GB2222555A - High speed boats - Google Patents

Abstract

A rigid-inflatable or fully-inflatable boat 1 is equipped with a permanent, or removable, ram wing structure 5, typically covering substantially the whole outline of the boat 1 from above. The boat when used at high speed lifts from all but minimal contact with the water 4 in stable "ram wing", or ground-effect, flight. The covering wing 5 also protects against weather, visual reconnaissance, infra-red sensor equipment, etc. when the boats are used as assault craft. <IMAGE>

Description

IMPROVEMENTS IN HIGHSPEED BOATS This invention relates to modification of high speed boats to improve performance characteristics, and involves application to boat design of a feature known from aircraft design.

Lift of an aircraft wing in mid-air arises mainly from reduced pressure above the wing and to a lesser extent from increased pressure of air flowing beneath the wing, typically in a ratio of about 2:1.

If the wing flies low over the ground then an additional lift effect, of air pressure between the wing and the ground itself, begins to be noticeable. Typically. this ground effect"first starts becoming noticeable at a distance broadly equal to the wingspan and eventually becomes the dominant aerodynamic effect at very low flying levels. It is known, as a consequence of this, that aircraft can increase their effective range by flying at an extremely low altitude over the sea, in effect skimming ttie surface and not using power to create lift to the same extent as they do in mid-air.

Long distance patrol aircraft. or damaged aircraft, have conventionally used such techniques: even certain sea-birds have been observed to exhibit such behaviour.

With conventional aircraft design, however, this type of flying can be unstable. in the transition from the "ground effect" mode (close to the surface) to the normal mode of mid-air flight and vice versa. due to the change in the position of the centre of pressure during such transition. More specifically, high aspect ratio is required for efficiency in normal (subsonic) flight but in ground effect a low aspect ratio is preferable. Thus, for example, conventional aircraft are less prone to ground effect during take-off and landing than, for example, Concord, V-bombers, or the Space Shuttle(when landing ).

Aerodynamic analysis of the problem has led to proposals to construct a radically different form of wing arrangement in two separate parts. The first part of such an arrangement is a reverse delta shape in plan form, that is to say, a generally triangular shape flown with one side (the leading edge) forward and with the apex facing rearwardly. The tips of such a wing may be drooped (anhedral) to enhance the ram effect.The second part of such an assembly is a tail plane to the rear and high above the general plane of the reverse delta, and therefore away from any interaction with the changing downward air flow at the trailing edge of the reverse delta wing. Use of such a combination stabilised the position of the centre of lift in the transition phase and increased stability. It enables the machine to fly both into and out of ground-effect with little change in trim in pitch.

Models and prototypes have been made incorporating such a general type of wing arrangement and such prototypes have exhibited a unique combination of fuel consumption, speed. and range (albeit at speeds which are low in aircraft terms) in relation to their carrying capacity.

The present invention sets out to investigate reverse-delta (or other) ram-wing structures in combination with boats rather than aircraft.

With prior proposals. using aircraft which take off from the surface of the water, there is of course a transition stage, before take-off into the ground effect flying mode, and after water contact at the end of a trip, where the vessel essentially moves through the water surface as a boat, eventually coming to rest on the water at a level dependent upon its static load displacement. The present invention is based upon this observation, and sets out to provide a vessel which is a boat (in that It is contact with the water surface in calm water trin. even if waves occasionally cause it to leave the surface) but which utilises certain of the ram-wing i.e. ground-effect features discussed above.

In one aspect the invention provides the combination of a boat, a mounting means on the boat. and a ram-wing structure capable of being mounted in or by use of the mounting means as and when desired. and such as to give a ground-effect when the boat is moving at the design speed.

The ram wing can for example be physically inserted in, or lashed to, and removable from, the structure, or can at least be semi-permanently in place but foldable into or out of a wing configuration. It is envisaged that the wing or its structure would normally be capable of being adjusted to trim to suit prevailing weather conditions with resilient mounting, that is to say, springs or rubber mountings, if necessary.

