GB2103155A - Marine vessel with planing hull - Google Patents

Abstract

A marine vessel comprises a hull (2), two chamber wall members (4) which project downwardly from the hull and extend longitudinally of the vessel, the bottom of the hull and the two wall members defining a chamber below the water line of the vessel, and air supply means (14, 16, 18) for supplying air under pressure to the chamber, the arrangement being such that in use the air forms an air layer in said chamber between the water and the bottom of the hull and the air is at least in part prevented from escape laterally of the vessel by the two wall members. One or more longitudinal dividers (11) and transverse ridges (10) or circles divide the chamber into sub-chambers, fed by respective cross-ducts. Air is supplied by a fan (5) via plenum chambers 20 and surge towers (18) to longitudinal ducts (14) and then down-ducts (16). The planing arrangement is used with a propeller or dynamic fluid drive. <IMAGE>

Description

SPECIFICATION Marine vessels This invention relates to marine vessels and in particular though not exclusively to mono-hull vessels.

It has long been known that marine vessels can travel faster if they can "plane" on the surface of the water rather than moving with the substantial bulk of their hull submerged. Planing occurs when air dragged under the bow of a vessel forms a layer between the hull of the vessel and the water thus substantially reducing the frictional drag of the water on the hull. It is quite common for small boats, such as sailing dinghies, power boats and the like to achieve planing at quite low speeds by virtue of the vessels being light in weight and being provided with sutiable smooth hulls over which the required air layer can easily form.

Vessels of larger displacement cannot ususally obtain the necessary speed to allow planing to take place and indeed their hulls are not adapted for planing. Various methods are known to enable small vessels to travel at high speed on principles akin to planing, for example a hydrofoil has a plurality of aerofoil sectioned hydrofoil members mounted on struts extending from the hull of the vessel and once a critical velocity is achieved instead of riding in the water supported by the buoyancy of the hull the vessel will ride up and be supported by a planing effect caused by the hydrofoil members. Though this latter method is effective it is necessary for the vessel to be provided with the requisite hydrofoils, and a propulsion means of sufficient extent that it remains immersed in water even when the vessel is riding on the hydrofoil members.Such vessels consequently have a large draught and can only be of quite small displacement because of the power required initially to raise the boat into the hydroplaning condition.

According to the invention there is provided a marine vessel comprising: a hull; two at least partially coextensive wall members which project downwardly from the hull and extend longitudinally of the vessel, the bottom of the hull and the two wall members thus forming a polysided chamber below the water line of the vessel; means for supplying air at high pressure; and ducting connecting said air supply means to said chamber; the arrangement being such that in use air provided by said air supply means is partially trapped in said chamber to form an air layer between the water and the bottom of the hull and the air being at least in part prevented from escape laterally of the vessel by the two chamber wall members.

If desired the marine vessel may comprise more than one hull in a twin-hull or catamaran version.

It will be seen that the invention artificialiy creates the requisite air layer so that the marine vessel may be moved into a planing condition at a lower speed than heretofore possible. Further, since the air layer between the bottom of the hull and the water need only be sufficiently thick to reduce the frictional drag of the water on the hull, only sufficient air to sustain the presence of this layer need be supplied by the air supply means.

Heretofore only small vessels of low displacement have been able to achieve a planing condition but with the use of the invention vessels of considerably larger displacement, for example small cargo vessels, can readily be moved into a planing condition and therefore travel at greater speed and/or with reduced fuel consumption since the frictional drag of the water on the hull of the vessel is substantially reduced. A marine vessel according to the invention need not have the difficulties of increased draught associated with a hydrofoil since the walls of a marine vessel according to the invention need only project downwardly of the hull a sufficient amount so as to at least in part prevent the air in the chamber from escaping laterally of the vessel, and it is consequently not necessary to provide the extended propulsion means normally associated with hydrofoils.

Preferably the two downwardly projecting wall members extend coextensively over a major part of the length of the vessel and are disposed one on each side of a keel line of the hull and the wall members across the whole or a major portion of the beam of the vessel. It is advantageous for as large an area as possible of the submerged portion of the hull to be provided with the drag reducing air layer. It is further preferable that the two walls be equally distant from the keel line so that the air layer is evenly distributed over both port and starboard sides of the submerged portion of the hull so as to avoid unbalanced drag effects which might affect the steering of the vessel.

Preferably there is at least one downwardly projecting dividing wall member disposed between and substantially coextensive with the two chamber wall members and a duct connecting said air supply means to each sub-chamber formed by the bottom of the hull, the dividing wall member and one of the chamber wall members.

