead of the bow below the waterline during use.

2. A hull according to claim 1 , wherein the elongate projection projects forward from the bow.

3. A hull according to claim 2, wherein the elongate projection is at an angle of less than 30° relative to the longitudinal axis of the hull.

4. A hull according to claim 3, wherein the elongate projection is parallel to the longitudinal axis of the hull.

5. A hull according to any one of claims 1 to 4, wherein the elongate projection is the forward-most part of the hull.

6. A hull according to claim 5, wherein the elongate projection has at least 50% of its length ahead of the forward-most part of the prow.

7. A hull according to any one of claims 1 to 6, wherein the elongate projection has a length to width ratio of at least 3:1.

8. A hull according to any one of claims 1 to 7, wherein the elongate projection has a length to width ratio of at least 5:1.

9. A hull according to any one of the preceding claims, wherein at least the final 40% of the elongate projection tapers towards the tip of the elongate projection.

10. A hull according to claim 9, wherein the elongate projection is a lance.

I I . A hull according to any one of the preceding claims, wherein the elongate projection includes a bulbous portion and relatively narrower portion, wherein the bulbous portion is closer to the bow than the narrower portion.

12. A hull according to claim 11 , wherein the ratio of the length of the bulbous portion to the length of the narrower portion is 1 :2.

13. A hull according to claim 11 , wherein the ratio of the length of the bulbous portion to the length of the narrower portion is 1 :3.

14. A hull according to claim 11 , wherein the ratio of the length of the bulbous portion to the length of the narrower portion is 1 :5.

15. A hull according to any one of claims 1 to 14 wherein at least 50% of the elongate projection is below the waterline of the hull.

16. A hull according to any one of claims 1 to 14, wherein at least 80% of the elongate projection is below the waterline of the hull.

17. A hull according to any one of claims 1 to 14, wherein at least 90% of the elongate projection is below the waterline of the hull.

18. A hull according to any one of the preceding claims, wherein the elongate projection is retractable.

19. A hull according to claim 18, wherein the elongate projection is telescopic.

20. A hull according to any one of the preceding claims, wherein the elongate projection has a plurality of gas outlets for expelling gas ahead of the bow below the waterline during use.

21. A hull according to claim 20, wherein the gas outlets are distributed along the length of the elongate projection.

22. A hull according to claim 20, wherein the elongate projection is the forward-most part of the hull, and at least one of the plurality of gas outlets is positioned further forward than the forward-most part of the prow of the hull.

23. A hull according to claim 22, wherein more than one of the plurality of gas outlets is positioned further forward than the forward-most part of the prow of the hull.

24. A hull according to any one of claims claim 20 to 23, wherein the gas outlets are distributed around the perimeter of the elongate projection.

25. A hull according to claim 24, wherein the gas outlets are distributed along the length and around the perimeter of the elongate projection.

26. A hull according to any one of claims 20 to 25, wherein each of the gas outlets has an opening, and each of the openings is the same size.

27. A hull according to any one of claims 20 to 25, wherein the plurality of gas outlets comprises gas outlets having a relatively larger opening and gas outlets having a relatively smaller opening.

28. A hull according to claim 27, wherein the gas outlets having larger openings are interspersed with the gas outlets having smaller openings.

29. A hull according to claim 27, wherein the gas outlets having larger openings are positioned on different sections of the elongate projection.

30. A hull according to any one of the preceding claims wherein at least one gas outlet is a nozzle.

31. A hull according to any one of the preceding claims, comprising a valve to control the flow of gas to at least one gas outlet.

32. A hull according to any one of the preceding claims, wherein the hull comprises a plurality of gas outlets and a valve that controls the flow of gas to all of the gas outlets.

33. A hull according to any one of the preceding claims, wherein the hull comprises a plurality of gas outlets and a valve that controls the flow of gas to a subset of the gas outlets.

34. A hull according to any one of the preceding claims, wherein the hull comprises a plurality of gas outlets, each of which has a valve to control the flow of gas.

35. A hull according to any one of claims 31 to 34, wherein the valve has an open configuration and a closed configuration.

36. A hull according to claim 35, wherein the valve can be partially opened.

37. A hull according to any one of the preceding claims, comprising a stored gas source.

38. A hull according to any one of the preceding claims, comprising a pump to supply gas to the at least one gas outlet.

39. A hull according to any one of the preceding claims, wherein the elongate projection is an integral part of the bow.

40. A hull according to any one of claims 1 to 39, wherein the elongate projection is a separate apparatus attached to the hull.

41. A hull according to any one of the preceding claims, comprising one or more sponsons.

42. A hull according to claim 41 , wherein the hull is a cathedral hull.

43. A hull substantially as described herein with reference to Figures 2 to 10.

44. A vessel comprising a hull of any one of claims 1 to 43.

45. A vessel according to claim 44, comprising a propeller assembly, wherein the propeller of the propeller assembly is positioned further below the waterline of the hull than the or each gas outlet.

46. A mould for forming the hull of claim 39.

47. Apparatus for expelling gas ahead of the bow of a hull below the waterline, comprising an elongate member having an attachment portion, for attaching to the bow of a hull, wherein the elongate member has at least one gas outlet for positioning ahead of the bow of the hull.

48. Apparatus for expelling gas ahead of the bow of a hull below the waterline, substantially as described herein with reference to Figures 2 to 10.

49. A mould for forming the apparatus of claim 47 or 48.

50. A kit of parts comprising the apparatus of claim 47 or 48 and attachment means, for attaching the attachment portion of the apparatus to a hull.

51. A hull comprising a bow, the hull having at least one gas outlet for expelling gas ahead of the bow below the waterline during use, and a propeller assembly attachment point, wherein the propeller assembly attachment point is configured to attach to a propeller assembly so that the propeller of the propeller assembly is further below the waterline of the hull than each gas outlet.

52. A hull substantially as described herein with reference to Figure 11.

53. A vessel comprising a hull of claim 51 or 52 and a propeller assembly attached to the propeller assembly attachment point.