It is especially envisaged that the boat shall be a fully "inflatable boat". i.e. a craft with an inflatable surround and a flexible or inflatable bottom. usually with some form of floor structure. Alternatively, the invention can be applied to a so called "rigid-inflatable boat", that is to say a boat with a rigid hull having fittedly attached to an upper edge an inflatable surround, as used in power boats or assault craft or rescue craft. The invention is especially valuable in both of these contexts since such boats normally have a rather hard ride (being light in weight compared with planing forces) and the ram-wing effect in lifting the boat stably in the water and carrying a substantial part of its weight minimises this discomfort.

In the case of a fully inflatable boat. the reduction in loading on the hull in a seaway helps to reduce hull distortion and can thus further improve performance.

A preferred feature of the invention is so to position the mounting means in relation to the ram-wing structure that the ram wing extends over the boat so as to give physical shelter e.g. from weather to the occupants, and/or to camouflage the craft and its contents, and further limit detectable radiation effects of the contents. Of course. the combination can be so proportioned that the disassembled structure can also be used for this purpose.

Typically, the ram-wing will be foldable and stowable.

preferably being formed of struts and flexible material in the same general manner as the sail of a boat or hang-glider wing. Alternatively, it can be formed in the style of an ordinary. or inflatable. parachute structure.

We have found that because a boat is in contact with water even when travelling with the ram-wing feature.

the exact shape of the wing is less critical and may not always require the tail plane configuration. However.

preferably, it is again of a reverse delta configuration.

There are certain advantages and differences to be noted between the structure as proposed above. and the existing ram-wing in aircraft. For example, high speed mono-hull craft such as rigid inflatable boats. as used for racing or for rescue purposes and especially the fully inflatable craft give a particularly uncomfortable ride. The use of a ram-wing structure lifts the greater part of the boat out of the water in a stable fashion and minimises this hardness of ride,to the comfort of the passengers who are not always seasoned sailors. It moreover can in certain applications increase the range and speed of the vessel to a useful extent.

The ability to use an erectable ram-wing structure rather than a permanent structure means that the existing stock of vessels can readily be modified with a simple holding bracket or like mounting means,and supplied with the demountable or mountable ram-wing equipment. Such demountable equipment is of course considerably cheaper and more convenient both in use and storage than the provision of a permanent structure.

Although there are to some extent weather limitations upon travel in boats equipped with a ram-wing in this fashion, there is of course always the alternative of taking in the demountable ram-wing and using the normal mode of travel, should weather conditions so require. It should be noted that. although for aviation purposes it is virtually inescapable to use some combination of a reverse delta-wing and a high tail plane structure, the use of a tail-plane is not generally necessary with the present invention since the conditions are aerodynamically less stringent.

The underlying form of the vessel can be varied, to take advantage of the new force arrangements afforded. Thus, it may be desirable to make attachments to. or modify, the underwater form of the vessel to improve its hydrodynamic performance and ability so that when the weather conditions are suitable. the full envelope of possible performance of the boat plus its folding ram wing can be achieved.Thus, it may be preferable to have a long slender hull shape to achieve to achieve such optimisation.

The invention will be further described with reference to the accompanying drawings, in which: Figures la and ib are respectively a diagrammatic side view and a diagrammatic top view of an inflatable boat provided with a ram-wing in accordance with the invention; Figures 2a and 2b are like views of a second embodiment; and Figures 3a and 3b are like views of a third embodiment.

In Figures la and lb an inflatable boat 1, of conventional design, has an outboard motor 2 with propeller 3 located beneath the water level 4.

The ram-wing construction shown is a foldable or furlable fabric, canvas or polymer structure in the shape of a reverse delta. It has a spine member 5, and transverse struts 6a, 6b forming an anhedral configuration, i.e. so that the ram-wing slopes downwards to each edge from the spine 5 thereby improving containment of air.

At or about the centre of lift there is located a mounting member 7. in the form of two struts 7a, 7b converging to a junction with the spine 5.Towards the rear of spine 5 ls attached a flexible tie 8 i.e. a rope. and towacds the front a tie 9 which is both flexible and elastically extensible (e.g. by the use of an elastic cable or by incorporation of an elastic portion into an otherwise non-elastic rope, possibly with a bridging rope limiting elastic extension, not shown.

