GB1597461A

GB1597461A - Air cushion craft

Info

Publication number: GB1597461A
Application number: GB41352/76A
Authority: GB
Original assignee: Carson P F R
Current assignee: Carson P F R
Priority date: 1972-08-01
Filing date: 1978-01-04
Publication date: 1981-09-09
Also published as: GB1453184A

Description

(54) IMPROVEMENTS IN AIR CUSHION CRAFT (71) I, PETER FRANCIS REID CORSON, a British subject of Park Hatch, Loxhill, Godalming, Surrey, do hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to air cushion craft, that is to say craft constructed for travel on water and in which means are provided for blowing air to the underside of the craft to provide an air cushion between the travel surface and at least a part of the bottom surface of the craft. It is particularly concerned with modifications of or improvements in the invention of my earlier patent No. 1 453 184.

According to the present invention, there is provided an air cushion craft having an under-surface with elongate dependent portions on opposite sides of the craft forming side boundaries of a cushion space between them extending longitudinally underneath the craft, and means for injecting a first flow of air into said space at its forward end region and for injecting a second flow into said space rearwardly of said first flow, the arrangement being such that said first flow acts as a curtain preventing the escape of said second flow of air forwardly of the bows of the craft but the cushion air being able to escape to the rear of the craft from said cushion space, said dependent portions on opposite sides of the craft being formed with laterally outer side walls that in their lower extent are, over at least a major part of their length, inclined obliquely outwardly and upwardly at an angle of 30 to 600 to the horizontal, preferably 35 to 550, and advantageously substantially 45".

Said inclined side walls preferably comprise upwardly swept leading portions at the bows of the craft and, at least over the region of the hull immediately rearwards of the bows they extend upwards to above waterlevel when the craft is in its raised position on the air cushion. Preferably said inclined side walls are continued over a similar height to the stern of the craft.

According to a preferred feature of the invention, the craft has a lower bow formation inwards of said dependent portions and forwards of the injection of said first flow of air into the cushion space, which bow formation comprises laterally opposite upwardly and inwardly inclined undersurfaces and the inner edges of said undersurfaces being disposed above the bottom of said dependent portions.

Preferably, the forward end region injection means comprises at least one nozzle with an upper wall region continued beyond the rearmost extent of its lower wall region.

Said at least one nozzle may be so disposed in the undersurface of the craft that it forms an upwards step terminating the undersurface of the bow formation of the craft hull.

Said upper wall region may be continued only for a short distance beyond the end of the lower wall region and there may then be a further upwards step from which a higher main cushion space of the craft extends.

According to another preferred feature of the invention, the craft has the rear terminal region of its undersurface branched into a plurality of mutually laterally spaced portions. Said branching may begin forwards of said second flow injection means.

A craft according to the invention may be provided with at least one longitudinally extending barrier or curtain along its underside in the cushion space, said barrier projecting downwardly in said space to close to, but preferably above, the water level therein when the craft is raised on its air cushion.

Embodiments of the invention will be more particularly described with reference to the accompanying diagrammatic drawings, wherein: Fig. 1 is a side view of a craft according to the invention, Fig. 2 is a perspective view from below of the hull of the craft of Fig. 1, Figs. 3 and 4 are detail transverse and axial sectional views of the forward cushion air outlet region in the craft of Figs. 1 and 2, Fig. 5 is a side view of another craft according to the invention, Figs. 6 and 7 are front and rear views respectively of the hull shape of the craft in Fig. 5, Fig. 8 is a transverse sectional view of the hull shape of the craft, looking aft from the plane A-A in Fig. 5, Fig. 9 is a perspective view from below of a further craft according to the invention that is similar in side view to the craft shown in Fig. 5, and Figs. 10 and 11 are front and rear views respectively of the hull shape of the craft of Figs. 9 and 10.

Referring firstly to the construction illustrated in Figs. 1 to 4, this is in many respects similar to the construction illustrated and described in the parent patent specification.

In particular it has a forward fan arrangement 2 blowing air through a slot-like outlet or outlets 4 in the bows region 6 of the craft, and a larger rearward fan arrangement 8 blowing air through a rear outlet or outlets 10, both flows entering a cushion space 12 under the craft between dependent side portions 14 of the hull. The air directed into said space is able to escape from the rear of the craft the flow pattern being generally as described in the parent patent with a restriction 16 reducing the height of the space immediately behind the rear outlet 10 and an upwardly directed step 18 at the extreme rear of the hull. It is to be noted that the restriction has a curved front profile giving a variation of height across its width. This can assist in reducing or preventing "slamming" disturbances from waves hitting the restriction.