With this arrangement when the vessel rolls the air layer is prevented by the dividing wall from moving across the beam of the boat. In one preferred embodiment the dividing wall member is disposed substantially on the keel line of the boat and the chamber wall members are laterally spaced equal distances on each side of the dividing wall member. With such an arrangement the air layer will be maintained at least to some extent on both sides of the vessel when the vessel rolls which helps to prevent loss of the planing condition on either side of the vessel and avoids reductions in speed and difficulties with the steering of the vessel.In an alternative embodiment two dividing wall members are provided and these are positioned between the two chamber wall members so that each of the sub-chambers have substantially equal lateral extent and each of the sub-chambers is connected by means of ducting to the air supply means.

Preferably the hull between the two chamber wall members depends downwardly in a series of laterally extending ridges, which ridges are longitudinally spaced along the vessel and a duct connects each region of the bottom of the hull between the lateral ridges to the air supply means.

In this manner the chamber formed by the bottom of the hull, the dividing wall and/or the chamber wall members is effectively further divided into a series of longitudinally spaced sub-chambers and if air is displaced from one of the sub-chambers so that the water exerts a frictional force upon that part of the outer surface of the hull, the planing ability of the vessel will be in part sustained since the air layer may be maintained in the remaining sub-chambers. Preferably the downwardly depending ridges are curved symmetrically or asymmetrically enabling smooth flow of excess air in the air layer of one sub-chamber to the subchamber immediately aft if the vessel is moving forward or to the sub-chamber immediately forward if the vessel is moving astern.Thus excess air in the sub-chambers will eventually escape either at the stern of the vessel if the vessel is moving forward or at the bow of the vessel if the vessel is moving astern. The smooth surface of the ridges substantially reduces turbulence effects at the lowest depending portion of the ridges, which turbulence would otherwise result in increased water contact with the hull and increased drag.

Preferably the rearmost of the downwardly depending ridges adjacent the stern of the vessel is adapted so that air from the sternmost subchambers is bled towards the port and starboard sides of the vessel so as to avoid a bubbling effect at the stern of the vessel. Further, a valve is preferably provided in the aftmost connecting duct on each side of the vessel so that the air pressure to the aftmost sub-chambers can be controlled so that the air bled into the region around the propeller in a vessel having such propulsion means does not produce cavitation around the blades of the propeller.If a dynamic drive is employed in the vessel, i.e. one where water is sucked in through an axial flow pump and then expelled at high pressure, the region of the hull adjacent the intake and outlet ports of the dynamic drive is preferably adapted so that the air layer does not cause turbulence or interfere with the operation of the dynamic drive.

In an alternative embodiment the hull instead of being formed with a series of depending ridges may be formed with a number of downwardly depending regions of circular horizontal crosssection, such circular depending portions being arranged in a square array and the outlet ducts being connected to the centres of the squares of the array, such that the overall effect is comparable to a pin cushion. In this embodiment the air is fed vertically into the centres of the squares and a sub-chamber is formed by four adjacent circular depending portions.

Preferably each of the ducts connecting the air supply means to each of the sub-chambers is provided with an output duct portion which extends laterally from one of the chamber side walls towards the keel line so as to provide air to the sub-chamber across substantially the entire lateral extent of the sub-chamber. Still more preferably each connecting duct joins the respective output duct proximate the chamber wall member and the output duct has a decreasing vertical cross-section towards the keel line of the vessel.With such an arrangement the ducts from the air supply means to the sub-chambers can be conveniently disposed around the sides of the vessel leaving the central area of the vessel open for cargo space etc. and the reduction in the vertical cross-sectional area of the output duct compensates for the increased air pressure supplied from the connecting duct in the region adjacent the chamber wall members and a more even air layer is provided than would be otherwise.

Preferably a grid is provided in the output duct so as to prevent extraneous matter entering the duct and so as to supply the air to the sub-chamber more evenly. Even with the grid present, the air pressure adjacent the chamber wall members will be slightly greater than that towards the keel line and this is preferred since it is important to maintain the air layer adjacent the sides of the submerged hull surface in order to exercise improved stability.

Preferably the air supply means is mounted above the waterline of the vessel and is provided with back water pressure relief means so that in the event of water being forced from the subchambers through the connecting duct towards the air supply means the water is prevented from entering the air supply means. Preferably the relief means is in the form of a surge tower with a duct extending upwards into the tower from the air supply means and then downwards to join with the connecting ducts.

The pressure supplied by the air supply means can be varied according to the nature and loading of the vessel but would normally be of the order of 1 psi. The pressures required can conveniently be supplied from a high power centrifugal fan and this is preferably connected to a plenum chamber and thence to the surge tower. It is preferred that the port and starboard sides of the vessel receive the air at high pressure separately from the plenum chamber and therefore two surge towers are provided, one on the port side of the vessel and one on the starboard side. The two surge towers join with a major connecting duct on each side of the vessel and each of these major connecting ducts extends substantially for the length of the vessel adjacent the inner side of the hull and the connecting ducts for each subchamber extend from the major duct to the output ducts.