The mounting member 7 can be formed of the two struts 7a and 7b positioned as shown. i.e. located on a fore-and-aft central line; alternatively the struts can be located on a transverse line. It is greatly preferred to incorporate some rigid mounting support for the strut. e.g. a transverse plank across the base of. or possibly lashed across the inflatable tubes of the boat.

Possibly, however, the ends of the struts 7a, 7b could be individually lashed to the boat structure, e.g. at the conventional rope handles along the sides of the tubes. Ties 8 and 9 can in anycase be so lashed, since they are flexible and always in tension. Length adjustment of stern tie 8 is possible (over the possible range of elastic extension of the tie 9) and alters the ram-wing angle of the structure.

In operation, the forward end of the inflatable boat is raised in a controllable fashion from the water, giving a more comfortable high-speed ride and higher speeds and/or range since less drag. The propellor, and usually some small amount of the rearward portion of the hull (although not necessarily) are of course always in contact with the water, except on brief occasions, as is usual with highspeed boats, when the whole boat leaves the water e.g. due to wave action. Even such occasions are more controllable and less dangerous with the stabilising effect of the ram-wing.

The plan view of Figure ib also shows that the occupants are to some extent weather-protected by the ram-wing.

Moreover, the number of occupants is concealed from overhead reconnaissance, and their body heat is shielded. by the ram-wing, from infra-red scanners. Of course, when not needed, the wing can be lashed and stowed.

Figures 2a and 2b show an embodiment in which the ram-wing structure is constituted by a parachute-type structure 10, fixed by ties 11 along its edges 12 to one or more points at the edge of the hull of the boat.

Again, the leading edge is raised, preferably anhedrally, or curved to be higher in the central region. Support by struts 13. and angle-adjustment capability 14, 15 is shown, but could in some cases be dispensed with.

We have found that such a rectangular shape, not resembling a reverse delta, is nonetheless capable of a stable ram-wing effect in the context of the present invention.

Figures 3a and 3b again show a reverse-delta configuration 16 for the ram-wing, useful for incorporation over an inflatable boat 17 of a long slender profile. The various ties and mountings can readily resemble those described above. and for clarity are therefore not shown. In operation, the structure shown forms a raised and rearwardly sloping central11 tunnel 18 with tapering side planes 19 sloping downwards on each side. use of such a boat gives somewhat more lateral control (in yaw) since although a high proportion of the boat is raised above water level there is still enough hull/water contact for good control against lateral wind or wave forces. Moreover, when not in use, the side planes 19 can be folded inboard,along the vessel, to give additional weather-protection or concealment. It is further envisaged that clear polymer sheets may be provided extending vertically downwards from the inner edges of planes 19 i.e. along the sides of the boat, for weather-protection purposes.

Claims (9)

1. Claims.

   l.The combination of a boat, a mounting means on the boat, and a ram-wing structure capable of being mounted in or by use of the mounting means as and when desired, and such as to give a ground-effect when the boat is moving at the design speed.
2. 2.The combination as claimed in claim 1 in which the ram wing structure is physically.insertable in or adapted to be lashed to, and removable from, the mounting means.
3. 3.The combination as claimed in claim 1 in which the ram wing structure is at least semipermanently in place and foldable into or out of a wing configuration.
4. 4.The combination as claimed in claim 1. 2 or 3 in which the ram wing is adjustably mounted so as to be capable of adapting to weather conditions.
5. 5.The combination as claimed in any one of claims 1 to 4 in which the board is a fully inflatable boat.
6. 6.The combination as claimed in any one of claims 1 to 4 in which the boat is a rigid inflatable boat.
7. 7.The combination as claimed in any one preceding claim in which the ram wing at least when assembled for flight attends to cover substantially the whole outline of the boat.
8. 8.The combination as claimed in any one preceding claim in which the ram wing is composed of a foldable structure of struts and flexible material.
9. 9.The combination as claimed in any one of claims 1 to 7 in which the ram wing is composed of flexible material only, shaped to expand to a ram wing shape in use.

   1O.The combination as claimed in any one preceding claim in which the ram wing is of a reverse delta configuration.

   1l.The combination as claimed in claim 1 and substantially as herein described with reference to the drawings.