It is a feature of the construction now illustrated that the outer sides of the hull have their lower regions formed by upwardly and outwardly inclined surfaces 22. In the drawings, these portions are shown at an angle of substantially 45" to the horizontal, but the angle can be varied between 30 and 60 , preferably between 35 and 55 . These inclined lower surfaces each flare out from a point in the V-shaped bows region of the hull and are shown extending to the rear of the hull although they may terminate forwards of the stern of the craft.

The surfaces may have an angular or rounded transition with said upper sides, but preferably they have a stepped transition 26 as seen in transverse cross-section. In the illustrated configuration, the ste is so formed that each lower inclined surface projects laterally outwardly of the adjoining upper side surface of the hull, but a converse arrangement could be provided instead, with each lower inclined surface recessed laterally inwards of the adjoining upper side surface by a similar amount. Either configuration will assist in deflecting spray away from the upper sides of the craft and so reduce drag, but the outwardly projecting form illustrated also facilitates matching a reasonably fine bow shape with a sufficiently broad beam for the cushion.

The main portion of the lower inclined surfaces are of substantially constant depth but they have upwardly swept leading portions 23 at the bows region. Over the main portion, the inclined surfaces 22 extend to above the waterline W so that when the craft is underway the upper more steeply inclined or substantially perpendicular upper sides 24 of the hull are not wetted, or at least are not normally submerged. It is found that by this measure the bows tend to rise slightly as the craft is moved at speed through the water in comparison with a vertical-sided hull form and a reduction of drag is obtained. These effects are noticeable in particular with the generally V-formation plan shape of the bows which without the inclined surfaces 22 tends to produce a water reaction lowering the bows of the craft with a resulting increase in drag.

The V-formation of the bows also extends to the undersurface of the bows section, below the leading portions of the inclined hull side surfaces. This is indicated by the regions 32, which terminate at a rearwardfacing outlet or outlets 4 from the forward fan arrangement. The hull shape of this lower region forwards of the fan outlet or outlets reduces the amount of air required from the forward fan arrangement 2 and provides better sea-going characteristics than a flat-bottomed configuration. For the former feature at least, the lowermost edge of the V-formation preferably extends substantially to the bottom level of the air cushion.

The upper and inner walls 34 of the trunking for the bows airflow continue rearwards of the undersurfaces 32 and form a short guide extension 38 of the bows air outlet or outlets that terminates at a step 36 rearwardly and upwardly inclined at an angle of approximately 45 , beyond which the air cushion space reaches its full height. The extension formed by the walls 34 is intended to assist the air discharge from the bows air outlet or outlets and to help to maintain the rearwards momentum of the air flow so as to prevent or minimise escape of air forwards from the bows.

In the main cushion space, a longitudinally directed barrier or curtain 42, preferably rigid, extends between the front and rear air discharge outlets 4, 10. This barrier does not normally come into contact with the water surface when the craft is raised on its air cushion, but acts when the craft rolls, and may then enter the water to restrict the transfer of the cushion air from side to side of the cushion space and so to damp the rolling motion. Although a single central barrier is shown, it will be understood that more than one such longitudinally extending barrier can be provided.

The craft of Figs. 5 to 8 is similar in many respects to that shown in Figs. 1 to 4 but illustrates a number of modifications that are themselves individually applicable to that first craft. Parts corresponding to those already described with reference to Figs. 1 to 4 are indicated by the same reference numbers.

In this alternative craft, the air flows to the cushion space operate in the manner already described although the bows air flow is here generated by a centrifugal fan arrangement 2a protected from oncoming seas. The main propulsion may be by means of water jets (not shown) or by an air propeller as shown in Fig. 1.

The inclined lower side surfaces now have a step 46 between the forward and rear reg- ions 22a, 22b respectively, both regions extending to above the waterline but the inclined surfaces being more steeply inclined, e.g. being increased from the 45" of the forward region to some 700-800 towards the rear of the craft. This feature can be employed instead of or in conjunction with the termination of the inclined surfaces forwards of the stern of the craft already referred to, in order to reduce the wetted area of the hull.