A preferred embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, wherein: Figure 1 is a plan view of a marine vessel according to the invention; Figure 2 is a cross-sectional side view taken along line 2-2 of Figure 1; Figure 3 is a cross-sectional front view taken along line 3-3 of Figure 1; and Figure 4 shows a perspective view of the internal structure of the marine vessel of Figure 1.

Referring to the drawings, a marine vessel 1 according a preferred embodiment of the invention generally comprises a hull 2 having downwardly depending wall members 3 and 4 on starboard and port sides respectively, and air supply means 5 in the form of a high power fan is connected via ducting 6 and 7 to the poly-sided chamber formed by the bottom of the hull 2 and the wall members 3 and 4.

The chamber 8 formed by the bottom of the hull 2 and the side walls 3 and 4 is divided longitudinally of the vessel by a keel plate 9 and further divided laterally into sub-chambers by means of the hull 2 being formed into downwardly depending curved ridges 10: thus a series of subchambers 11 are defined by the keel plate 9, adjacent depending ridges 10 and either side wall 3 or side wall 4. Each of the sub-chambers on the starboard side of the vessel is connected via an outlet duct portion 12 to the ducting 6 and those sub-chambers on the port side of the vessel are similarly connected via outlet ducts 13 to ducting 7.The outlet ducts 12 and 13 each have their lower side open to communicate with the subchambers 1 The ducting 6 and 7 repsectively comprise major supply ducts 14 and 1 5 extending substantially the length of the vessel adjacent the starboard and port sides of the hull and connecting ducts 1 6 and 1 7 which interconnect the outlet ducts 12 and 1 3 with the major supply ducts 14 and 15.

The major supply ducts 14 and 1 5 are connected to the air supply means 5 via back water pressure relief means 1 8 and 19, in the form of a surge tower or water trap and a plenum chamber 20. The surge towers 18 and 19 are each in the form of a folded over duct which extends first upwardly from the plenum chamber 20 and then downwardly to connect with one of the major supply ducts 14 and 15.

Referring in particular to Figure 4 of the drawings, the sides of the hull 2 are attached by welding to the major supply ducts 1 4 and 1 5 and internal support members 21. An angle bar 22 runs along each side of the vessel inside the hull to provide extra strength. The hull side plates of the hull 2 extend downwardly to form the outside surface of the chamber wall members 3 and 4.

The downwardly depending ridges 10 of the hull 2 are strengthened by lateral members 24 which extend from support members 21 on each side of the vessel to the keel plate 9, and longitudinally extending ribs 25 which have a profile curved to correspond to the internal curvature of the ridges 10 of the hull 2.

The construction of the downwardly depending ridges 10 may be readily achieved by first building a skeletal structure including the keel plate 9, the lateral strengthening members 24, ribs 25 and the outlet ducts 12 and 13. This skeletal structure may be constructed upside down. Metal sheets intended to form the downwardly depending ridges 1 0 can then be laid over the skeletal structure and the sheets will tend to conform to the contour of the skeletal structure. The metal sheets can then be stitch welded to the skeletal structure from underneath and the partially completed hull then inverted for further construction.

As previously mentioned, the outer surface of the hull 2, instead of being formed with downwardly depending ridges 10, may be provided with downwardly depending regions of circular horizontal cross-section arranged in a square array. With such an arrangement the air is fed into the centres of the squares of the array and a sub-chamber is formed by four adjacent depending regions.

The outlet ducts 12 and 13 are positioned between adjacent downwardly depending ridges 10 so that the lower open side of each of the outlet ducts joins the respective sub-chamber over its uppermost area. Each of the outlet ducts 1 2 and 1 3 is provided on its lower side with a grid (not shown). The outlet ducts 1 2 and 13 join with the lower ends of the interconnecting ducts 1 6 and 17 while the upper ends of the interconnecting ducts join with the major supply ducts 14 and 15. The major supply ducts 14 and 1 5 are square cross-sectioned tubular members and as with the outlet and interconnecting ducts the major supply ducts are preferably made from plate of between 5 and 7 mm thickness for vessels up to 20 m long.Preferably the hull and structural members thereof are made of aluminium so as to provide a vessel of lower weight than one made of wholly steel. The major ducts 14 and 15 are connected to the surge towers 18 and 19 by ducts 26 and 27. The ducts 26 and 27 connect with the surge towers 1 8 and 1 9 at the lower end of the down sides 1 8a and 1 9a of surge towers 18 and 19. The up sides 1 8b and 1 9b of the surge towers 1 8 and 19 connect at their lower ends with the plenum chamber 20, which chamber receives high pressure air from the high power fan 5.