Figs. 9 to 11 illustrate a further craft according to the invention in which features already described are indicated by the same reference numbers. In this embodiment also there are front and rear air injection means into the cushion space and the outer sides of the hull comprise inclined outer side surfaces 22 with upwardly swept leading portions 23 in the bows region, meeting at the hull centre line at the forward end. Above the leading portions 23, the upper region of the outer sides of the craft extend to main deck level and meet at their forward ends to form bow peak 58.

At the inner edges of the leading portions 23 of the underside of the hull comprises opposed undersurfaces 60 that are upwardly and inwardly inclined and that meet at the hull centerline to form an inverted Vcross-section, as best seen in Fig. 10. Preferably, the undersurfaces 60 have a rearward termination at an upwards step-like formation at least partly formed by the first air injection means. In the illustrated example, the termination is formed by a slot-like air outlet nozzle 62 extending across the width of the undersurface between the side walls, with the upper surface of the nozzle outlet continuing, at 64, a short distance rearwards, in the manner already described, to terminate at the further step 36 leading into the main cushion space.

By the provision of an undersurface in the bows region in this manner, exhibiting an inverted V-shape in front view, a better profile is presented during forward travel.

Towards the stern of the craft the hull, or at least its undersurface to above the waterline, is bifurcated into two portions 70 symmetrically disposed on each side of the hull centerline with a rearwardly widening wedge-like space between them. The inner sides 72 of the bifurcation extend vertically or nearly vertically from the main deck level to the adjoining regions of the hull undersurface and they meet each other at the forward limit of the bifurcated portions.

Over the greater part of the length of the bifurated portions 70, their undersurfaces comprise surfaces 74 that continue forwards into the main cushion space and that are inclined laterally upwardly and outwardly to run into the higher upper surface of the main cushion space. Said inclined surfaces 74, where they extend forwards of the limit of the bifurcation, are separated from each other by the central longitudinal barrier or curtain 42 in the main cushion space.

Each inclined surface 74 terminates at its rear at the lower edge of a respective slotlike outlet nozzle 76, the two nozzles providing the second air outlet means analogously to the preceding embodiments described.

The upper surface 78 of each of said nozzle outlets has a similar inclination laterally as its adjacent surface 74 and continues rearwardly and downwardly to terminate in a step 80 that is upwardly directed towards the rear to ensure, as already described, that any air issuing rearwards past the step 80 is not deflected upwards by meeting the water surface at that point and therefore the forward thrust effect of the escaping air is improved.

Rearward of the step 80, terminal'side faces 82 of the bifurcated portions are disposed parallel with each other, again to assist in guiding the air discharge rearwards, from the nozzles in a direction parallel to the central vertical plane of the craft. The surface 84 extending rearwards from the step 80 in each bifurcated portion are inclined laterally upwardly and outwardly at the same angle as their adjoining surfaces 78. The inclination of the surfaces 74,78, 84 downwards and laterally inwards helps to prevent or limit the escape of air laterally into the space between the opposed sides 72.

Any such escape of air laterally inwards between the bifurcated portions is also inhibited by virtue of the fact that the water surface in the cushion area below the craft will assume a slightly humped lateral crosssection which coupled with the inclination of the undersurfaces of the bifurcated portions outwardly and upwardly from the bottom edges of said sides 72, preferably at substantially 20 to the horizontal, produces a narrow strip of contact with the water surface inside the cushion along the lower edge of said inclined surfaces. This can be sufficient to substantially retain the cushion air within the space defined by the bottom edges of said sides 72 without spilling laterally into the space between the bifurcated portions 70.

The water surface in this region is subjected to the cushion pressure and is to some extent aerated as a result, so that at said region of contact the water surface has a reduced viscosity, being in effect airlubricated, and relatively little drag is generated there. Between the bifurcated portions, because of viscosity the water surface is inclined away from said bottom edge which minimises skin friction on the hull in this region.

The outer side walls of the craft in Figs. 9 to 11, similarly to the preceding embodiment, have their lower inclined surfaces 22 ending at a stepped transition 88 before the stern of the craft, from where the side walls are continued parallel to each other as near vertical surfaces 90 to reduce the wetted area. In the provision of a change of inclination of the outer side walls, as described in either embodiment, the region astern of the transition may be at an angle of between 60 and 90" to the horizontal, and if desired the change of angle may be effected gradually.

As compared with the preceding embodiments, dividing the rear end of the craft into a plurality of portions as described (and there can be more than two such portions) while maintaining the overall width of the cushion in this area reduces the amount of air which must be discharged from the rear nozzle outlets to maintain the same clearance under the rear steps 80 if the air flow from those outlets is to be sufficient to provide a major part of the cushion air as already indicated. The thrust generated by this flow of air is reduced accordingly, but so also is the power required to drive the fans.

Further means of propulsion will be provided, as described earlier, and the thrust from said further means will need to be increased to compensate for the fact that less or no forward thrust is being generated by the cushion air discharge, but because it is possible then to provide propulsion means with a more efficient thrust:power relationship than the cushion air discharge fans the overall power requirement for the craft may be significantly reduced without affecting the performance of the craft.

A further advantage of the division of the rear of the hull into two or more laterally spaced portions is that because of the mod ified hull structure, there is less surface area presented to the water in the vertical direction and the tendency to "slam" in rough weather is correspondingly reduced and a smoother ride is obtained.

Variations of this embodiment of the invention are possible. For example, the said dependent portions and inclined surfaces at the rear of the craft may be extended to the rear to meet the sidewalls, which are also extended to the rear, in a point; and the after fans' airflow is now reduced to that which is necessary merely to provide air for the cushion.

It will be understood that while the different embodiments show particular combinations of features, these features can be combined in other ways within the scope of the appended claims. For example, the inverted-V bows undersurface and the bifurcated rear hull region can each be employed independently of each other.

WHAT I CLAIM IS: 1. An air cushion craft having an undersurface with elongate dependent portions on opposite sides of the craft forming side boundaries of a cushion space between them extending longitudinally underneath the craft, and means for injecting a first flow of air into said space at its forward end region and for injecting a second flow into said space rearwardly of said first flow, the arrangement being such that said first flow acts as a curtain preventing the escape of said second flow of air forwardly of the bows of the craft but the cushion air being able to escape to the rear of the craft from said cushion space, said dependent portions on opposite sides of the craft being formed with laterally outer side walls that is their lower extent are, over at least a major part of their length inclined obliquely outwardly and upwardly at an angle of 30 to 600 to the horizontal.

2. A craft according to claim 1 wherein said angle of inclination is between 35 and 55".

3. A craft according to claim 2 wherein said angle of inclination is substantially 45".

4. A craft according to any one of claims 1 to 3 having a bows portion where said inclined outer side walls are extended into upwardly swept leading portions.

5. A craft according to any one of the preceding claims wherein said outer side walls have a stepped transition between said lower inclined regions and adjoining upper regions of the walls.

6. A craft according to any one of the preceding claims wherein said inclined side walls extend to above water level, at least over the region of the hull immediately rearwards of the bows portion, when the craft is in its raised position on the air cushion.

7. A craft according to any one of the preceding claims wherein said inclined side walls extend at a substantially constant height over the main part of the craft to its stern region.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. inside the cushion along the lower edge of said inclined surfaces. This can be sufficient to substantially retain the cushion air within the space defined by the bottom edges of said sides 72 without spilling laterally into the space between the bifurcated portions 70. The water surface in this region is subjected to the cushion pressure and is to some extent aerated as a result, so that at said region of contact the water surface has a reduced viscosity, being in effect airlubricated, and relatively little drag is generated there. Between the bifurcated portions, because of viscosity the water surface is inclined away from said bottom edge which minimises skin friction on the hull in this region. The outer side walls of the craft in Figs. 9 to 11, similarly to the preceding embodiment, have their lower inclined surfaces 22 ending at a stepped transition 88 before the stern of the craft, from where the side walls are continued parallel to each other as near vertical surfaces 90 to reduce the wetted area. In the provision of a change of inclination of the outer side walls, as described in either embodiment, the region astern of the transition may be at an angle of between 60 and 90" to the horizontal, and if desired the change of angle may be effected gradually. As compared with the preceding embodiments, dividing the rear end of the craft into a plurality of portions as described (and there can be more than two such portions) while maintaining the overall width of the cushion in this area reduces the amount of air which must be discharged from the rear nozzle outlets to maintain the same clearance under the rear steps 80 if the air flow from those outlets is to be sufficient to provide a major part of the cushion air as already indicated. The thrust generated by this flow of air is reduced accordingly, but so also is the power required to drive the fans. Further means of propulsion will be provided, as described earlier, and the thrust from said further means will need to be increased to compensate for the fact that less or no forward thrust is being generated by the cushion air discharge, but because it is possible then to provide propulsion means with a more efficient thrust:power relationship than the cushion air discharge fans the overall power requirement for the craft may be significantly reduced without affecting the performance of the craft. A further advantage of the division of the rear of the hull into two or more laterally spaced portions is that because of the mod ified hull structure, there is less surface area presented to the water in the vertical direction and the tendency to "slam" in rough weather is correspondingly reduced and a smoother ride is obtained. Variations of this embodiment of the invention are possible. For example, the said dependent portions and inclined surfaces at the rear of the craft may be extended to the rear to meet the sidewalls, which are also extended to the rear, in a point; and the after fans' airflow is now reduced to that which is necessary merely to provide air for the cushion. It will be understood that while the different embodiments show particular combinations of features, these features can be combined in other ways within the scope of the appended claims. For example, the inverted-V bows undersurface and the bifurcated rear hull region can each be employed independently of each other. WHAT I CLAIM IS:

1. An air cushion craft having an undersurface with elongate dependent portions on opposite sides of the craft forming side boundaries of a cushion space between them extending longitudinally underneath the craft, and means for injecting a first flow of air into said space at its forward end region and for injecting a second flow into said space rearwardly of said first flow, the arrangement being such that said first flow acts as a curtain preventing the escape of said second flow of air forwardly of the bows of the craft but the cushion air being able to escape to the rear of the craft from said cushion space, said dependent portions on opposite sides of the craft being formed with laterally outer side walls that is their lower extent are, over at least a major part of their length inclined obliquely outwardly and upwardly at an angle of 30 to 600 to the horizontal.

8. A craft according to any one of the

preceding claims wherein the hull has a lower bow formation comprising laterally opposite upwardly and inwardly inclined surfaces located transversely inwards of the said dependent portions on opposite sides of the craft and forwards of the air flow from said first injection means.

9. A craft according to any one of the preceding claims wherein the rear terminal region of the undersurface of the craft is branched into a plurality of mutually laterally spaced portions.

10. An air cushion craft according to claim 9 wherein said second air flow injection means are disposed in said spaced portions.

11. A craft according to claim 9 or claim 10 wherein there are two symmertically disposed spaced portions in said rear terminal region.

12. A craft according to any one of claims 9 to 11 wherein the spacing between said rear terminal region portions widens rearwardly.

13. A craft according to any one of claims 9 to 12 wherein the craft has substantially parallel outer side walls over said rear terminal region.

14. A craft according to any one of claims 9 to 13 wherein the height of the undersurface is reduced progressively in said spaced portions forwards of the second flow injection means.

15. A craft according to claim 14 wherein in the region of said progressive reduction of height the undersurface is inclined downwards both rearwardly and laterally towards the spacing between adjacent spaced portions.

16. A craft according to claim 15 wherein an upwardly stepped transition is provided in the undersurface between said second flow injection means and the stern of the craft, in each said spaced portion the preceding lower surface of said transition and the succeeding upper surface both being laterally inclined in the same sense as in said region of progressive reduction of height.

17. A craft according to any one of the preceding claims having a longitudinally extending barrier or curtain along its underside in the cushion space, said barrier projecting downwardly in said space to adjacent the water level when the craft is raised on its air cushion.

18. A craft according to any one of claims 14 to 16 together with claim 17 wherein the barrier or curtain extends into said region of progressive reduction of height of the undersurface of the spaced portions.

19. A craft according to any one of the preceding claims wherein there is a stepped transition in the undersurface of the hull adjacent the bows of the craft and preceding a main region of the air cushion space, said transition being at least partly formed by said first outlet means.

20. A craft according to claim 19 wherein the forward air flow injection means comprises at least one nozzle with an upper wall region continued beyond the rearmost extent of its lower wall region to provide said stepped transition.

21. A craft according to claim 20 wherein said upper wall region terminates at a further upwards step from which the main cushion space of the craft extends.

22. A craft according to any one of the preceding claims having a lower bows formation inwards of said elongate dependent portions and forwards of the injection of said first flow of air into the cushion space, said bows formation comprising laterally opposite upwardly and inwardly inclined undersurfaces and the inner edges of said undersurfaces being disposed above the bottom of said dependent portions.

23. A craft according to claim 22 wherein said undersurface terminate at a nozzle or nozzles providing said first flow of air.

24. An air cushion craft constructed and arranged for use and operation substantially as described herein with reference to any of the examples illustrated in the accompanying drawings.