Butterfly valves 28 and 29 are fitted in the sternmost of the interconnecting ducts 1 6 and 1 7 and similar valves may be fitted in the foremost interconnecting ducts, which valves may control the supply of high pressure air to the aftmost and foremost sub-chambers.

The vessel shown in the drawings is primarily intended to have two propeller propulsion outdrive-cum-steering units but it will be readily understood that a dynamic drive may be employed with suitable modification of the hull. In use the vessel as described will operate as a normal vessel up to a speed of the order of 1 5 knots. Above this speed the air supplied from the high power fan 5 via the plenum chamber 20, the surge towers 1 8 and 19, the major supply ducts 14 and 1 5, the interconnecting ducts 1 6 and 1 7 and the outlet ducts 12 and 13 to the subchambers 1 will form a layer over the ridges 10 and the frictional drag of the water on these portions of the submerged hull will be reduced.Therefore at a speed above the critical planing speed the vessel will be able to travel faster and/or with reduced fuel consumption. The air layer is clearly thickest immediately beneath the outlet ducts 12 and 1 3 and decreases in thickness towards the lowest depending portions of the ridges 10. Thus as the vessel travels forward and water pressure varies over the bottom of the hull due to the swell, waves etc. at various times, the water pressure over the lowest depending portions of one or more of the ridges 10 may be temporarily sufficient to remove part of the air layer and force the air backwards into the outlet ducts.However, by provision of a plurality of outlet ducts and therefore air supply points, even if the air layer is disturbed over a number of ridges 10 it is unlikely that all of the ridges will have the air layer sufficiently disturbed for the vessel to be caused to slow down below the critical planing speed. If the sea is sufficiently rough to cause water to be forced up into the outlet ducts, for example in a heavy sea, water forced into the supplying ducts 14 and 1 5 will be prevented from entering the plenum chamber 20 by the surge towers 18 and 19.

To avoid cavitation around the propeller of the vessel the air pressure to the aftmost of the subchambers 11 is controllable by the butterfly valves 28 and 29 and the hull to the rear of the aftmost of the downwardly depending ridges 10 is preferably formed so that air is bled to the sides of the propeller 30. Thus cavitation around the propeller is reduced in two ways.

It will be appreciated that although described in conjunction with a propeller drive the vessel according to the invention is readily adaptable to a dynamic drive. Such a dynamic drive would generally include a water inlet duct, an axial flow pump and an outlet duct; water drawn in through the inlet duct being expelled at high pressure through the outlet duct by the axial flow pump.

The outlet duct would normally have a rotatable nozzle to direct the expelled high pressure water, thereby to steer the vessel. Such a dynamic drive may be mounted either forward or aft, or both, of the sub-chambers 11 so that the inlet duct(s) to the axial flow pump(s) can be located below the level of the planing surface in one or more longitudinal troughs (not shown), thus avoiding air ingestion by the dynamic drive(s).

Claims (11)

1. A marine vessel comprising a hull, two chamber wall members which project downwardly from the hull and extend longitudinally of the vessel, the bottom of the hull and the two wall members defining a chamber below the water line of the vessel, and air supply means for supplying air under pressure to the chamber, the arrangement being such that in use the air forms an air layer in said chamber between the water and the bottom of the hull and the air is at least in part prevented from escape laterally of the vessel by the two wall members.

2. A vessel as claimed in claim 1, wherein the wall members extend over at least a major part of the length of the vessel.

3. A vessel as claimed in claim 1 or 2, wherein the wall members are disposed one on each side of a keel line of the hull and are laterally spaced apart to such an extent that the chamber extends across at least a major portion of the beam of the vessel.

4. A vessel as claimed in claim 3, wherein the wall members are equaily distant from the keel line.

5. A vessel as claimed in any preceding claim, further comprising at least one dividing wall member extending longitudinally of the vessel and projecting downwardly from the hull so as to divide said chamber into at least two subchambers, said air supply means being adapted to supply air to each of said sub-chambers.

6. A vessel as claimed in claim 5, wherein the or one of the dividing wall members is arranged substantially on the keel line of the hull.

7. A vessel as claimed in any preceding claim, wherein the bottom of the hull between the two chamber wall members comprises a series of laterally extending ridges spaced longitudinally of the vessel, said air supply means being adapted to supply air to each region of the bottom of the hull between said ridges.

8. A vessel as claimed in claim 7, wherein said ridges are curved in longitudinal cross-section.

9. A vessel as claimed in any preceding claim, wherein said air supply means comprises ducting extending from a source of air under pressure to the chamfer or each sub-chamber.

10. A vessel as claimed in claim 9, wherein said ducting comprises at least one supply duct extending longitudinally of the vessel from which a plurality of output ducts extend laterally.

11. A marine vessel substantially as herein described with reference to the accompanying drawings.